Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

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  • 2021 • 762 A new water-soluble thermosensitive star-like copolymer as a promising carrier of the chemotherapeutic drug doxorubicin
    Chernykh, M. and Zavalny, D. and Sokolova, V. and Ponomarenko, S. and Prylutska, S. and Kuziv, Y. and Chumachenko, V. and Marynin, A. and Kutsevol, N. and Epple, M. and Ritter, U. and Piosik, J. and Prylutskyy, Y.
    Materials 14 (2021)
    A new water-soluble thermosensitive star-like copolymer, dextran-graft-poly-N-iso-propilacrylamide (D-g-PNIPAM), was created and characterized by various techniques (size-exclusion chromatography, differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) spectroscopy). The viability of cancer cell lines (human transformed cervix epithelial cells, HeLa) as a model for cancer cells was studied using MTT and Live/Dead assays after incubation with a D-g-PNIPAM copolymer as a carrier for the drug doxorubicin (Dox) as well as a D-g-PNIPAM + Dox mixture as a function of the concentration. FTIR spectroscopy clearly indicated the complex formation of Dox with the D-g-PNIPAM copolymer. The size distribution of particles in Hank’s solution was determined by the DLS technique at different temperatures. The in vitro uptake of the studied D-g-PNIPAM + Dox nanoparticles into cancer cells was demonstrated by confocal laser scanning microscopy. It was found that D-g-PNIPAM + Dox nanoparticles in contrast to Dox alone showed higher toxicity toward cancer cells. All of the aforementioned facts indicate a possibility of further preclinical studies of the water-soluble D-g-PNIPAM particles’ behavior in animal tumor models in vivo as promising carriers of anticancer agents. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133517
  • 2021 • 761 Biological and Medical Applications of Calcium Phosphate Nanoparticles
    Sokolova, V. and Epple, M.
    Chemistry - A European Journal 27 7471-7488 (2021)
    Calcium phosphate nanoparticles have a high biocompatibility and biodegradability due to their chemical similarity to human hard tissue, for example, bone and teeth. They can be used as efficient carriers for different kinds of biomolecules such as nucleic acids, proteins, peptides, antibodies, or drugs, which alone are not able to enter cells where their biological effect is required. They can be loaded with cargo molecules by incorporating them, unlike solid nanoparticles, and also by surface functionalization. This offers protection, for example, against nucleases, and the possibility for cell targeting. If such nanoparticles are functionalized with fluorescing dyes, they can be applied for imaging in vitro and in vivo. Synthesis, functionalization and cell uptake mechanisms of calcium phosphate nanoparticles are discussed together with applications in transfection, gene silencing, imaging, immunization, and bone substitution. Biodistribution data of calcium phosphate nanoparticles in vivo are reviewed. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202005257
  • 2021 • 760 Coating of cochlear implant electrodes with bioactive DNA-loaded calcium phosphate nanoparticles for the local transfection of stimulatory proteins
    Wey, K. and Schirrmann, R. and Diesing, D. and Lang, S. and Brandau, S. and Hansen, S. and Epple, M.
    Biomaterials 276 (2021)
    Calcium phosphate nanoparticles were loaded with nucleic acids to enhance the on-growth of tissue to a cochlear implant electrode. The nanoparticle deposition on a metallic electrode surface is possible by electrophoretic deposition (EPD) or layer-by-layer deposition (LbL). Impedance spectroscopy showed that the coating layer did not interrupt the electrical conductance at physiological frequencies and beyond (1–40,000 Hz). The transfection was demonstrated with the model cell lines HeLa and 3T3 as well as with primary explanted spiral ganglion neurons (rat) with the model protein enhanced green fluorescent protein (EGFP). The expression of the functional protein brain-derived neurotrophic factor (BDNF) was also shown. Thus, a coating of inner-ear cochlear implant electrodes with nanoparticles that carry nucleic acids will enhance the ongrowth of spiral ganglion cell axons for an improved transmission of electrical pulses. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.biomaterials.2021.121009
  • 2021 • 759 From volatility to solubility: Thermodynamics of imidazolium-based ionic liquids containing chloride and bromide anions
    Zaitsau, D.H. and Siewert, R. and Pimerzin, A.A. and Bülow, M. and Held, C. and Loor, M. and Schulz, S. and Verevkin, S.P.
    Journal of Molecular Liquids 323 (2021)
    Ionic liquids (ILs) are effectively used for tuning the composition and the morphology of nanoparticles or stabilizing agents for nanoparticles for catalytic dehydrogenation. Thermodynamic properties of ionic liquids, e.g. vapor pressures and vaporization enthalpies help optimise these processes. Vapor pressures and vaporization enthalpies of the series of 1-alkyl-3-methylimidazolium ionic liquids with chloride and bromide anions have been measured by using quartz-crystal microbalance (QCM). Possible thermal decomposition pathways of [C2C1Im][Br] during vaporization were analyzed by using high-level quantum-chemical methods. These theoretical results explained and supported the absence of decomposition in QCM experimental conditions. According to the measured vapor pressures the [CnC1Im][Cl] and [CnC1Im][Br] series are very suitable for catalytic applications, taking also into account their sufficient thermal stability at the level of 523–543 K. Solubility parameters of ILs and practically relevant solutes were assessed with help of experimental vaporization enthalpies. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.molliq.2020.114998
  • 2021 • 758 Gas-Phase Synthesis of Silicon-Rich Silicon Nitride Nanoparticles for High Performance Lithium–Ion Batteries
    Kilian, S.O. and Wiggers, H.
    Particle and Particle Systems Characterization 38 (2021)
    The practical application of silicon-based anodes is severely hindered by continuous capacity fade during cycling. A very promising way to stabilize silicon in lithium–ion battery (LIB) anodes is the utilization of nanostructured silicon-rich silicon nitride (SiNx), a conversion-type anode material. Here, SiNx with structure sizes in the sub-micrometer range have been synthesized in a hot-wall reactor by pyrolysis of monosilane and ammonia. This work focusses on understanding process parameter–particle property correlations. Further, a model for the growth of SiNx nanoparticles in this hot–wall–reactor design is proposed. This synthesis concept is of specific interest regarding simplicity, flexibility, and scalability: A way utilizing any mixtures of precursor gases to build multi-functional nanoparticles that can be directly used for LIBs instead of focusing on modification of nanostructures after they have been formed. Lab-scale production rates as high as 30 g h−1 can be easily achieved and further scaled. SiN0.7 nanoparticles provide a first cycle coulombic efficiency of 54%, a specific discharge capacity of 1367 mAh g−1, and a capacity retention over 80% after 300 cycles at 0.5 C (j = 0.68 mA cm−2). These results imply that silicon-rich silicon nitrides are promising candidates for high-performance LIBs with very high durability. © 2021 The Authors. Particle & Particle Systems Characterization published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/ppsc.202100007
  • 2021 • 757 How the Physicochemical Properties of the Bulk Material Affect the Ablation Crater Profile, Mass Balance, and Bubble Dynamics During Single-Pulse, Nanosecond Laser Ablation in Water
    Kalus, M.-R. and Barcikowski, S. and Gökce, B.
    Chemistry - A European Journal 27 5978-5991 (2021)
    Understanding the key steps that drive the laser-based synthesis of colloids is a prerequisite for learning how to optimize the ablation process in terms of nanoparticle output and functional design of the nanomaterials. Even though many studies focus on cavitation bubble formation using single-pulse ablation conditions, the ablation efficiency and nanoparticle properties are typically investigated under prolonged ablation conditions with repetition rate lasers. Linking single-pulse and multiple-pulse ablation is difficult due to limitations induced by gas formation cross-effects, which occur on longer timescales and depend on the target materials’ oxidation-sensitivity. Therefore, this study investigates the ablation and cavitation bubble dynamics under nanosecond, single laser pulse conditions for six different bulk materials (Au, Ag, Cu, Fe, Ti, and Al). Also, the effective threshold fluences, ablation volumes, and penetration depths are quantified for these materials. The thermal and chemical properties of the corresponding bulk materials not only favor the formation of larger spot sizes but also lead to the highest molar ablation efficiencies for low melting materials such as aluminum. Furthermore, the concept of the cavitation bubble growth linked with the oxidation sensitivity of the ablated material is discussed. With this, evidence is provided that intensive chemical reactions occurring during the very early timescale of ablation are significantly enhanced by the bubble collapse. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202005087
  • 2021 • 756 Improved process efficiency in laser-based powder bed fusion of nanoparticle coated maraging tool steel powder
    Pannitz, O. and Großwendt, F. and Lüddecke, A. and Kwade, A. and Röttger, A. and Sehrt, J.T.
    Materials 14 (2021)
    Research and development in the field of metal-based additive manufacturing are advancing steadily every year. In order to increase the efficiency of powder bed fusion of metals using a laser beam system (PBF LB/M), machine manufacturers have implemented extensive optimizations with regard to the laser systems and build volumes. However, the optimization of metallic powder materials using nanoparticle additives enables an additional improvement of the laser–material interaction. In this work, tool steel 1.2709 powder was coated with silicon carbide (SiC), few-layer graphene (FLG), and iron oxide black (IOB) on a nanometer scale. Subsequently, the feedstock material and the modified powder materials were analyzed concerning the reflectance of the laser radiation and processed by PBF-LB/M in a systematic and consistent procedure to evaluate the impact of the nano-additivation on the process efficiency and mechanical properties. As a result, an increased build rate is achieved, exhibiting a relative density of 99.9% for FLG/1.2709 due to a decreased reflectance of this modified powder material. Furthermore, FLG/1.2709 provides hardness values after precipitation hardening with only aging comparable to the original 1.2709 material and is higher than the SiC- and IOB-coated material. Additionally, the IOB coating tends to promote oxide‐formation and lack‐of‐fusion defects. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133465
  • 2021 • 755 In situ photothermal response of single gold nanoparticles through hyperspectral imaging anti-stokes thermometry
    Gargiulo, J. and Cortes, E. and Stefani, F.D. and Barella, M. and Violi, I.L. and Martinez, L.P. and Goschin, F. and Guglielmotti, V. and Pallarola, D. and Schlücker, S. and Pilo-Pais, M. and Acuna, G.P. and Maier, S.A.
    ACS Nano 15 2458-2467 (2021)
    Several fields of applications require a reliable characterization of the photothermal response and heat dissipation of nanoscopic systems, which remains a challenging task for both modeling and experimental measurements. Here, we present an implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, potentially applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media. With it, we first studied the photothermal response of spherical gold NPs of different sizes on glass substrates, immersed in water, and found that heat dissipation is mainly dominated by the water for NPs larger than 50 nm. Then, the role of the substrate was studied by comparing the photothermal response of 80 nm gold NPs on glass with sapphire and graphene, two materials with high thermal conductivity. For a given irradiance level, the NPs reach temperatures 18% lower on sapphire and 24% higher on graphene than on bare glass. The fact that the presence of a highly conductive material such as graphene leads to a poorer thermal dissipation demonstrates that interfacial thermal resistances play a very significant role in nanoscopic systems and emphasize the need for in situ experimental thermometry techniques. The developed method will allow addressing several open questions about the role of temperature in plasmon-assisted applications, especially ones where NPs of arbitrary shapes are present in complex matrixes and environments. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsnano.0c06185
  • 2021 • 754 Influence of sub-monolayer quantities of carbon nanoparticles on the melting and crystallization behavior of polyamide 12 powders for additive manufacturing
    Sommereyns, A. and Hupfeld, T. and Gann, S. and Wang, T. and Wu, C. and Zhuravlev, E. and Lüddecke, A. and Baumann, S. and Rudloff, J. and Lang, M. and Gökce, B. and Barcikowski, S. and Schmidt, M.
    Materials and Design 201 (2021)
    In this paper, the influence of 0.005 vol% and 0.05 vol% of carbon nanoparticles on the surface of polyamide 12 powder particles by dry coating and colloidal additivation is evaluated in great detail concerning thermal and microstructural properties. The dispersion of the nanoparticles on the polymer surface influences the flowability of the feedstock powder already during the additivation process. When analyzing the composite powders dynamically and isothermally with fast scanning and differential scanning calorimetry, carbon nanoparticles influence the crystallization behavior of the feedstock material significantly by acting as nucleation seeds, already at a few percent of a monolayer coating, while showing no effect on the fast heating process. The difference in calorimetric properties and crystallization behavior between the additivation methods of different abrasive forces is discussed. The surface-additivated carbon nanoparticles significantly increase the crystalline area by up to a threefold and the crystallization rate by up to a hundredfold. Furthermore, they change the crystal growth from a typical two- to three-dimensional growth of spherulites to a one- to two-dimensional growth of ellipsoidal impinged lamellar structures. Between 0.005 vol% and 0.05 vol% of well-dispersed carbon nanoparticles should be added to polyamide 12 to trigger an anisotropic heterogeneous nucleation while avoiding agglomerates. © 2021 The Authors
    view abstractdoi: 10.1016/j.matdes.2021.109487
  • 2021 • 753 Influence of the PVD process conditions on the incorporation of TiN nanoparticles into magnetron sputtered CrN thin films
    Tillmann, W. and Kokalj, D. and Stangier, D. and Fu, Q. and Kruis, F.E.
    Surface and Coatings Technology 409 (2021)
    CrTiN thin films are known to form a solid solution independent from the Ti content. Using a novel spatially separated synthesis approach, consisting of magnetron sputtering and atmospheric-pressure arc evaporation, artificial CrTiN nanocomposites were deposited. For the nanocomposite formation, TiN nanoparticles were synthesized using a transferred arc reactor and directly injected into growing CrN thin films using an aerodynamic lens system. The CrN and CrTiN thin films were deposited using various deposition conditions, such as heating power, substrate rotation velocity, nanoparticle injection distance, and cathode setup. The deposited thin films were analyzed regarding their physical structure, microstructure and mechanical properties. Based on the investigations, between 0.02 and 0.11 at.-% of TiN nanoparticles are embedded in the CrN matrix dependent on the deposition parameters. 2D GI-XRD experiments using synchrotron radiation confirm the nanocomposite structure for the two thin films with the highest TiN nanoparticle content. The crystallite size of the CrN thin film decreases from 9.4 ± 2.3 nm to 5.3 ± 1.2 nm due to the embedding of the nanoparticles. Concerning the physical structure, the nanoparticle injection leads to a change of the texture, as shown by the Debbye-Scherrer rings. Based on TEM-investigations, TiN nanoparticle agglomerates lead to a coarser microstructure of the CrN matrix. The hardness of the thin films is not significantly affected by the nanoparticle embedment. The nanoparticle injection distance and cathode setup reveal the highest impact on the film properties. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2021.126935
  • 2021 • 752 Interrogating Gas-Borne Nanoparticles Using Laser-Based Diagnostics and Bayesian Data Fusion
    Menser, J. and Daun, K. and Schulz, C.
    Journal of Physical Chemistry C 125 8382-8390 (2021)
    We demonstrate how the evaporation properties of gas-borne nanoscale materials, here liquid silicon and germanium nanoparticles, can be obtained through a novel combination of in situ time-resolved laser-induced incandescence (TiRe-LII) and phase-selective laser-induced breakdown spectroscopy (PS-LIBS) based on Bayesian data fusion. This approach reduces the uncertainty in the parameters describing evaporation and condensation by more than a factor of 2 compared to the conventional path and has the capability to provide much needed particle-size-dependent information on nanomaterial phase transitions at high temperature. The inferred parameters are generally consistent with those repeated in the literature but with reduced uncertainty and an extended temperature range. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c10026
  • 2021 • 751 Large-Scale Production of Carbon-Supported Cobalt-Based Functional Nanoparticles for Oxygen Evolution Reaction
    Bähr, A. and Petersen, H. and Tüysüz, H.
    ChemCatChem (2021)
    A series of Co-based nanoparticles supported on activated carbon was synthesized by using waste tea leaves as a template as well as a sustainable carbon source. The crystal structure of the Co particles was adjusted by post-treatments with H2O2, ethanol vapor, and H2, which result in Co3O4, CoO, and metallic Co phases, respectively. After these different treatments, the composite materials consist of small Co-based nanoparticles with an average crystallite size of 6–14 nm supported on activated carbon with apparent specific surface areas up to 1065 m2 g−1. Correlations between the structure of the materials and their activity for the oxygen evolution reaction (OER) were established, whereby the post-treatment with ethanol vapor was found to yield the most effective electrocatalyst. The material shows good stability at 10 mA cm−2 over 10 h and reaches a mass activity of 2.9 A mgCo−1, which is even higher than pristine ordered mesoporous Co3O4. The superior electrocatalytic performance is ascribed to a high dispersion of Co-based nanoparticles and the conductivity of the activated carbon that facilitate the charge transport. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202100594
  • 2021 • 750 Link between Structural and Optical Properties of CoxFe3- xO4Nanoparticles and Thin Films with Different Co/Fe Ratios
    Kampermann, L. and Klein, J. and Korte, J. and Kowollik, O. and Pfingsten, O. and Smola, T. and Saddeler, S. and Piotrowiak, T.H. and Salamon, S. and Landers, J. and Wende, H. and Ludwig, A. and Schulz, S. and Bacher, G.
    Journal of Physical Chemistry C (2021)
    CoxFe3-xO4 nanoparticles (x = 0.4 to x = 2.5) and thin films (x = 0.9 to x = 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+ and Fe3+ cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3-xO4 nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles' surface. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c11277
  • 2021 • 749 Maximize mixing in highly polyelemental solid solution alloy nanoparticles
    Ludwig, Al.
    Matter 4 2100-2101 (2021)
    In this issue of Matter, Yao et al. report on advanced non-equilibrium high-temperature entropy-controlled synthesis of polyelemental nanoparticles. They achieve extreme mixing of 15 metals, some of them previously immiscible, in the form of a single phase solid solution. The compositionally tunable properties of such atomic scale mixtures within a simple crystal structure makes them highly interesting for the design of new materials, e.g., electrocatalysts. © 2021 Elsevier Inc.
    view abstractdoi: 10.1016/j.matt.2021.06.015
  • 2021 • 748 Microstructure formation and mechanical properties of ODS steels built by laser additive manufacturing of nanoparticle coated iron-chromium powders
    Doñate-Buendia, C. and Kürnsteiner, P. and Stern, F. and Wilms, M.B. and Streubel, R. and Kusoglu, I.M. and Tenkamp, J. and Bruder, E. and Pirch, N. and Barcikowski, S. and Durst, K. and Schleifenbaum, J.H. and Walther, F. and G...
    Acta Materialia 206 (2021)
    Oxide dispersion strengthened (ODS) steels are known for their enhanced mechanical performance at high temperatures or under radiation exposure. Their microstructure depends on the manufacturing process, from the nanoparticle addition to the base steel powder, to the processing of the nanoparticle enriched powder. The optimization and control of the processing steps still represent a challenge to establish a clear methodology for the additive manufacturing of ODS steels. Here, we evaluate the microstructure, nanoparticle evolution, and mechanical properties of ODS steels prepared by dielectrophoretic controlled adsorption of 0.08 wt% laser-synthesized yttrium oxide (Y2O3) on an iron-chromium ferritic steel powder (PM2000). The influence of the ODS steel fabrication technique is studied for two standard additive manufacturing techniques, directed energy deposition (DED) and laser powder bed fusion (LPBF). The compressive strength of the ODS steels at 600 °C is increased by 21% and 29% for the DED and LPBF samples, respectively, compared to the DED and LPBF steels manufactured without Y2O3 nanoparticle addition. The Martens hardness is enhanced by 9% for the LPBF ODS steel while no significant change is observed in the DED ODS steel. The microstructure and nanoparticle composition and distribution are evaluated by electron backscatter diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and atom probe tomography, to compare the microstructural features of DED and LPBF manufactured parts. Smaller grain size and more homogeneous distribution with lower agglomeration of Y-O nanoparticles in the LPBF sample are found to be key factors for enhanced mechanical response at 600 °C. The enhanced mechanical properties of the LPBF-processed sample and the more homogeneous nanoparticle dispersion can be linked to results obtained by finite element methods simulations of the melt pool that show two orders of magnitude faster cooling rates for LPBF than for DED. Therefore, this work presents and validates a complete laser-based methodology for the preparation and processing of an ODS steel, proving the modification of the microstructure and enhancement of the high-temperature strength of the as-built parts. © 2020
    view abstractdoi: 10.1016/j.actamat.2020.116566
  • 2021 • 747 Multidimensional thermally-induced transformation of nest-structured complex Au-Fe nanoalloys towards equilibrium
    Johny, J. and Prymak, O. and Kamp, M. and Calvo, F. and Kim, S.-H. and Tymoczko, A. and El-Zoka, A. and Rehbock, C. and Schürmann, U. and Gault, B. and Kienle, L. and Barcikowski, S.
    Nano Research (2021)
    Bimetallic nanoparticles are often superior candidates for a wide range of technological and biomedical applications owing to their enhanced catalytic, optical, and magnetic properties, which are often better than their monometallic counterparts. Most of their properties strongly depend on their chemical composition, crystallographic structure, and phase distribution. However, little is known of how their crystal structure, on the nanoscale, transforms over time at elevated temperatures, even though this knowledge is highly relevant in case nanoparticles are used in, e.g., high-temperature catalysis. Au-Fe is a promising bimetallic system where the low-cost and magnetic Fe is combined with catalytically active and plasmonic Au. Here, we report on the in situ temporal evolution of the crystalline ordering in Au-Fe nanoparticles, obtained from a modern laser ablation in liquids synthesis. Our in-depth analysis, complemented by dedicated atomistic simulations, includes a detailed structural characterization by X-ray diffraction and transmission electron microscopy as well as atom probe tomography to reveal elemental distributions down to a single atom resolution. We show that the Au-Fe nanoparticles initially exhibit highly complex internal nested nanostructures with a wide range of compositions, phase distributions, and size-depended microstrains. The elevated temperature induces a diffusion-controlled recrystallization and phase merging, resulting in the formation of a single face-centered-cubic ultrastructure in contact with a body-centered cubic phase, which demonstrates the metastability of these structures. Uncovering these unique nanostructures with nested features could be highly attractive from a fundamental viewpoint as they could give further insights into the nanoparticle formation mechanism under non-equilibrium conditions. Furthermore, the in situ evaluation of the crystal structure changes upon heating is potentially relevant for high-temperature process utilization of bimetallic nanoparticles, e.g., during catalysis. © 2021, The Author(s).
    view abstractdoi: 10.1007/s12274-021-3524-7
  • 2021 • 746 Nickel nanoparticles supported on nitrogen–doped carbon nanotubes are a highly active, selective and stable CO2 methanation catalyst
    Gödde, J. and Merko, M. and Xia, W. and Muhler, M.
    Journal of Energy Chemistry 54 323-331 (2021)
    CO2 methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route. Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation, calcination and reduction and characterized by elemental analysis, X-ray powder diffraction, H2 temperature-programmed reduction, CO pulse chemisorption and transmission electron microscopy. The Ni/NCNT catalysts were highly active in CO2 methanation at atmospheric pressure, reaching over 50% CO2 conversion and over 95% CH4 selectivity at 340 °C and a GHSV of 50,000 mL g−1 h−1 under kinetically controlled conditions. The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs. The optimum loading of 30 wt%–40 wt% Ni was found to result in the highest Ni surface area, the highest degree of conversion and the highest selectivity to methane. A constant TOF of 0.3 s−1 was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt% to 50 wt% Ni loading. Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream. © 2020 Science Press
    view abstractdoi: 10.1016/j.jechem.2020.06.007
  • 2021 • 745 Nitrogen and Oxygen Functionalization of Multi-walled Carbon Nanotubes for Tuning the Bifunctional Oxygen Reduction/Oxygen Evolution Performance of Supported FeCo Oxide Nanoparticles
    Kazakova, M.A. and Koul, A. and Golubtsov, G.V. and Selyutin, A.G. and Ishchenko, A.V. and Kvon, R.I. and Kolesov, B.A. and Schuhmann, W. and Morales, D.M.
    ChemElectroChem (2021)
    The combination of nanostructured transition metal oxides and carbon materials is a promising approach to obtain inexpensive, highly efficient, and stable bifunctional electrocatalysts for the oxygen reduction (ORR) and the oxygen evolution (OER) reactions. We present a strategy for improving the bifunctional ORR/OER activity of supported FeCoOx nanoparticles by tuning the properties of multi-walled carbon nanotubes (MWCNT) via nitrogen doping during their synthesis in the presence of ammonia and subsequent oxidative functionalization. In-depth structural characterization indicates that oxidative treatment provides fine control of the dispersion and localization of FeCoOx nanoparticles in MWCNT, while the optimal degree of nitrogen doping leads to increased bifunctional activity due to enhanced electrical conductivity as well as improved catalyst stability, in both OER and ORR conditions, for nanoparticles formed by two different synthesis routes. The findings reported can be strategically considered for the design of high-performance reversible ORR/OER electrocatalysts. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202100556
  • 2021 • 744 On the synthesis and structural evolution of artificial CrN/TiN nanocomposites
    Tillmann, W. and Kokalj, D. and Stangier, D. and Fu, Q. and Kruis, F.E. and Kesper, L. and Berges, U. and Westphal, C.
    Applied Surface Science 535 (2021)
    The synthesis of nanocomposites is limited to thermodynamically immiscible phases or to phase separation by exceeding the limits of solution. Hence, the formation of nanocomposites based on transition metals, revealing a nanocrystalline Metal-Nitride/nanocrystalline Metal-Nitride structure, is restricted. These restrictions can be overruled by a spatially separated synthesis of the two phases and a recombination during the deposition. With this approach, the limits of current systems can be expanded, enabling the synthesis of artificial nanocomposites based on a variety of materials. We demonstrate the synthesis of a composite of two nanocrystalline phases of the miscible transition metal-nitrides CrN and TiN. TiN nanoparticles were synthesized using an atmospheric-pressure arc reactor and in-situ injected into a growing CrN thin film. The thin films are analyzed regarding their physical- and microstructure using two-dimensional GIXRD, XPS based on synchrotron radiation and TEM. The CrTiN thin film reveals a two-phase structure consisting of nanocrystalline CrN and TiN phases with crystallite sizes of 9 nm and 4 nm according to GIXRD. XPS indicates bonding of Cr-N, Cr-Cr, and Ti-N. No hint for Cr-Ti bonding was found, excluding (Cr,Ti)N solid solution formation. Based on the TEM-investigations, TiN nanoparticles are embedded as agglomerates in the CrN matrix. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2020.147736
  • 2021 • 743 Phase-sensitive detection of gas-borne Si nanoparticles via line-of-sight UV/VIS attenuation
    Asif, M. and Menser, J. and Endres, T. and Dreier, T. and Daun, K. and Schulz, C.
    Optics Express 29 21795-21809 (2021)
    The distinct optical properties of solid and liquid silicon nanoparticles are exploited to determine the distribution of gas-borne solid and liquid particles in situ using line-of-sight attenuation measurements carried out across a microwave plasma reactor operated at 100 mbar. The ratio between liquid and solid particles detected downstream of the plasma varied with measurement location, microwave power, and flow rate. Temperatures of the liquid particles were pyrometrically-inferred using a spectroscopic model based on Drude theory. The phase-sensitive measurement supports the understanding of nanoparticle formation and interaction and thus the overall gas-phase synthesis process. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.426528
  • 2021 • 742 Pore penetration of porous catalyst supports by in-situ-adsorbed, agglomeration-quenched nanoparticles from pulsed laser ablation in supercritical CO2
    Labusch, M. and Puthenkalam, S. and Cleve, E. and Barcikowski, S. and Reichenberger, S.
    Journal of Supercritical Fluids 169 (2021)
    To synthesize nanoparticles for catalytic applications, pulsed laser ablation (PLA) in liquids has been established as a cost-effective method complementary to wet-chemical synthesis routes. Due to mass transport limitations in water, recent studies conducted PLA in supercritical CO2 (scCO2) to use the superior transport properties. Unfortunately, PLA in scCO2 so far led to the formation of bigger particles and agglomerates, which are unfavorable for the application as catalytically active material. As will be shown in this paper, the former are being avoided by means of an in-situ deposition approach of gold and platinum in scCO2 in presence of mesoporous γ-Al2O3 support. Transmission electron microscopy reveals that the resulting nanoparticle size is quenched while careful adjustment of the mixing conditions during PLA is shown to significantly reduce the agglomeration tendency. Cross-sections of the heterogeneous catalyst prove, that the nanoparticles penetrate the mesoporous support up to 109 nm deep. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.supflu.2020.105100
  • 2021 • 741 Room temperature synthesized solid solution AuFe nanoparticles and their transformation into Au/Fe Janus nanocrystals
    Efremova, M.V. and Spasova, M. and Heidelmann, M. and Grebennikov, I.S. and Li, Z.-A. and Garanina, A.S. and Tcareva, I.O. and Savchenko, A.G. and Farle, M. and Klyachko, N.L. and Majouga, A.G. and Wiedwald, U.
    Nanoscale 13 10402-10413 (2021)
    Solid solution AuFe nanoparticles were synthesized for the first time under ambient conditions by an adapted method previously established for the Fe3O4-Au core-shell morphology. These AuFe particles preserved the fcc structure of Au incorporated with paramagnetic Fe atoms. The metastable AuFe can be segregated by transformation into Janus Au/Fe particles with bcc Fe and fcc Au upon annealing. The ferromagnetic Fe was epitaxially grown on low index fcc Au planes. This preparation route delivers new perspective materials for magnetoplasmonics and biomedical applications and suggests the reconsideration of existing protocols for magnetite-gold core-shell synthesis. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1nr00383f
  • 2021 • 740 Single-Entity Electrocatalysis of Individual “Picked-and-Dropped” Co3O4 Nanoparticles on the Tip of a Carbon Nanoelectrode
    Quast, T. and Aiyappa, H.B. and Saddeler, S. and Wilde, P. and Chen, Y.-T. and Schulz, S. and Schuhmann, W.
    Angewandte Chemie - International Edition 60 3576-3580 (2021)
    Nano-electrochemical tools to assess individual catalyst entities are critical to comprehend single-entity measurements. The intrinsic electrocatalytic activity of an individual well-defined Co3O4 nanoparticle supported on a carbon-based nanoelectrode is determined by employing an efficient SEM-controlled robotic technique for picking and placing a single catalyst particle onto a modified carbon nanoelectrode surface. The stable nanoassembly is microscopically investigated and subsequently electrochemically characterized. The hexagonal-shaped Co3O4 nanoparticles demonstrate size-dependent electrochemical activity and exhibit very high catalytic activity with a current density of up to 11.5 A cm−2 at 1.92 V (vs. RHE), and a turnover frequency of 532±100 s−1 at 1.92 V (vs. RHE) towards catalyzing the oxygen evolution reaction. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202014384
  • 2021 • 739 Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles
    Al-Zubeidi, A. and Stein, F. and Flatebo, C. and Rehbock, C. and Hosseini Jebeli, S.A. and Landes, C.F. and Barcikowski, S. and Link, S.
    ACS Nano 15 8363-8375 (2021)
    Gold-silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold-silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles. ©
    view abstractdoi: 10.1021/acsnano.0c10150
  • 2021 • 738 Spatial distribution of gas-phase synthesized germanium nanoparticle volume-fraction and temperature using combined in situ line-of-sight emission and extinction spectroscopy
    Liu, G. and Asif, M. and Menser, J. and Dreier, T. and Mohri, K. and Schulz, C. and Endres, T.
    Optics Express 29 8387-8406 (2021)
    In this study, emission and extinction spectroscopy were combined to in situ measure temperature and volume fraction distributions of liquid germanium nanoparticle gas-phase synthesized in an argon/hydrogen/germane flow through a microwave plasma. Emission of the hot particles and extinction against a continuous background were recorded by a spectrometer in the 380-703 nm and 230-556 nm ranges, respectively, selected based on the specific optical properties of the material. Absorption coefficients were deconvoluted from line-of-sight attenuation (LOSA) measurements by a least-square algorithm and then used to determine the local volume fraction distribution. The temperature field was derived from the line-of-sight emission (LOSE) spectra with the prior knowledge of absorption coefficients. A multi-wavelength reconstruction model was developed for the determination of the spatially-resolved distribution of the measured quantities assuming a stationary axisymmetric flow. Advantages of the method include experimental simplicity, low cost, and adaptability to up-scaled reactor sizes. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
    view abstractdoi: 10.1364/OE.418922
  • 2021 • 737 The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction
    Jalalpoor, D. and Göhl, D. and Paciok, P. and Heggen, M. and Knossalla, J. and Radev, I. and Peinecke, V. and Weidenthaler, C. and Mayrhofer, K.J.J. and Ledendecker, M. and Schüth, F.
    Journal of the Electrochemical Society 168 (2021)
    Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and platinum and its impact on the catalytic activity and durability has only received minor attention. This is partly due to difficulties in the preparation of morphology- and surface-area-controlled antimony-doped tin oxide materials. The presented study sheds light onto catalyst-support interaction on a fundamental level, specifically between platinum as a catalyst and ATO as a support material. By using a previously described hard-templating method, a series of morphology controlled ATO support materials for platinum nanoparticles with different antimony doping concentrations were prepared. Compositional and morphological changes before and during accelerated stress tests are monitored, and underlying principles of deactivation, dissolution and catalytic performance are elaborated. We demonstrate that mobilized antimony species and strong metal support interactions lead to Pt/Sb alloy formation as well as partially blocking of active sites. This has adverse consequences on the accessible platinum surface area, and affects negatively the catalytic performance of platinum. Operando time-resolved dissolution experiments uncover the potential boundary conditions at which antimony dissolution can be effectively suppressed and how platinum influences the dissolution behavior of the support. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
    view abstractdoi: 10.1149/1945-7111/abd830
  • 2021 • 736 Triple Modification of Alginate Hydrogels by Fibrin Blending, Iron Nanoparticle Embedding, and Serum Protein-Coating Synergistically Promotes Strong Endothelialization
    Richter, A. and Li, Y. and Rehbock, C. and Barcikowski, S. and Haverich, A. and Wilhelmi, M. and Böer, U.
    Advanced Materials Interfaces 8 (2021)
    Stent therapy can reduce both morbidity and mortality of chronic coronary stenosis and acute myocardial infarction. However, delayed re-endothelialization, endothelial dysfunction, and chronic inflammation are still unsolved problems. Alginate hydrogels can be used as a coating for stent surfaces; however, complete and fast endothelialization cannot be achieved. In this study, alginate hydrogels are modified by fibrin blending, iron nanoparticle (Fe-NP) embedding, and serum protein coating (SPC) while surface properties and endothelialization capacity are monitored. Only a triple, synergetic modification of the alginate coating by simultaneous I) fibrin blending, II) Fe-NP addition complemented by III) SPC is found to significantly improve endothelial cell viability (live–dead-staining) and proliferation (WST-8 assay). These conditions yield formation of closed endothelial cell monolayers and an up to threefold increase (p < 0.01) in viability, while, interestingly, no effect is found when the modifications (I)–(III) are conducted individually. This synergetic effect is attributed to an accumulation of agglomerated Fe-NP and serum proteins along fibrin fibers, observed via laser scanning microscopy tracking nanoparticle scattering and tetramethylrhodamine (TRITC)-albumin fluorescence. These synergetic effects can pave the way toward a novel strategy for the modification of various hydrogel-based biomaterials and biomaterial coatings. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/admi.202002015
  • 2021 • 735 Upscaling nanoparticle synthesis by sputter deposition in ionic liquids
    Meischein, M. and Ludwig, Al.
    Journal of Nanoparticle Research 23 (2021)
    Upscaling of nanoparticle fabrication by sputtering into an ionic liquid is shown for the example of Cu. Long-time sputtering (24 h) into a large amount (50 mL) of the ionic liquid 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide [Bmim][(Tf)2 N] yields an amount of approximately 1 g Cu nanoparticles (mean spherical diameter (2.6 ± 1.1) nm), stabilized in ionic liquid without agglomerations. Extraction of Cu nanoparticles from the stabilizing ionic liquid was performed with the capping agent hexadecylamine. Extracted particles could be redispersed in other solvents, thus enabling applications of sputtered nanoparticles beyond ionic liquids. © 2021, The Author(s).
    view abstractdoi: 10.1007/s11051-021-05248-8
  • 2021 • 734 Wavelet neural network modeling for the retention efficiency of sub-15 nm nanoparticles in ultrafiltration under small particle to pore diameter ratio
    Fan, Z. and Ji, P.-P. and Zhang, J. and Segets, D. and Chen, D.-R. and Chen, S.-C.
    Journal of Membrane Science 635 (2021)
    Ultrafiltration (UF) using membranes with a small ratio of particle to pore diameter (PPD) would be very desirable for energy saving. The nanoparticle (NP) retention efficiency of membranes with a small PPD ratio depends on various physical and chemical properties of NPs, membranes and solutions as well as the filtration conditions. Until now, no simple model is available for the calculation of NP retention efficiency in UF membranes, besides, it is unlikely to conduct experiments covering all conditions for obtaining the efficiency. The artificial neural network (ANN) has been attracting much attention for studying the performance of a highly nonlinear system. In this study, a wavelet ANN model was developed to predict the NP retentions in membranes for the dead-ended UFs under different conditions. A total of 13 parameters, including the membrane features, particle properties, water solution characteristics, operating conditions, etc., are considered as ANN inputs and the NP retention efficiency as the output. A total of 200 datasets with high quality from literature were selected, in which 50% were for the model training, 30% for the model validation and the remaining 20% for the model testing. A high correlation between the output and inputs was obtained and the significance of the 13 parameters on the NP retention was ranked. A case study was performed to further validate the trained ANN model in the prediction of the retention efficiency of 10 nm gold NPs in a 50 nm pore sized polycarbonate track etched (PCTE) membrane at different pH conditions (5–9). Focusing on the variation of pH, an excellent agreement between the model prediction and the calculation by the modified extended Derjaguin Landau Verwey Overbeek-Maxwell (MEDLVO-Maxwell) model originating from classical and extended DLVO theory was obtained. The interaction energy in the MEDLVO-Maxwell model was based on the separation distance calculated by a quench molecular dynamics (MD) simulation. This study illustrates and validates the application of ANN modeling on the NP retention efficiency prediction in the UF with small PPD ratios. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2021.119503
  • 2021 • 733 X-ray-Based Techniques to Study the Nano-Bio Interface
    Sanchez-Cano, C. and Alvarez-Puebla, R.A. and Abendroth, J.M. and Beck, T. and Blick, R. and Cao, Y. and Caruso, F. and Chakraborty, I. and Chapman, H.N. and Chen, C. and Cohen, B.E. and Conceição, A.L.C. and Cormode, D.P. and C...
    ACS Nano 15 3754-3807 (2021)
    X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use in vivo. ©
    view abstractdoi: 10.1021/acsnano.0c09563
  • 2020 • 732 A model flow reactor design for the study of nanoparticle structure formation under well-defined conditions
    Rosenberger, T. and Sellmann, J. and Wlokas, I. and Kruis, F.E.
    Review of Scientific Instruments 91 (2020)
    Structure formation models describe the change of the particle structure, e.g., by sintering or coating, as a function of the residence time and temperature. For the validation of these models, precise experimental data are required. The precise determination of the required data is difficult due to simultaneously acting mechanisms leading to particle structure formation as well as their dependency on various particle properties and process conditions in the reactor. In this work, a model flow reactor (MFR) is designed and optimized, supported by a validated computational fluid dynamic simulation, to determine the structure formation of nanoparticles under well-defined conditions. Online instrumentation is used to measure the particle mass and different equivalent diameter to detect changes of the particle shape and to calculate the particle structure, defined by the primary particle size, the number of primary particles per agglomerate, coating thickness, effective density, and fractal dimension, by means of structural models. High precision is achieved by examining size-selected particles in a low number concentration and a laminar flow field. Coagulation can be neglected due to the low particle number concentration. Structure formation is restricted to a defined region by direct particle trajectories from the water-cooled aerosol inlet to the water-cooled outlet. A preheated sheath gas is used to concentrate the aerosol on the centerline. The simulated particle trajectories exhibit a well-defined and narrow temperature residence time distribution. Residence times of at least 1 s in the temperature range from 500 K to 1400 K are achieved. The operation of the MFR is demonstrated by the sintering of size-selected FexOy agglomerates with measurements of the particle size and mass distribution as a function of the temperature. An increase of the effective density, resulting from the decreasing particle size at constant particle mass, is observed. © 2020 Author(s).
    view abstractdoi: 10.1063/5.0018880
  • 2020 • 731 A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation
    Dai, Y. and Poidevin, C. and Ochoa-Hernández, C. and Auer, A.A. and Tüysüz, H.
    Angewandte Chemie - International Edition 59 5788-5796 (2020)
    Direct selective oxidation of hydrocarbons to oxygenates by O2 is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C−H bonds at benzylic positions. In this work, stable, lead-free, Cs3Bi2Br9 halide perovskites are integrated within the pore channels of mesoporous SBA-15 silica and demonstrate their photocatalytic potentials for C−H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C5 to C16 including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol gcat−1 h−1 and excellent selectivity (&gt;99 %) towards aldehydes and ketones under visible-light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well-dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp3)−H bond activation by photoinduced charges. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201915034
  • 2020 • 730 Aerosol synthesis of titanium nitride nanoparticles by direct current arc discharge method
    Fu, Q. and Kokalj, D. and Stangier, D. and Kruis, F.E. and Tillmann, W.
    Advanced Powder Technology 31 4119-4128 (2020)
    Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N2 and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12 A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip. © 2020 The Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2020.08.012
  • 2020 • 729 Analysis of the nanoparticle dispersion and its effect on the crystalline microstructure in carbon-additivated PA12 feedstock material for laser powder bed fusion
    Hupfeld, T. and Sommereyns, A. and Riahi, F. and Doñate-Buendía, C. and Gann, S. and Schmidt, M. and Gökce, B. and Barcikowski, S.
    Materials 13 (2020)
    Driven by the rapid development of additive manufacturing technologies and the trend towards mass customization, the development of new feedstock materials has become a key aspect. Additivation of the feedstock with nanoparticles is a possible route for tailoring the feedstock material to the printing process and to modify the properties of the printed parts. This study demonstrates the colloidal additivation of PA12 powder with laser-synthesized carbon nanoparticles at >95% yield, focusing on the dispersion of the nanoparticles on the polymer microparticle surface at nanoparticle loadings below 0.05 vol%. In addition to the descriptors "wt%" and "vol%", the descriptor "surf%" is discussed for characterizing the quantity and quality of nanoparticle loading based on scanning electron microscopy. The functionalized powders are further characterized by confocal dark field scattering, differential scanning calorimetry, powder rheology measurements (avalanche angle and Hausner ratio), and regarding their processability in laser powder bed fusion (PBF-LB). We find that heterogeneous nucleation is induced even at a nanoparticle loading of just 0.005 vol%. Finally, analysis of the effect of low nanoparticle loadings on the final parts' microstructure by polarization microscopy shows a nanoparticle loading-dependent change of the dimensions of the lamellar microstructures within the printed part. © 2020 by the authors.
    view abstractdoi: 10.3390/ma13153312
  • 2020 • 728 Anchoring of palladium nanoparticles on N-doped mesoporous carbon
    Warczinski, L. and Hu, B. and Eckhard, T. and Peng, B. and Muhler, M. and Hättig, C.
    Physical Chemistry Chemical Physics 22 21317-21325 (2020)
    Pd nanoparticles deposited on nitrogen-doped mesoporous carbon are promising catalysts for highly selective and effective catalytic hydrogenation reactions. To design and utilize these novel catalysts, it is essential to understand the effect of N doping on the metal-support interactions. A combined experimental (X-ray photoelectron spectroscopy) and computational (density functional theory) approach is used to identify preferential adsorption sites and to give detailed explanations of the corresponding metal-support interactions. Pyridinic N atoms turned out to be the preferential adsorption sites for Pd nanoparticles on nitrogen-doped mesoporous carbon, interacting through their lone pairs (LPs) with the Pd atoms via N-LP-Pd dσ and N-LP-Pd s and Pd dπ-π∗ charge transfer, which leads to a change in the Pd oxidation state. Our results evidence the existence of bifunctional palladium nanoparticles containing Pd0 and Pd2+ centers. © the Owner Societies.
    view abstractdoi: 10.1039/d0cp03234d
  • 2020 • 727 Assembly, Stability, and Electrical Properties of Sparse Crystalline Silicon Nanoparticle Networks Applied to Solution-Processed Field-Effect Transistors
    Chryssikos, D. and Wiesinger, M. and Bienek, O. and Wiggers, H. and Stutzmann, M. and Cattani-Scholz, A. and Pereira, R.N.
    ACS Applied Electronic Materials 2 692-700 (2020)
    Thin films of crystalline silicon nanoparticles (Si NPs) processed from liquid dispersions of NPs (NP inks) using printing-type deposition methods are currently being intensively investigated for the development of electronic and optoelectronic nanotechnologies. Various (opto)electronic applications have already been demonstrated based on these materials, but so far, devices exhibit modest performance because of relatively low electrical conductivity and charge carrier mobility. In this work, we aim at unveiling the major factors affecting the long-range transport of charges in Si NP thin films. For this, we monitor the electrical properties of thin-film field effect transistors (FETs) as the active channel of the devices is gradually filled with Si NPs. To produce these FET devices featuring stable, sparse Si NP networks within the active channel, we developed a fabrication protocol based on NP deposition by device substrate immersion in a NP ink, made of Si NPs and chlorobenzene, followed by annealing and ultrasonication. We found that both the electrical conductivity and the charge carrier mobility of the FETs increase extremely rapidly as the device channel coverage with NPs increases. Thus, the NP network corresponds effectively to an inhomogeneous blend of conducting and insulating Si NPs, with the most efficient charge percolation paths involving only a fraction of the NPs. We discuss the factors that may lead to this behavior, in view of developing Si NP thin films with competitive charge transport characteristics. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsaelm.9b00786
  • 2020 • 726 Assessing the Influence of Supercritical Carbon Dioxide on the Electrochemical Reduction to Formic Acid Using Carbon-Supported Copper Catalysts
    Junge Puring, K. and Evers, O. and Prokein, M. and Siegmund, D. and Scholten, F. and Mölders, N. and Renner, M. and Roldan Cuenya, B. and Petermann, M. and Weidner, E. and Apfel, U.-P.
    ACS Catalysis 10 12783-12789 (2020)
    The electrocatalytic reduction of carbon dioxide (CO2) by means of renewable energies is widely recognized as a promising approach to establish a sustainable closed carbon cycle economy. However, widespread application is hampered by the inherent difficulty in suppressing the hydrogen evolution reaction and controlling the overall process selectivity. Further critical parameters are the limited solubility of CO2 in many electrolytes and its hindered mass transport to the electrodes. Herein we report on a series of nanoparticle Cu electrocatalysts on different carbon supports and their potential to perform the electrochemical CO2 reduction under supercritical conditions (scCO2). Herein, CO2 serves as the reaction medium and reactant alike. By a detailed comparison to ambient conditions we show that scCO2 conditions largely suppress the undesirable hydrogen evolution and favor the production of formic acid by the Cu electrodes. Furthermore, we show that scCO2 conditions significantly prevent Cu nanoparticle agglomeration during electrocatalysis. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.0c02983
  • 2020 • 725 Characterization of few-layer graphene aerosols by laser-induced incandescence
    Musikhin, S. and Fortugno, P. and Corbin, J.C. and Smallwood, G.J. and Dreier, T. and Daun, K.J. and Schulz, C.
    Carbon 167 870-880 (2020)
    Gas-phase synthesis is a promising route for producing large amounts of high quality few-layer graphene (FLG) nanoparticles economically, but optimizing these processes requires a detailed understanding of the formation kinetics, which in turn demands diagnostics for characterizing this material in situ. This work reports the first laser-induced incandescence measurements on FLG aerosols. Temporally- and spectrally-resolved incandescence signals from FLG particles are measured and used to calculate pyrometric temperatures. Differences between incandescence signals and pyrometric temperatures obtained from FLG and aerosolized soot nanoaggregates are attributed to the larger absorption cross-section and specific surface area of FLG compared to soot. LII signal intensity is found to vary linearly with particle number concentration measured independently by a condensation particle counter. Overall, these results demonstrate the potential for laser-induced incandescence to measure FLG nanoparticle mass (volume) fraction and active surface area in situ, as well as to differentiate graphene from other types of carbonaceous nanomaterials online. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.carbon.2020.05.052
  • 2020 • 724 Continuous-Flow Flat Jet Setup for Uniform Pulsed Laser Postprocessing of Colloids
    Zerebecki, S. and Reichenberger, S. and Barcikowski, S.
    Journal of Physical Chemistry A 124 11125-11132 (2020)
    Pulsed laser postprocessing (PLPP) of colloidal nanoparticles and related laser fragmentation in liquid (LFL) using a liquid jet setup have become an acknowledged tool to reduce the nanoparticle diameter down to a few nanometers, alter the crystal phase, or increase the defect density under high-purity and continuous-flow conditions. In recent studies on LFL that were conducted with a cylindrical liquid jet, intensity gradients and related incomplete illumination of the volume element passing through the laser beam path were reported to cause a broadening of the product particle size distribution, melting, and phase segregation. In this paper, we present a new flat jet design, which reduces the deviation of the laser intensity up to 10 times compared to the conventional cylindrical liquid jet. The experimental threshold intensity for gold nanoparticle fragmentation found with the cylindrical setup strongly deviates from the theoretical prediction, while they are in very good agreement for the flat jet setup. Additionally, a narrow product size fraction of 3 ± 2 nm was found for the flat jet, while the main product fraction gained from the cylindrical jet was 10 ± 8 nm in size under the same conditions. Consequently, the flat jet setup allows us not only to study laser fragmentation mechanisms with higher precision but also to gain product particles with narrow particle size distribution at single pulse per particle conditions even at elevated mass concentrations (>50 mg L-1). In future studies, these promising results also render the flat jet setup relevant for the other disciplines of PLPP such as laser melting and defect engineering. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpca.0c08787
  • 2020 • 723 Controlling the Number of Branches and Surface Facets of Pd-Core Ru-Branched Nanoparticles to Make Highly Active Oxygen Evolution Reaction Electrocatalysts
    Myekhlai, M. and Benedetti, T.M. and Gloag, L. and Poerwoprajitno, A.R. and Cheong, S. and Schuhmann, W. and Gooding, J.J. and Tilley, R.D.
    Chemistry - A European Journal 26 15501-15504 (2020)
    Producing stable but active materials is one of the enduring challenges in electrocatalysis and other types of catalysis. Producing branched nanoparticles is one potential solution. Controlling the number of branches and branch size of faceted branched nanoparticles is one of the major synthetic challenges to achieve highly active and stable nanocatalysts. Herein, we use a cubic-core hexagonal-branch mechanism to synthesize branched Ru nanoparticles with control over the size and number of branches. This structural control is the key to achieving high exposure of active {10–11} facets and optimum number of Ru branches that enables improved catalytic activity for oxygen evolution reaction while maintaining high stability. © 2020 Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202003561
  • 2020 • 722 Dual pH-Induced Reversible Self-Assembly of Gold Nanoparticles by Surface Functionalization with Zwitterionic Ligands
    He, H. and Ostwaldt, J.-E. and Hirschhäuser, C. and Schmuck, C. and Niemeyer, J.
    Small 16 (2020)
    The dual pH-induced reversible self-assembly (PIRSA) of Au-nanoparticles (Au NPs) is reported, based on their decoration with the self-complementary guanidiniocarbonyl pyrrole carboxylate zwitterion (GCPZ). The assembly of such functionalized Au NPs is found at neutral pH, based on supramolecular pairing of the GCPZ groups. The resulting self-assembled system can be switched back to the disassembled state by addition of base or acid. Two predominant effects that contribute to the dual-PIRSA of Au NPs are identified, namely the ionic hydrogen bonding between the GCPZ groups, but also a strong hydrophobic effect. The contribution of each interaction is depending on the concentration of GCPZ on NPs, which allows to control the self-assembly state over a wide range of different water/solvent ratios. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.202001044
  • 2020 • 721 Effect of nanoparticle additivation on the microstructure and microhardness of oxide dispersion strengthened steels produced by laser powder bed fusion and directed energy deposition
    Doñate-Buendia, C. and Streubel, R. and Kürnsteiner, P. and Wilms, M.B. and Stern, F. and Tenkamp, J. and Bruder, E. and Barcikowski, S. and Gault, B. and Durst, K. and Schleifenbaum, J.H. and Walther, F. and Gökce, B.
    Procedia CIRP 94 41-45 (2020)
    In this contribution, the effect of nanoparticle additivation on the microstructure and microhardness of oxide dispersion strengthened steels (ODS) manufactured by laser powder bed fusion (L-PBF) and directed energy deposition (DED) additive manufacturing (AM) is studied. The powder composites are made of micrometer-sized iron-chromium-alloy based powder which are homogenously decorated with Y2O3 nanoparticles synthesized by pulsed laser fragmentation in water. Consolidated by L-PBF and DED, an enhanced microhardness of the AM-built ODS sample is found. This increase is related to the significant microstructural differences found between the differently processed samples. © 2020 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2020.09.009
  • 2020 • 720 Effective size separation of laser-generated, surfactant-free nanoparticles by continuous centrifugation
    Kohsakowski, S. and Seiser, F. and Wiederrecht, J.-P. and Reichenberger, S. and Vinnay, T. and Barcikowski, S. and Marzun, G.
    Nanotechnology 31 (2020)
    High-power, nanosecond, pulsed-laser ablation in liquids enables the continuous synthesis of highly pure colloidal nanoparticles (NPs) at an application-relevant scale. The gained mass-weighted particle size distribution is however often reported to be broad, requiring post treatment like centrifugation to remove undesired particle size fractions. To date, available centrifugation techniques are generally discontinuous, limiting the throughput and hindering economic upscaling. Hence, throughout this paper, a scalable, continuously operating centrifugation of laser-generated platinum NPs in a tubular bowl centrifuge is reported for the first time. To that end, using a 121 W ns-laser, the continuous production of a colloidal suspension of NPs, yet with broad particle size distribution has been employed, yielding productivities of 1-2 g h-1 for gold, silver, and platinum. The power-specific productivities (Au: 18 mg h-1 W-1, Pt: 13 mg h-1 W-1, Ag: 8 mg h-1 W-1, Ni: 6 mg h-1 W-1) are far higher than reported before. Subsequent downstream integration of a continuously operating tubular bowl centrifuge was successfully achieved for Pt NPs allowing the removal of undesired particle size with high throughput. By means of a systematic study of relevant centrifugation parameters involved, effective size optimization and respective size sharpness parameters for a maximum Pt NP diameter of 10 nm are reported. The results of the experimental centrifugation of laser-generated Pt NPs were in excellent agreement with the theoretically calculated cut-off diameter. After centrifugation with optimized parameters (residence time of 5 min; g-force of 38,454 g), the polydispersity indices of the Pt NPs size distributions were reduced by a factor of six, and high monodispersity was observed. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab55bd
  • 2020 • 719 Effects of filter structure, flow velocity, particle concentration and fouling on the retention efficiency of ultrafiltration for sub-20 nm gold nanoparticles
    Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
    Separation and Purification Technology 241 (2020)
    Ultrafiltration techniques with membranes of pore sizes under 100 nm have been widely applied in drinking water, wastewater, semiconductor and pharmaceutical process water treatments for nanoparticle (NP) and pathogen removal. The most direct way to evaluate the membrane performance is to experimentally obtain the size fractional retention efficiency. However, the real-life performance of the membrane in terms of fouling (or loading) characteristics and the effects of the concentration of challenging particles and rate of flux (or filtration velocities) on the filtration efficiency during fouling have not been well understood. In this study, systematic filtration experiments for filtration efficiency at clean and loaded conditions were conducted for three different 50 nm rated membrane filters, including PTFE (Polytetrafluoroethylene), PCTE (Polycarbonate Track-Etched) and MCE (Mixed Cellulose Ester) membranes, against 5, 10 and 20 nm Au NPs at different feed concentrations and fluxes. The results showed that the effects of feed concentration and flux are significant. This study provides important insights of retention mechanisms and efficiency for different ultrafiltration membrane structures at varied filtration velocities and fouling characteristics giving clear directions of future NP ultrafiltration research. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2020.116689
  • 2020 • 718 Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony-Doped Tin Oxide Support
    Böhm, D. and Beetz, M. and Schuster, M. and Peters, K. and Hufnagel, A.G. and Döblinger, M. and Böller, B. and Bein, T. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 30 (2020)
    A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open-porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO-supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO-supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr −1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2-supported IrO2 reference catalyst under the same measurement conditions. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201906670
  • 2020 • 717 Ejector-based nanoparticle sampling from pressures down to 20 mbar
    Rosenberger, T. and Neises, J. and Kiesler, D. and Kruis, F.E.
    Journal of Aerosol Science 144 (2020)
    The application of standard online instrumentation, such as scanning mobility particle sizer (SMPS), centrifugal particle mass analyzer or aerosol particle mass analyzer (CPMA/APM), and electrical low-pressure impactor (ELPI+) to low-pressure processes is only possible with extensive modification of the devices and extensive calibrations. A low-pressure ejector is a suitable device to transfer aerosol nanoparticles from low-pressure regions to atmospheric pressure and allows the direct use of standard online instrumentation. In this work, a commercial low-pressure ejector is investigated in the pressure range from 20–180 mbar with fully-sintered and size-selected nanoparticles (15–80 nm) in order to extend the application range of online instruments to low-pressure processes and open up a new variety of analysis methods. Results are compared to our previous work which was limited to pressures above 120 mbar. A change in particle size during the measurements for fully-sintered silver particles was not observed. A particle dilution factor between 60–6500 was found. High particle losses in the ejector for large particle sizes are compensated by a lower gas dilution factor. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.jaerosci.2020.105531
  • 2020 • 716 Electrochemical dealloying as a tool to tune the porosity, composition and catalytic activity of nanomaterials
    Rurainsky, C. and Manjón, A.G. and Hiege, F. and Chen, Y.-T. and Scheu, C. and Tschulik, K.
    Journal of Materials Chemistry A 8 19405-19413 (2020)
    Electrochemical dealloying as a post-Treatment can greatly improve the catalytic activity of nanoparticles. To date, selecting suitable conditions to reach desired porosity, composition and catalytic activity is based on trial-And-error-Attempts, due to insufficient understanding of the electrochemically induced morphological and compositional changes of the nanoparticles. These changes are elucidated here by combining electrochemistry with identical location electron microscopy analyses and linking them to the electrocatalytic properties of the obtained nanocatalysts. Using AgAu alloy nanoparticles and the hydrogen evolution reaction as a model system, the influence of cyclic voltammetry parameters on the catalytic activity upon electrochemical dealloying is investigated. Increasing the number of cycles initially results in a decreased Ag content and a sharp improvement in activity. Additional dealloying increases the nanoparticle porosity, while marginally altering their composition, due to surface motion of atoms. Since this is accompanied by particle aggregation, a decrease in catalytic activity results upon extensive cycling. This transition between porosity formation and particle aggregation marks the optimum for nanocatalyst post-production. The gained insights may aid speeding up the development of new materials by electrochemical dealloying as an easy-To-control post-processing route to tune the properties of existing nanoparticles, instead of having to alter usually delicate synthesis routes as a whole. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ta04880a
  • 2020 • 715 Faceted Branched Nickel Nanoparticles with Tunable Branch Length for High-Activity Electrocatalytic Oxidation of Biomass
    Poerwoprajitno, A.R. and Gloag, L. and Watt, J. and Cychy, S. and Cheong, S. and Kumar, P.V. and Benedetti, T.M. and Deng, C. and Wu, K.-H. and Marjo, C.E. and Huber, D.L. and Muhler, M. and Gooding, J.J. and Schuhmann, W. and Wan...
    Angewandte Chemie - International Edition 59 15487-15491 (2020)
    Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic-core hexagonal-branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), as an example for biomass conversion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
    view abstractdoi: 10.1002/anie.202005489
  • 2020 • 714 Ferroelectric nanocomposites: Influence of nanoparticle size distribution on electrocaloric conversion parameters
    Shevliakova, H.V. and Morozovska, A.N. and Morozovsky, N.V. and Svechnikov, G.S. and Shvartsman, V.V.
    2020 IEEE 40th International Conference on Electronics and Nanotechnology, ELNANO 2020 - Proceedings 2020-April 105-108 (2020)
    The study of the electrocaloric effect in ensembles of ferroelectric nanoparticles is of significant interest for fundamental research and its practical applications in solidstate coolers. The exploration of electrocaloric cooling is of great importance to finding solutions to environmental and energyefficiency issues in currently available refrigeration technologies. In this work we calculated the polarization, electrocaloric temperature change, and dielectric permittivity of the nanocomposite containing non-interacting ferroelectric nanoparticles with different size distributions, and analyzed the dependences of polarization, dielectric permittivity and electrocaloric temperature change on the distribution function of the particles sizes. As anticipated, the properties of the nanocomposite approach that of the average size nanoparticles with a narrowing in the dispersion of particles sizes within the nanocomposite. A widening in the particles size distribution increases the coercivity (i.e. half-width of the ferroelectric hysteresis loop), but the hysteresis width decreases for the maximum particle radius, which is significantly smaller than the dispersion of the distribution function. © 2020 IEEE.
    view abstractdoi: 10.1109/ELNANO50318.2020.9108206
  • 2020 • 713 Formic Acid-Assisted Selective Hydrogenolysis of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Bifunctional Pd Nanoparticles Supported on N-Doped Mesoporous Carbon
    Hu, B. and Warczinski, L. and Li, X. and Lu, M. and Bitzer, J. and Heidelmann, M. and Eckhard, T. and Fu, Q. and Schulwitz, J. and Merko, M. and Li, M. and Kleist, W. and Hättig, C. and Muhler, M. and Peng, B.
    Angewandte Chemie - International Edition (2020)
    Biomass-derived 5-hydroxymethylfurfural (HMF) is regarded as one of the most promising platform chemicals to produce 2,5-dimethylfuran (DMF) as a potential liquid transportation fuel. Pd nanoparticles supported on N-containing and N-free mesoporous carbon materials were prepared, characterized, and applied in the hydrogenolysis of HMF to DMF under mild reaction conditions. Quantitative conversion of HMF to DMF was achieved in the presence of formic acid (FA) and H2 over Pd/NMC within 2 h. The reaction mechanism, especially the multiple roles of FA, was explored through a detailed comparative study by varying hydrogen source, additive, and substrate as well as by applying in situ ATR-IR spectroscopy. The major role of FA is to shift the dominant reaction pathway from the hydrogenation of the aldehyde group to the hydrogenolysis of the hydroxymethyl group via the protonation by FA at the C-OH group, lowering the activation barrier of the C−O bond cleavage and thus significantly enhancing the reaction rate. XPS results and DFT calculations revealed that Pd2+ species interacting with pyridine-like N atoms significantly enhance the selective hydrogenolysis of the C−OH bond in the presence of FA due to their high ability for the activation of FA and the stabilization of H−. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202012816
  • 2020 • 712 Forming amorphous calcium carbonate within hydrogels by enzyme-induced mineralization in the presence of N-(phosphonomethyl)glycine
    Milovanovic, M. and Unruh, M.T. and Brandt, V. and Tiller, J.C.
    Journal of Colloid and Interface Science 579 357-368 (2020)
    Amorphous inorganic materials have a great potential in material science. Amorphous calcium carbonate (ACC) is a widely useable system, however, its stabilization often turns out to be difficult and the synthesis is mostly limited to precipitation in solution as nanoparticles. Stable ACC in bulk phases would create new composite materials. Previous work described the enzyme-induced mineralization of hydrogels with crystalline calcium carbonate by entrapping urease into a hydrogel and treating this with an aqueous mineralization solution containing urea und calcium chloride. Here, this method was modified using a variety of crystallization inhibitors attached to the hydrogel matrix or added to the surrounding mineralization solution. It was found that only N-(phosphonomethyl)glycine (PMGly) in solution completely inhibits the crystallization of ACC in the hydrogel matrix. The stability of the homogeneously precipitated ACC could be accounted to the combination of stabilizing effects of the additive and stabilization through confinement. The crystallization could be accelerated at higher temperatures up to 60 °C. Here, a combination of Mg ions and PMGly was required to stabilize ACC in the hydrogel. Variation of these two compounds can be used to control a number of different calcium carbonate morphologies within the hydrogel. While the ACC nanoparticles within the hydrogel are stable over weeks even in water, a calcite layer grows on the surface of the hydrogel, which might be used as self-hardening mechanism of a surface. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2020.06.047
  • 2020 • 711 Iron Nanoparticle Composite Hydrogels for Studying Effects of Iron Ion Release on Red Blood Cell in Vitro Production
    Brändle, K. and Bergmann, T.C. and Raic, A. and Li, Y. and Million, N. and Rehbock, C. and Barcikowski, S. and Lee-Thedieck, C.
    ACS Applied Bio Materials 3 4766-4778 (2020)
    Growing numbers of complex surgical interventions increase the need for blood transfusions, which cannot be fulfilled by the number of donors. Therefore, the interest in producing erythrocytes from their precursors-the hematopoietic stem and progenitor cells (HSPCs)-in laboratories is rising. To enable this, in vitro systems are needed, which allow analysis of the effects of essential factors such as iron on erythroid development. For this purpose, iron ion-releasing systems based on poly(ethylene glycol) (PEG)-iron nanocomposites are developed to assess if gradual iron release improves iron bioavailability during in vitro erythroid differentiation. The nanocomposites are synthesized using surfactant-free pulsed laser ablation of iron directly in the PEG solution. The iron concentrations released from the material are sufficient to influence in vitro erythropoiesis. In this way, the production of erythroid cells cultured on flat PEG-iron nanocomposite hydrogel pads can be enhanced. In contrast, erythroid differentiation is not enhanced in the biomimetic macroporous 3D composite scaffolds, possibly because of local iron overload within the pores of the system. In conclusion, the developed iron nanoparticle-PEG composite hydrogel allows constant iron ion release and thus paves the way (i) to understand the role of iron during erythropoiesis and (ii) toward the development of biomaterials with a controlled iron release for directing erythropoiesis in culture. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsabm.0c00297
  • 2020 • 710 Laser Fragmentation-Induced Defect-Rich Cobalt Oxide Nanoparticles for Electrochemical Oxygen Evolution Reaction
    Yu, M. and Waag, F. and Chan, C.K. and Weidenthaler, C. and Barcikowski, S. and Tüysüz, H.
    ChemSusChem 13 520-528 (2020)
    Sub-5 nm cobalt oxide nanoparticles are produced in a flowing water system by pulsed laser fragmentation in liquid (PLFL). Particle fragmentation from 8 nm to 4 nm occurs and is attributed to the oxidation process in water where oxidative species are present and the local temperature is rapidly elevated under laser irradiation. Significantly higher surface area, crystal phase transformation, and formation of structural defects (Co2+ defects and oxygen vacancies) through the PLFL process are evidenced by detailed structural characterizations by nitrogen physisorption, electron microscopy, synchrotron X-ray diffraction, and X-ray photoelectron spectroscopy. When employed as electrocatalysts for the oxygen evolution reaction under alkaline conditions, the fragmented cobalt oxides exhibit superior catalytic activity over pristine and nanocast cobalt oxides, delivering a current density of 10 mA cm−2 at 369 mV and a Tafel slope of 46 mV dec−1, which is attributed to a larger exposed active surface area, the formation of defects, and an increased charge transfer rate. The study provides an effective approach to engineering cobalt oxide nanostructures in a flowing water system, which shows great potential for sustainable production of active cobalt catalysts. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cssc.201903186
  • 2020 • 709 Matrix-specific mechanism of Fe ion release from laser-generated 3D-printable nanoparticle-polymer composites and their protein adsorption properties
    Li, Y. and Rehbock, C. and Nachev, M. and Stamm, J. and Sures, B. and Blaeser, A. and Barcikowski, S.
    Nanotechnology 31 (2020)
    Nanocomposites have been widely applied in medical device fabrication and tissue-engineering applications. In this context, the release of metal ions as well as protein adsorption capacity are hypothesized to be two key processes directing nanocomposite-cell interactions. The objective of this study is to understand the polymer-matrix effects on ion release kinetics and their relations with protein adsorption. Laser ablation in macromolecule solutions was employed for synthesizing Au and Fe nanoparticle-loaded nanocomposites based on thermoplastic polyurethane (TPU) and alginate. Confocal microscopy revealed a three-dimensional homogeneous dispersion of laser-generated nanoparticles in the polymer. The physicochemical properties revealed a pronounced dependence upon embedding of Fe and Au nanoparticles in both polymer matrices. Interestingly, the total Fe ion concentration released from alginate gels under static conditions decreased with increasing mass loadings, a phenomenon only found in the Fe-alginate system and not in the Cu/Zn-alginate and Fe-TPU control system (where the effects were proportioonal to the nanoparticle load). A detailed mechanistic examination of iron the ion release process revealed that it is probably not the redox potential of metals and diffusion of metal ions alone, but also the solubility of nano-metal oxides and affinity of metal ions for alginate that lead to the special release behaviors of iron ions from alginate gels. The amount of adsorbed bovine serum albumin (BSA) and collagen I on the surface of both the alginate and TPU composites was significantly increased in contrast to the unloaded control polymers and could be correlated with the concentration of released Fe ions and the porosity of composites, but was independent of the global surface charge. Interestingly, these effects were already highly pronounced at minute loadings with Fe nanoparticles down to 200 ppm. Moreover, the laser-generated Fe or Au nanoparticle-loaded alginate composites were shown to be a suitable bioink for 3D printing. These findings are potentially relevant for ion-sensitive bio-responses in cell differentiation, endothelisation, vascularisation, or wound healing. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab94da
  • 2020 • 708 Nanocellulose-Mediated Transition of Lithium-Rich Pseudo-Quaternary Metal Oxide Nanoparticles into Lithium Nickel Cobalt Manganese Oxide (NCM) Nanostructures
    Zehetmaier, P.M. and Zoller, F. and Beetz, M. and Plaß, M.A. and Häringer, S. and Böller, B. and Döblinger, M. and Bein, T. and Fattakhova-Rohlfing, D.
    ChemNanoMat 6 618-628 (2020)
    We report the syntheses of various compounds within the pseudo-quaternary system of the type LiwNixCoyMnzOδ (δ≤1) (pre-NCMs). Four different compositions of this compound were realized as ultrasmall crystalline nanoparticles of 1–4 nm diameter using low-temperature solvothermal reaction conditions in tert-butanol at only 170 °C. All of the pre-NCMs crystallize in the rock-salt structure and their lithium content is between 20% and 30% with respect to the complete metal content. By adjusting the lithium content to 105% stoichiometry in the solvothermal reaction, the pre-NCMs can easily react to the respective Li(NixCoyMnz)O2 (NCM) nanoparticles. Furthermore, nanosized desert-rose structured NCMs were obtained after addition of nanocellulose during the synthesis. By using the mixed metal monoxides as precursor for the NCMs, cation mixing between lithium and nickel is favored and gets more pronounced with increasing nickel content. The cation mixing effect compromises good electrochemical capacity retention, but the desert-rose structure nevertheless enables enhanced stability at high power conditions, especially for NCM333. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cnma.201900748
  • 2020 • 707 Origin of Laser-Induced Colloidal Gold Surface Oxidation and Charge Density, and Its Role in Oxidation Catalysis
    Ziefuß, A.R. and Haxhiaj, I. and Müller, S. and Gharib, M. and Gridina, O. and Rehbock, C. and Chakraborty, I. and Peng, B. and Muhler, M. and Parak, W.J. and Barcikowski, S. and Reichenberger, S.
    Journal of Physical Chemistry C 124 20981-20990 (2020)
    Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of understanding the chemical processes that are triggered by the laser pulses, which may dictate the surface properties that are highly important in heterogeneous oxidation catalytic reactions. We observed the formation of radical oxygen species during LFL, which suggested that LFL is a physicochemical process that leads to particle size reductions and initiates oxidative processes. When the ionic strength in the nanoenvironment was increased, the oxidation of the first atomic layer saturated at 50%, whereby the surface charge density increases continuously. We found a correlation between the surface charge density after synthesis of colloidal nanoparticles and its behavior in catalysis. The properties of the laser-generated nanoparticles in the colloidal state appear to have predetermined the catalytic performance. We found that a smaller surface charge density of the usAu NPs was beneficial for the catalytic activity in CO and ethanol oxidation, while their peroxidase-like activity was affected less. The catalytic activity was 2 times higher for samples prepared by chloride-free LFL after ozone pretreatment compared to samples prepared in pure water. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c06257
  • 2020 • 706 Plasma-assisted gas-phase synthesis and in-line coating of silicon nanoparticles
    Dasgupta, M. and Fortugno, P. and Wiggers, H.
    Plasma Processes and Polymers 17 (2020)
    This study investigates the feasibility of plasma-supported in-line functionalization of silicon nanoparticles (NPs) in an atmospheric pressure gas-phase reactor. The approach utilizes the synthesis of core silicon NPs and their subsequent coating downstream of the particle formation zone. In-line coating is accomplished with a cylindrical coating nozzle to achieve homogenous mixing of coating precursor vapors with in-coming NPs. Multiple siloxanes were tested for their coating suitability and their ability towards coating homogeneity. It was found that tetraethyl orthosilicate is favored for thin layers consisting of almost pure silica while hexamethyldisiloxane and octamethylcyclotetrasiloxane (OMCTS) coatings contained reasonable amounts of hydrocarbons. Moreover, OMCTS showed a pronounced tendency towards homogeneous nucleation, thus leading to the additional formation of silica NPs due to homogeneous nucleation. © 2020 The Authors. Plasma Processes and Polymers published by WILEY-VCH Verlag GmbH & Co. KGaA
    view abstractdoi: 10.1002/ppap.201900245
  • 2020 • 705 Polymer nanocomposite ultrafiltration membranes: The influence of polymeric additive, dispersion quality and particle modification on the integration of zinc oxide nanoparticles into polyvinylidene difluoride membranes
    Berg, T.D. and Ulbricht, M.
    Membranes 10 1-19 (2020)
    This study aims to improve the understanding of the influence of metal oxide nanofillers on polyvinylidene difluoride (PVDF) ultrafiltration membranes. Zinc oxide nanoparticles were chosen as the model filler material. The membranes were prepared by non-solvent induced phase separation from PVDF solutions in N-methylpyrrolidone. The influences of the addition of polyvinylpyrrolidone (PVP), the nanoparticle dispersion quality, and a surface modification of the ZnO particles with PVP on the nanofiller integration into the polymer matrix and the resulting membrane separation performance, were evaluated. Unmodified and PVP-modified nanoparticles were characterized by evaluation of their Hansen solubility parameters. The membranes were characterized by ultrafiltration experiments, scanning electron microscopy (SEM) and with respect to mechanical properties, while the dope solutions were analyzed by rheology in order to judge about dispersion quality. Pure water permeability and solute rejection data revealed that the dominant effect of the addition of pristine ZnO nanoparticles was a major decrease in permeability caused by pore blocking. In SEM analyses, it was seen that the plain nanofiller did not integrate well into the polymer matrix. Importantly, it was found that the surface modification of the nanofiller, as well as a high dispersion quality, can be strategically used to enhance the integration of the nanofiller and thus suppress pore blocking, leading to membranes with high ultrafiltration rejection and permeability simultaneously. Overall, the study provides relevant insights into a new approach to integrating nanofillers into polymer nanocomposite membranes for improving their properties and performance. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/membranes10090197
  • 2020 • 704 Preparation of antibiofouling nanocomposite PVDF/Ag-SiO2 membrane and long-term performance evaluation in the MBR system fed by real pharmaceutical wastewater
    Ahsani, M. and Hazrati, H. and Javadi, M. and Ulbricht, M. and Yegani, R.
    Separation and Purification Technology 249 (2020)
    In this work, the Ag-SiO2 nanoparticles were successfully synthesized and their antibacterial property was confirmed using the plate colony counting method. The SiO2 and Ag-SiO2 nanoparticles were used to prepare the PVDF/SiO2 and PVDF/Ag-SiO2 nanocomposite membranes, respectively. Pure water flux, contact angle and mechanical strength measurement analyses were conducted to characterize and compare the performance of the neat and nanocomposite membranes. Moreover, in order to investigate the structure of the prepared membranes scanning electron microscope (SEM) was used to obtain surface and cross-section images. A long-term filtration test was carried out in a bench scale submerged membrane bioreactor (MBR) system, fed by real pharmaceutical wastewater, to evaluate the antibiofouling performance of the prepared neat and nanocomposite membranes. In comparison to the neat PVDF, the pure water flux of the nanocomposite PVDF membrane (PVDF/Ag-SiO2; 0.6 wt%) increased about 60% and the water contact angle decreased from about 99° to 89°. The obtained results showed that the nanocomposite PVDF/Ag-SiO2 membrane exhibits considerable antibiofouling properties such that the accumulated dried biofilm as well as the extra cellular polymeric substances (EPSs) collected from the cake layer decreased considerably for the nanocomposite membrane. Moreover, the flux recovery ratio increased from 58% for the neat PVDF membrane to 76% for the nanocomposite PVDF/Ag-SiO2 membrane. The excitation and emission matrix (EEM) fluorescence spectroscopy analysis revealed that the accumulated protein on the surface of nanocomposite membranes decreased considerably in a way that the peak corresponding to tryptophan protein-like substances diminished completely, indicating the high antibiofouling potential of nanocomposite membranes. The chemical oxygen demand (COD) and ammonium removal efficiencies of the neat and nanocomposite membranes were higher than 90% and 95%, respectively, indicating negligible impact of the membrane modification on the effluents’ quality. © 2020
    view abstractdoi: 10.1016/j.seppur.2020.116938
  • 2020 • 703 Response to Comment on "high-surface-area corundum by mechanochemically induced phase transformation of boehmite"
    Amrute, A.P. and Lodziana, Z. and Schreyer, H. and Weidenthaler, C. and Schüth, F.
    Science 368 (2020)
    Li et al. commented that our report claims that methods reported thus far cannot enable the production of high-purity corundum with surface areas greater than 100 m2g-1, and that our obtained material could be porous aggregates rather than nanoparticles. We disagree with both of these suggestions. © 2020 American Association for the Advancement of Science. All rights reserved.
    view abstractdoi: 10.1126/science.abb0948
  • 2020 • 702 Self-assembled nano-silicon/graphite hybrid embedded in a conductive polyaniline matrix for the performance enhancement of industrial applicable lithium-ion battery anodes
    Wiggers, H. and Sehlleier, Y.H. and Kunze, F. and Xiao, L. and Schnurre, S.M. and Schulz, C.
    Solid State Ionics 344 (2020)
    Nano-structured silicon-based composite materials have generated significant excitement for use as anode materials in high-performance Li-ion batteries. For making these materials commercially applicable, a high Coulombic efficiency at the first cycle must be achieved. Additionally, scalable synthesis routes need to be developed to provide access to practically-relevant material quantities. In this work, we propose a strategy for the production of Si/graphite/polyaniline (Si/graphite/PANI) composites that addresses both above mentioned challenges. Si nanoparticles were produced in a pilot-plant-scale microwave-plasma reactor using monosilane (SiH4) as precursor. This process enables the formation of high-purity Si nanoparticles with controllable crystal sizes at a production rate of 45 g/h. Si/graphite hybrids are fabricated through self-assembly by electrostatic attraction. The Si/graphite/PANI nanocomposite is then prepared by in situ polymerization of aniline monomer in the presence of the Si/graphite hybrid. With this approach, ~40 g of Si/graphite/PANI composite per batch can be produced at lab scale. The scalability of the underlying processes enables the use for commercial products. The nanocomposite shows favorable characteristics inherited from its three components: Si nanoparticles provide high capacity, graphite acts as an electrical conductor and gives a high Coulombic efficiency, and the polyaniline coating further enhances the electrical conductivity and protects the entire structure. A very good Coulombic efficiency of 86.2% at the initial cycle is recorded for this nanocomposite material. Galvanostatic charge/discharge tests demonstrate that this material can deliver a discharge capacity of 2000 mAh/g with a very good capacity retention of 76% after 500 cycles at a discharge rate of 0.5C (1.25 A/g). The capacity is 870 mAh/g measured at 5C (12.5 A/g). © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.ssi.2019.115117
  • 2020 • 701 Silicon Nanoparticle Films Infilled with Al2O3Using Atomic Layer Deposition for Photosensor, Light Emission, and Photovoltaic Applications
    Botas, A.M.P. and Leitão, J.P. and Falcão, B.P. and Wiesinger, M. and Eckmann, F. and Teixeira, J.P. and Wiggers, H. and Stutzmann, M. and Ferreira, R.A.S. and Pereira, R.N.
    ACS Applied Nano Materials 3 5033-5044 (2020)
    Solution-processed thin films of crystalline silicon nanoparticles (Si NPs) have a great potential for a wide variety of electronic and optoelectronic applications. However, such films are inherently unstable due to their huge surface-to-volume ratios and high surface energies, making them prone to degradation associated with spontaneous oxidation in ambient conditions. In this work, we explore the use of atomic layer deposition (ALD) as a means to stabilize and potentially functionalize solution-processed thin films of Si NPs for (opto)electronics, e.g., thin-film transistors, photosensors, light-emitting devices, and photovoltaics. We prepared films of randomly distributed Si NPs with ultrashort surface ligands (Si-H termination) using wet chemistry and spray-coating and then use ALD to infill the films with Al2O3. Through microscopy and optical structural/morphological analysis, we demonstrate the achievability of ALD infilling of films of Si NPs and probe the stability of these films against oxidation. Moreover, we show that the ALD infilling leads to changes in the light emission properties of the Si NP films, including a relative quenching of disorder-related emission features and variations in surface-related dielectric confinement effects. Our studies reveal ALD as a relevant technique toward manufacturing de facto robust, functional nanomaterials based on Si NPs and on nanoscale silicon materials more generally. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsanm.0c00116
  • 2020 • 700 Silver clusters shape determination from in-situ XANES data
    Timoshenko, J. and Roese, S. and Hövel, H. and Frenkel, A.I.
    Radiation Physics and Chemistry 175 (2020)
    Knowledge of nanoparticle size, shape and morphology and of their in-situ transformations is crucial for establishing structure-properties relationship in nanosized materials that find applications, e.g., in plasmonic devices and heterogenous catalysis. Here we demonstrate that this information can be extracted reliably from in-situ X-ray absorption near edge structure (XANES) data, by combining ab-initio XANES simulations and machine learning (artificial neural network (NN)) approaches. Here we use NN-XANES method to extract information about the size, shape and interatomic distances in silver clusters, and to monitor their changes during the temperature-controlled particle aggregation. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.radphyschem.2018.11.003
  • 2020 • 699 Smart Glycopolymeric Nanoparticles for Multivalent Lectin Binding and Stimuli-Controlled Guest Release
    Saha, S. and Klein-Hitpaß, M. and Vallet, C. and Knauer, S.K. and Schmuck, C. and Voskuhl, J. and Giese, M.
    Biomacromolecules 21 2356-2364 (2020)
    The synthesis and self-assembly of a polymer featuring a self-complementary supramolecular binding motif guanidiniocarbonyl pyrrole carboxylate zwitterion (GCP-zwitterion) bearing lactose moieties are reported. The GCP-zwitterion acts as a cross-linker to facilitate self-assembly of the polymeric chain into nanoparticles (NPs) at neutral pH in an aqueous medium. The formation of polymeric NPs can be controlled by addition of external stimuli (acid or base), which disfavors self-assembly of the GCP-zwitterion because of protonation or deprotonation of the GCP units in the polymer chain. The small-sized (<40 nm) NPs have a hydrophobic cavity and accessible lactose units on the outer shell for multivalent lectin binding. The multivalent interaction between NPs and the lectin peanut agglutinin was confirmed by agglutination experiments. In addition, the stimuli-responsive property of NPs was exploited for the uptake and release of a hydrophobic guest Nile red. Furthermore, the selectivity toward different cell lines (HEK 296T, HeLa, and Hep2G) was tested, and a cellular uptake of cargo-loaded NPs was found for Hep2G cells bearing the lactose-specific asialogylcoprotein receptor, whereas all other cells showed no NP interaction. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.biomac.0c00292
  • 2020 • 698 Sputter deposition of highly active complex solid solution electrocatalysts into an ionic liquid library: Effect of structure and composition on oxygen reduction activity
    Manjón, A.G. and Löffler, T. and Meischein, M. and Meyer, H. and Lim, J. and Strotkötter, V. and Schuhmann, W. and Ludwig, Al. and Scheu, C.
    Nanoscale 12 23570-23577 (2020)
    Complex solid solution electrocatalysts (often called high-entropy alloys) present a new catalyst class with highly promising features due to the interplay of multi-element active sites. One hurdle is the limited knowledge about structure-activity correlations needed for targeted catalyst design. We prepared Cr-Mn-Fe-Co-Ni nanoparticles by magnetron sputtering a high entropy Cantor alloy target simultaneously into an ionic liquid library. The synthesized nanoparticles have a narrow size distribution but different sizes (from 1.3 ± 0.1 nm up to 2.6 ± 0.3 nm), different crystallinity (amorphous, face-centered cubic or body-centered cubic) and composition (i.e. high Mn versus low Mn content). The Cr-Mn-Fe-Co-Ni complex solid solution nanoparticles possess an unprecedented intrinsic electrocatalytic activity for the oxygen reduction reaction in alkaline media, some of them even surpassing that of Pt. The highest intrinsic activity was obtained for body-centered cubic nanoparticles with a low Mn and Fe content which were synthesized using the ionic liquid 1-etyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Emimi][(Tf)2N]. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0nr07632e
  • 2020 • 697 Structural evolution of bimetallic Co-Cu catalysts in CO hydrogenation to higher alcohols at high pressure
    Göbel, C. and Schmidt, S. and Froese, C. and Fu, Q. and Chen, Y.-T. and Pan, Q. and Muhler, M.
    Journal of Catalysis 383 33-41 (2020)
    Bimetallic Co-Cu catalysts are widely applied in higher alcohol synthesis (HAS), but the formation of the final active structure has not yet been fully clarified, especially for Co-rich catalysts. We investigated the structural evolution of a Co-Cu catalyst (Co:Cu = 2) from the hydrotalcite precursor containing additional Al3+ and Zn2+ to the final active state after 80 h under reaction conditions at 280 °C and 60 bar. The reconstruction of the bimetallic Co-Cu nanoparticles obtained by H2 reduction was induced by the feed gas consisting of an equimolar H2 and CO syngas mixture resulting in fast phase separation and sintering of metallic Cu0 and Co0 in the first 2 h time on stream (TOS) and a continuous carbidization of Co0 forming Co2C and its sintering until steady state was reached after 40 h TOS. An intergrowth of metallic Cu0 nanoparticles with Co2C nanoparticles was observed to occur under reaction conditions. The high selectivity to oxygenates amounting to 41% compared with 29% to hydrocarbons is ascribed to the multi-functional Co2C/Cu0 interface enabling dissociative CO adsorption, hydrogenation and CO insertion. The formation of hydrogenated carbon species (CxHy) originating from dissociative CO chemisorption is assumed to be favored by hydrogen spillover from Cu0 to Co2C. The adsorption sites for molecular CO provided by both Cu0 and Co2C facilitate its insertion into the CxHy intermediates thus leading to a higher selectivity to alcohols following the Anderson-Schulz-Flory distribution. © 2020 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2020.01.004
  • 2020 • 696 Superconducting NbN and CaFe0.88Co0.12AsF studied by point-contact spectroscopy with a nanoparticle Au array
    Wu, Y.F. and Yu, A.B. and Lei, L.B. and Zhang, C. and Wang, T. and Ma, Y.H. and Huang, Z. and Chen, L.X. and Liu, Y.S. and Schneider, C.M. and Mu, G. and Xiao, H. and Hu, T.
    Physical Review B 101 (2020)
    The point-contact-spectroscopy measurement is a powerful method to detect the superconducting gap and the spin polarization of materials. However, it is difficult to get a stable and clean point contact by conventional techniques. In this work, we fabricate multiple point contacts by depositing Au nanoparticle arrays on the surface of a superconductor through an anodic aluminum oxide patterned shadow mask. We obtained the superconducting gaps of niobium nitride thin film (NbN, Tc=16 K) and iron superconductors CaFe0.88Co0.12AsF single crystals (Ca-1111, Tc=21.3 K) by fitting the point-contact spectroscopy with the Blonder-Tinkham-Klapwijk theory. We found that NbN's gap (Δ) exhibits the BCS-like temperature dependence with Δ≈2.88 meV at 0 K and 2Δ/kBTc≈4.22 in agreement with previous reports. By contrast, Ca-1111 has a multigap structure with Δ1≈1.99 meV and Δ2≈5.01 meV at 0 K, and the ratio between the superconducting gap and Tc is 2Δ1/kBTc=2.2 and 2Δ2/kBTc=5.5, suggesting an unconventional paring mechanism of Ca-1111 also in agreement with previous reports on other Fe-based superconductors. Our multiple point-contacts method thus provides an alternative way to perform measurements of the superconducting gap. © 2020 American Physical Society. ©2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.174502
  • 2020 • 695 Synthesis and characterization of PLGA/HAP scaffolds with DNA-functionalised calcium phosphate nanoparticles for bone tissue engineering
    Sokolova, V. and Kostka, K. and Shalumon, K.T. and Prymak, O. and Chen, J.-P. and Epple, M.
    Journal of Materials Science: Materials in Medicine 31 (2020)
    Porous scaffolds of poly(lactide-co-glycolide) (PLGA; 85:15) and nano-hydroxyapatite (nHAP) were prepared by an emulsion-precipitation procedure from uniform PLGA–nHAP spheres (150–250 µm diameter). These spheres were then thermally sintered at 83 °C to porous scaffolds that can serve for bone tissue engineering or for bone substitution. The base materials PLGA and nHAP and the PLGA–nHAP scaffolds were extensively characterized by X-ray powder diffraction, infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The scaffold porosity was about 50 vol% as determined by relating mass and volume of the scaffolds, together with the computed density of the solid phase (PLGA–nHAP). The cultivation of HeLa cells demonstrated their high cytocompatibility. In combination with DNA-loaded calcium phosphate nanoparticles, they showed a good activity of gene transfection with enhanced green fluorescent protein (EGFP) as model protein. This is expected enhance bone growth around an implanted scaffold or inside a scaffold for tissue engineering. [Figure not available: see fulltext.] © 2020, The Author(s).
    view abstractdoi: 10.1007/s10856-020-06442-1
  • 2020 • 694 Synthesis and intracellular tracing surface-functionalized calcium phosphate nanoparticles by super-resolution microscopy (STORM)
    Rojas-Sánchez, L. and Loza, K. and Epple, M.
    Materialia 12 (2020)
    Calcium phosphate nanoparticles with covalently attached fluorescent dye molecules were prepared by copper-catalysed azide-alkyne cycloaddition (CuAAC) and by strain-promoted azide-alkyne cycloaddition (SPAAC), i.e. click chemistry. The reaction kinetics and labeling degrees of the two click reactions were compared and quantified. For oxidation-sensitive molecules, the SPAAC method is preferable due to the milder reaction conditions and the absence of copper(II). The highly fluorescent AF-488-labeled nanoparticles were applied for super-resolution fluorescence microscopy, i.e. stochastic optical reconstruction microscopy (STORM). By this method, individual nanoparticles (diameter about 60 nm) were observed in endolysosomes inside HeLa cells after cellular uptake at a resolution of 20–30 nm. © 2020
    view abstractdoi: 10.1016/j.mtla.2020.100773
  • 2020 • 693 Synthesis, Structure, Properties, and Applications of Bimetallic Nanoparticles of Noble Metals
    Loza, K. and Heggen, M. and Epple, M.
    Advanced Functional Materials 30 (2020)
    Bimetallic nanoparticles of noble metals are of high interest in imaging, biomedical devices, including nanomedicine, and heterogeneous catalysis. Synthesis, properties, characterization, biological properties, and practical applicability of nanoparticles on the basis of platinum group metals and the coin metals Ag and Au are discussed, also in comparison with the corresponding monometallic nanoparticles. In addition to the parameters that are required to characterize monometallic nanoparticles (mainly size, size distribution, shape, crystallographic nature, surface functionalization, charge), further information is required for a full characterization of bimetallic nanoparticles. This concerns the overall elemental composition of a bimetallic nanoparticle population (ratio of the two metals) and the internal distribution of the elements in individual nanoparticles (e.g., the presence of homogeneous alloys, core–shell systems, and possible intermediate stages). It is also important to ensure that all particles are identical in terms of elemental composition, that is, that the homogeneity of the particle population is given. Macroscopic properties like light absorption, antibacterial effects, and catalytic activity depend on these properties. The currently available methods for a full characterization of bimetallic nanoparticles are discussed, and future developments in this field are outlined. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201909260
  • 2020 • 692 Tailoring the Size, Inversion Parameter, and Absorption of Phase-Pure Magnetic MgFe2O4Nanoparticles for Photocatalytic Degradations
    Bloesser, A. and Kurz, H. and Timm, J. and Wittkamp, F. and Simon, C. and Hayama, S. and Weber, B. and Apfel, U.-P. and Marschall, R.
    ACS Applied Nano Materials 3 11587-11599 (2020)
    Phase-pure magnesium ferrite (MgFe2O4) spinel nanocrystals are synthesized by a fast microwave-assisted route. The elemental composition is optimized via the ratio of the precursor mixture and controlled by energy-dispersive X-ray spectroscopy. Fine-tuning of the magnetic properties without changing the overall elemental composition is demonstrated by superconducting quantum interference device (SQUID) magnetometry and Mössbauer spectroscopy. Together with X-ray absorption spectroscopy and X-ray emission spectroscopy, we confirm that the degree of cation inversion is altered by thermal annealing. We can correlate the magnetic properties with both the nanosize influence and the degree of inversion. The resulting nonlinear course of saturation magnetization (Ms) in correlation with the particle diameter allows to decouple crystallite size and saturation magnetization, by this providing a parameter for the production of very small nanoparticles with high Ms with great potential for magnetic applications like ferrofluids or targeted drug delivery. Our results also suggest that the optical band gap of MgFe2O4 is considerably larger than the fundamental electronic band gap because of the d5 electronic configuration of the iron centers. The presented different electronic transitions contributing to the absorption of visible light are the explanation for the large dissent among the band gaps and band potentials found in the literature. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsanm.0c02705
  • 2020 • 691 The importance of nanoscale confinement to electrocatalytic performance
    Wordsworth, J. and Benedetti, T.M. and Alinezhad, A. and Tilley, R.D. and Edwards, M.A. and Schuhmann, W. and Gooding, J.J.
    Chemical Science 11 1233-1240 (2020)
    Electrocatalytic nanoparticles that mimic the three-dimensional geometric architecture of enzymes where the reaction occurs down a substrate channel isolated from bulk solution, referred to herein as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions. Surfactant covered Pt-Ni nanozyme nanoparticles, with Ni etched from the nanoparticles, possess a nanoscale channel in which the active sites for electrocatalysis of oxygen reduction are located. Different particle compositions and etching parameters allowed synthesis of nanoparticles with different average substrate channel diameters that have varying amounts of nano-confinement. The results showed that in the kinetically limited regime at low overpotentials, the smaller the substrate channels the higher the specific activity of the electrocatalyst. This is attributed to higher concentrations of protons, relative to bulk solution, required to balance the potential inside the nano-confined channel. However, at higher overpotentials where limitation by mass transport of oxygen becomes important, the nanozymes with larger substrate channels showed higher electrocatalytic activity. A reaction-diffusion model revealed that the higher electrocatalytic activity at low overpotentials with smaller substrate channels can be explained by the higher concentration of protons. The model suggests that the dominant mode of mass transport to achieve these high concentrations is by migration, exemplifying how nano-confinement can be used to enhance reaction rates. Experimental and theoretical data show that under mass transport limiting potentials, the nano-confinement has no effect and the reaction only occurs at the entrance of the substrate channel at the nanoparticle surface. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9sc05611d
  • 2020 • 690 The Influence of the Distribution Function of Ferroelectric Nanoparticles Sizes on Their Electrocaloric and Pyroelectric Properties
    Shevliakova, H.V. and Morozovska, A.N. and Morozosky, N.V. and Svechnikov, G.S. and Shvartsman, V.V.
    IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 67 2445-2453 (2020)
    We consider a model of a nanocomposite based on noninteracting spherical single-domain ferroelectric nanoparticles (NPs) of various sizes embedded in a dielectric matrix. The size distribution function of these NPs is selected as a part of the truncated Gaussian distribution from minimum to maximum radius. For such nanocomposites, we calculate the dependences of the reversible part of the electric polarization, the electrocaloric (EC) temperature change, and the dielectric permittivity on the external electric field, which have the characteristic form of hysteresis loops. We then analyze the change in the shape of the hysteresis loops relative to the particle size distribution parameters. We demonstrate that the remanent polarization, coercive field, dielectric permittivity maximums, and maximums and minimums of the EC temperature change depend most strongly on the most probable radius, moderately on the dispersion, and have the weakest dependence on the maximum radius of the NP. We calculate and analyze the dependences of pyroelectric figures of merit on the average radius of the NPs in the composite. The dependences confirm the presence of a phase transition induced by the size of the NPs, which is characterized by the presence of a maxima near the critical average radius of the particles, the value of which increases with an increasing dispersion of the distribution function. © 1986-2012 IEEE.
    view abstractdoi: 10.1109/TUFFC.2020.3004740
  • 2020 • 689 Tunable and switchable nanoparticle separation with thermo-responsive track-etched membranes prepared by controlled surface-initiated polymerization of poly(N-isopropylacrylamide)
    Daumann, K. and Frost, S. and Ulbricht, M.
    RSC Advances 10 21028-21038 (2020)
    This work describes how the control of grafting density and grafted chain length of a thermo-responsive polymer in membrane pores can be utilized to tune the pore size and the switchability of size-based selectivity in the ultrafiltration range. Using a previously established methodology for controlled synthesis, surface-initiated atom transfer polymerization (ATRP) of poly(N-isopropylacrylamide) (PNIPAAm) to the pore walls of poly(ethylene terephthalate) track-etched membranes with experimentally determined pore diameters of 35 nm (PET30) and 110 nm (PET80) is performed. Characterization in this study is mainly done with filtration experiments, making use of the well-defined pore structure of the base membranes. It is demonstrated that both the gravimetrically determined degree of functionalization and the effective pore size determined from water permeability are a linear function of ATRP time. For the grafted PET30 membranes, it is shown that the rejection of lysozyme (diameter ∼ 4 nm) can be switched between 99% at 23 °C and 65% at 45 °C for the membrane with the highest degree of functionalization. For the grafted PET80 membranes, it is found that two different types of membranes can be obtained. Membranes with long grafted chains at low grafting density show very large changes of water permeability as a function of temperature (effective pore size switching ratio of up to 10) and, for example, rejection for 20 nm silica particles of 95% and 23% at 23 °C and 45 °C, respectively. Membranes with PNIPAAm at high grafting density show much lower switching ratios (as low as 1.4, for long enough grafted chains). Effective pore size and thermo-responsive change of pore size can therefore be tuned by the combination of both synthesis parameters, initiator density and ATRP time. The switchable thermo-responsive separation of two colloids with a tailored membrane is demonstrated for mixtures of bovine serum albumin (BSA; ∼7 nm) and silica nanoparticles (20 nm); at 23 °C silica is completely rejected and only BSA is in the permeate; at 40 °C both colloids permeate through the membrane. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ra03418e
  • 2020 • 688 Ultrasmall gold and silver/gold nanoparticles (2 nm) as autofluorescent labels for poly(D,L-lactide-co-glycolide) nanoparticles (140 nm)
    Wey, K. and Epple, M.
    Journal of Materials Science: Materials in Medicine 31 (2020)
    Ultrasmall metallic nanoparticles show an efficient autofluorescence after excitation in the UV region, combined with a low degree of fluorescent bleaching. Thus, they can be used as fluorescent labels for polymer nanoparticles which are frequently used for drug delivery. A versatile water-in-oil-in-water emulsion-evaporation method was developed to load poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles with autofluorescent ultrasmall gold and silver/gold nanoparticles (diameter 2 nm). The metallic nanoparticles were prepared by reduction of tetrachloroauric acid with sodium borohydride and colloidally stabilised with 11-mercaptoundecanoic acid. They were characterised by UV–Vis and fluorescence spectroscopy, showing a large Stokes shift of about 370 nm with excitation maxima at 250/270 nm and emission maxima at 620/640 nm for gold and silver/gold nanoparticles, respectively. The labelled PLGA nanoparticles (140 nm) were characterised by dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV–Vis and fluorescence spectroscopy. Their uptake by HeLa cells was followed by confocal laser scanning microscopy. The metallic nanoparticles remained inside the PLGA particle after cellular uptake, demonstrating the efficient encapsulation and the applicability to label the polymer nanoparticle. In terms of fluorescence, the metallic nanoparticles were comparable to fluorescein isothiocyanate (FITC). [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstractdoi: 10.1007/s10856-020-06449-8
  • 2020 • 687 Unravelling the nucleation, growth, and faceting of magnetite-gold nanohybrids
    Nalench, Y.A. and Shchetinin, I.V. and Skorikov, A.S. and Mogilnikov, P.S. and Farle, M. and Savchenko, A.G. and Majouga, A.G. and Abakumov, M.A. and Wiedwald, U.
    Journal of Materials Chemistry B 8 3886-3895 (2020)
    The chemical synthesis of nanoparticles with a preassigned size and shape is important for an optimized performance in any application. Therefore, systematic monitoring of the synthesis is required for the control and detailed understanding of the nucleation and growth of the nanoparticles. Here, we study Fe3O4-Au hybrid nanoparticles in detail using probes of the reaction mixture during synthesis and their thorough characterization. The proposed approach eliminates the problem of repeatability and reproducibility of the chemical synthesis and was carried out using laboratory equipment (standard transmission electron microscopy, X-ray diffraction, and magnetometry) for typically 10 μL samples instead of, for example, a dedicated synthesis and inspection at a synchrotron radiation facility. From the three independent experimental techniques we extract the nanoparticle size at 12 stages of the synthesis. These diameters show identical trends and good quantitative agreement. Two consecutive processes occur during the synthesis of Fe3O4-Au nanoparticles, the nucleation and the growth of spherical Fe3O4nanoparticles on the surface of Au seeds during the heating stage and their faceting towards octahedral shape during reflux. The final nanoparticles with sizes of 15 nm Fe3O4and 4 nm Au exhibit superparamagnetic behavior at ambient temperature. These are high-quality, close to stoichiometric Fe3O4nanocrystals with nearly volumetric magnetic behavior as confirmed by the presence of the Verwey transition. Understanding the processes occurring during the synthesis allows the nanoparticle size and shape to be adjusted, improving their capabilities in biomedical applications. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/c9tb02721a
  • 2019 • 686 Ablation target cooling by maximizing the nanoparticle productivity in laser synthesis of colloids
    Waag, F. and Gökce, B. and Barcikowski, S.
    Applied Surface Science 466 647-656 (2019)
    Even if ultrashort laser pulses are used during the laser synthesis of colloids, a significant amount of laser energy is converted into thermal energy, which results in heating the ablation target and the colloid. To date, little attention has been paid to these heating effects in the literature. This study was focused on measurements of the process temperature during the high-power, ultrashort-pulsed laser ablation of a nickel target in a continuous water flow setup. Time-resolved monitoring of the temperature of the ablation target and of the colloid indicated that there was an initial rapid uptake of thermal energy followed by a thermally-stable state in which there was very little additional heating. Shifting the focal plane from behind the target onto its surface and further into the fluid provided insight concerning the different mechanisms of heat generation, dissipation, and transfer in the laser synthesis of colloids. It even was possible to distinguish the fluence effects and the colloid re-irradiation effects. New possibilities of process control were identified by correlating the productivity of laser ablation at different focal plane shifts with the measured thermal data. Counterintuitively, the temperature of the target was minimized via ablation cooling when the productivity of the process was maximized. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2018.10.030
  • 2019 • 685 Acoustic emission control avoids fluence shifts caused by target runaway during laser synthesis of colloids
    Labusch, M. and Cunha, A.P.A. and Wirtz, S.F. and Reichenberger, S. and Cleve, E. and Söffker, D. and Barcikowski, S.
    Applied Surface Science 479 887-895 (2019)
    Pulsed laser ablation in liquids (PLAL) has been established as a scalable method to synthesize ligand-free nanoparticles. However, for continuous nanoparticle synthesis with high nanoparticle yield, it is mandatory to maintain a constant fluence, demanding a fixed distance between the focusing lens and target. The latter becomes a non-trivial task during continuous gram-scale nanoparticle production due to the quick removal of target material causing a diminishing productivity. Hence, to maintain a stable process, a perpetual optimization of the working distance is required. In this paper, a field programmable gate array-based measurement and control system is used for online adjustment of the working distance based on acoustic emission (AE) measurements. Ablation-characteristic acoustic frequencies were detected at base frequency correlating to the repetition rate as well as higher harmonics of the latter. The harmonic distortion of AE during laser ablation could be correlated to the location of the focal point. The amplitude intensities correlate well with the nanoparticle productivity. The optimal working distance was reproducibly adjusted in 5.79 min ± 0.41 min with a deviation of 0.33 mm ± 0.04 mm. The automated system provides the basis for temporal stability and scalability of the ablation process. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2019.02.080
  • 2019 • 684 Adhesion, proliferation, and osteogenic differentiation of human mesenchymal stem cells on additively manufactured Ti6Al4V alloy scaffolds modified with calcium phosphate nanoparticles
    Chudinova, E.A. and Surmeneva, M.A. and Timin, A.S. and Karpov, T.E. and Wittmar, A. and Ulbricht, M. and Ivanova, A. and Loza, K. and Prymak, O. and Koptyug, A. and Epple, M. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 176 130-139 (2019)
    In the present study, biocomposites based on 3D porous additively manufactured Ti6Al4V (Ti64) scaffolds modified with biocompatible calcium phosphate nanoparticles (CaPNPs) were investigated. Ti64 scaffolds were manufactured via electron beam melting technology using an Arcam machine. Electrophoretic deposition was used to modify the scaffolds with CaPNPs, which were synthesized by precipitation in the presence of polyethyleneimine (PEI). Dynamic light scattering revealed that the CaP/PEI nanoparticles had an average size of 46 ± 18 nm and a zeta potential of +22 ± 9 mV. Scanning electron microscopy (SEM) revealed that the obtained spherical CaPNPs had an average diameter of approximately 90 nm. The titanium-based scaffolds coated with CaPNPs exhibited improved hydrophilic surface properties, with a water contact angle below 5°. Cultivation of human mesenchymal stem cells (hMSCs) on the CaPNPs-coated Ti64 scaffolds indicated that the improved hydrophilicity was beneficial for the attachment and growth of cells in vitro. The Ti6Al4V/CaPNPs scaffold supported an increase in the alkaline phosphatase (ALP) activity of cells. In addition to the favourable cell proliferation and differentiation, Ti6Al4V/CaPNPs scaffolds displayed increased mineralization compared to non-coated Ti6Al4V scaffolds. Thus, the developed composite 3D scaffolds of Ti6Al4V functionalized with CaPNPs are promising materials for different applications related to bone repair. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2018.12.047
  • 2019 • 683 Cascade Reactions in Nanozymes: Spatially Separated Active Sites inside Ag-Core-Porous-Cu-Shell Nanoparticles for Multistep Carbon Dioxide Reduction to Higher Organic Molecules
    O'Mara, P.B. and Wilde, P. and Benedetti, T.M. and Andronescu, C. and Cheong, S. and Gooding, J.J. and Tilley, R.D. and Schuhmann, W.
    Journal of the American Chemical Society 141 14093-14097 (2019)
    Enzymes can perform complex multistep cascade reactions by linking multiple distinct catalytic sites via substrate channeling. We mimic this feature in a generalized approach with an electrocatalytic nanoparticle for the carbon dioxide reduction reaction comprising a Ag core surrounded by a porous Cu shell, providing different active sites in nanoconfined volumes. The architecture of the nanozyme provides the basis for a cascade reaction, which promotes C-C coupling reactions. The first step occurs on the Ag core, and the subsequent steps on the porous copper shell, where a sufficiently high CO concentration due to the nanoconfinement facilitates C-C bond formation. The architecture yields the formation of n-propanol and propionaldehyde at potentials as low as-0.6 V vs RHE. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/jacs.9b07310
  • 2019 • 682 Catalytic Carbon Monoxide Oxidation over Potassium-Doped Manganese Dioxide Nanoparticles Synthesized by Spray Drying
    Ollegott, K. and Peters, N. and Antoni, H. and Muhler, M.
    Emission Control Science and Technology (2019)
    Manganese oxides are promising catalysts for the oxidation of CO as well as the removal of volatile organic compounds from exhaust gases because of their structural versatility and their ability to reversibly change between various oxidation states. MnO2 nanoparticles doped with Na+ or K+ were synthesized by a semi-continuous precipitation method based on spray drying. Specific surface area, crystallite size, and morphology of these particles were predominantly determined by the spray-drying parameters controlling the quenching of the crystallite growth, whereas thermal stability, reducibility, and phase composition were strongly influenced by the alkali ion doping. Pure α-MnO2 was obtained by K+ doping under alkaline reaction conditions followed by calcination at 450 °C, which revealed a superior catalytic activity in comparison to X-ray amorphous or Mn2O3-containing samples. Thus, the phase composition is identified as a key factor for the catalytic activity of manganese oxides, and it was possible to achieve a similar activation of a K+-doped X-ray amorphous catalyst under reaction conditions resulting in the formation of crystalline α-MnO2. The beneficial effect of K+ doping on the catalytic activity of MnO2 is mainly associated with the stabilizing effect of K+ on the α-MnO2 tunnel structure. © 2019, Springer Nature Switzerland AG.
    view abstractdoi: 10.1007/s40825-019-00125-2
  • 2019 • 681 Combination of an atmospheric pressured arc reactor and a magnetron sputter device for the synthesis of novel nanostructured thin films
    Tillmann, W. and Kokalj, D. and Stangier, D. and Fu, Q. and Kruis, E.
    Thin Solid Films 689 (2019)
    Nanocomposite coatings are state of the art, nevertheless the possible material combinations are restricted. Therefore, this work demonstrates an approach to synthesize novel nanostructured thin films by producing the nanoparticles and thin films independently. An atmospheric-pressure transferred arc reactor is used to synthesize TiN nanoparticles. The device is linked to a magnetron sputter device with an aerodynamic lens system. The aerodynamic lens enables the in-situ introduction of the synthesized nanoparticles into the PVD chamber by compensating the pressure differences. In this study, the influence of the linkage on the properties of a CrN thin film as well as the chamber conditions (pressure, temperature, bias-voltage, and plasma) on the TiN nanoparticles are analyzed. The CrN thin film is only slightly affected by the incoming working gas of the nanoparticle reactor. The TiN nanoparticles reveal a crystallite size of 9.3 ± 2.3 nm and are successfully introduced into the PVD chamber as agglomerates with sizes of 0.04 μm2 and are then deposited onto substrates. It is shown that the particle distribution, agglomerate size, morphology, and crack behavior can be influenced by the chamber conditions. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2019.137528
  • 2019 • 680 Confinement Assembly of ABC Triblock Terpolymers for the High-Yield Synthesis of Janus Nanorings
    Steinhaus, A. and Chakroun, R. and Mullner, M. and Nghiem, T.-L. and Hildebrandt, M. and Groschel, A.H.
    ACS Nano 13 6269-6278 (2019)
    Block copolymers are versatile building blocks for the self-assembly of functional nanostructures in bulk and solution. While spheres, cylinders, and bilayer sheets are thermodynamically preferred shapes and frequently observed, ring-shaped nanoparticles are more challenging to realize due to energetic penalties that originate from their anisotropic curvature. Today, a handful of concepts exist that produce core shell nanorings, while more complex (e.g., patchy) nanorings are currently out of reach and have only been predicted theoretically. Here, we demonstrate that confinement assembly of properly designed ABC triblock terpolymers is a general route to synthesize Janus nanorings in high purity. The triblock terpolymer self-assembles in the spherical confinement of nanoemulsion droplets into prolate ellipsoidal microparticles with an axially stacked lamellar-ring (lr)-morphology. We clarified and visualized this complex, yet well-ordered, morphology with transmission electron tomography. Blocks A and C formed stacks of lamellae with the B microdomain sandwiched in-between as nanorings. Cross-linking of the B-rings allowed disassembly of the microparticles into Janus nanorings carrying two strictly separated polymer brushes of A and C on the top and bottom. Decreasing the B volume leads to Janus spheres and rods, while an increase of B results in perforated and filled Janus disks. The confinement assembly of ABC triblock terpolymers is a general process that can be extended to other block chemistries and will allow to synthesize a large variety of complex micro- A nd nanoparticles that inspire studies in self-assembly, interfacial stabilization, colloidal packing, and nanomedicine. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.8b09546
  • 2019 • 679 Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre-equilibrium Species
    Yeung, H.H.M. and Sapnik, A.F. and Massingberd-Mundy, F. and Gaultois, M.W. and Wu, Y. and Fraser, D.A.X. and Henke, S. and Pallach, R. and Heidenreich, N. and Magdysyuk, O.V. and Vo, N.T. and Goodwin, A.L.
    Angewandte Chemie - International Edition 58 566-571 (2019)
    There is an increasing amount of interest in metal–organic frameworks (MOFs) for a variety of applications, from gas sensing and separations to electronics and catalysis. However, the mechanisms by which they crystallize remain poorly understood. Herein, an important new insight into MOF formation is reported. It is shown that, prior to network assembly, crystallization intermediates in the canonical ZIF-8 system exist in a dynamic pre-equilibrium, which depends on the reactant concentrations and the progress of reaction. Concentration can, therefore, be used as a synthetic handle to directly control particle size, with potential implications for industrial scale-up and gas sorption applications. These findings enable the rationalization of apparent contradictions between previous studies of ZIF-8 and opens up new opportunities for the control of crystallization in network solids more generally. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201810039
  • 2019 • 678 Decreased bacterial colonization of additively manufactured Ti6Al4V metallic scaffolds with immobilized silver and calcium phosphate nanoparticles
    Surmeneva, M. and Lapanje, A. and Chudinova, E. and Ivanova, A. and Koptyug, A. and Loza, K. and Prymak, O. and Epple, M. and Ennen-Roth, F. and Ulbricht, M. and Rijavec, T. and Surmenev, R.
    Applied Surface Science 480 822-829 (2019)
    The design of an ideal bone graft substitute has been a long-standing effort, and a number of strategies have been developed to improve bone regeneration. Electron beam melting (EBM) is an additive manufacturing method allowing for the production of porous implants with highly defined external dimensions and internal architectures. The increasing surface area of the implant may also increase the abilities of pathogenic microorganisms to adhere to the surfaces and form a biofilm, which may result in serious complications. The aim of this study was to explore the modifications of Ti6Al4V alloy scaffolds to reduce the abilities of bacteria to attach to the EBM-manufactured implant surface. The layers composed of silver (Ag), calcium phosphate (CaP) nanoparticles (NPs) and combinations of both were formed on the EBM-fabricated metallic scaffolds by electrophoretic deposition in order to provide them with antimicrobial properties. The assay of bacterial colonization on the surface was performed with the exposure of scaffold surfaces to Staphylococcus aureus cells for up to 17 h. Principal component analysis (PCA) was used to assess the relationships between different surface features of the studied samples and bacterial adhesion. The results indicate that by modifying the implant surface with appropriate nanostructures that change the hydrophobicity and the surface roughness at the nano scale, physical cues are provided that disrupt bacterial adhesion. Our results clearly show that AgNPs at a concentration of approximately 0.02 mg/сm 2 that were deposited together with CaPNPs covered by positively charge polyethylenimine (PEI) on the surface of EBM-sintered Ti6Al4V scaffolds hindered bacterial growth, as the total number of attached cells (NAC) of S. aureus remained at the same level during the 17 h of exposure, which indicates bacteriostatic activity. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2019.03.003
  • 2019 • 677 Development of a high flow rate aerodynamic lens system for inclusion of nanoparticles into growing PVD films to form nanocomposite thin films
    Kiesler, D. and Bastuck, T. and Kennedy, M.K. and Kruis, F.E.
    Aerosol Science and Technology 53 630-646 (2019)
    Hard coatings for wear protection of tools, bearings, and sliding parts play an important role in industrial manufacturing. Nanocomposite coatings are being used in this context to improve the mechanical properties. The technology applied therefore is often based on physical vapor deposition (PVD), in which the different materials are co-deposited. In these processes it is not possible to control the properties of the disperse phase and continuous phase independently. Here, we present a technology which combines aerosol technology with thin film technology to produce nanocomposite coatings directly, which gives us full control over both phases. It is based on an upscaled three-stage aerodynamic lens, which allows to bring nanoparticles from an atmospheric-pressure aerosol reactor into a PVD vacuum chamber operating at low pressure (2 Pa). This requires the use of a higher mass flow rate than conventionally used in aerodynamic lenses, so that a rational upscaling strategy for designing an aerodynamic lens for larger mass flow rates is proposed. Here, an array consisting of eight parallel three-stage aerodynamic lenses having each a mass flow rate of 0.6 slm using argon and 0.71 slm using nitrogen is built and optimized, assisted by CFD and numerical trajectory analysis. The transfer efficiency has been investigated numerically and experimentally. It is possible to transfer 80% of the particles with only 1.3% of the gas into the deposition chamber. A number of coatings consisting of titanium carbonitride nanoparticles embedded in a PVD chromium oxynitride film with varying nanoparticle content were produced. Electron microscopy shows the successful incorporation of the nanoparticles in the thin film. A reduction in film crystallite size with increasing nanoparticle content was found. A reverse Hall–Petch behavior was observed. Copyright © 2019 American Association for Aerosol Research. © 2019, © 2019 American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2019.1587149
  • 2019 • 676 Discrimination of effects leading to gas formation during pulsed laser ablation in liquids
    Kalus, M.-R. and Reimer, V. and Barcikowski, S. and Gökce, B.
    Applied Surface Science 465 1096-1102 (2019)
    Pulsed laser ablation of a bulk target in liquid induces the formation of cavitation bubbles and persistent gas bubbles, which both shield subsequent laser pulses leading to a decrease in nanoparticle productivity. A further shielding entity and a source for gas formation when post-irradiated are the synthesized nanoparticles. In this study, an experimental setup is developed, which allows quantitative measurement of the gas volume produced by these shielding entities. It can be shown that 1 cm3 gas is produced in 10 min ablation time when 8 W picosecond-laser power is applied. By a combined experimental and mathematical approach, the gas volumes induced by silver bulk ablation and post-irradiation effects of the produced colloids are discriminated. It is shown that a characteristic nanoparticle mass concentration threshold exists, where post-irradiation effects mostly dominate gas formation. In a synergistic process, the effective laser fluence available for bulk ablation decreases with increasing nanoparticle mass concentration and up to 80% of the laser power is coupled into the nanoparticles. At the same time, the interparticle distance between the nanoparticles decreases favoring the laser-induced breakdown of the liquid. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2018.09.224
  • 2019 • 675 Durability study of platinum nanoparticles supported on gas-phase synthesized graphene in oxygen reduction reaction conditions
    Bertin, E. and Münzer, A. and Reichenberger, S. and Streubel, R. and Vinnay, T. and Wiggers, H. and Schulz, C. and Barcikowski, S. and Marzun, G.
    Applied Surface Science 467-468 1181-1186 (2019)
    Ligand-free platinum nanoparticles were prepared by pulsed laser ablation in liquids (PLAL) and employed as a benchmarking catalyst to evaluate the durability of a new gas-phase synthesized graphene support in oxygen reduction conditions. Raman measurements showed that the graphene, as compared to Vulcan, was almost defect free. Transmission electron microscopy and initial electrochemically active surface area measurements confirmed good dispersion of the catalysts on both supports. During durability tests, graphene supported Pt nanoparticles showed much better ECSA retention (75% on graphene as compared to 38% on Vulcan), ultimately retaining a higher ECSA than a commercial sample subjected to the same procedure. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2018.10.061
  • 2019 • 674 Evalution of Drude parameters for liquid Germanium nanoparticles through aerosol-based line-of-sight attenuation measurements
    Daun, K.J. and Menser, J. and Asif, M. and Musikhin, S. and Dreier, T. and Schulz, C.
    Journal of Quantitative Spectroscopy and Radiative Transfer 226 146-156 (2019)
    The objective of this study is to infer Drude model parameters for liquid germanium nanoparticles from extinction measurements made across an aerosol within a microwave plasma reactor using a halogen lamp (410–700 nm) and a laser-driven light source (205–585 nm). The plasma frequency and relaxation time are inferred using Rayleigh theory, Mie theory, and a fourth-order Mie approximation. These parameters are compared with those found using the ellipsometry-derived complex dielectric function as well as the bulk density and electrical resistivity of liquid germanium. The analysis is carried out in a probabilistic context using Bayesian inference, which accounts for both the measurement noise and model error. While all the candidate models can reproduce the shape of the experimentally-derived extinction spectra, the Bayesian inference showed that extinction-derived parameters differed from those obtained from the density and electrical resistivity in a statistically-significant way. This highlights the limitations of the free-electron model that underpins Drude theory, and suggests potential opportunities for model refinement. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.jqsrt.2019.01.021
  • 2019 • 673 Evolution of the Ligand Shell Around Small ZnO Nanoparticles During the Exchange of Acetate by Catechol: A Small Angle Scattering Study
    Schindler, T. and Lin, W. and Schmutzler, T. and Lindner, P. and Peukert, W. and Segets, D. and Unruh, T.
    ChemNanoMat 5 116-123 (2019)
    The core-shell structure of colloids surrounded by ligands is of great importance for their later application as it can significantly alter the chemical and physical properties of the nanoparticles (NPs). A combination of small angle X-ray and neutron scattering (SAXS/SANS) in the native solution with additional ex situ measurements (titration-UV) was applied to study the NP/ligand interface of ZnO NPs after functionalization with catechol derivatives. Based on SAXS data, it was found that within the multimodal particle size distribution the fraction of agglomerates is shifted to smaller sizes and nearly disappeared upon the binding of ethyl 3,4-dihydroxybenzoate (CAT) molecules. This is ascribed to improved stabilization at the primary particle level by CAT molecules. By combining the neutron scattering contrast with the input of bound CAT molecules from a previously developed titration-UV method, the heterogeneous composition of the ligand shell became accessible for the first time. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cnma.201800465
  • 2019 • 672 Excellent Oxygen Reduction Reaction Performance in Self-Assembled Amyloid-β/Platinum Nanoparticle Hybrids with Effective Platinum-Nitrogen Bond Formation
    Jindal, A. and Tashiro, K. and Kotani, H. and Takei, T. and Reichenberger, S. and Marzun, G. and Barcikowski, S. and Kojima, T. and Yamamoto, Y.
    ACS Applied Energy Materials 2 6536-6541 (2019)
    The development of highly efficient catalysts for electrochemical oxygen reduction reactions (ORRs) is crucial for energy applications such as metal-air batteries and fuel cells. Here, we show an enhanced electrocatalytic activity of a new functional material composed of Pt nanoparticles (PtNPs) and self-assembled β-sheet peptides (βPs). The PtNP/βP hybrids, under an optimized assembly condition, display an ORR electrocatalytic activity that is higher than that of a commercially available benchmark Pt/C electrocatalyst in terms of the onset potential and reaction kinetics. Moreover, the PtNP/βP hybrids show one order of magnitude higher ORR mass activity than previously reported peptide-based ORR electrocatalysts. The superb ORR activity with high durability is derived from the well-dispersed PtNPs on βPs, where 50% of the amine groups on the side chain bound with Pt to form Pt-N bonds that function as active sites for the catalytic reaction. This work opens new avenues for efficient ORR electrocatalysts using self-assembled peptides. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsaem.9b01103
  • 2019 • 671 First PEM fuel cell based on ligand-free, laser-generated platinum nanoparticles
    Kohsakowski, S. and Streubel, R. and Radev, I. and Peinecke, V. and Barcikowski, S. and Marzun, G. and Reichenberger, S.
    Applied Surface Science 467-468 486-492 (2019)
    For the first time, surfactant-free platinum nanoparticles (Pt-NPs) prepared by pulsed laser ablation in liquids were employed in a real proton exchange membrane fuel cell (PEMFC). Laser-generated Pt-NPs show a larger size in comparison to a commercial Pt/C catalyst, being 6.6 nm for the laser-based and 3.8 nm for the reference, respectively. The laser-based Pt/C electrocatalyst was synthesized by colloidal deposition of laser-generated Pt-NPs onto carbonic Vulcan as support. The durability tests showed a much better stability of the laser-based catalyst in the electrochemical active surface area (ECSA) with an ECSA retention of 88% of its initial area. This better durability is probably caused by a reduced Pt dissolution rate which is higher for the reference catalyst containing NPs smaller than 3 nm. The occurrence of Pt dissolution is further indicated by X-ray photoelectron spectroscopy (XPS) of the electrodes after electrocatalytic testing showing no Pt signal in case of the reference catalyst. Performance tests of both PEMFC show a 20% higher mass-specific power density for the laser-based proton exchange membrane fuel cell. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2018.10.145
  • 2019 • 670 Functionalization of titania nanotubes with electrophoretically deposited silver and calcium phosphate nanoparticles: Structure, composition and antibacterial assay
    Chernozem, R.V. and Surmeneva, M.A. and Krause, B. and Baumbach, T. and Ignatov, V.P. and Prymak, O. and Loza, K. and Epple, M. and Ennen-Roth, F. and Wittmar, A. and Ulbricht, M. and Chudinova, E.A. and Rijavec, T. and Lapanje, A...
    Materials Science and Engineering C 97 420-430 (2019)
    Herein TiO2 nanotubes (NTs) were fabricated via electrochemical anodization and coated with silver and calcium phosphate (CaP) nanoparticles (NPs) by electrophoretic deposition. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ag and CaP NPs were successfully deposited onto the TiO2 NTs. Using X-ray diffraction, only anatase and Ti were observed after deposition of Ag and CaP NPs. However, X-ray photoelectron spectroscopy (XPS) analysis revealed that the binding energy (BE) of the Ag and CaP NP core levels corresponded to metallic Ag, hydroxyapatite and amorphous calcium phosphate, based on the knowledge that CaP NPs synthesized by precipitation have the nanocrystalline structure of hydroxyapatite. The application of Ag NPs allows for decreasing the water contact angle and thus increasing the surface free energy. It was concluded that the CaP NP surfaces are superhydrophilic. A significant antimicrobial effect was observed on the TiO2 NT surface after the application of Ag NPs and/or CaP NPs compared with that of the pure TiO2 NTs. Thus, fabrication of TiO2 NTs, Ag NPs and CaP NPs with PEI is promising for diverse biomedical applications, such as in constructing a biocompatible coating on the surface of Ti that includes an antimicrobial effect. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2018.12.045
  • 2019 • 669 Induction of herpes simplex virus type 1 cell-to-cell spread inhibiting antibodies by a calcium phosphate nanoparticle-based vaccine
    Kopp, M. and Aufderhorst, U.W. and Alt, M. and Dittmer, U. and Eis-Hübinger, A.-M. and Giebel, B. and Roggendorf, M. and Epple, M. and Krawczyk, A.
    Nanomedicine: Nanotechnology, Biology, and Medicine 16 138-148 (2019)
    Herpes simplex viruses 1 and 2 are among the most ubiquitous human infections and persist lifelong in their host. Upon primary infection or reactivation from ganglia, the viruses spread by direct cell–cell contacts (cell-to-cell spread) and thus escape from the host immune response. We have developed a monoclonal antibody (mAb 2c), which inhibits the HSV cell-to-cell spread, thereby protecting from lethal genital infection and blindness in animal models. In the present study we have designed a nanoparticle-based vaccine to induce protective antibody responses exceeding the cell-to-cell spread inhibiting properties of mAb 2c. We used biodegradable calcium phosphate (CaP) nanoparticles coated with a synthetic peptide that represents the conformational epitope on HSV-1 gB recognized by mAb 2c. The CaP nanoparticles additionally contained a TLR-ligand CpG m and were formulated with adjuvants to facilitate the humoral immune response. This vaccine effectively protected mice from lethal HSV-1 infection by inducing cell-to-cell spread inhibiting antibodies. © 2018 The Authors
    view abstractdoi: 10.1016/j.nano.2018.12.002
  • 2019 • 668 Investigating temporal variation in the apparent volume fraction measured by time-resolved laser-induced incandescence
    Sipkens, T.A. and Menser, J. and Mansmann, R. and Schulz, C. and Daun, K.J.
    Applied Physics B: Lasers and Optics 125 (2019)
    In many time-resolved laser-induced incandescence (TiRe-LII) experiments, it is common practice to relate the intensity emitted by laser-heated nanoparticles to the detected LII signal through a factor (here called the intensity scaling factor, ISF) that includes the particle volume fraction and other parameters that may not be the focus of the analysis. While, in the absence of evaporation or sublimation, the ISF should theoretically remain constant with respect to time, recent multi-wavelength measurements show that, in reality, it may vary with both time and fluence. We consider four candidate effects that contribute to this behavior: particle annealing; polydispersity in the nanoparticle-size distribution; background luminosity due to emission from nanoparticles in the line-of-sight before and behind the probe volume; and the temporal resolution of the detector. We demonstrate these effects by simulating TiRe-LII data for in-flame soot at atmospheric pressure, using new simplified heat transfer and annealing models. Analysis of experimental signals collected from flame-generated soot at atmospheric pressure reveals trends in the ISF similar to those predicted by simulations. These temporal variations provide important insights that can help to diagnose problems in TiRe-LII experiments and improve TiRe-LII models. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00340-019-7251-7
  • 2019 • 667 Microwave plasma-assisted silicon nanoparticles: Cytotoxic, molecular, and numerical responses against cancer cells
    Wahab, R. and Khan, F. and Gupta, A. and Wiggers, H. and Saquib, Q. and Faisal, M. and Ansari, S.M.
    RSC Advances 9 13336-13347 (2019)
    Silicon nanoparticles (SiNPs), which have a special place in material science due to their strong luminescent property and wide applicability in various physicochemical arenas, such as solar cells and LEDs, were synthesised by a microwave plasma-assisted process using an argon-silane mixture. Several characterization tools were applied to check the crystallinity (XRD) and morphological (FESEM, TEM, ∼20 ± 2 nm size) and topographical (AFM, ∼20 nm) details of the NPs. The high-purity SiNPs were applied on myoblast cancer cells to investigate the reactivity of the NPs at different doses (200, 1000 and 2000 ng mL-1) for different incubation periods (24 h, 48 h &amp; 72 h). The MTT assay was utilized to determine the percentage of viable and non-viable cells, while the cell organization was observed via microscopy and CLSM. Additionally, the molecular responses (RT-PCR), such as apoptosis, were analyzed in presence of caspase 3 and 7, and the results showed an upregulation with SiNPs. To validate the obtained data, analytical studies were also performed for the SiNPs via statistical analysis and the most reliable data values were evaluated and acceptable as per the ICH guidelines. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8ra10185j
  • 2019 • 666 Modular Pd/Zeolite Composites Demonstrating the Key Role of Support Hydrophobic/Hydrophilic Character in Methane Catalytic Combustion
    Losch, P. and Huang, W. and Vozniuk, O. and Goodman, E.D. and Schmidt, W. and Cargnello, M.
    ACS Catalysis 9 4742-4753 (2019)
    Complete catalytic oxidation of methane in the presence of steam at low temperatures (T &lt; 400 °C) is a crucial reaction for emission control, yet it presents profound challenges. The activation of the strong C-H bond of methane at low temperature is difficult, and the water present in any realistic application poisons the active surface and promotes sintering of Pd particles during the reaction. Finding materials that can deliver high reaction rates while being more resistant to the presence of water is imperative for advancing several technological applications of natural gas-based systems. However, methods to fairly compare the activity of Pd catalysts (the most active metal for methane combustion) are needed in order to perform useful structure-property relationship studies. Here, we report a method to study how zeolite hydrophobicity affects the activity of Pd nanoparticles in the reaction, which led to a significant improvement in the water resistance. Mesoporous zeolites were synthesized starting from commercially available microporous zeolites. In this way, a variety of hierarchically porous zeolites, with different hydrophobic/hydrophilic character, were prepared. Preformed colloidal Pd nanoparticles could be deposited within mesostructured zeolites. This approach enabled the systematic study of key parameters such as zeolite framework, Al content, and the Pd loading while maintaining the same Pd particle size and structure for all the samples. Detailed catalytic studies revealed an optimum hydrophobic/hydrophilic character, and a promising steam-resistant catalyst, namely, 3.2 nm Pd particles supported on mesoporous zeolite beta or USY with a Si/Al ratio of 40, emerged from this multiparametric study with a T50 of 355 °C and T90 of 375 °C (where T50 and T90 are temperature values at which the samples reach 50% and 90% methane conversion, respectively) in steam-containing reaction conditions. Finally, we verified that the designed catalysts were stable by in-depth postcatalysis characterization and operando diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) analyses confirming that water adsorbs less strongly on the active PdO surface due to interaction with the zeolite acid sites. This method can be of general use to study how zeolite supports affect the reactivity of supported metals in several catalytic applications. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.9b00596
  • 2019 • 665 Nanoscale Physical and Chemical Structure of Iron Oxide Nanoparticles for Magnetic Particle Imaging
    Hufschmid, R. and Landers, J. and Shasha, C. and Salamon, S. and Wende, H. and Krishnan, K.M.
    Physica Status Solidi (A) Applications and Materials Science 216 (2019)
    In this work, the role of the nanoscale chemical and magnetic structure on relaxation dynamics of iron oxide nanoparticles in the context of magnetic particle imaging (MPI) is investigated with Mössbauer spectroscopy (MS) and electron energy loss spectroscopy (EELS). Two samples of 27 nm monodisperse iron oxide nanoparticles are compared, with and without an additional oxidation optimization step, with corresponding differences in structure and properties. Iron oxide nanoparticles synthesized in the presence of sufficient oxygen form single crystalline, inverse-spinel magnetite (Fe 3 O 4 ) and display magnetic properties suitable for MPI. A secondary wüstite (FeO) phase is observed in the diffraction pattern of unoptimized nanoparticles, which is antiferromagnetic and therefore unsuitable for MPI. Mössbauer spectra confirm the composition of the optimized nanoparticles to be ≈70% magnetite, with the remaining 30% oxidized to maghemite; in contrast, the as-synthesized particles (without the oxidation step) contained about 40% wüstite and 60% magnetite. The authors use scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) to probe iron 2p-3d electronic transitions and correlate their intensities with the oxidation state with sub-nanometer spatial resolution. The optimally oxidized nanoparticles are uniform in crystallography and phase, while the mixed phase nanoparticles are core-shell wüstite/magnetite. Further confirming the core-shell structure of the mixed phase nanoparticles, considerable spin canting in the in-field Mössbauer spectrum, likely caused by interface coupling, is observed. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/pssa.201800544
  • 2019 • 664 Nanosized Lithium-Rich Cobalt Oxide Particles and Their Transformation to Lithium Cobalt Oxide Cathodes with Optimized High-Rate Morphology
    Zehetmaier, P.M. and Cornélis, A. and Zoller, F. and Böller, B. and Wisnet, A. and Döblinger, M. and Böhm, D. and Bein, T. and Fattakhova-Rohlfing, D.
    Chemistry of Materials (2019)
    We report the formation of crystalline dispersible LixCo1-xOy (with y 1) nanoparticles with an unusual rock-salt phase containing â¼15 at. % Li in the crystalline structure. This is the first time that this composition was formed at temperatures as low as 150 °C under conditions of a solvothermal process, although it is referred to as a higherature metastable phase in a very limited number of known publications. The Li0.15Co0.85Oy nanoparticles of 2-3 nm size completely transform to higherature LiCoO2 (HT-LCO) nanoparticles at 560 °C in the presence of slightly overstoichiometric amounts of Li source. The presence of lithium in the CoO lattice slows down the kinetics of its phase transformation, enabling to obtain very small HT-LCO nanocrystals during the subsequent calcination. The HT-LCO particles formed after this transformation have an elongated shape with a mean size of about 17 × 60 nm, which is targeted as an optimum size for battery applications. An attractive feature of the Li0.15Co0.85Oy nanoparticles is their high dispersibility enabling their assembly into different nanostructures with optimized morphology. Open porous HT-LCO electrodes prepared via self-assembly of Li0.15Co0.85Oy nanoparticles and Pluronic F127 as a structure-directing agent demonstrate very good performances at high current densities representing short charge/discharge times below 10 min. Even at a charge/discharge time of 72 s (50C), 50% of the theoretical capacity has been preserved. After 250 cycles at a charge/discharge time of 6 min (10C), over 60% of the initial discharge capacity was retained. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.9b02231
  • 2019 • 663 Nitrogen-Doped Mesostructured Carbon-Supported Metallic Cobalt Nanoparticles for Oxygen Evolution Reaction
    Bähr, A. and Moon, G.-H. and Tüysüz, H.
    ACS Applied Energy Materials 2 6672-6680 (2019)
    A series of metallic cobalt nanoparticles supported on mesostructured nitrogen-doped carbons was successfully synthesized through soft-templating by using poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a structure directing agent. The formation of metallic cobalt nanoparticles and nitrogen-doping into carbon structures were simultaneously achieved by ammonia treatment. The physicochemical properties of the resulting materials and consequently their performance for the oxygen evolution were systematically altered by varying the cobalt loading (5-89 wt %), pyrolysis atmosphere (argon or ammonia), and temperature (600-800 °C). Thereby, up to 37 wt % of the cobalt nanoparticles were confined in the pores of the mesostructured nitrogen-doped carbon materials with a high BET surface area. At temperatures above 700 °C, the cobalt additionally catalyzes the graphitization of the carbon support. The catalyst with a cobalt loading of 37 wt % pyrolyzed at 700 °C under an ammonia atmosphere shows the highest turnover frequency (TOF) of 311 h-1 in the oxygen evolution reaction due to the improved electronic properties of the carbon support from the incorporation of nitrogen atoms combined with a large amount of accessible cobalt sites. This class of materials shows even higher activity in comparison with ordered mesoporous Co3O4. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsaem.9b01183
  • 2019 • 662 Optimizing the synthesis of Co/Co–Fe nanoparticles/N-doped carbon composite materials as bifunctional oxygen electrocatalysts
    Medina, D. and Barwe, S. and Masa, J. and Seisel, S. and Schuhmann, W. and Andronescu, C.
    Electrochimica Acta 318 281-289 (2019)
    A future widespread application of electrochemical energy conversion and storage technologies strongly depends on the substitution of precious metal-based electrocatalysts for the high-overpotential oxygen reduction and oxygen evolution reactions. We report a novel Co/Co–Fe nanoparticles/N-doped carbon composite electrocatalyst (Co/CoxFey/NC) obtained by pyrolysis of CoFe layered double hydroxide (CoFe LDH) embedded in a film of a bisphenol A and tetraethylenepentamine-based polybenzoxazine poly(BA-tepa). During pyrolysis poly(BA-tepa) forms a highly conductive nitrogen-doped carbon matrix encapsulating Co/Co–Fe nanoparticles, thereby circumventing the need of any additional binder material and conductive additives. Optimization with respect to pyrolysis temperature, the CoFe LDH/BA-tepa ratio, as well as of the gas atmosphere used during the thermal treatment was performed. The optimized Co/CoxFey/NC composite material catalyst exhibits remarkable bifunctional activity towards oxygen reduction (ORR) and oxygen evolution (OER) reactions in 0.1 M KOH represented by a potential difference of only 0.77 V between the potentials at which current densities of −1 mA cm−2 for the ORR and 10 mA cm−2 for the OER were recorded. Moreover, the Co/CoxFey/NC composite material pyrolyzed in ammonia atmosphere exhibits promising stability during both the ORR and the OER. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2019.06.048
  • 2019 • 661 Perspective of Surfactant-Free Colloidal Nanoparticles in Heterogeneous Catalysis
    Reichenberger, S. and Marzun, G. and Muhler, M. and Barcikowski, S.
    ChemCatChem 11 4489-4518 (2019)
    Due to material gaps and synthesis-related cross-correlations in heterogeneous catalysis, chemists and physicists are constantly motivated to develop novel catalyst preparation methods for independent control of morphology, size, and composition. Within this article, advances, opportunities, and the current limits of laser-based catalyst preparation technique, as well as synergies with conventional methods will be reviewed in terms of purity, particle size, morphology, composition, and nanoparticle-support interaction. It will be shown, that the surfactant-free particles represent ideal model materials to validate kinetic models and conduct parametric activity studies by independent adjustment of functional properties like nanoparticle size, composition, and load. Consequently, the importance of transient plasma dynamics tailoring nanoparticle formation will be pointed out, comparing experimental studies with own calculations and novel simulations taken from literature. Finally, perspectives of surfactant-free colloidal nanoparticles for unrevealing active sites in heterogeneous catalysts are presented. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201900666
  • 2019 • 660 Piece by Piece—Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis
    Evers, M.V. and Bernal, M. and Roldan Cuenya, B. and Tschulik, K.
    Angewandte Chemie - International Edition 58 8221-8225 (2019)
    The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well-defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution-phase precursor entities are then reduced electrochemically—one by one—to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4-filled micelles. These Au NP-decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor-filled nanocontainers are presented as a new route to nanoparticle-modified electrodes with high catalyst utilization. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201813993
  • 2019 • 659 Platinum nanoparticles supported on reduced graphene oxide prepared in situ by a continuous one-step laser process
    Haxhiaj, I. and Tigges, S. and Firla, D. and Zhang, X. and Hagemann, U. and Kondo, T. and Nakamura, J. and Marzun, G. and Barcikowski, S.
    Applied Surface Science 469 811-820 (2019)
    A large research emphasis is still placed on improvement of production routes of nanosized materials with enhanced catalytic properties. Here we developed a continuous process for generation of platinum (Pt) nanoparticles supported on reduced graphene oxide (rGO) in situ via pulsed laser ablation in liquid (PLAL) dispersion of rGO. This in situ PLAL technique is a single step procedure that allows the synthesis of heterogeneous catalysts with a simultaneous control of particle size and mass loading. By this method, Pt particles with mean particle diameters around 2.5 nm and in a regime of 3–4 nm have been produced in ethanol and saline water, respectively, and adsorbed on rGO with up to 50 wt%. Both inorganic and organic solvents used during in situ synthesis lead to production of CO tolerant Pt/rGO catalysts, which are relevant for fuel cell applications due to the remarkably low CO desorption temperatures around 65–80 °C. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2018.10.257
  • 2019 • 658 Review on experimental and theoretical investigations of the early stage, femtoseconds to microseconds processes during laser ablation in liquid-phase for the synthesis of colloidal nanoparticles
    Kanitz, A. and Kalus, M.-R. and Gurevich, E.L. and Ostendorf, A. and Barcikowski, S. and Amans, D.
    Plasma Sources Science and Technology 28 (2019)
    Laser ablation in liquid-phase (LAL) has been developed since the 1990s, but the interest in laser synthesis of colloids has emerged in the last decade due to a significant improvement in the production rate, proven comparative advantages in biomedical and catalysis applications, and recent commercialization. However, the method relies on highly transient phenomena, so that the fundamental understanding lacks behind the LAL synthesis refinement research. The complexity of the physics and chemistry involved has led to experimental and theoretical investigations that attempt to provide a basic description of the underlying processes but face the challenge of temporal and spatial resolution as well as non-equilibrium conditions. It appears that the processes occurring at the early time scales, ranging from femtoseconds to several microseconds are critical in the definition of the final product. The review is mainly dedicated to the comprehensive description of the processes occurring at early time scales, which include the description of laser-matter interaction for ultrashort and short laser pulses, plasma formation processes as well as comparison of the measured plasma parameters at these time scales, and subsequent description of the cavitation bubble dynamics. Furthermore, the plasma and cavitation bubble chemistry are addressed, and their impact on the nanoparticle formation is emphasized. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ab3dbe
  • 2019 • 657 Scalable classification of nanoparticles: A proof of principle for process design
    Menter, C. and Segets, D.
    Advanced Powder Technology 30 2801-2811 (2019)
    Nanoparticles like quantum confined ZnS semiconductor nanocrystals, exhibit unique structure-property relationships. Narrow particle size distributions (PSDs) become one of the most important factors to tailor product performance. Size selective precipitation has already been proven to be an effective post processing strategy for ZnS nanoparticles. It is based on the titration of a poor liquid into a stable dispersion, which leads to the preferred flocculation of larger particles. Afterwards, these flocks must be separated from the continuous phase. While on lab scale the formed flocks can be easily separated by centrifugation from the fine fraction, for larger scale production using continuous processes, new concepts are urgently needed. Herein we developed a filtration process for flock removal that allows the handling of larger quantities. For process design, we first investigated the flock properties in order to know how stable the generated flocks are and how the flock properties can be controlled. Then, we replaced the classical flock separation by centrifugation through separation by surface filtration under the constraint that the underlying separation efficiency was not affected. By the future use of properly controlled, alternating filtration modules, our work opens the door for establishing an urgently needed, scalable post-processing for sub-10 nm nanoparticles. © 2019 Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2019.08.027
  • 2019 • 656 Scanning Electrochemical Cell Microscopy Investigation of Single ZIF-Derived Nanocomposite Particles as Electrocatalysts for Oxygen Evolution in Alkaline Media
    Tarnev, T. and Aiyappa, H.B. and Botz, A. and Erichsen, T. and Ernst, A. and Andronescu, C. and Schuhmann, W.
    Angewandte Chemie - International Edition 58 14265-14269 (2019)
    “Single entity” measurements are central for an improved understanding of the function of nanoparticle-based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF-67)-derived Co−N-doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non-interfering Os complex as free-diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s−1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201908021
  • 2019 • 655 Selective 2-Propanol Oxidation over Unsupported Co3O4 Spinel Nanoparticles: Mechanistic Insights into Aerobic Oxidation of Alcohols
    Anke, S. and Bendt, G. and Sinev, I. and Hajiyani, H. and Antoni, H. and Zegkinoglou, I. and Jeon, H. and Pentcheva, R. and Roldan Cuenya, B. and Schulz, S. and Muhler, M.
    ACS Catalysis 9 5974-5985 (2019)
    Crystalline Co3O4 nanoparticles with a uniform size of 9 nm as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM) were synthesized by thermal decomposition of cobalt acetylacetonate in oleylamine and applied in the oxidation of 2-propanol after calcination. The catalytic properties were derived under continuous flow conditions as a function of temperature up to 573 K in a fixed-bed reactor at atmospheric pressure. Temperature-programmed oxidation, desorption (TPD), surface reaction (TPSR), and 2-propanol decomposition experiments were performed to study the interaction of 2-propanol and O2 with the exposed spinel surfaces. Co3O4 selectively catalyzes the oxidative dehydrogenation of 2-propanol, yielding acetone and H2O and only to a minor extent the total oxidation to CO2 and H2O at higher temperatures. The high catalytic activity of Co3O4 reaching nearly full conversion with 100% selectivity to acetone at 430 K is attributed to the high amount of active Co3+ species at the catalyst surface as well as surface-bound reactive oxygen species observed in the O2 TPD, 2-propanol TPD, TPSR, and 2-propanol decomposition experiments. Density functional theory calculations with a Hubbard U term support the identification of the 5-fold-coordinated octahedral surface Co5c3+ as the active site, and oxidative dehydrogenation involving adsorbed atomic oxygen was found to be the energetically most favored pathway. The consumption of surface oxygen and reduction of Co3+ to Co2+ during 2-propanol oxidation derived from X-ray absorption spectroscopy and X-ray photoelectron spectroscopy measurements before and after reaction and poisoning by strongly bound carbonaceous species result in the loss of the low-temperature activity, while the high-temperature reaction pathway remained unaffected. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.9b01048
  • 2019 • 654 Size-Selective Optical Printing of Silicon Nanoparticles through Their Dipolar Magnetic Resonance
    Zaza, C. and Violi, I.L. and Gargiulo, J. and Chiarelli, G. and Schumacher, L. and Jakobi, J. and Olmos-Trigo, J. and Cortes, E. and König, M. and Barcikowski, S. and Schlücker, S. and Sáenz, J.J. and Maier, S.A. and Stefani, F.D.
    ACS Photonics 6 815-822 (2019)
    Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- and microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsphotonics.8b01619
  • 2019 • 653 Smart Polymeric Membranes with Magnetic Nanoparticles for Switchable Separation
    Ulbricht, M.
    RSC Smart Materials 2019-January 297-328 (2019)
    This chapter provides an overview on the topic of magneto-responsive membranes for switchable mass separation. The combination of concepts, materials and methods in the field of filtration membranes with the application of magnetic materials and magnetic fields is described. Combining organic polymer-based membranes with inorganic magnetic nanoparticles is the most efficient approach to obtain "smart" membranes that can show large and reversible changes in barrier and surface properties upon activation with static or alternating magnetic fields of different frequencies. Two general approaches can be distinguished: (i) addressing secondary interactions during membrane separation such as concentration polarization or fouling, or (ii) focussing on intrinsic membrane barrier properties. Until now, the most progress toward switchable separations has been achieved by membranes that change effective pore size in the micro- or ultrafiltration range, either via reversible deformations induced by static or low frequency magnetic fields or via the synergistic combination of magneto-heating by stimulation with high frequency alternating magnetic fields and thermo-responsive hydrogels as building blocks for mixed matrix composite membranes. This pioneering work will trigger much more research and development toward real applications, e.g., in bioseparations and/or for bioanalytical or biomedical applications, wherever the option of remote-controlled switching of separation selectivity is of interest. © The Royal Society of Chemistry 2019.
    view abstractdoi: 10.1039/9781788016377-00297
  • 2019 • 652 Structures of carbonaceous nanoparticles formed in various pyrolysis systems
    Jander, H. and Borchers, C. and Böhm, H. and Emelianov, A. and Schulz, C.
    Carbon 150 244-258 (2019)
    In the pyrolysis of different hydrocarbon/carbon suboxid fuels formation of carbon particles with the special view to their structures was examined. For this, the following three very different pyrolysis systems were investigated experimentally i)a pyrolysis reactor, ii)a shock tube and iii)a plasma reactor with respect to the influence of varying reaction parameters on the carbonaceous nanoparticles. The particles formed in these reaction systems were studied in view of their morphology and state of crystallization by use of electron microscopy (Philips CM30)at low- and high resolution combined with micro-diffraction measurements. As to be seen at low resolution of the transmission electron microscopy studies, the particle sizes in the pyrolysis reactor and shock tube do not differ significantly, but distinguished considerably from those particle sizes obtained in the plasma reactor. While the particles obtained in the pyrolysis reactor and shock-tube had particle diameters of about d≈ 30 nm, the particles in the plasma reactor consisted of fluffy-like units, and their sizes were about d≈ 4 nm. The various carbon layers consisted of different polyaromatic hydrocarbon units with variable sizes arranged to diverse states in the course of graphitization. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.carbon.2019.02.034
  • 2019 • 651 Synergism between Specific Halide Anions and pH Effects during Nanosecond Laser Fragmentation of Ligand-Free Gold Nanoparticles
    Ziefuß, A.R. and Barcikowski, S. and Rehbock, C.
    Langmuir (2019)
    Gold nanoclusters (AuNCs) with diameters smaller than 3 nm are an emerging field of research because they possess interesting optical properties, such as photoluminescence. However, to date, it is still difficult to distinguish whether these properties originate from the cores of the nanoparticles or from the adsorbates on their surfaces. Hence, there is a high demand for ligand-free, ultra-small particles because they make it possible to study ligand and core effects separately. Pulsed laser fragmentation in liquids (LFL) is a convenient route for the synthesis of ligand-free AuNCs. The influence of physical parameters, such as melting and evaporation, on the LFL process is well understood both theoretically and experimentally. However, the impact of the chemical composition of the medium during LFL, which critically affects the particle formation process, has been less well examined. Therefore, in this work, we elucidate the extent to which the ionic strength, the pH value, and the nature of the halide anion that is present, that is, F-, Cl-, Br-, or I-, influence the particle size distribution of the LFL product and the mean yield of small particles (&lt;3 nm) of the product. We showed that the yield of small particles can be enhanced by the synergism between pH and specific ion effects, which probably is attributable to the adsorption of specific anions. In addition, our findings indicated that anion-based stabilization depends critically on the type of anion. A direct Hofmeister effect was observed for anions in the neutral pH regime, whereas an indirect Hofmeister series was reported in alkaline solution, which probably was due to the more hydrophilic surfaces of the AuNCs that were formed. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.9b00418
  • 2019 • 650 Synthesis of silicon nanoparticles in a pilot-plant-scale microwave plasma reactor: Impact of flow rates and precursor concentration on the nanoparticle size and aggregation
    Kunze, F. and Kuns, S. and Spree, M. and Hülser, T. and Schulz, C. and Wiggers, H. and Schnurre, S.M.
    Powder Technology 342 880-886 (2019)
    This work is devoted to scale-up the microwave plasma synthesis of silicon nanoparticles from gaseous precursor monosilane (SiH4), previously investigated in lab-scale processes, to the pilot-plant-scale with production rates up to 200 g/h. The aim is to ensure reproducible, long-term operation of the reactor through gas-dynamic stabilization of the reacting flow and to control particle size and morphology via the gas flow velocity and the precursor concentration. Based on a newly designed nozzle, the lab-scale approach of stabilizing the plasma flow via a tangential sheath gas flow and an axial precursor gas flow was successfully transferred to the pilot-plant scale. At precursor concentrations up to 16 vol% of SiH4 diluted in argon and hydrogen, the as-synthesized particles have similar characteristics compared to those from lab-scale reactors. They are spherical, crystalline, mostly soft-agglomerated, and show a log-normal size distribution with a geometric standard deviation around 1.45 as expected for self-preserving aerosol size-distributions. In contrast to lab-scale experiments, an increase in SiH4 concentration up to 48 vol% does not lead to further growth of isolated primary particles but promotes aggregate formation from smaller primary particles. This is attributed to massive initial nucleation of very small particles due to strong supersaturation and their subsequent strong aggregation while suppressing complete coalescence due to the limited residence time at high temperature. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2018.10.042
  • 2019 • 649 Tailoring the Surface Structure of Silicon Carbide Support for Copper Catalyzed Ethanol Dehydrogenation
    Li, M.-Y. and Lu, W.-D. and He, L. and Schüth, F. and Lu, A.-H.
    ChemCatChem 11 481-487 (2019)
    The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu−Si−C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201801742
  • 2019 • 648 Templated Dealloying: Designing Ultrastructures by Memory Effect
    Kamp, M. and Tymoczko, A. and Schürmann, U. and Jakobi, J. and Rehbock, C. and Barcikowski, S. and Kienle, L.
    Crystal Growth and Design 19 4957-4963 (2019)
    Tailoring the morphology of nanoporous structures widens the scope of applications in catalysis and sensing. The synthesis of versatile nanoporous morphologies with the spatial distribution of porosity is permitted by the dealloying of unique, metastable Au-Fe alloy template nanoparticles generated by laser ablation in liquids. This approach opens the door to a novel process, which involves a special transformation mechanism, including oxidation and Kirkendall effect, which is decisive for the stabilization of hollow structures with the spatial distribution of porosity and represents a memory effect of morphology. Within this work, nanoporous Au particles, hollow nanoporous Au shells with the spatial distribution of porosity, and yolk-shell-like Au nanoparticles encapsulated in ultrathin Au shells are synthesized. A distinct variation of crystallinity and an increased lattice strain is observed, which implies an improved catalytic activity for oxidation reactions. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.9b00175
  • 2019 • 647 Template-Free Synthesis and Selective Filling of Janus Nanocups
    Qiang, X. and Steinhaus, A. and Chen, C. and Chakroun, R. and Gröschel, A.H.
    Angewandte Chemie - International Edition 58 7122-7126 (2019)
    We report on the formation of shape- and surface-anisotropic Janus nanocups (JNCs) by evaporation-induced confinement assembly (EICA) of ABC triblock terpolymers. During microphase separation in spherical confinement, the triblock terpolymer spontaneously adopted a hemispherical shape with an inner concentric lamella–lamella (ll) morphology. Cross-linking and disassembly of the microparticles resulted in well-defined JNCs with different chemistry on the inside and outside. By synthesizing polymers with increasing length of the cross-linkable block, we tuned the mechanical stability of the nanocups, which is relevant to control opening and closing of the cup cavity. We utilize the Janus properties for selective uptake of cargo exemplified by the filling of JNCs with polymer or gold nanoparticles. The directional properties of JNCs suggest applications in locomotion, oil-spill recovery, storage and release, templating, and as nanoreactors with attoliter volume. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201814014
  • 2019 • 646 Time and Mechanism of Nanoparticle Functionalization by Macromolecular Ligands during Pulsed Laser Ablation in Liquids
    Letzel, A. and Reich, S. and Dos Santos Rolo, T. and Kanitz, A. and Hoppius, J. and Rack, A. and Olbinado, M.P. and Ostendorf, A. and Gökce, B. and Plech, A. and Barcikowski, S.
    Langmuir 35 3038-3047 (2019)
    Laser ablation of gold in liquids with nanosecond laser pulses in aqueous solutions of inorganic electrolytes and macromolecular ligands for gold nanoparticle size quenching is probed inside the laser-induced cavitation bubble by in situ X-ray multicontrast imaging with a Hartmann mask (XHI). It is found that (i) the in situ size quenching power of sodium chloride (NaCl) in comparison to the ablation in pure water can be observed by the scattering contrast from XHI already inside the cavitation bubble, while (ii) for polyvinylpyrrolidone (PVP) as a macromolecular model ligand an in situ size quenching cannot be observed. Complementary ex situ characterization confirms the overall size quenching ability of both additive types NaCl and PVP. The macromolecular ligand as well as its monomer N-vinylpyrrolidone (NVP) are mainly effective for growth quenching of larger nanoparticles on later time scales, leading to the conclusion of an alternative interaction mechanism with ablated nanoparticles compared to the electrolyte NaCl, probably outside of the cavitation bubble, in the surrounding liquid phase. While monomer and polymer have similar effects on the particle properties, with the polymer being slightly more efficient, only the polymer is effective against hydrodynamic aggregation. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b01585
  • 2019 • 645 Toward a Paradigm Shift in Electrocatalysis Using Complex Solid Solution Nanoparticles
    Löffler, T. and Savan, A. and Garzón-Manjón, A. and Meischein, M. and Scheu, C. and Ludwig, Al. and Schuhmann, W.
    ACS Energy Letters 4 1206-1214 (2019)
    Complex solid solution (CSS) nanoparticles were recently discovered as efficient electrocatalysts for a variety of reactions. As one of many advantages, they exhibit the potential to replace noble-metal catalysts with multinary combinations of transition metals because they offer formation of new unique and tailorable active sites of multiple elements located next to each other. This Perspective reports on the current state and on challenges of the (combinatorial) synthesis of multinary nanoparticles and advanced electron microscopy characterization techniques for revealing structure-activity correlations on an atomic scale. We discuss what distinguishes this material class from common catalysts to highlight their potential to act as electrocatalysts and rationalize their nontypical electrochemical behavior. We provide an overview about challenges in synthesis, characterization, and electrochemical evaluation and propose guidelines for future design of CSS catalysts to achieve further progress in this research field, which is still in its infancy. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsenergylett.9b00531
  • 2019 • 644 Tuning the optical, structural and multiferroic properties of Bismuth Ferrite (BiFeO3) Nanoparticles by Doping with Ba
    Dubey, A. and Castillo, M.E. and Shvartsman, V.V. and Lupascu, D.C. and Salamon, S. and Wende, H.
    2019 IEEE International Symposium on Applications of Ferroelectrics, ISAF 2019 - Proceedings (2019)
    Bismuth Ferrite Nanoparticles (BiFeO3 NPs) are interesting single-phase multiferroic materials due to their notable magnetoelectric properties at room temperature. We enhance the magnetization of BFO NPs via doping 5 % Ba at the Bi site. These NPs were synthesized by a modified and reproducible sol-gel technique and further characterized by XRD (x-ray diffraction), VSM (Vibrating Sample Magnetometer), PFM (Piezoresponse Force Microscopy), DSC (Differential Scanning Calorimetry) and UV-Vis (Absorption spectroscopy) techniques. Rietveld refinement unveils a lattice distortion and shows that the average crystallite size is reduced from 43.7 to 38.4 nm after Ba incorporation. 5 % Ba enhances the ferromagnetism from 0.71 to 0.86 Am2/kg at 300 K. DSC curves confirm no significant variation in magnetic transition temperature (TN) after Ba doping. Moreover, PFM data show the ferroelectric behavior of 5 % Ba doped NPs with reduced piezoresponse. UV-Vis spectra show the presence of crystal field transition and a doubly degenerate d-d transition, whereas the band gap of 5 % Ba doped BFO NPs increases from 2.18 eV for BFO NPs to 2.23 eV. © 2019 IEEE.
    view abstractdoi: 10.1109/ISAF43169.2019.9034963
  • 2019 • 643 Vacancy doping and charge transport in B i2 S3 nanoparticle films for photovoltaic applications
    Mock, J. and Klingebiel, B. and Schillings, D. and Nuys, M. and Flohre, J. and Wang, S. and Kirchartz, T. and Carius, R.
    Physical Review Materials 3 (2019)
    Native point defect doping via thermal treatment is an easy and promising method to tune the electrical transport properties of semiconductors made for renewable-energy conversion. In this study, we investigate the vacancy doping of the lowly toxic semiconductor Bi2S3 using electrical conductivity as well as thermoelectric power measurements. We enhance the electrical conductivity of bismuth sulfide nanoparticle layers by more than four orders of magnitude by a stepwise thermal treatment in a moderate temperature range (300-480 K). Via thermoelectric power measurements we attribute this enhancement to an increase in charge-carrier mobility by two orders of magnitude and to an increase in charge-carrier density by more than two orders of magnitude. We find that the energetic position of the electron-doping sulfur vacancies of bismuth sulfide nanoparticles is significantly shallower than previously reported for bulk material. Subsequently, we implement Bi2S3 nanoparticles doped with sulfur vacancies by thermal annealing in photovoltaic devices using P3HT as an electron donor molecule. We find that annealing up to 383 K yields the best compromise between improving charge-carrier transport and increasing defect densities. ©2019 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.3.105406
  • 2018 • 642 A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering
    Hupfeld, T. and Laumer, T. and Stichel, T. and Schuffenhauer, T. and Heberle, J. and Schmidt, M. and Barcikowski, S. and Gökce, B.
    Procedia CIRP 74 244-248 (2018)
    The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
    view abstractdoi: 10.1016/j.procir.2018.08.103
  • 2018 • 641 Agglomeration-Free Preparation of Modified Silica Nanoparticles for Emulsion Polymerization - A Well Scalable Process
    Hübner, C. and Fettkenhauer, C. and Voges, K. and Lupascu, D.C.
    Langmuir 34 376-383 (2018)
    To prepare modified silica nanospheres for emulsion polymerization, a new agglomeration-free change of dispersion media has been developed. Nanosized silica spheres were synthesized by the Stöber method and directly modified with a silane coupling agent. To prepare these particles for subsequent polymerization, the dispersion medium was changed in a two-step process from ethanol to water without agglomeration of the particles. The emulsion polymerization leads to hemispherical single-core-structured silica-polystyrene composite particles. The thickness of the polymer shell can be altered by varying the amount of styrene. The developed change of dispersion media provides nonagglomerated modified silica particles for the encapsulation with polystyrene and enables the synthesis of narrowly distributed single-core composite particles. The developed process is a promising approach for the preparation of nanoparticles for subsequent polymerization and can be scaled-up for industrial applications. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03753
  • 2018 • 640 Bifunctional Oxygen Reduction/Oxygen Evolution Activity of Mixed Fe/Co Oxide Nanoparticles with Variable Fe/Co Ratios Supported on Multiwalled Carbon Nanotubes
    Elumeeva, K. and Kazakova, M.A. and Morales, D.M. and Medina, D. and Selyutin, A. and Golubtsov, G. and Ivanov, Y. and Kuznetzov, V. and Chuvilin, A. and Antoni, H. and Muhler, M. and Schuhmann, W. and Masa, J.
    ChemSusChem 11 1204-1214 (2018)
    A facile strategy is reported for the synthesis of Fe/Co mixed metal oxide nanoparticles supported on, and embedded inside, high purity oxidized multiwalled carbon nanotubes (MWCNTs) of narrow diameter distribution as effective bifunctional catalysts able to reversibly drive the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline solutions. Variation of the Fe/Co ratio resulted in a pronounced trend in the bifunctional ORR/OER activity. Controlled synthesis and in-depth characterization enabled the identification of an optimal Fe/Co composition, which afforded a low OER/OER reversible overvoltage of only 0.831 V, taking the OER at 10 mA cm−2 and the ORR at −1 mA cm−2. Importantly, the optimal catalyst with a Fe/Co ratio of 2:3 exhibited very promising long-term stability with no evident change in the potential for both the ORR and the OER after 400 charge/discharge (OER/ORR) cycles at 15 mA cm−2 in 6 m KOH. Moreover, detailed investigation of the structure, size, and phase composition of the mixed Fe/Co oxide nanoparticles, as well as their localization (inside of or on the surface of the MWCNTs) revealed insight of the possible contribution of the individual catalyst components and their synergistic interaction in the catalysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cssc.201702381
  • 2018 • 639 Cluster Assemblies Produced by Aggregation of Preformed Ag Clusters in Ionic Liquids
    Roese, S. and Kononov, A. and Timoshenko, J. and Frenkel, A.I. and Hövel, H.
    Langmuir 34 4811-4819 (2018)
    Room-temperature ionic liquids (RTILs) can be used as electrosterical stabilizers for nanoparticles without adding stabilizing agents. However, the nanoparticle stability and its mechanisms are still in discussion. We deposited preformed 2 nm ±0.6 nm silver clusters into the ionic liquid C4MIM PF6 using in situ UV/vis absorption to monitor the deposition process. The time- and temperature-dependent cluster aggregation process was studied with ex situ UV/vis absorption spectroscopy analyzed with electrodynamic calculations using generalized Mie theory. On an atomistic level, the sample structure was investigated using EXAFS and a neural network based analysis of XANES. The combination of all methods shows that an aggregation of the original 2 nm clusters without coalescence takes place, which can be controlled or stopped by choosing an appropriate sample temperature. This approach allows the controlled production of chainlike cluster aggregates in RTIL, promising for a number of applications. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03984
  • 2018 • 638 Comparative biological effects of spherical noble metal nanoparticles (Rh, Pd, Ag, Pt, Au) with 4-8 nm diameter
    Rostek, A. and Breisch, M. and Pappert, K. and Loza, K. and Heggen, M. and Köller, M. and Sengstock, C. and Epple, M.
    Beilstein Journal of Nanotechnology 9 2763-2774 (2018)
    For a comparative cytotoxicity study, nanoparticles of the noble metals Rh, Pd, Ag, Pt, and Au (spherical, average diameter 4 to 8 nm) were prepared by reduction in water and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Thus, their shape, size, and surface functionalization were all the same. Size and morphology of the nanoparticles were determined by dynamic light scattering (DLS), analytical disc centrifugation (differential centrifugal sedimentation, DCS), and high-resolution transmission electron microscopy (HRTEM). Cell-biological experiments were performed to determine the effect of particle exposure on the viability of human mesenchymal stem cells (hMSCs). Except for silver, no adverse effect of any of the metal nanoparticles was observed for concentrations up to 50 ppm (50 mg L-1) incubated for 24 h, indicating that noble metal nanoparticles (rhodium, palladium, platinum, gold) that do not release ions are not cytotoxic under these conditions. © 2018 Rostek et al.
    view abstractdoi: 10.3762/bjnano.9.258
  • 2018 • 637 Covalent Surface Functionalization of Calcium Phosphate Nanoparticles with Fluorescent Dyes by Copper-Catalysed and by Strain-Promoted Azide-Alkyne Click Chemistry
    Rojas-Sánchez, L. and Sokolova, V. and Riebe, S. and Voskuhl, J. and Epple, M.
    ChemNanoMat (2018)
    Spherical calcium phosphate nanoparticles with a solid core diameter around 90 nm (from scanning electron microscopy, SEM) were coated with a silica shell and then covalently functionalized by azide groups. To these azide groups, all kinds of alkyne-carrying molecules can be covalently attached by copper-catalysed azide-alkyne cycloaddition (CuAAC) and by strain-promoted azide-alkyne cycloaddition (SPAAC) at a very high density. This was demonstrated for a number of dyes (FAM, TAMRA, Cy5, Alexa Fluor™ 488, and an aromatic thioether with aggregation-induced emission (AIE) properties). It was also possible to attach more than one molecule to the surface of one particle by two-step click reaction, permitting the synthesis of multimodal nanoparticles that are stable under biological conditions. The nanoparticles have a hydrodynamic diameter of around 200 nm (from dynamic light scattering, DLS), which makes them suitable for uptake by cells. The strongly fluorescing nanoparticles were easily taken up by cells as demonstrated by fluorescence microscopy, confocal laser scanning microscopy (CLSM), and structured illuminated microscopy (SIM). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cnma.201800509
  • 2018 • 636 Crystallographic characterization of laser-generated, polymer-stabilized 4 nm silver-gold alloyed nanoparticles
    Prymak, O. and Jakobi, J. and Rehbock, C. and Epple, M. and Barcikowski, S.
    Materials Chemistry and Physics 207 442-450 (2018)
    Monometallic silver and gold nanoparticles and bimetallic silver-gold (AgAu) nanoparticles were prepared by laser ablation in liquids in the atomic composition range of Ag:Au from 0:100 to 100:0 with steps of 10 at% and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). As metallic bulk targets for laser ablation, pure silver, pure gold, and alloyed AgAu foils with the desired composition were used. Size separation by centrifugation and freeze-drying gave monodisperse spherical nanoparticles with a diameter of 4 nm as determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). A crystallographic characterization of the nanoparticles was carried out by X-ray powder diffraction (XRD) and Rietveld refinement, leading to highly precise cubic lattice parameters (fcc crystal system) and crystallite sizes. For comparison, the same analysis including the determination of the microstrain was carried out for the bulk target materials (AgAu alloys in the full concentration range). Both nanoparticles and bulk target materials obeyed Vegard's rule, with only slight deviations. The fact that the crystallite size as determined by XRD was identical to the hydrodynamic diameter by DCS and the Feret diameter by TEM indicates that the particles consist of only one domain, i.e. they are single crystals. The combination of UV-vis spectroscopy with energy-dispersive X-ray spectroscopy (EDX) as line scan along the nanoparticle showed a homogenous distribution of the gold and silver inside the nanoparticles, indicating solid solution alloys, in contrast to what was observed earlier for chemically prepared AgAu nanoparticles by reduction of metal ions in water. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2017.12.080
  • 2018 • 635 Cytotoxicity of doxorubicin-conjugated poly[N-(2-hydroxypropyl)methacrylamide]-modified ?-Fe2O3 nanoparticles towards human tumor cells
    Plichta, Z. and Kozak, Y. and Panchuk, R. and Sokolova, V. and Epple, M. and Kobylinska, L. and Jendelová, P. and Horák, D.
    Beilstein Journal of Nanotechnology 9 2533-2545 (2018)
    Doxorubicin-conjugated magnetic nanoparticles containing hydrolyzable hydrazone bonds were developed using a non-toxic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) coating, which ensured good colloidal stability in aqueous media and limited internalization by the cells, however, enabled adhesion to the cell surface. While the neat PHPMA-coated particles proved to be non-toxic, doxorubicin-conjugated particles exhibited enhanced cytotoxicity in both drug-sensitive and drug-resistant tumor cells compared to free doxorubicin. The newly developed doxorubicin-conjugated PHPMA-coated magnetic particles seem to be a promising magnetically targeted vehicle for anticancer drug delivery. © 2018 Plichta et al.
    view abstractdoi: 10.3762/bjnano.9.236
  • 2018 • 634 Determination of Hansen parameters for particles: A standardized routine based on analytical centrifugation
    Süß, S. and Sobisch, T. and Peukert, W. and Lerche, D. and Segets, D.
    Advanced Powder Technology 29 1550-1561 (2018)
    The Hansen Solubility Parameters (HSP) are powerful descriptors to evaluate interactions of (polymer) molecules and their solubility in different liquids. Although approaches do exist to transfer the HSP-concept to the question of dispersibility of particles, HSP determination of slowly sedimenting (nano)particles (NPs) is time consuming and depends on the subjective evaluation of the experimenter. Herein, we introduce a new method for HSP determination for colloidal systems using analytical centrifugation (AC) which was applied to standardize and accelerate the experimental procedure. However, as not dissolution but dispersion is in focus, we propose to use the term Hansen Dispersibility Parameters (HDP) instead of HSP whenever dispersibility and stability of particles against agglomeration/flocculation are to be discussed. First, we implemented a standard dispersion routine for the well-known, industrially highly relevant pigment carbon black (CB). Then, a standardized method for the evaluation of measured AC profiles and appropriate ranking of NPs dispersibility in different media was developed. We demonstrate outstanding reproducibility of our results by comparing HDP derived for the same CB material from independent experiments performed at two different affiliations. Finally, we show the predictive power of HDP and the accuracy of our approach by evaluating the dispersibility of CB in additional liquids and mixtures of so-called “good” and “poor” liquid media crossing the border from stable to unstable medium conditions. Our study evidences the enormous potential of AC to determine the HDP of colloidal systems using a standardized and non-subjective method to access particle interactions and colloidal stability. © 2018 The Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2018.03.018
  • 2018 • 633 Determination of pore size gradients of virus filtration membranes using gold nanoparticles and their relation to fouling with protein containing feed streams
    Kosiol, P. and Müller, M.T. and Schneider, B. and Hansmann, B. and Thom, V. and Ulbricht, M.
    Journal of Membrane Science 548 598-608 (2018)
    Virus filtration membranes contribute to the virus safety of biopharmaceutical drugs due to their capability to retain virus particles mainly based on size-exclusion mechanisms. Typical product molecules like monoclonal antibodies with 9–12 nm in hydrodynamic diameter have to be transmitted by >95% while small viruses, e.g. parvoviridae (B19, MVM, PPV) with a diameter of 18–26 nm, have to be retained by at least 99.99%. Therefore, membrane fouling caused by product aggregates, which are similar in size compared to the viruses that have to be retained, is a common observation. Minimal membrane fouling is a requirement for economical processes and is influenced by both the membrane surface chemistry and the membrane structure, particularly with regard to the pore size gradient (PSG). In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine PSGs for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. GNP adsorption to the membrane material was suppressed by the use of an anionic surfactant, allowing to gain insights into size-exclusion properties of the membranes. Membrane performance with regard to fouling was further investigated by determination of protein mass throughputs up-to a defined membrane flux decay using solutions containing intravenous immunoglobulin (IVIG) as model protein. Additionally, the fouling mechanism of IVIG was investigated and confirmed to be caused by trace amounts of species larger than IVIG monomers and dimers, which were already present in the feed. The fouling results are discussed in relationship to the determined PSGs, since the porous support structure of virus filtration membranes can act as a depth pre-filter protecting the separation-active layer from particulate foulants. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.11.048
  • 2018 • 632 Development of a low-cost FPGA-based measurement system for real-time processing of acoustic emission data: Proof of concept using control of pulsed laser ablation in liquids
    Wirtz, S.F. and Cunha, A.P.A. and Labusch, M. and Marzun, G. and Barcikowski, S. and Söffker, D.
    Sensors (Switzerland) 18 (2018)
    Today, the demand for continuous monitoring of valuable or safety critical equipment is increasing in many industrial applications due to safety and economical requirements. Therefore, reliable in-situ measurement techniques are required for instance in Structural Health Monitoring (SHM) as well as process monitoring and control. Here, current challenges are related to the processing of sensor data with a high data rate and low latency. In particular, measurement and analyses of Acoustic Emission (AE) are widely used for passive, in-situ inspection. Advantages of AE are related to its sensitivity to different micro-mechanical mechanisms on the material level. However, online processing of AE waveforms is computationally demanding. The related equipment is typically bulky, expensive, and not well suited for permanent installation. The contribution of this paper is the development of a Field Programmable Gate Array (FPGA)-based measurement system using ZedBoard devlopment kit with Zynq-7000 system on chip for embedded implementation of suitable online processing algorithms. This platform comprises a dual-core Advanced Reduced Instruction Set Computer Machine (ARM) architecture running a Linux operating system and FPGA fabric. A FPGA-based hardware implementation of the discrete wavelet transform is realized to accelerate processing the AE measurements. Key features of the system are low cost, small form factor, and low energy consumption, which makes it suitable to serve as field-deployed measurement and control device. For verification of the functionality, a novel automatically realized adjustment of the working distance during pulsed laser ablation in liquids is established as an example. A sample rate of 5 MHz is achieved at 16 bit resolution. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s18061775
  • 2018 • 631 Effect of Antigen Retrieval Methods on Nonspecific Binding of Antibody-Metal Nanoparticle Conjugates on Formalin-Fixed Paraffin-Embedded Tissue
    Zhang, Y. and Wang, X.-P. and Perner, S. and Bankfalvi, A. and Schlücker, S.
    Analytical Chemistry 90 760-768 (2018)
    Immunohistochemical analysis of formalin-fixed paraffin-embedded (FFPE) tissues provides important diagnostic and prognostic information in pathology. Metal nanoparticles (NPs) and, in particular, surface-enhanced Raman scattering (SERS) nanotags as a new class of labeling reagents are promising to be used for multiplexed protein profiling on tissue sections. However, nonspecific binding of NPs onto the tissue specimens greatly hampers their clinical applications. In this study, we found that the antigen retrieval method strongly influences the extent of nonspecific binding of the antibody-SERS NP conjugates to the tissue. Our SERS labels comprised ca. 70 nm Au nanostars coated with ethylene glycol-modified Raman reporter molecules for hydrophilic stabilization and subsequent covalent bioconjugation to antibodies. We systematically investigated the influence of heat- and protease-induced epitope retrieval (HIER and PIER, respectively) on the immunostaining quality of prostate-specific antigen (PSA) on human prostate tissue sections. The best staining results were obtained with PIER. Pretreatment of the tissue sections by HIER led to selective but nonspecific adsorption of the antibody-Au nanostar conjugates onto epithelial cells, while enzymatic treatment within PIER did not. In addition to gold nanostars, also other types of metal NPs with different shapes and sizes (including ca. 20 nm quasi-spherical Au NPs and ca. 60 nm quasi-spherical Au/Ag nanoshells) as well as tissue sections from different organs (including prostate and breast) were tested; in each case the same tendency was observed, i.e., PIER yielded better results than HIER. Therefore, we recommend PIER for future NP-based tissue immunostaining such as immuno-SERS microscopy. Alternatively, for antigens that can only be unmasked by heating, PEGylation of the NPs is recommended to avoid nonspecific binding. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.7b03144
  • 2018 • 630 Ejector-based sampling from low-pressure aerosol reactors
    Rosenberger, T. and Münzer, A. and Kiesler, D. and Wiggers, H. and Kruis, F.E.
    Journal of Aerosol Science 123 105-115 (2018)
    Online measurements of nanoparticles are necessary when rapid information about the particle size and mass distribution is needed. Currently, the application of online measurement techniques with commonly used instruments such as SMPS, CPMA and ELPI+ is not possible at low-pressure conditions. In this work, a commercial vacuum ejector is used as a simple tool to transfer nanoparticles from a low-pressure region to atmospheric pressure. The vacuum ejector is investigated for different process pressures between 120 and 170 mbar to measure size-selected aerosols in the range from 10 to 100 nm. It was found that the sampling with the vacuum ejector does not change the particle size. The gas and particle dilution factors as well as the particle losses are determined, so that quantitative measurements of the aerosol size distribution can be obtained. Additionally, the applicability of the vacuum ejector is tested during particle synthesis in a low-pressure microwave plasma reactor with a combination of online instrumentation. The direct transfer of the aerosol to atmospheric pressure allows real-time measurements. The primary particle size, mass mobility exponent and effective density are calculated exemplary based on parallel online ELPI+, SMPS and CPMA measurements and are compared to offline TEM analysis. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.jaerosci.2018.06.003
  • 2018 • 629 Fluoride doped γ-Fe2O3 nanoparticles with increased MRI relaxivity
    Jones, N.E. and Burnett, C.A. and Salamon, S. and Landers, J. and Wende, H. and Lazzarini, L. and Gibbs, P. and Pickles, M. and Johnson, B.R.G. and Evans, D.J. and Archibald, S.J. and Francesconi, M.G.
    Journal of Materials Chemistry B 6 3665-3673 (2018)
    Iron oxide nanoparticles (IONs) are being actively researched and experimented with as contrast agents for Magnetic Resonance Imaging (MRI), as well as image-directed delivery of therapeutics. The efficiency of an MRI contrast agent can be described by its longitudinal and transverse relaxivities, r1 and r2. γ-Fe2O3 nanoparticles-doped with fluoride in a controlled manner and functionalised with citric acid-showed a 3-fold increase in r1 and a 17-fold increase in r2 in a magnetic field of 3 T and almost 6-fold increase in r1 and a 14-fold increase in r2 at 11 T. Following fluorination, PXRD shows that the crystal structure of γ-Fe2O3 is maintained, Mössbauer spectroscopy shows that the oxidation state of the Fe cation is unchanged and HREM shows that the particle size does not vary. However, magnetisation curves show a large increase in the coercive field, pointing towards a large increase in the magnetic anisotropy for the fluorinated nanoparticles compared to the un-doped γ-Fe2O3 nanoparticles. Therefore, a chemically induced increase in magnetic anisotropy appears to be the most relevant parameter responsible for the large increase in relaxivity for γ-Fe2O3 nanoparticles. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8tb00360b
  • 2018 • 628 Formation of nickel nanoparticles and magnetic matrix in nickel phthalocyanine by doping with potassium
    Manukyan, A.S. and Avakyan, L.A. and Elsukova, A.E. and Zubavichus, Y.V. and Sulyanov, S.N. and Mirzakhanyan, A.A. and Kolpacheva, N.A. and Spasova, M. and Kocharian, A.N. and Farle, M. and Bugaev, L.A. and Sharoyan, E.G.
    Materials Chemistry and Physics 214 564-571 (2018)
    A method for synthesis of nickel nanoparticles in a magnetic nickel phthalocyanine anions matrix has been developed. The method is based on intercalation of potassium atoms to the nickel phthalocyanine (NiPc) polycrystalline powder at 300 °C. The structure of (K2NiPc) was investigated by using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopes. Magnetic properties were studied by SQUID magnetometry and magnetic resonances methods. It is revealed that the resultant compound contains of 1 wt% Ni nanoparticles with the average size of 15 nm. The measured values of the magnetization and absorption of the ferromagnetic resonance considerably exceed the magnetism which can be attributed to metallic Ni nanoparticles. The obtained results indicate the presence of room temperature molecular ferromagnetism caused by anionic molecules of NiPc. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2018.04.068
  • 2018 • 627 Formation of Polymeric Particles by Direct Polymerization on the Surface of a Supramolecular Template
    Li, M. and Zellermann, E. and Schmuck, C.
    Chemistry - A European Journal 24 9061-9065 (2018)
    Formation of polymeric materials on the surface of supramolecular assemblies is rather challenging because of the often weak noncovalent interactions between the self-assembled template and the monomers before polymerization. We herein show that the introduction of a supramolecular anion recognition motif, the guanidiniocarbonyl pyrrole cation (GCP), into a short Fmoc-dipeptide 1 leads to self-assembled spherical nanoparticles in aqueous solution. Negatively charged diacetylene monomers can be attached onto the surface of these nanoparticles, which, after UV polymerization, leads to the formation of a polymer shell around the self-assembled template. The hybrid supramolecular and polymeric nanoparticles demonstrate intriguing thermal hysteresis phenomena. The template nanoparticles could be disassembled upon treatment with organic base, which cleaved the Fmoc moiety on 1. This strategy thus showed that a supramolecular anion recognition motif allows the post-assembly formation of polymeric nanomaterials from anionic monomers around a cationic self-assembled template. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201705209
  • 2018 • 626 Glycerol Oxidation Using MgO- and Al2O3-supported Gold and Gold–Palladium Nanoparticles Prepared in the Absence of Polymer Stabilizers
    Dodekatos, G. and Abis, L. and Freakley, S.J. and Tüysüz, H. and Hutchings, G.J.
    ChemCatChem 10 1351-1359 (2018)
    Au and AuPd nanoparticles supported on MgO and Al2O3 were employed for the selective aqueous phase oxidation of glycerol under basic conditions. Catalysts were prepared by sol-immobilization without the addition of a stabilizing agent such as polyvinyl alcohol (PVA), which is generally added to stabilize the noble metal sol prior to immobilization. The obtained materials prepared with and without stabilizing agent were active for glycerol oxidation and showed similar catalytic performances—implying that the stabilizing polymer is not required to obtain active materials. Depending on the support used, it was possible to tailor the selectivity towards the desired oxidation products by using catalysts prepared with or without stabilizing agent. PVA-free Au/γ-Al2O3 exhibited a remarkably high selectivity towards tartronic acid (40 % at 97 % conversion), which was not observed for Au/γ-Al2O3 prepared with PVA (27 % at isoconversion). Selective glycerol oxidation performed under base-free conditions over AuPd/MgO catalysts also corroborated the previous results that the presence of a stabilizing polymer is not required to prepare active catalysts by sol-immobilization. Thus, a facile way to circumvent the inherent drawbacks encountered by the use of polymer stabilizers during catalyst preparation is presented herein. Experimental results suggest that the presence of the polymer stabilizers can affect the reaction pathways and control selectivity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201800074
  • 2018 • 625 Ideal Dimers of Gold Nanospheres for Precision Plasmonics: Synthesis and Characterization at the Single-Particle Level for Identification of Higher Order Modes
    Yoon, J.H. and Selbach, F. and Langolf, L. and Schlücker, S.
    Small 14 (2018)
    Ideal dimers comprising gold nanoparticles with a smooth surface and high sphericity are synthesized by a substrate-based assembly strategy with efficient cetyltrimethylammonium bromide removal. An unprecedented structural and plasmonic uniformity at the single-particle level is observed since inhomogeneities resulting from variations in gap morphology are eliminated. Single ideal dimers are analyzed by polarization-resolved dark-field scattering spectroscopy. Contributions from transverse as well as quadrupolar and octupolar longitudinal plasmon coupling modes can be discriminated because of their orthogonal polarization behavior. The assignment of these higher order coupling modes is supported by computer simulations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201702754
  • 2018 • 624 Improved Models for Metallic Nanoparticle Cores from Atomic Pair Distribution Function (PDF) Analysis
    Banerjee, S. and Liu, C.-H. and Lee, J.D. and Kovyakh, A. and Grasmik, V. and Prymak, O. and Koenigsmann, C. and Liu, H. and Wang, L. and Abeykoon, A.M.M. and Wong, S.S. and Epple, M. and Murray, C.B. and Billinge, S.J.L.
    Journal of Physical Chemistry C 122 29498-29506 (2018)
    X-ray atomic pair distribution functions (PDFs) were collected from a range of canonical metallic nanomaterials, both elemental and alloyed, prepared using different synthesis methods and exhibiting drastically different morphological properties. Widely applied shape-tuned attenuated crystal (AC) fcc models proved inadequate, yielding structured, coherent, and correlated fit residuals. However, equally simple discrete cluster models could account for the largest amplitude features in these difference signals. A hypothesis testing based approach to nanoparticle structure modeling systematically ruled out effects from crystallite size, composition, shape, and surface faceting as primary factors contributing to the AC misfit. On the other hand, decahedrally twinned cluster cores were found to be the origin of the AC structure misfits for a majority of the nanomaterials reported here. It is further motivated that the PDF can readily differentiate between the arrangement of domains in these multiply twinned motifs. Most of the nanomaterials surveyed also fall within the sub-5 nm size regime where traditional electron microscopy cannot easily detect and quantify domain structures, with sampling representative of the average nanocrystal synthesized. The results demonstrate that PDF analysis is a powerful method for understanding internal atomic interfaces in small noble metallic nanomaterials. Such core cluster models, easily built algorithmically, should serve as starting structures for more advanced models able to capture atomic positional disorder, ligand induced or otherwise, near nanocrystal surfaces. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b05897
  • 2018 • 623 Local Structure of Nanocrystalline Aluminum Nitride
    Ognjanović, S.M. and Zähres, M. and Mayer, C. and Winterer, M.
    Journal of Physical Chemistry C 122 23749-23757 (2018)
    The local structure of chemical-vapor-synthesized (CVS) crystalline AlN nanoparticles is investigated by combining magic angle spinning nuclear magnetic resonance and X-ray absorption spectroscopies. Extended X-ray absorption fine structure data are analyzed by reverse Monte Carlo method, and X-ray absorption near edge structure is interpreted by first principles FEFF calculations. The measurements show behavior characteristic of partially disordered systems. Nevertheless, combined analysis of the data, supported by Rietveld refinement of X-ray diffraction patterns, leads to the conclusion that the observed behavior is due to the small size (large surface to volume ratios) of the nanoparticles (dXRD &lt; 6 nm) and that highly crystalline wurtzite AlN is formed during the CVS process. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b06610
  • 2018 • 622 Nano Impact Electrochemistry: Effects of Electronic Filtering on Peak Height, Duration and Area
    Kanokkanchana, K. and Saw, E.N. and Tschulik, K.
    ChemElectroChem 5 3000-3005 (2018)
    Nano impact electrochemistry is used to measure a transient signal while a nanoparticle (NP) hits an electrode due to its motion in a solution. A variety of information can be obtained from this current pulse, yet its accurate measurement is challenging due to its short duration (μs to s) and small amplitude (≤10 nA). A typically used low bandwidth low-pass filter can improve the signal-to-noise ratio, but it may cost severely in the accuracy of the data. Here, we demonstrate the effects of electronic filters by using generated current impulses with duration from 125 μs to 8 ms. Initially, a system dedicated to measure short and low current impulses was employed. There, an 8th order Bessel filter was used and the effect of varying the cut-off frequency between 50 Hz and 20 kHz on the impulse response is studied. Even though the charge is generally conserved by the filter, amplitude and duration of the pulse vary greatly in dependence of the cut-off frequency. In comparison, the response of widely used potentiostats was tested and significant deviations of the measured signal from the input were detected. Supported by destructive nano impact experiments with Ag NPs in KCl(aq), we show how the filtering affects the experimentally determined size of Ag NPs and Cl− diffusion coefficient, using impact charges and duration, respectively. As a result, we suggest a general guideline to researchers for accurate electrochemical nano impact measurements, in particular with respect to current peak duration analysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800738
  • 2018 • 621 Oxygen Reduction Activity and Reversible Deactivation of Single Silver Nanoparticles during Particle Adsorption Events
    Öhl, D. and Clausmeyer, J. and Barwe, S. and Botz, A. and Schuhmann, W.
    ChemElectroChem 5 1886-1890 (2018)
    The activity towards the oxygen reduction reaction (ORR) of single silver nanoparticles (AgNP) was quantified by using AgNP impacts on dual-bore carbon nanoelectrodes in highly alkaline media. We found suitable conditions for the particles to adhere sufficiently stably for detailed electrochemical characterization of a single particle. The special electrode design opens the possibility to dose gaseous oxygen to the nanoparticle under study. Deactivation of the catalytic activity of the AgNP upon excessive exposure to oxygen as well as the recovery of catalytic activity under reducing conditions is presumably attributed to hydrogen evolution at the applied low potentials. The proposed approach allows mechanistic parameters for the ORR to be extracted at a single AgNP in highly alkaline media in the absence of any binder materials and under exclusion of averaging ensemble effects. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800094
  • 2018 • 620 Primary particle diameter differentiation and bimodality identification by five analytical methods using gold nanoparticle size distributions synthesized by pulsed laser ablation in liquids
    Letzel, A. and Gökce, B. and Menzel, A. and Plech, A. and Barcikowski, S.
    Applied Surface Science 435 743-751 (2018)
    For a known material, the size distribution of a nanoparticle colloid is a crucial parameter that defines its properties. However, measured size distributions are not easy to interpret as one has to consider weighting (e.g. by light absorption, scattering intensity, volume, surface, number) and the way size information was gained. The radius of a suspended nanoparticle can be given as e.g. sphere equivalent, hydrodynamic, Feret or radius of gyration. In this study, gold nanoparticles in water are synthesized by pulsed-laser ablation (LAL) and fragmentation (LFL) in liquids and characterized by various techniques (scanning transmission electron microscopy (STEM), small-angle X-ray scattering (SAXS), analytical disc centrifugation (ADC), dynamic light scattering (DLS) and UV–vis spectroscopy with Mie-Gans Theory) to study the comparability of different analytical techniques and determine the method that is preferable for a given task related to laser-generated nanoparticles. In particular, laser-generated colloids are known to be bimodal and/or polydisperse, but bimodality is sometimes not analytically resolved in literature. In addition, frequently reported small size shifts of the primary particle mode around 10 nm needs evaluation of its statistical significance related to the analytical method. Closely related to earlier studies on SAXS, different colloids in defined proportions are mixed and their size as a function of the nominal mixing ratio is analyzed. It is found that the derived particle size is independent of the nominal mixing ratio if the colloid size fractions do not overlap considerably. Conversely, the obtained size for colloids with overlapping size fractions strongly depends on the nominal mixing ratio since most methods cannot distinguish between such fractions. Overall, SAXS and ADC are very accurate methods for particle size analysis. Further, the ability of different methods to determine the nominal mixing ratio of sizes fractions is studied experimentally. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.11.130
  • 2018 • 619 Production, deformation and mechanical investigation of magnetic alginate capsules
    Zwar, E. and Kemna, A. and Richter, L. and Degen, P. and Rehage, H.
    Journal of Physics Condensed Matter 30 (2018)
    In this article we investigated the deformation of alginate capsules in magnetic fields. The sensitivity to magnetic forces was realised by encapsulating an oil in water emulsion, where the oil droplets contained dispersed magnetic nanoparticles. We solved calcium ions in the aqueous emulsion phase, which act as crosslinking compounds for forming thin layers of alginate membranes. This encapsulating technique allows the production of flexible capsules with an emulsion as the capsule core. It is important to mention that the magnetic nanoparticles were stable and dispersed throughout the complete process, which is an important difference to most magnetic alginate-based materials. In a series of experiments, we used spinning drop techniques, capsule squeezing experiments and interfacial shear rheology in order to determine the surface Young moduli, the surface Poisson ratios and the surface shear moduli of the magnetically sensitive alginate capsules. In additional experiments, we analysed the capsule deformation in magnetic fields. In spinning drop and capsule squeezing experiments, water droplets were pressed out of the capsules at elevated values of the mechanical load. This phenomenon might be used for the mechanically triggered release of water-soluble ingredients. After drying the emulsion-filled capsules, we produced capsules, which only contained a homogeneous oil phase with stable suspended magnetic nanoparticles (organic ferrofluid). In the dried state, the thin alginate membranes of these particles were rather rigid. These dehydrated capsules could be stored at ambient conditions for several months without changing their properties. After exposure to water, the alginate membranes rehydrated and became flexible and deformable again. During this swelling process, water diffused back in the capsule. This long-term stability and rehydration offers a great spectrum of different applications as sensors, soft actuators, artificial muscles or drug delivery systems. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/aaa6f5
  • 2018 • 618 Prolonged release of bone morphogenetic protein-2 in vivo by gene transfection with DNA-functionalized calcium phosphate nanoparticle-loaded collagen scaffolds
    Tenkumo, T. and Vanegas Sáenz, J.R. and Nakamura, K. and Shimizu, Y. and Sokolova, V. and Epple, M. and Kamano, Y. and Egusa, H. and Sugaya, T. and Sasaki, K.
    Materials Science and Engineering C 92 172-183 (2018)
    In the combination of scaffolds immersed in growth factor solutions, the release of growth factors mainly depends on scaffold degradation. However, the release of bone morphogenetic protein (BMP)-2 at an appropriate concentration during the stage of tissue regeneration would enhance bone regeneration. To achieve this condition, the present study was performed to investigate the effects of scaffolds combined with gene transfection using non-viral vectors. Nanohydroxyapatite-collagen (nHAC) scaffolds cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) or ascorbic acid/copper chloride, and a collagen scaffold (Terdermis®) were prepared, loaded with BMP-2-encoding plasmid DNA-functionalized calcium phosphate nanoparticles (CaP), naked plasmid DNA, or BMP-2 solution, and implanted in rats. The yield of released BMP-2 and its releasing period, respectively, were larger and longer from the scaffolds loaded with CaP than from those incubated with BMP-2 solution. In addition, the alkaline phosphatase activity induced by the CaP-loaded scaffolds was higher. Histological analysis showed that released BMP-2 could be observed on the macrophages or multinuclear giant cells surrounding the nHAC fragments or collagen fibres. TRAP-positive or OCN-positive sites were observed in all groups and a mineralization area was observed in the Terdermis®/CaP sample. The present study demonstrates that gene transfection by scaffold loaded with CaP gene transfer vectors induces a larger yield of BMP-2 for a longer period than by scaffolds loaded with BMP-2 solution or naked plasmid. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2018.06.047
  • 2018 • 617 Quantitative evaluation of nanoparticle classification by size-exclusion chromatography
    Süß, S. and Metzger, C. and Damm, C. and Segets, D. and Peukert, W.
    Powder Technology 339 264-272 (2018)
    Although few attempts for classification of nanoparticles (NPs) in labscale do exist, the transfer to industrial applications is still challenging. One promising separation method, which is already established for biological molecules, is chromatography. Herein, we study the classification of differently sized gold NPs (AuNPs) by size-exclusion chromatography (SEC). First, we investigated the interactions of AuNPs with potential stationary phases in order to identify a suitable material for the chromatographic process where irreversible NP adhesion is excluded. Then, we demonstrate the high reproducibility of our SEC experiments by multiple sample injections that lead to constant peak areas. In particular, we show the size-dependent elution behavior of AuNP mixtures resulting in bimodal elution peaks, where size separation was confirmed by inline measured UV/Vis spectra. Finally, NP classification results by using a fraction collector are characterized by retention time, mass balances and size-dependent separation efficiencies. The adjustment of the particle size distributions (PSDs) is demonstrated by changing the switching time of the fraction collector. Our study evidences the high potential of SEC for preparative and continuous separation of NPs. © 2018 The Authors
    view abstractdoi: 10.1016/j.powtec.2018.08.008
  • 2018 • 616 Rechargeable, flexible and mediator-free biosupercapacitor based on transparent ITO nanoparticle modified electrodes acting in µM glucose containing buffers
    Bobrowski, T. and González Arribas, E. and Ludwig, R. and Toscano, M.D. and Shleev, S. and Schuhmann, W.
    Biosensors and Bioelectronics 101 84-89 (2018)
    We present a transparent and flexible self-charging biosupercapacitor based on an optimised mediator- and membrane-free enzymatic glucose/oxygen biofuel cell. Indium tin oxide (ITO) nanoparticles were spray-coated on transparent conducting ITO supports resulting in a flocculent, porous and nanostructured electrode surface. By this, high capacitive currents caused by an increased electrochemical double layer as well as enhanced catalytic currents due to a higher number of immobilised enzyme molecules were obtained. After a chemical pre-treatment with a silane derivative, bilirubin oxidase from Myrothecium verrucaria was immobilized onto the ITO nanostructured electrode surface under formation of a biocathode, while bioanodes were obtained by either immobilisation of cellobiose dehydrogenase from Corynascus thermophilus or soluble PQQ-dependent glucose dehydrogenase from Acinetobacter calcoaceticus. The latter showed a lower apparent KM value for glucose conversion and higher catalytic currents at µM glucose concentrations. Applying the optimised device as a biosupercapacitor in a discontinuous charge/discharge mode led to a generated power output of 0.030 mW/cm2 at 50 µM glucose, simulating the glucose concentration in human tears. This represents an enhancement by a factor of 350 compared to the power density obtained from the continuously operating biofuel cell with a maximum power output of 0.086 µW/cm2 under the same conditions. After 17 h of charging/discharging cycles a remarkable current enhancement was still measured. The entire device was transferred to flexible materials and applied for powering a flexible display showing its potential applicability as an intermittent power source in smart contact lenses. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2017.10.016
  • 2018 • 615 Retention mechanisms of 1.7 nm ZnS quantum dots and sub-20 nm Au nanoparticles in ultrafiltration membranes
    Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
    Journal of Membrane Science 567 58-67 (2018)
    Membrane processes are considered to be a very effective and promising method for drinking water and wastewater treatments. However, particle removal mechanisms have not been fully elucidated due to complex surface interactions between colloids and membranes, especially for very small colloidal particles. In this study, a series of systematic filtration tests for eight different types of membrane filters, having nominal pore sizes from 0.005 to 0.1 µm, against 1.7 nm ZnS quantum dots (QDs) and 5, 10 and 20 nm Au nanoparticles (NPs) was performed to understand their retention mechanisms, including rejection in front of the filter surface and adsorption inside the filter. By comparing rejection, adsorption and recovery, it was found that the predominant retention mechanisms for retaining small NPs varied from filter to filter. For instance, electrostatic repulsion played a significant role for the rejection of NPs, i.e. impeding them entering the membrane pores in most membranes. In comparison, the Nylon membrane had a significant adsorption retention ability for Au NPs due to electrostatic attraction. Besides, it was found that filtration flow rate, or flux, was also an important parameter for the final retention because the enhanced hydrodynamic drag could trigger the detachment of deposited NPs or press NPs flowing through the superficial entrance leading to penetration. Tests of 10 nm Au NP retention using five different membranes with the same nominal pore size of 0.1 µm showed large variation of NP retention efficiencies demonstrating that pore size should not be used as the only criterion for rating filter performance, especially for small NPs. Our results provide not only detailed insights into the retention mechanisms of various membranes but also suggestions on how to select membrane filters for different filtration purposes. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2018.09.033
  • 2018 • 614 Segregation Phenomena in Size-Selected Bimetallic CuNi Nanoparticle Catalysts
    Pielsticker, L. and Zegkinoglou, I. and Divins, N.J. and Mistry, H. and Chen, Y.-T. and Kostka, A. and Boscoboinik, J.A. and Cuenya, B.R.
    Journal of Physical Chemistry B 122 919-926 (2018)
    Surface segregation, restructuring, and sintering phenomena in size-selected copper-nickel nanoparticles (NPs) supported on silicon dioxide substrates were systematically investigated as a function of temperature, chemical state, and reactive gas environment. Using near-ambient pressure (NAP-XPS) and ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), we showed that nickel tends to segregate to the surface of the NPs at elevated temperatures in oxygen- or hydrogen-containing atmospheres. It was found that the NP pretreatment, gaseous environment, and oxide formation free energy are the main driving forces of the restructuring and segregation trends observed, overshadowing the role of the surface free energy. The depth profile of the elemental composition of the particles was determined under operando CO2 hydrogenation conditions by varying the energy of the X-ray beam. The temperature dependence of the chemical state of the two metals was systematically studied, revealing the high stability of nickel oxides on the NPs and the important role of high valence oxidation states in the segregation behavior. Atomic force microscopy (AFM) studies revealed a remarkable stability of the NPs against sintering at temperatures as high as 700 °C. The results provide new insights into the complex interplay of the various factors which affect alloy formation and segregation phenomena in bimetallic NP systems, often in ways different from those previously known for their bulk counterparts. This leads to new routes for tuning the surface composition of nanocatalysts, for example, through plasma and annealing pretreatments. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.7b06984
  • 2018 • 613 Shape-Dependent Dissolution and Cellular Uptake of Silver Nanoparticles
    Graf, C. and Nordmeyer, D. and Sengstock, C. and Ahlberg, S. and Diendorf, J. and Raabe, J. and Epple, M. and Köller, M. and Lademann, J. and Vogt, A. and Rancan, F. and Rühl, E.
    Langmuir 34 1506-1519 (2018)
    The cellular uptake and dissolution of trigonal silver nanoprisms (edge length 42 ± 15 nm, thickness 8 ± 1 nm) and mostly spherical silver nanoparticles (diameter 70 ± 25 nm) in human mesenchymal stem cells (hMSC's) and human keratinocytes (HaCaT cells) were investigated. Both particles are stabilized by polyvinylpyrrolidone (PVP), with the prisms additionally stabilized by citrate. The nanoprisms dissolved slightly in pure water but strongly in isotonic saline or at pH 4, corresponding to the lowest limit for the pH during cellular uptake. The tips of the prisms became rounded within minutes due to their high surface energy. Afterward, the dissolution process slowed down due to the presence of both PVP stabilizing Ag{100} sites and citrate blocking Ag{111} sites. On the contrary, nanospheres, solely stabilized by PVP, dissolved within 24 h. These results correlate with the finding that particles in both cell types have lost >90% of their volume within 24 h. hMSC's took up significantly more Ag from nanoprisms than from nanospheres, whereas HaCaT cells showed no preference for one particle shape. This can be rationalized by the large cellular interaction area of the plateletlike nanoprisms and the bending stiffness of the cell membranes. hMSC's have a highly flexible cell membrane, resulting in an increased uptake of plateletlike particles. HaCaT cells have a membrane with a 3 orders of magnitude higher Young's modulus than for hMSC. Hence, the energy gain due to the larger interaction area of the nanoprisms is compensated for by the higher energy needed for cell membrane deformation compared to that for spheres, leading to no shape preference. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03126
  • 2018 • 612 Simultaneous Rayleigh/Mie and Raman/Fluorescence Characterization of Molecularly Functionalized Colloids by Correlative Single-Particle Real-Time Imaging in Suspension
    Wissler, J. and Wehmeyer, M. and Bäcker, S. and Knauer, S. and Schlücker, S.
    Analytical Chemistry 90 723-728 (2018)
    Many applications of nano- and microparticles require molecular functionalization. Assessing the heterogeneity of a colloidal sample in terms of its molecular functionalization is highly desirable but not accessible by conventional ensemble experiments. Retrieving this information necessitates single-particle experiments which simultaneously detect both functionalized and nonfunctionalized particles via two separate imaging channels. In this contribution, we present an optical setup for performing correlative single-particle imaging using laser light-sheet illumination: the first detection channel records elastic light scattering (Rayleigh/Mie), while the second channel detects inelastic light scattering (Raman) or fluorescence. The instrument is tested with Raman reporter-functionalized SERS-active metal nanoparticles (core/satellite silver nanoparticles, dimers and monomers of gold nanoparticles) and fluorophore-functionalized colloids (fluorescent polymer microparticles, dye-labeled protein on gold nanoparticles). © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.7b02528
  • 2018 • 611 Single Nanoparticle Growth from Nanoparticle Tracking Analysis: From Monte Carlo Simulations to Nanoparticle Electrogeneration
    Brasiliense, V. and Noël, J.-M. and Wonner, K. and Tschulik, K. and Combellas, C. and Kanoufi, F.
    ChemElectroChem 5 3036-3043 (2018)
    By scrutinizing the trajectory of individual nanoparticles (NPs) in solution, NP tracking analysis (NTA) allows sizing individual NPs and providing meaningful complementary information to single NP electrochemistry. Herein, a model is developed to extend NTA to allow dynamic NP sizing and to analyze the kinetics of growth of NPs in solution. Interpreting the NP trajectories as scaled Brownian motion, Monte Carlo simulations produce stochastic trajectories of growing NPs (under diffusion-controlled growth). These trajectories are grounds for determining a strategy to estimate the growth parameters of individual NPs from the time evolution analysis of the mean square displacement (MSD) curves. In particular, we evaluate the accuracy and precision of the parameter estimates from MSD analysis. In addition, the strategy is illustrated to depict the homogeneous electrosynthesis of silver NPs from the oxidation of a sacrificial Ag ultramicroelectrode (UME) in Fe2+ solution. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800742
  • 2018 • 610 Size-selected Fe3O4-Au hybrid nanoparticles for improved magnetism-based theranostics
    Efremova, M.V. and Nalench, Y.A. and Myrovali, E. and Garanina, A.S. and Grebennikov, I.S. and Gifer, P.K. and Abakumov, M.A. and Spasova, M. and Angelakeris, M. and Savchenko, A.G. and Farle, M. and Klyachko, N.L. and Majouga, A....
    Beilstein Journal of Nanotechnology 9 2684-2699 (2018)
    Size-selected Fe3O4-Au hybrid nanoparticles with diameters of 6-44 nm (Fe3O4) and 3-11 nm (Au) were prepared by high temperature, wet chemical synthesis. High-quality Fe3O4 nanocrystals with bulk-like magnetic behavior were obtained as confirmed by the presence of the Verwey transition. The 25 nm diameter Fe3O4-Au hybrid nanomaterial sample (in aqueous and agarose phantom systems) showed the best characteristics for application as contrast agents in magnetic resonance imaging and for local heating using magnetic particle hyperthermia. Due to the octahedral shape and the large saturation magnetization of the magnetite particles, we obtained an extraordinarily high r2-relaxivity of 495 mM-1·s-1 along with a specific loss power of 617 W·gFe-1 and 327 W·gFe-1 for hyperthermia in aqueous and agarose systems, respectively. The functional in vitro hyperthermia test for the 4T1 mouse breast cancer cell line demonstrated 80% and 100% cell death for immediate exposure and after precultivation of the cells for 6 h with 25 nm Fe3O4-Au hybrid nanomaterials, respectively. This confirms that the improved magnetic properties of the bifunctional particles present a next step in magnetic-particle-based theranostics. © 2018 Efremova et al.
    view abstractdoi: 10.3762/bjnano.9.251
  • 2018 • 609 Strong Deformation of Ferrofluid-Filled Elastic Alginate Capsules in Inhomogenous Magnetic Fields
    Wischnewski, C. and Zwar, E. and Rehage, H. and Kierfeld, J.
    Langmuir 34 13534-13543 (2018)
    We present a new system based on alginate gels for the encapsulation of a ferrofluid drop, which allows us to create millimeter-sized elastic capsules that are highly deformable by inhomogeneous magnetic fields. We use a combination of experimental and theoretical work in order to characterize and quantify the deformation behavior of these ferrofluid-filled capsules. We introduce a novel method for the direct encapsulation of unpolar liquids by sodium alginate. By adding 1-hexanol to the unpolar liquid, we can dissolve sufficient amounts of CaCl2 in the resulting mixture for ionotropic gelation of sodium alginate. The addition of polar alcohol molecules allows us to encapsulate a ferrofluid as a single phase rather than an emulsion without impairing ferrofluid stability. This encapsulation method increases the amount of encapsulated magnetic nanoparticles resulting in high deformations of approximately 30% (in height-to-width ratio) in inhomogeneous magnetic field with magnetic field variations of 50 mT over the size of the capsule. This offers possible applications of capsules as actuators, switches, or valves in confined spaces like microfluidic devices. We determine both elastic moduli of the capsule shell, Young's modulus and Poisson's ratio, by employing two independent mechanical methods, spinning capsule measurements and capsule compression between parallel plates. We then show that the observed magnetic deformation can be fully understood from magnetic forces exerted by the ferrofluid on the capsule shell if the magnetic field distribution and magnetization properties of the ferrofluid are known. We perform a detailed analysis of the magnetic deformation by employing a theoretical model based on nonlinear elasticity theory. Using an iterative solution scheme that couples a finite element/boundary element method for the magnetic field calculation to the solution of the elastic shape equations, we achieve quantitative agreement between theory and experiment for deformed capsule shapes using the Young modulus from mechanical characterization and the surface Poisson ratio as a fit parameter. This detailed analysis confirms the results from mechanical characterization that the surface Poisson ratio of the alginate shell is close to unity, that is, deformations of the alginate shell are almost area conserving. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b02357
  • 2018 • 608 Suppression of the Verwey Transition by Charge Trapping
    Schmitz-Antoniak, C. and Schmitz, D. and Warland, A. and Darbandi, M. and Haldar, S. and Bhandary, S. and Sanyal, B. and Eriksson, O. and Wende, H.
    Annalen der Physik (2018)
    The Verwey transition in Fe3O4 nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO2. By X-ray absorption spectroscopy and its associated X-ray magnetic circular dichroism this suppression can be correlated to localized Fe2+ states and a reduced double exchange visible in different site-specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe3O4/ SiO2 interface and the consequent difficulties in the formation of the common phases of Fe3O4. By comparison to X-ray absorption spectra of bare Fe3O4 nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/andp.201700363
  • 2018 • 607 Suspension- and powder-based derivation of Hansen dispersibility parameters for zinc oxide quantum dots
    Süß, S. and Lin, W. and Getmanenko, O. and Pflug, L. and Sobisch, T. and Peukert, W. and Lerche, D. and Segets, D.
    Particuology (2018)
    For most particle-based applications, formulation in the liquid phase is a decisive step, and thus, particle interactions and stability in liquid media are of major importance. The concept of Hansen solubility parameters (HSP) was initially invented to describe the interactions of (polymer) molecules and their solubility in different liquids and is increasingly being used in particle technology to describe dispersibility. Because dispersions are not thermodynamically stable, the term Hansen dispersibility parameters (HDP) is used instead of HSP (Süß Sobisch, Peukert, Lerche, & Segets, 2018). Herein, we extend a previously developed standardized and non-subjective method for determination of Hansen parameters based on analytical centrifugation to the important class of quantum materials. As a technically relevant model system, zinc oxide quantum dots (QDs) were used to transfer our methodology to nanoparticles (NPs) with sizes below 10 nm. The results obtained using the standard procedure starting from a dried powder were compared with those obtained through redispersion from the wet sediment produced during the typical washing procedure of QDs, and drying was observed to play an important role. In conclusion, our study reveals the high potential of HDP for quantifying the interfacial properties of NPs as well as their link to dispersibility. © 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences
    view abstractdoi: 10.1016/j.partic.2018.05.010
  • 2018 • 606 Temperature-Dependent Ultrastructure Transformation of Au-Fe Nanoparticles Investigated by in Situ Scanning Transmission Electron Microscopy
    Kamp, M. and Tymoczko, A. and Schürmann, U. and Jakobi, J. and Rehbock, C. and Rätzke, K. and Barcikowski, S. and Kienle, L.
    Crystal Growth and Design 18 5434-5440 (2018)
    Three-dimensional morphology changes of bimetallic nanoparticles (NPs) with nominal composition Au50Fe50 and Au20Fe80, generated by pulsed laser ablation in liquid, are monitored in situ and ex situ via scanning transmission electron microscopy and electron tomography. The samples are made up of a chemically segregated core-shell (CS) NPs structure, with an Au-rich shell and Fe-rich core, and solid solution (SS) NPs in the pristine state. Further, the examinations reveal information about a sequence of characteristic changes from the pristine metastable and intermediate ultrastructures up to thermodynamically stable products. In the case of the Au20Fe80 sample, a metastable spherical CS morphology is transformed at equilibrium conditions into a cube-shaped Fe-rich core faceted by truncated Au-rich pyramids. For the Au50Fe50 sample, the Au-rich shell is solved into the Fe-rich core, and chemically homogeneous (SS) NPs are formed. Interestingly, this transformation was proven to occur via an intermediate ultrastructure with lamellar segregation, not previously reported as a transient state during in situ heating. On the basis of these observations, a correlation between the composition and the morphology at equilibrium is suggested, in accordance with the bulk phase diagram of Au-Fe. At the same time, our examinations directly prove that laser ablation synthesis creates nonequilibrium NP morphologies, frozen in metastable, spherical core-shell particles. Copyright © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.8b00809
  • 2018 • 605 The Role of Composition of Uniform and Highly Dispersed Cobalt Vanadium Iron Spinel Nanocrystals for Oxygen Electrocatalysis
    Chakrapani, K. and Bendt, G. and Hajiyani, H. and Lunkenbein, T. and Greiner, M.T. and Masliuk, L. and Salamon, S. and Landers, J. and Schlögl, R. and Wende, H. and Pentcheva, R. and Schulz, S. and Behrens, M.
    ACS Catalysis 8 1259-1267 (2018)
    Cation substitution in transition-metal oxides is an important approach to improve electrocatalysts by the optimization of their composition. Herein, we report on phase-pure spinel-type CoV2-xFexO4 nanoparticles with 0 ≤ x ≤ 2 as a new class of bifunctional catalysts for the oxygen evolution (OER) and oxygen reduction reactions (ORR). The mixed-metal oxide catalysts exhibit high catalytic activity for both OER and ORR that strongly depends on the V and Fe content. CoV2O4 is known to exhibit a high conductivity, while in CoFe2O4 the cobalt cation distribution is expected to change due to the inversion of the spinel structure. The optimized catalyst, CoV1.5Fe0.5O4, shows an overpotential for the OER of â300 mV for 10 mA cm-2 with a Tafel slope of 38 mV dec-1 in alkaline electrolyte. DFT+U+SOC calculations on cation ordering confirm the tendency toward the inverse spinel structure with increasing Fe concentration in CoV2-xFexO4 that starts to dominate already at low Fe contents. The theoretical results also show that the variations of oxidation states are related to the surface region, where the redox activity was found experimentally to be manifested in the transformation of V3+ ↠V2+. The high catalytic activity, facile synthesis, and low cost of the CoV2-xFexO4 nanoparticles render them very promising for application in bifunctional electrocatalysis. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.7b03529
  • 2018 • 604 Thermodynamic properties of selenoether-functionalized ionic liquids and their use for the synthesis of zinc selenide nanoparticles
    Klauke, K. and Zaitsau, D.H. and Bülow, M. and He, L. and Klopotowski, M. and Knedel, T.-O. and Barthel, J. and Held, C. and Verevkin, S.P. and Janiak, C.
    Dalton Transactions 47 5083-5097 (2018)
    Three selenoether-functionalized ionic liquids (ILs) of N-[(phenylseleno)methylene]pyridinium (1), N-(methyl)- (2) and N-(butyl)-N'-[(phenylseleno)methylene]imidazolium (3) with bis(trifluoromethanesulfonyl)imide anions ([NTf2]) were prepared from pyridine, N-methylimidazole and N-butylimidazole with in situ obtained phenylselenomethyl chloride, followed by ion exchange to give the desired compounds. The crystal structures of the bromide and tetraphenylborate salts of the above cations (1-Br, 2-BPh4 and 3-BPh4) confirm the formation of the desired cations and indicate a multitude of different supramolecular interactions besides the dominating Coulomb interactions between the cations and anions. The vaporization enthalpies of the synthesized [NTf2]-containing ILs were determined by means of a quartz-crystal microbalance method (QCM) and their densities were measured with an oscillating U-tube. These thermodynamic data have been used to develop a method for assessment of miscibility of conventional solvents in the selenium-containing ILs by using Hildebrandt solubility parameters, as well as for modeling with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) method. Furthermore, structure-property relations between selenoether-functionalized and similarly shaped corresponding aryl-substituted imidazolium- and pyridinium-based ILs were analyzed and showed that the contribution of the selenium moiety to the enthalpy of vaporization of an IL is equal to the contribution of a methylene (CH2) group. An incremental approach to predict vaporization enthalpies of ILs by a group contribution method has been developed. The reaction of these ILs with zinc acetate dihydrate under microwave irradiation led to ZnSe nanoparticles of an average diameter between 4 and 10 nm, depending on the reaction conditions. © The Royal Society of Chemistry 2018.
    view abstractdoi: 10.1039/c8dt00233a
  • 2018 • 603 X-ray spectroscopic and stroboscopic analysis of pulsed-laser ablation of Zn and its oxidation
    Reich, S. and Göttlicher, J. and Letzel, A. and Gökce, B. and Barcikowski, S. and dos Santos Rolo, T. and Baumbach, T. and Plech, A.
    Applied Physics A: Materials Science and Processing 124 (2018)
    Pulsed laser ablation in liquids (PLAL) as an attractive process for ligand-free nanoparticle synthesis represents a multiscale problem to understand the mechanisms and achieve control. Atomic and nanoscale processes interacting with macroscale dynamics in the liquid demand for sensitive tools for in-situ and structural analysis. By adding X-ray methods, we enlarge the available information on millimeter-scale bubble formation down to atomic-scale nanoparticle reactions. X-ray spectroscopy (XAS) can resolve the chemical speciation of the ablated material during the ablation from a zinc wire target showing a first oxidation step from zinc to zinc oxide within some 10 min followed by a slower reaction to hydrozincite. X-ray imaging investigations also give additional information on the bubble dynamics as we demonstrate by comparing the microsecond radiography and optical stroboscopy. We show different features of the detachment of the ablation bubble from a free wire. The location of the first collapse occurs in front of the target. While a first rebound bubble possesses an homogeneous interior, the subsequent rebound consists merely of a cloud of microbubbles. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00339-017-1503-3
  • 2017 • 602 Adhesion properties of a three-layer system based on RF-magnetron sputter deposited calcium-phosphate coating and silver nanoparticles
    Tkachev, M.S. and Melnikov, E.S. and Surmeneva, M.A. and Sharonova, A.A. and Surmenev, R.A. and Korneva, O.S. and Shulepov, I.A. and Loza, K. and Epple, M.
    Proceedings of the 11th International Forum on Strategic Technology, IFOST 2016 88-90 (2017)
    A three-layer system of hydroxyapatite (HA) coating - Ag nanoparticles - HA coating with an overall thickness of 1.2 μm was prepared. The radio-frequency (RF) magnetron sputtering was used to prepare the first layer of hydroxyapatite coating on titanium. Then electrophoretic deposition of silver nanoparticles on the prepared HA layer was done followed by deposition of the second layer of HA by RFmagnetron sputtering. The adhesion strength was investigated by the scratch test method. Scanning electron microscopy and optical microscopy allowed to qualitatively estimate the deformation mechanisms of the biocomposites after the scratch test. © 2016 IEEE.
    view abstractdoi: 10.1109/IFOST.2016.7884197
  • 2017 • 601 Advanced SERS Sensor Based on Capillarity-Assisted Preconcentration through Gold Nanoparticle-Decorated Porous Nanorods
    Xue, L. and Xie, W. and Driessen, L. and Domke, K.F. and Wang, Y. and Schlücker, S. and Gorb, S.N. and Steinhart, M.
    Small (2017)
    A preconcentrating surface-enhanced Raman scattering (SERS) sensor for the analysis of liquid-soaked tissue, tiny liquid droplets and thin liquid films without the necessity to collect the analyte is reported. The SERS sensor is based on a block-copolymer membrane containing a spongy-continuous pore system. The sensor's upper side is an array of porous nanorods having tips functionalized with Au nanoparticles. Capillarity in combination with directional evaporation drives the analyte solution in contact with the flat yet nanoporous underside of the SERS sensor through the continuous nanopore system toward the nanorod tips where non-volatile components of the analyte solution precipitate at the Au nanoparticles. The nanorod architecture increases the sensor surface in the detection volume and facilitates analyte preconcentration driven by directional solvent evaporation. The model analyte 5,5'-dithiobis(2-nitrobenzoic acid) can be detected in a 1 × 10-3m solution ≈300 ms after the sensor is brought into contact with the solution. Moreover, a sensitivity of 0.1 ppm for the detection of the dissolved model analyte is achieved. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201603947
  • 2017 • 600 Airborne engineered nanomaterials in the workplace—a review of release and worker exposure during nanomaterial production and handling processes
    Ding, Y. and Kuhlbusch, T.A.J. and Van Tongeren, M. and Jiménez, A.S. and Tuinman, I. and Chen, R. and Alvarez, I.L. and Mikolajczyk, U. and Nickel, C. and Meyer, J. and Kaminski, H. and Wohlleben, W. and Stahlmecke, B. and Clava...
    Journal of Hazardous Materials 322 17-28 (2017)
    For exposure and risk assessment in occupational settings involving engineered nanomaterials (ENMs), it is important to understand the mechanisms of release and how they are influenced by the ENM, the matrix material, and process characteristics. This review summarizes studies providing ENM release information in occupational settings, during different industrial activities and using various nanomaterials. It also assesses the contextual information — such as the amounts of materials handled, protective measures, and measurement strategies — to understand which release scenarios can result in exposure. High-energy processes such as synthesis, spraying, and machining were associated with the release of large numbers of predominantly small-sized particles. Low-energy processes, including laboratory handling, cleaning, and industrial bagging activities, usually resulted in slight or moderate releases of relatively large agglomerates. The present analysis suggests that process-based release potential can be ranked, thus helping to prioritize release assessments, which is useful for tiered exposure assessment approaches and for guiding the implementation of workplace safety strategies. The contextual information provided in the literature was often insufficient to directly link release to exposure. The studies that did allow an analysis suggested that significant worker exposure might mainly occur when engineering safeguards and personal protection strategies were not carried out as recommended. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.jhazmat.2016.04.075
  • 2017 • 599 Albumin-derived perfluorocarbon-based artificial oxygen carriers: A physico-chemical characterization and first in vivo evaluation of biocompatibility
    Wrobeln, A. and Laudien, J. and Groß-Heitfeld, C. and Linders, J. and Mayer, C. and Wilde, B. and Knoll, T. and Naglav, D. and Kirsch, M. and Ferenz, K.B.
    European Journal of Pharmaceutics and Biopharmaceutics 115 52-64 (2017)
    Until today, artificial oxygen carriers have not been reached satisfactory quality for routine clinical treatments. To bridge this gap, we designed albumin-derived perfluorocarbon-based nanoparticles as novel artificial oxygen carriers and evaluated their physico-chemical and pharmacological performance. Our albumin-derived perfluorocarbon-based nanoparticles (capsules), composed of an albumin shell and a perfluorodecalin core, were synthesized using ultrasonics. Their subsequent analysis by physico-chemical methods such as scanning electron-, laser scanning- and dark field microscopy as well as dynamic light scattering revealed spherically-shaped, nano-sized particles, that were colloidally stable when dispersed in 5% human serum albumin solution. Furthermore, they provided a remarkable maximum oxygen capacity, determined with a respirometer, reflecting a higher oxygen transport capacity than the competitor Perftoran®. Intravenous administration to healthy rats was well tolerated. Undesirable effects on either mean arterial blood pressure, hepatic microcirculation (determined by in vivo microscopy) or any deposit of capsules in organs, except the spleen, were not observed. Some minor, dose-dependent effects on tissue damage (release of cellular enzymes, alterations of spleen's micro-architecture) were detected. As our promising albumin-derived perfluorocarbon-based nanoparticles fulfilled decisive physico-chemical demands of an artificial oxygen carrier while lacking severe side-effects after in vivo administration they should be advanced to functionally focused in vivo testing conditions. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.ejpb.2017.02.015
  • 2017 • 598 Amine-Functionalized Silica Nanoparticles Incorporating Covalently Linked Visible-Light-Excitable Eu3+ Complexes: Synthesis, Characterization, and Cell-Uptake Studies
    Francis, B. and Neuhaus, B. and Reddy, M.L.P. and Epple, M. and Janiak, C.
    European Journal of Inorganic Chemistry 2017 3205-3213 (2017)
    We report the synthesis, characterization, photophysical investigations, and cell-uptake studies of luminescent silica nanoparticles incorporating covalently linked visible-light-excitable Eu3+ complexes. Visible-light excitation was accomplished by using highly conjugated carbazole-based β-diketonate ligands. Covalent incorporation of the Eu3+ complexes into the silica nanoparticles was achieved by modification of the bidentate phosphine oxide 4,6-bis(diphenylphosphoryl)-10H-phenoxazine (DPOXPO), which was used as the neutral donor for the Eu3+ ion. The surface amine functionalization of the nanoparticles was carried out using aminopropyltriethoxysilane (APTES). The prepared nanoparticles (Eu@Si-OH and Eu@Si-NH2) are around 35–40 nm in diameter, monodisperse, stable in aqueous dispersion, and also retain the luminescent properties of the incorporated Eu3+ complex. The synthesized nanoparticles exhibit a promising luminescence quantum yield of 38 % and an excited-state lifetime of 638 µs at physiological pH. The photobleaching experiments revealed that the developed nanoparticles are more photostable than the parent Eu3+ complex 1. In vitro experiments with Eu@Si-NH2 nanoparticles on HeLa cells showed that they are biocompatible and are readily taken up by cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ejic.201700240
  • 2017 • 597 Automated synthesis of quantum dot nanocrystals by hot injection: Mixing induced self-focusing
    Salaheldin, A.M. and Walter, J. and Herre, P. and Levchuk, I. and Jabbari, Y. and Kolle, J.M. and Brabec, C.J. and Peukert, W. and Segets, D.
    Chemical Engineering Journal 320 232-243 (2017)
    The hot injection technique for the synthesis of quantum dots (QDs) is a well-established and widely used method in the lab. However, scale-up rules do not exist. One reason is that in particular the role of process parameters like mixing on particle formation is largely unknown, as systematic examination of the latter is impossible for the laborious and complex manual synthesis. Herein we studied the mixing induced self-focusing of particle size distributions (PSDs) of CdSe QDs using automation in combination with a defined stirrer geometry. Basis for our study is a platform that allows parallelization with inline temperature monitoring, defined injection rate, accurate sampling times as well as controlled stirring. Reproducibility in terms of optical product properties was analyzed by absorption and emission whereas reproducibility in terms of the PSD was verified by deconvolution of UV/Vis absorbance spectra and especially by analytical ultracentrifugation (AUC) complemented by transmission electron microscopy (TEM). In line with previous results, AUC confirmed that even QDs made by hot injection in an automated setup are polydisperse with multimodal size distributions. Finally, reproducibility in combination with early stage sampling and controlled mixing allowed us for the first time to analyze the influence of stirring on focusing and defocusing of PSDs, that has been expressed in terms of the evolution of the relative standard deviation (RSD). Our work paves the way to gain in-depth understanding of often forgotten process-structure relationships of colloidal nanoparticles which eventually is a first step in the direction of the development of scalable synthesis and reliable application of high-quality QDs in technical applications. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2017.02.154
  • 2017 • 596 Avidin-conjugated calcium phosphate nanoparticles as a modular targeting system for the attachment of biotinylated molecules in vitro and in vivo
    van der Meer, S.B. and Knuschke, T. and Frede, A. and Schulze, N. and Westendorf, A.M. and Epple, M.
    Acta Biomaterialia 57 414-425 (2017)
    Avidin was covalently conjugated to the surface of calcium phosphate nanoparticles, coated with a thin silica shell and terminated by sulfhydryl groups (diameter of the solid core about 50 nm), with a bifunctional crosslinker connecting the amino groups of avidin to the sulfhydryl group on the nanoparticle surface. This led to a versatile nanoparticle system where all kinds of biotinylated (bio-)molecules can be easily attached to the surface by the non-covalent avidin-biotin-complex formation. It also permits the attachment of different biomolecules on the same nanoparticle (heteroavidity), creating a modular system for specific applications in medicine and biology. The variability of the binding to the nanoparticle surface of the was demonstrated with various biotinylated molecules, i.e. fluorescent dyes and antibodies. The accessibility of the conjugated avidin was demonstrated by a fluorescence-quenching assay. About 2.6 binding sites for biotin were accessible on each avidin tetramer. Together with a number of about 240 avidin tetramer units per nanoparticle, this offers about 600 binding sites for biotin on each nanoparticle. The uptake of fluorescently labelled avidin-conjugated calcium phosphate nanoparticles by HeLa cells showed the co-localization of fluorescent avidin and fluorescent biotin, indicating the stability of the complex under cell culture conditions. CD11c-antibody functionalized nanoparticles specifically targeted antigen-presenting immune cells (dendritic cells; DCs) in vitro and in vivo (mice) with high efficiency. Statement of significance Calcium phosphate nanoparticles have turned out to be very useful transporters for biomolecules into cells, both in vitro and in vivo. However, their covalent surface functionalization with antibodies, fluorescent dyes, or proteins requires a separate chemical synthesis for each kind of surface molecule. We have therefore developed avidin-terminated calcium phosphate nanoparticles to which all kinds of biotinylated molecules can be easily attached, also as a mixture of two or more molecules. This non-covalent bond is stable both in cell culture and after injection into mice in vivo. Thus, we have created a highly versatile system for many applications, from the delivery of biomolecules over the targeting of cells and tissue to in vivo imaging. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actbio.2017.05.049
  • 2017 • 595 Changes within the stabilizing layer of ZnO nanoparticles upon washing
    Schindler, T. and Schmutzler, T. and Schmiele, M. and Lin, W. and Segets, D. and Peukert, W. and Appavou, M.-S. and Kriele, A. and Gilles, R. and Unruh, T.
    Journal of Colloid and Interface Science 504 356-362 (2017)
    ZnO nanoparticles (NPs) are highly relevant for various industrial applications, however, after synthesis of the NPs residual chemicals need to be removed from the colloidal raw product by washing, as they may influence the performance of the final device. In the present study we focus on the effect of washing by antisolvent flocculation with subsequent redispersion of the NPs on the stabilizing acetate shell. Purification of the ZnO nanoparticles is reported to be optimal with respect to zeta potential that has a maximum after one washing cycle. In this work, we will shed light on this observation using small angle X-ray and neutron scattering (SAXS, SANS) by demonstrating that after the first washing cycle the content of acetate in the ligand shell around the ZnO NPs increases. In detail, it was observed that the diffuse acetate shell shrinks to the size of a monolayer upon washing but the acetate content of this monolayer is higher than within the diffuse shell of the particles of the native dispersion. A second washing cycle reduces the acetate concentration within the stabilizing shell and the stability of the dispersion drops accordingly. After another (third) washing cycle strong agglomeration was observed for all investigated samples. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2017.05.059
  • 2017 • 594 Characterization of anisotropically shaped silver nanoparticle arrays via spectroscopic ellipsometry supported by numerical optical modeling
    Gkogkou, D. and Shaykhutdinov, T. and Oates, T.W.H. and Gernert, U. and Schreiber, B. and Facsko, S. and Hildebrandt, P. and Weidinger, I.M. and Esser, N. and Hinrichs, K.
    Applied Surface Science 421 460-464 (2017)
    The present investigation aims to study the optical response of anisotropic Ag nanoparticle arrays deposited on rippled silicon substrates by performing a qualitative comparison between experimental and theoretical results. Spectroscopic ellipsometry was used along with numerical calculations using finite-difference time-domain (FDTD) method and rigorous coupled wave analysis (RCWA) to reveal trends in the optical and geometrical properties of the nanoparticle array. Ellipsometric data show two resonances, in the orthogonal x and y directions, that originate from localized plasmon resonances as demonstrated by the calculated near-fields from FDTD calculations. The far-field calculations by RCWA point to decoupled resonances in x direction and possible coupling effects in y direction, corresponding to the short and long axis of the anisotropic nanoparticles, respectively. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2016.10.105
  • 2017 • 593 Chemoenzymatic one-pot reaction of noncompatible catalysts: Combining enzymatic ester hydrolysis with Cu(i)/bipyridine catalyzed oxidation in aqueous medium
    Sand, H. and Weberskirch, R.
    RSC Advances 7 33614-33626 (2017)
    The combination of chemical catalysts and biocatalysts in a one-pot reaction has attracted considerable interest in the past years. However, since each catalyst requires very different reaction conditions, chemoenzymatic one-pot reactions in aqueous media remain challenging and are limited today to metal-catalysts that display high activity in aqueous media. Here, we report the first combination of two incompatible catalytic systems, a lipase based ester hydrolysis with a water-sensitive Cu/bipyridine catalyzed oxidation reaction, in a one-pot reaction in aqueous medium (PBS buffer). Key to the solution was the compartmentalization of the Cu/bipyridine catalyst in a core-shell like nanoparticle. We show the synthesis and characterization of the Cu/bipyridine functionalized nanoparticles and the application in the oxidation of allylic and benzylic alcohols in aqueous media. Furthermore, the work demonstrates the implementation of a one-pot reaction process with optimized reaction conditions involving a lipase (CAL-B) to hydrolyze various acetate ester substrates in the first step, followed by oxidation of the resulting alcohols to the corresponding aldehydes under aerobic conditions in aqueous media. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7ra05451c
  • 2017 • 592 Choosing the right nanoparticle size-designing novel ZnO electrode architectures for efficient dye-sensitized solar cells
    Pfau, M.W. and Kunzmann, A. and Segets, D. and Peukert, W. and Wallace, G.G. and Officer, D.L. and Clark, T. and Costa, R.D. and Guldi, D.M.
    Journal of Materials Chemistry A 5 7516-7522 (2017)
    A novel concept for constructing optimized ZnO-based photoanodes as integrative components of dye-sensitized solar cells (DSSCs) is realized by deploying differently sized nanoparticles, ranging from 2 to 10 nm, together with commercially available 20 nm nanoparticles. The 2 nm nanoparticles were used to construct an efficient buffer layer for transparent electrodes based on 10 nm nanoparticles, resulting in a relative increase of device efficiency from 1.8 to 3.0% for devices without and with a buffer layer, respectively. A mixture of 10 and 20 nm nanoparticles was optimized to maximize the diffuse reflection and to minimize the charge transport resistance in a light-scattering layer. This optimization resulted in a homogenous layer of more than 15 μm that provided a device efficiency of 3.3%. The buffer layer, transparent electrode, and light-scattering electrode, were then combined to give an overall efficiency of around 5%. Thus, this work demonstrates that varying the electrode architecture with nanoparticles of different diameters is a powerful strategy for improving the overall efficiency of ZnO-based DSSCs. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ta11012f
  • 2017 • 591 Co3O4@Co/NCNT Nanostructure Derived from a Dicyanamide-Based Metal-Organic Framework as an Efficient Bi-functional Electrocatalyst for Oxygen Reduction and Evolution Reactions
    Sikdar, N. and Konkena, B. and Masa, J. and Schuhmann, W. and Maji, T.K.
    Chemistry - A European Journal 23 18049-18056 (2017)
    There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)2(N(CN)2)]⋅(N(CN)2)⋅(5 H2O)}n [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN)2 −=dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H2/Ar atmosphere (at 800 °C) and further mild calcination yielded Co3O4@Co core–shell nanoparticle-encapsulated N-doped carbon nanotubes (Co3O4@Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core–shell Co3O4@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of −1 mA cm−2 and the OER with a potential of 1.61 V at 10 mA cm−2, which is competitive with the most active bi-functional catalysts reported previously. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201704211
  • 2017 • 590 Cobalt boride modified with N-doped carbon nanotubes as a high-performance bifunctional oxygen electrocatalyst
    Elumeeva, K. and Masa, J. and Medina, D. and Ventosa, E. and Seisel, S. and Kayran, Y.U. and Genç, A. and Bobrowski, T. and Weide, P. and Arbiol, J. and Muhler, M. and Schuhmann, W.
    Journal of Materials Chemistry A 5 21122-21129 (2017)
    The development of reversible oxygen electrodes, able to drive both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), is still a great challenge. We describe a very efficient and stable bifunctional electrocatalytic system for reversible oxygen electrodes obtained by direct CVD growth of nitrogen-doped carbon nanotubes (NCNTs) on the surface of cobalt boride (CoB) nanoparticles. A detailed investigation of the crystalline structure and elemental distribution of CoB before and after NCNT growth reveals that the NCNTs grow on small CoB nanoparticles formed in the CVD process. The resultant CoB/NCNT system exhibited outstanding activity in catalyzing both the OER and the ORR in 0.1 M KOH with an overvoltage difference of only 0.73 V between the ORR at -1 mA cm-2 and the OER at +10 mA cm-2. The proposed CoB/NCNT catalyst showed stable performance during 50 h of OER stability assessment in 0.1 M KOH. Moreover, CoB/NCNT spray-coated on a gas diffusion layer as an air-breathing electrode proved its high durability during 170 galvanostatic charge-discharge (OER/ORR) test cycles (around 30 h) at ±10 mA cm-2 in 6 M KOH, making it an excellent bifunctional catalyst for potential Zn-air battery application. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7ta06995b
  • 2017 • 589 Colloidal Stability and Surface Chemistry Are Key Factors for the Composition of the Protein Corona of Inorganic Gold Nanoparticles
    Johnston, B.D. and Kreyling, W.G. and Pfeiffer, C. and Schäffler, M. and Sarioglu, H. and Ristig, S. and Hirn, S. and Haberl, N. and Thalhammer, S. and Hauck, S.M. and Semmler-Behnke, M. and Epple, M. and Hühn, J. and Del Pino, ...
    Advanced Functional Materials 27 (2017)
    To study the influence of colloidal stability on protein corona formation, gold nanoparticles are synthesized with five distinct surface modifications: coating with citric acid, bis(p-sulfonatophenyl)phenylphosphine dihydrate dipotassium salt, thiol-terminated methoxy-polyethylene glycol, dodecylamine-grafted poly(isobutylene-alt-maleic anhydride), and dodecylamine-grafted poly(isobutylene-alt-maleic anhydride) conjugated with polyethylene glycol. The nanoparticles are incubated with serum or bronchoalveolar lavage fluid from C57BL/6 mice (15 min or 24 h) to assess the effect of differential nanoparticle surface presentation on protein corona formation in the air–blood barrier exposure pathway. Proteomic quantification and nanoparticle size measurements are used to assess protein corona formation. We show that surface modification has a clear effect on the size and the composition of the protein corona that is related to the colloidal stability of the studied nanoparticles. Additionally, differences in the composition and size of the protein corona are shown between biological media and duration of exposure, indicating evolution of the corona through this exposure pathway. Consequently, a major determinant of protein corona formation is the colloidal stability of nanoparticles in biological media and chemical or environmental modification of the nanoparticles alters the surface presentation of the functional epitope in vivo. Therefore, the colloidal stability of nanoparticles has a decisive influence on nano–bio interactions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201701956
  • 2017 • 588 Comparison between periodicity and randomness from an effective refractive index point of view; Applicable to thin-film solar cells
    Jalali, M. and Nadgaran, H. and Erni, D.
    Scientia Iranica 24 3536-3541 (2017)
    In this paper, embedding plasmonic nanoparticles inside the solar cell's active layer, both in a periodic and in a random manner, is extensively investigated. The aim of this study is to investigate optical mechanisms inside the active layer as a consequence of nanoparticle inclusion as well as to compare periodicity and randomness in such structures, where the intended maximization of the ultra-broadband absorption renders the analysis complicated. To perform such study, an effective refractive index analysis is employed to simultaneously cover the influential parameters. The results show that although fully periodic structures are more desirable in narrow-band applications such as grating-assisted waveguide coupling, random inclusion of plasmonic nanoparticles in the solar cell's active layer yields a much higher optical absorption. Furthermore, random inclusion of nanoparticles is easier and much cheaper than periodic inclusion to implement in solar cell fabrication. © 2017 Sharif University of Technology. All rights reserved.
    view abstractdoi: 10.24200/sci.2017.4596
  • 2017 • 587 Concentrating light in Cu-In;Ga-Se2 solar cells
    Schmid, M. and Yin, G. and Song, A.M. and Duan, S. and Heidmann, B. and Sancho-Martinez, D. and Kämmer, S. and Köhler, T. and Manley, P. and Lux-Steiner, M.Ch.
    Journal of Photonics for Energy 7 (2017)
    Light concentration has proven beneficial for solar cells, most notably for highly efficient but expensive absorber materials using high concentrations and large scale optics. Here, we investigate the light concentration for cost-efficient thin-film solar cells that show nano- or microtextured absorbers. Our absorber material of choice is CuIn; GaSe2 (CIGSe), which has a proven stabilized record efficiency of 22.6% and which-despite being a polycrystalline thin-film material-is very tolerant to environmental influences. Taking a nanoscale approach, we concentrate light in the CIGSe absorber layer by integrating photonic nanostructures made from dielectric materials. The dielectric nanostructures give rise to resonant modes and field localization in their vicinity. Thus, when inserted inside or adjacent to the absorber layer, absorption and efficiency enhancement are observed. In contrast to this internal absorption enhancement, external enhancement is exploited in the microscaled approach: mm-sized lenses can be used to concentrate light onto CIGSe solar cells with lateral dimensions reduced down to the micrometer range. These micro solar cells come with the benefit of improved heat dissipation compared with the large scale concentrators and promise compact high-efficiency devices. Both approaches of light concentration allow for reduction in material consumption by restricting the absorber dimension either vertically (ultrathin absorbers for dielectric nanostructures) or horizontally (microabsorbers for concentrating lenses) and have significant potential for efficiency enhancement. ©2017 Society of Photo-Optical Instrumentation Engineers (SPIE).
    view abstractdoi: 10.1117/1.JPE.7.018001
  • 2017 • 586 Decoupling the Effects of High Crystallinity and Surface Area on the Photocatalytic Overall Water Splitting over β-Ga2O3 Nanoparticles by Chemical Vapor Synthesis
    Lukic, S. and Menze, J. and Weide, P. and Busser, G.W. and Winterer, M. and Muhler, M.
    ChemSusChem 10 4190-4197 (2017)
    Chemical vapor synthesis (CVS) is a unique method to prepare well-defined photocatalyst materials with both large specific surface area and a high degree of crystallinity. The obtained β-Ga2O3 nanoparticles were optimized for photocatalysis by reductive photodeposition of the Rh/CrOx co-catalyst system. The influence of the degree of crystallinity and the specific surface area on photocatalytic aqueous methanol reforming and overall water splitting (OWS) was investigated by synthesizing β-Ga2O3 samples in the temperature range from 1000 °C to 1500 °C. With increasing temperature, the specific surface area and the microstrain were found to decrease, whereas the degree of crystallinity and the crystallite size increased. Whereas the photocatalyst with the highest specific surface area showed the highest aqueous methanol reforming activity, the highest OWS activity was that for the sample with an optimum ratio between high degree of crystallinity and specific surface area. Thus, it was possible to show that the facile aqueous methanol reforming and the demanding OWS have different requirements for high photocatalytic activity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cssc.201701309
  • 2017 • 585 Delivery of the autofluorescent protein Rphycoerythrin by calcium phosphate nanoparticles into four different eukaryotic cell lines (HeLa, HEK293T, MG-63, MC3T3): Highly efficient, but leading to endolysosomal proteolysis in HeLa and MC3T3 cells
    Kopp, M. and Rotan, O. and Papadopoulos, C. and Schulze, N. and Meyer, H. and Epple, M.
    PLoS ONE 12 (2017)
    Nanoparticles can be used as carriers to transport biomolecules like proteins and synthetic molecules across the cell membrane because many molecules are not able to cross the cell membrane on their own. The uptake of nanoparticles together with their cargo typically occurs via endocytosis, raising concerns about the possible degradation of the cargo in the endolysosomal system. As the tracking of a dye-labelled protein during cellular uptake and processing is not indicative of the presence of the protein itself but only for the fluorescent label, a label-free tracking was performed with the red-fluorescing model protein R-phycoerythrin (R-PE). Four different eukaryotic cell lines were investigated: HeLa, HEK293T, MG-63, and MC3T3. Alone, the protein was not taken up by any cell line; only with the help of calcium phosphate nanoparticles, an efficient uptake occurred. After the uptake into HeLa cells, the protein was found in early endosomes (shown by the marker EEA1) and lysosomes (shown by the marker Lamp1). There, it was still intact and functional (i.e. properly folded) as its red fluorescence was detected. However, a few hours after the uptake, proteolysis started as indicated by the decreasing red fluorescence intensity in the case of HeLa and MC3T3 cells. 12 h after the uptake, the protein was almost completely degraded in HeLa cells and MC3T3 cells. In HEK293T cells and MG-63 cells, no degradation of the protein was observed. In the presence of Bafilomycin A1, an inhibitor of acidification and protein degradation in lysosomes, the fluorescence of R-PE remained intact over the whole observation period in the four cell lines. These results indicate that despite an efficient nanoparticle-mediated uptake of proteins by cells, a rapid endolysosomal degradation may prevent the desired (e.g. therapeutic) effect of a protein inside a cell. © 2017 Kopp et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    view abstractdoi: 10.1371/journal.pone.0178260
  • 2017 • 584 Dependence of the optical constants and the performance in the SPREE gas measurement on the thickness of doped tin oxide over coatings
    Fischer, D. and Hertwig, A. and Beck, U. and Negendank, D. and Lohse, V. and Kormunda, M. and Esser, N.
    Applied Surface Science 421 480-486 (2017)
    In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29-56. nm, the second was iron doped on gold/glass substrate with 1.6-6.3. nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6. nm to 5.1. nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3. nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much. © 2016.
    view abstractdoi: 10.1016/j.apsusc.2016.11.188
  • 2017 • 583 Direct Integration of Laser-Generated Nanoparticles into Transparent Nail Polish: The Plasmonic "goldfinger"
    Lau, M. and Waag, F. and Barcikowski, S.
    Industrial and Engineering Chemistry Research 56 3291-3296 (2017)
    A transparent nail varnish can be colored simply and directly with laser-generated nanoparticles. This does not only enable coloring of the varnish for cosmetic purposes, but also gives direct access to nanodoped varnishes to be used on any solid surface. Therefore, nanoparticle properties such as plasmonic properties or antibacterial effects can be easily adapted to surfaces for medical or optical purposes. The presented method for integration of metal (gold, platinum, silver, and alloy) nanoparticles into varnishes is straightforward and gives access to nanodoped polishes with optical properties, difficult to be achieved by dispersing powder pigments in the high-viscosity liquids. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.7b00039
  • 2017 • 582 Effect of titania surface modification of mesoporous silica SBA-15 supported Au catalysts: Activity and stability in the CO oxidation reaction
    Kučerová, G. and Strunk, J. and Muhler, M. and Behm, R.J.
    Journal of Catalysis 356 214-228 (2017)
    As part of an ongoing effort to understand the deactivation and improve the stability of metal oxide-supported Au catalysts in the low-temperature CO oxidation reaction while maintaining their high activity, we have investigated the influence of a mesoporous silica SBA-15 substrate on the activity and stability of Au/TiO2 catalysts, which consist of a SBA-15 support surface modified by a monolayer of TiOx with Au nanoparticles on top. The extent of the TiOx surface modification was systematically increased, while the Au loading and the Au particle sizes were largely kept constant. Employing kinetic measurements at three different temperatures (30 °C, 80 °C, 180 °C) and a number of ex situ methods as well as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for catalyst characterization, we found that the activity of these catalysts increases significantly with the Ti concentration and with reaction temperature. The tendency for deactivation remains essentially unchanged. Detailed in situ DRIFTS measurements reveal that the Au nanoparticles are largely formed on the TiOx surface-modified areas of the SBA-15 support and that the tendency for surface carbonate formation is very low. The observed deactivation may at least partly be related to the accumulation of molecularly adsorbed H2O species, in particular at low temperatures (30 °C). These are likely to be formed from surface hydroxyl groups, they may affect the reaction either by blocking of active sites or by blocking the adsorption of reactants on the substrate. Other effects, such as reaction induced changes in the titania layer, must however, play a role as well, both at 80 °C and in particular at 180 °C, where accumulation of adsorbed species is negligible. The mechanistic ideas are supported by reactivation tests subsequent to calcination at 400 °C, which were found to fully restore the initial activity. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2017.09.017
  • 2017 • 581 Efficient Gene Transfection through Inhibition of β-Sheet (Amyloid Fiber) Formation of a Short Amphiphilic Peptide by Gold Nanoparticles
    Jana, P. and Samanta, K. and Bäcker, S. and Zellermann, E. and Knauer, S. and Schmuck, C.
    Angewandte Chemie - International Edition (2017)
    The effect of citrate-stabilized gold nanoparticles (AuNPs) on the secondary structure of an artificial β-sheet-forming cationic peptide has been studied. The AuNPs inhibited β-sheet formation and led to fragmented fibrils and spherical oligomers with assembled AuNPs on their surface. Besides this structural change, the functional properties of the peptide are also different. Whereas the peptide was unable to act as a vector for gene delivery, formation of a complex with AuNPs allowed successful gene delivery into cells. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201700713
  • 2017 • 580 Encapsulation of Bimetallic Metal Nanoparticles into Robust Zirconium-Based Metal-Organic Frameworks: Evaluation of the Catalytic Potential for Size-Selective Hydrogenation
    Rösler, C. and Dissegna, S. and Rechac, V.L. and Kauer, M. and Guo, P. and Turner, S. and Ollegott, K. and Kobayashi, H. and Yamamoto, T. and Peeters, D. and Wang, Y. and Matsumura, S. and Van Tendeloo, G. and Kitagawa, H. and Mu...
    Chemistry - A European Journal 23 3583-3594 (2017)
    The realization of metal nanoparticles (NPs) with bimetallic character and distinct composition for specific catalytic applications is an intensively studied field. Due to the synergy between metals, most bimetallic particles exhibit unique properties that are hardly provided by the individual monometallic counterparts. However, as small-sized NPs possess high surface energy, agglomeration during catalytic reactions is favored. Sufficient stabilization can be achieved by confinement of NPs in porous support materials. In this sense, metal-organic frameworks (MOFs) in particular have gained a lot of attention during the last years; however, encapsulation of bimetallic species remains challenging. Herein, the exclusive embedding of preformed core-shell PdPt and RuPt NPs into chemically robust Zr-based MOFs is presented. Microstructural characterization manifests partial retention of the core-shell systems after successful encapsulation without harming the crystallinity of the microporous support. The resulting chemically robust NP@UiO-66 materials exhibit enhanced catalytic activity towards the liquid-phase hydrogenation of nitrobenzene, competitive with commercially used Pt on activated carbon, but with superior size-selectivity for sterically varied substrates. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201603984
  • 2017 • 579 Enhancement of photocurrent in an ultra-thin perovskite solar cell by Ag nanoparticles deposited at low temperature
    Liu, Y. and Lang, F. and Dittrich, T. and Steigert, A. and Fischer, C.-H. and Köhler, T. and Plate, P. and Rappich, J. and Lux-Steiner, M.Ch. and Schmid, M.
    RSC Advances 7 1206-1214 (2017)
    Ultra-thin perovskite absorber layers have attracted increasing interest since they are suitable for application in semi-transparent perovskite and tandem solar cells. In this study, size and density controlled plasmonic silver nanoparticles are successfully incorporated into ultra-thin perovskite solar cells through a low temperature spray chemical vapor deposition method. Incorporation of Ag nanoparticles leads to a significant enhancement of 22.2% for the average short-circuit current density. This resulted in a relative improvement of 22.5% for the average power conversion efficiency. Characterization by surface photovoltage and photoluminescence provides evidence that the implemented silver nanoparticles can enhance the charge separation and the trapping of electrons into the TiO2 layer at the CH3NH3PbI3/TiO2 interface. The application of these silver nanoparticles therefore has promise to enhance the ultra-thin perovskite solar cells. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/C6RA25149H
  • 2017 • 578 Experimental and numerical study of a HMDSO-seeded premixed laminar low-pressure flame for SiO2 nanoparticle synthesis
    Feroughi, O.M. and Deng, L. and Kluge, S. and Dreier, T. and Wiggers, H. and Wlokas, I. and Schulz, C.
    Proceedings of the Combustion Institute 36 1045-1053 (2017)
    Silicon dioxide nanoparticles are generated in a lean hydrogen/oxygen flat flame doped with small amounts of hexamethyldisiloxane (HMDSO) stabilized by a water-cooled sintered bronze matrix. The burner is housed in an optically-accessible low-pressure (3kPa) chamber. Temperature fields were determined via multi-line laser-induced fluorescence (LIF) using added NO as target species. Gas-phase silicon oxide (SiO) was detected via laser-induced fluorescence (LIF) by exciting the weakly temperature-dependent rovibrational Q11(32) transition in the A-X (0,0) vibronic band system at 235.087nm. Semi-quantitative concentration profiles as a function of height-above-burner (HAB) were obtained after exploiting the measured temperature fields and correcting measured LIF intensities for the temperature-dependence of the ground-state population and collisional quenching using measured effective fluorescence lifetimes. Particle sizes were determined as a function of HAB via molecular-beam sampling with subsequent particle mass spectrometry (PMS). The experimental data were used to develop a simple kinetics model of HMDSO combustion and SiO2 particle precursor formation with subsequent nucleation and particle growth in the H2/O2 flame. The model was incorporated in a CFD simulation to account for facility effects that arise from modified flow fields and heat transfer between the flame and the reactor chamber. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.proci.2016.07.131
  • 2017 • 577 Experimental and Theoretical Understanding of Nitrogen-Doping-Induced Strong Metal-Support Interactions in Pd/TiO2 Catalysts for Nitrobenzene Hydrogenation
    Chen, P. and Khetan, A. and Yang, F. and Migunov, V. and Weide, P. and Stürmer, S.P. and Guo, P. and Kähler, K. and Xia, W. and Mayer, J. and Pitsch, H. and Simon, U. and Muhler, M.
    ACS Catalysis 7 1197-1206 (2017)
    By doping the TiO2 support with nitrogen, strong metal-support interactions (SMSI) in Pd/TiO2 catalysts can be tailored to obtain high-performance supported Pd nanoparticles (NPs) in nitrobenzene (NB) hydrogenation catalysis. According to the comparative studies by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance CO FTIR (CO-DRIFTS), N-doping induced a structural promoting effect, which is beneficial for the dispersion of Pd species on TiO2. High-angle annular dark-field scanning transmission electron microscopy study of Pd on N-doped TiO2 confirmed a predominant presence of sub-2 nm Pd NPs, which are stable under the applied hydrogenation conditions. XPS and CO-DRIFTS revealed the formation of strongly coupled Pd-N species in Pd/TiO2 with N-doped TiO2 as support. Density functional theory (DFT) calculations over model systems with Pdn (n = 1, 5, or 10) clusters deposited on TiO2(101) surface were performed to verify and supplement the experimental observations. In hydrogenation catalysis using NB as a model molecule, Pd NPs on N-doped TiO2 outperformed those on N-free TiO2 in terms of both catalytic activity and stability, which can be attributed to the presence of highly dispersed Pd NPs providing more active sites, and to the formation of Pd-N species favoring the dissociative adsorption of the reactant NB and the easier desorption of the product aniline. (Figure Presented). © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b02963
  • 2017 • 576 Experimental identification of unique angular dependent scattering behavior of nanoparticles
    Yin, G. and Song, M. and Raja, W. and Andrae, P. and Schmid, M.
    Journal of the European Optical Society 13 (2017)
    Background: Nanoparticles exhibit unique light scattering properties and are applied in many research fields. Methods: In this work, we perform angular resolved scattering measurements to study the scattering behaviour of random and periodic silver (Ag), and periodic polystyrene (PS) nanoparticles. Results: The random Ag nanoparticles, with a wide particle size distribution, are able to broadbandly scatter light into large angles. In contrast, both types of periodic nanoparticles are characterized by a strong scattering zone where scattering angles are increasing as the wavelength increases. Conclusions: Angular resolved scattering measurements enable experimentally revealing the particular scattering properties of different nanostructures. © 2017, The Author(s).
    view abstractdoi: 10.1186/s41476-017-0066-4
  • 2017 • 575 Film forming properties of silicon nanoparticles on SixNy coated substrates during excimer laser annealing
    Caninenberg, M. and Kiesler, D. and Benson, N. and Schmechel, R.
    Optics and Laser Technology 90 33-39 (2017)
    In this article we investigate the film forming properties of excimer laser annealed silicon nanoparticles on non-silicon substrates. In contrast to their film forming properties on oxide free silicon substrates, the nanoparticle thin film tends to dewet and form a porous µ-structure on the silicon nitrite covered glass model substrates considered for our investigation. This is quantified using a SEM study in conjunction with image processing software, in order to evaluate the µ-structure size and inter µ-structure distance in dependence of the laser energy density. To generalize our results, the film forming process is described using a COMSOL Multiphysics ® fluid dynamics model, which solves the Navier Stokes equation for incompressible Newtonian fluids. To account for the porous nanoparticle thin film structure in the simulation, an effective medium approach is used by applying a conservative level set one phase method to our mesh. This effort allows us to predict the Si melt film formation ranging from a porous Si µ-structure to a compact 100% density Si thin film in dependence of the substrate / thin film interaction, as well as the laser energy used for the nanoparticle processing. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.optlastec.2016.11.010
  • 2017 • 574 Fluence Threshold Behaviour on Ablation and Bubble Formation in Pulsed Laser Ablation in Liquids
    Reich, S. and Schönfeld, P. and Letzel, A. and Kohsakowski, S. and Olbinado, M. and Gökce, B. and Barcikowski, S. and Plech, A.
    ChemPhysChem 18 1084-1090 (2017)
    The ablation yield and bubble-formation process during nanosecond pulsed-laser ablation of silver in water are analysed by stroboscopic videography, time-resolved X-ray radiography and in situ UV/Vis spectroscopy. This process is studied as function of lens–target distance and laser fluence. Both the ablation yield and the bubble-cavitation process exhibit threshold behaviour as a function of fluence, which is linked to the efficiency of coupling of energy at the water/target interface. Although ablation happens below this threshold, quantitative material emission is linked to bubble formation. Above the threshold, both bubble size and ablation show linear behaviour. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cphc.201601198
  • 2017 • 573 Formation Mechanism of Laser-Synthesized Iron-Manganese Alloy Nanoparticles, Manganese Oxide Nanosheets and Nanofibers
    Zhang, D. and Ma, Z. and Spasova, M. and Yelsukova, A.E. and Lu, S. and Farle, M. and Wiedwald, U. and Gökce, B.
    Particle and Particle Systems Characterization 34 1600225 (2017)
    Laser ablation in liquids (LAL) has emerged as a versatile approach for the synthesis of alloy particles and oxide nanomaterials. However, complex chemical reactions often take place during synthesis due to inevitable atomization and ionization of the target materials and decomposition/hydrolysis of solvent/solution molecules, making it difficult to understand the particle formation mechanisms. In this paper, a possible route for the formation of FeMn alloy nanoparticles as well as MnOx nanoparticles, -sheets, and -fibers by LAL is presented. The observed structural, compositional, and morphological variations are clarified by transmission electron microscopy (TEM). The studies suggest that a reaction between Mn atoms and Fe ions followed by surface oxidation result in nonstoichiometric synthesis of Fe-rich FeMn@FeMn2O4 core-shell alloy particles. Interestingly, a phase transformation from Mn3O4 to Mn2O3 and finally to Ramsdellite γ-MnO2 is accompanied by a morphology change from nanosheets to nanofibers in gradually increasing oxidizing environments. High-resolution TEM images reveal that the particle-attachment mechanism dominates the growth of different manganese oxides. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppsc.201600225
  • 2017 • 572 High productive and continuous nanoparticle fabrication by laser ablation of a wire-target in a liquid jet
    Kohsakowski, S. and Santagata, A. and Dell'Aglio, M. and de Giacomo, A. and Barcikowski, S. and Wagener, P. and Gökce, B.
    Applied Surface Science 403 487-499 (2017)
    To scale-up pulsed laser ablation in liquids for nanoparticle synthesis, we combine two promising approaches, a wire-shaped target and a small liquid layer, in one setup. Using thin liquid layers a significant increase in nanoparticle productivity (up to 5 times) is obtained. This increase is attributed to the dynamics, shape of the cavitation bubble and the spring-board like behavior of the wires in the small liquid filament. It is found that despite the increase in productivity, the particle size is independent of the productivity-related ablation parameters such as repetition rate, liquid layer thickness and wire diameter. In addition to the cavitation bubble, further shielding effects have been related to both, the laser ablated material and the presence of generated small vapor bubbles. The obtained results show that this setup can provide a good strategy to realize a continuous and process-stable (particle size and quality) ablation process without the need of target replacement. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.01.077
  • 2017 • 571 High surface area, amorphous titania with reactive Ti3+ through a photo-assisted synthesis method for photocatalytic H2 generation
    Zywitzki, D. and Jing, H. and Tüysüz, H. and Chan, C.K.
    Journal of Materials Chemistry A 5 10957-10967 (2017)
    Amorphous titania-based photocatalysts are synthesized using a facile, UV-light mediated method and evaluated as photocatalysts for hydrogen evolution from water/methanol mixtures. The photocatalysts are prepared through the direct injection of a titanium alkoxide precursor into a water/methanol mixture, with subsequent hydrolysis, condensation, and polycondensation to form TiOx(OH)y species under UV-irradiation. The resulting amorphous titania materials exhibit an overall higher hydrogen evolution rate compared to a crystalline TiO2 reference (P25) on a molar basis of the photocatalyst due to their highly porous structure and high surface area (∼500 m2 g-1). The employed titanium alkoxide precursor did not play a major role in affecting the hydrogen evolution rate or the catalyst surface and morphology. A blue coloration, which is associated with the formation of Ti3+ species, was observed in the amorphous titania but not in P25 upon light irradiation and is enabled by the porous and disordered structure of the amorphous photocatalyst. The Ti3+ species are also used to reduce protons to H2 in the absence of light irradiation or reduce Pt2+ to form Pt nanoparticles. These Pt nanoparticles are smaller and better dispersed on the photocatalyst compared to particles prepared using conventional photodeposition, leading to higher H2 evolution rates. The results show that the direct injection method is a facile approach for the preparation of high surface area titania photocatalysts containing Ti3+ species with good photocatalytic activity for the production of H2. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7ta01614j
  • 2017 • 570 High-Performance Energy Storage and Conversion Materials Derived from a Single Metal-Organic Framework/Graphene Aerogel Composite
    Xia, W. and Qu, C. and Liang, Z. and Zhao, B. and Dai, S. and Qiu, B. and Jiao, Y. and Zhang, Q. and Huang, X. and Guo, W. and Dang, D. and Zou, R. and Xia, D. and Xu, Q. and Liu, M.
    Nano Letters 17 2788-2795 (2017)
    Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon-graphene composite electrode (denoted as C/NG-A) displayed exceptional capacitance and rate capability in a supercapacitor. Further, this method is readily applicable to creation of functional metal oxide hollow nanoparticles on the surface of other carbon materials such as graphene and carbon nanotubes, providing a good opportunity to tune their physical or chemical activities. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.6b05004
  • 2017 • 569 Imaging techniques: Nanoparticle atoms pinpointed
    Farle, M.
    Nature 542 35-36 (2017)
    The locations of atoms in a metallic alloy nanoparticle have been determined using a combination of electron microscopy and image simulation, revealing links between the particle's structure and magnetic properties.
    view abstractdoi: 10.1038/542035a
  • 2017 • 568 Improving the zT value of thermoelectrics by nanostructuring: tuning the nanoparticle morphology of Sb2Te3 by using ionic liquids
    Schaumann, J. and Loor, M. and Ünal, D. and Mudring, A. and Heimann, S. and Hagemann, U. and Schulz, S. and Maculewicz, F. and Schierning, G.
    Dalton Transactions 46 656-668 (2017)
    A systematic study on the microwave-assisted thermolysis of the single source precursor (Et2Sb)2Te (1) in different asymmetric 1-alkyl-3-methylimidazolium- and symmetric 1,3-dialkylimidazolium-based ionic liquids (ILs) reveals the distinctive role of both the anion and the cation in tuning the morphology and microstructure of the resulting Sb2Te3 nanoparticles as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). A comparison of the electrical and thermal conductivities as well as the Seebeck coefficient of the Sb2Te3 nanoparticles obtained from different ILs reveals the strong influence of the specific IL, from which C4mimI was identified as the best solvent, on the thermoelectric properties of as-prepared nanosized Sb2Te3. This work provides design guidelines for ILs, which allow the synthesis of nanostructured thermoelectrics with improved performances. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6dt04323b
  • 2017 • 567 Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating
    Surmeneva, M.A. and Sharonova, A.A. and Chernousova, S. and Prymak, O. and Loza, K. and Tkachev, M.S. and Shulepov, I.A. and Epple, M. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 156 104-113 (2017)
    A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000 nm thick), silver nanoparticles (second layer; 1.5 μg Ag cm−2) and calcium phosphate (third layer, either 150 or 1000 nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3 days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150 nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2017.05.016
  • 2017 • 566 Influence of Ni to Co ratio in mixed Co and Ni phosphides on their electrocatalytic oxygen evolution activity
    Barwe, S. and Andronescu, C. and Vasile, E. and Masa, J. and Schuhmann, W.
    Electrochemistry Communications 79 41-45 (2017)
    Prompted by the impact of Ni-based support materials on the intrinsic activity of electrocatalysts, we investigated the influence of partial Co substitution by Ni during the reductive thermal synthesis of cobalt-cobalt phosphide nanoparticles from triphenylphosphine complexes. The obtained catalysts were characterised by X-ray diffraction and electrochemistry. Increasing the amount of Ni in the precursor complexes leads to materials with lower overpotential for the OER at low current densities, and lower Tafel slopes. Co nanoparticles, which are only formed in materials with low Ni content, increase the intrinsic material conductivity and reduce the OER overpotential at high current densities. © 2017
    view abstractdoi: 10.1016/j.elecom.2017.04.014
  • 2017 • 565 Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence
    Lin, W. and Schmidt, J. and Mahler, M. and Schindler, T. and Unruh, T. and Meyer, B. and Peukert, W. and Segets, D.
    Langmuir 33 13581-13589 (2017)
    We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basis. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03079
  • 2017 • 564 Large eddy simulation of particle aggregation in turbulent jets
    Pesmazoglou, I. and Kempf, A.M. and Navarro-Martinez, S.
    Journal of Aerosol Science 111 1-17 (2017)
    Aggregation is an inter-particle process that involves a multitude of different physical and chemical mechanisms. Aggregation processes often occur within turbulent flows; for example in spray drying, soot formation, or nanoparticle formation. When the concentration of particles is very large, a direct simulation of individual particles is not possible and alternative approaches are needed. The present work follows the stochastic aggregation modelling based on a Lagrangian framework by Pesmazoglou, Kempf, and Navarro-Martinez (2016) and implements it in the Large Eddy Simulation context. The new coupled model is used to investigate particle aggregation in turbulent jets. Two cases are considered: an existent Direct Numerical Simulation of nanoparticle agglomeration in a planar jet and an experimental configuration of SiO2 nanoparticles in a round jet. The results show a good agreement in both cases, demonstrating the advantages of the Lagrangian framework to model agglomeration and it capacity to describe the full particle size distribution. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.jaerosci.2017.06.002
  • 2017 • 563 Large eddy simulations of nanoparticle synthesis from flame spray pyrolysis
    Rittler, A. and Deng, L. and Wlokas, I. and Kempf, A.M.
    Proceedings of the Combustion Institute 36 1077-1087 (2017)
    Large eddy simulations of the nanoparticle synthesis from flame spray pyrolysis are presented. A standard reactor is investigated, with ethanol/hexamethyldisiloxane (HMDSO) mixture as spray/precursor composition and oxygen as dispersion gas for the production of silica nanoparticles. Spray evaporation, ignition and stabilisation of the flame are achieved by a premixed methane/oxygen pilot flame. The gas, spray and nanoparticle phases are modelled with Eulerian, Lagrangian and Eulerian approaches, respectively. A modified tabulated chemistry model, adapted from the premixed flamelet generated manifold approach (PFGM) with artificial flame thickening (ATF) is proposed, tested and applied for the system. The control variables are the element mass fractions of hydrogen and carbon together with a joint progress variable. The population balance equation of the nanoparticles is modelled in terms of number, volume and surface area concentration, its subfilter distribution is modelled with a delta function. The combustion of HMDSO and formation of silica particle monomers is described by a two-step global mechanism. The nucleation source term is tabulated as a function of the control variables. The submodels for spray and combustion are validated separately to compensate for the shortage in detailed experimental data for nanoparticle spray flames. Subsequently, simulation results for the particles are presented and discussed, in particular the polydisperse particle size distributions resulting from turbulence. © 2016 The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2016.08.005
  • 2017 • 562 Laser Synthesis and Processing of Colloids: Fundamentals and Applications
    Zhang, D. and Gökce, B. and Barcikowski, S.
    Chemical Reviews 117 3990-4103 (2017)
    Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts. Accurate size control of LSPC-synthesized materials ranging from quantum dots to submicrometer spheres and recent upscaling advancement toward the multiple-gram scale are helpful for extending the applicability of LSPC-synthesized nanomaterials to various fields. By discussing key reports on both the fundamentals and the applications related to laser ablation, fragmentation, and melting in liquids, this Article presents a timely and critical review of this emerging topic. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemrev.6b00468
  • 2017 • 561 Laser synthesis, structure and chemical properties of colloidal nickel-molybdenum nanoparticles for the substitution of noble metals in heterogeneous catalysis
    Marzun, G. and Levish, A. and Mackert, V. and Kallio, T. and Barcikowski, S. and Wagener, P.
    Journal of Colloid and Interface Science 489 57-67 (2017)
    Platinum and iridium are rare and expensive noble metals that are used as catalysts for different sectors including in heterogeneous chemical automotive emission catalysis and electrochemical energy conversion. Nickel and its alloys are promising materials to substitute noble metals. Nickel based materials are cost-effective with good availability and show comparable catalytic performances. The nickel-molybdenum system is a very interesting alternative to platinum in water electrolysis. We produced ligand-free nickel-molybdenum nanoparticles by laser ablation in water and acetone. Our results show that segregated particles were formed in water due to the oxidation of the metals. X-ray diffraction shows a significant change in the lattice parameter due to a diffusion of molybdenum atoms into the nickel lattice with increasing activity in the electrochemical oxygen evolution reaction. Even though the solubility of molecular oxygen in acetone is higher than in water, there were no oxides and a more homogeneous metal distribution in the particles in acetone as seen by TEM-EDX. This showed that dissolved molecular oxygen does not control oxide formation. Overall, the laser ablation of pressed micro particulate mixtures in liquids offers a combinational synthesis approach that allows the screening of alloy nanoparticles for catalytic testing and can convert micro-mixtures into nano-alloys. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2016.09.014
  • 2017 • 560 Laser-induced atomic emission of silicon nanoparticles during laser-induced heating
    Menser, J. and Daun, K. and Dreier, T. and Schulz, C.
    Applied Optics 56 E50-E57 (2017)
    The temporal luminescence behavior of silicon atoms during and after laser-heating of gas-borne silicon nano-particles was investigated. Silicon nanoparticles were formed in the exhaust stream of a microwave plasma reactor at 100 mbar. The observed prompt atomic line intensities correspond with thermal excitation of the evaporated species. A prompt signal at 251.61 and 288.15 nm originating from the 3s23p2 → 3s23p4s transitions showed a lifetime of 16 ns that matches the documented excited-state lifetime for the respective transitions. A secondary delayed signal contribution with similar peak intensities was observed commencing approximately 100-300 ns after the laser pulse and persisting for hundreds of nanoseconds. This signal contribution is attributed to electron impact excitation or recombination after electron impact ionization of the silicon evaporated as a consequence of the laser heating of the plasma leading to non-thermal population of electronically excited silicon. The observations support a nanoparticle evaporation model that can be used to recover nanoparticle sizes from time-resolved LII data. © 2017 Optical Society of America.
    view abstractdoi: 10.1364/AO.56.000E50
  • 2017 • 559 Laser-induced growth of YVO4:Eu3+ nanoparticles from sequential flowing aqueous suspension
    Wang, H. and Lau, M. and Sannomiya, T. and Gökce, B. and Barcikowski, S. and Odawara, O. and Wada, H.
    RSC Advances 7 9002-9008 (2017)
    Ligand-free lanthanide ion-doped oxide nanoparticles have critical biological applications. An environmentally friendly and chemically green synthesis of YVO4:Eu3+ nanoparticles with high crystallinity is achieved using a physical method, laser irradiation from sequential flowing aqueous suspension in a free liquid reactor. The fabricated nanoparticles have an ovoid or spindle shape depending on the number of laser irradiation cycles. A transmission electron microscopy study showed that spindle-like particles are single-crystalline with high crystallinity, which is beneficial for high luminescence efficiency. Strong light emission even from a single particle was confirmed by cathodoluminescence mapping. A possible mechanism of nanoparticle formation was proposed as follows. Primary nanocrystals were produced from the plasma plume and self-assembled into ovoid-like nanoparticles via oriented attachment. After several cycles of laser irradiation, we observed spindle-like nanoparticles that were much longer than the ovoid-like particles. The spindle-like nanoparticles grew as a result of the diffusion and coalescence of the ovoid-like nanoparticles during repetitive laser irradiation. These findings provide useful information for the formation of ligand-free luminescent nanoparticles with different sizes based on YVO4. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra28118d
  • 2017 • 558 Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling
    Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
    Journal of Membrane Science 524 682-690 (2017)
    Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4 µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494 nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05 M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2016.11.023
  • 2017 • 557 Local characterization of light trapping effects of metallic and dielectric nanoparticles in ultra-thin Cu(In,Ga)Se2 solar cells via scanning near-field optical microscopy
    Song, M. and Yin, G. and Fumagalli, P. and Schmid, M.
    Proceedings of SPIE - The International Society for Optical Engineering 10114 (2017)
    Plasmonic and photonic nanoparticles have proven beneficial for solar cells in the aspect of light management. For improved exploitation of nanoparticles in solar cells, it is necessary to reveal the absorption enhancement mechanism from the nanoparticles. In this study, we investigated the nanoparticle-enhanced solar cells in near-field regime with optic and opto-electric scanning near-field optical microscopy (SNOM). The near-field distribution of regularly arranged silver and polystyrene nanoparticles produced by nanosphere lithography on Cu(In,Ga)Se2 (CIGSe) solar cells is characterized using a custom-built SNOM, which gives insight into the optical mechanism of light trapping from nanoparticles to solar cells. On the other hand, the photocurrent of CIGSe solar cells with and without nanoparticles is studied with an opto-electric SNOM by recording the photocurrent during surface scanning, further revealing the opto-electrical influences of the nanoparticles. In addition, finite element method simulations have been performed and agree with the results from SNOM. We found the dielectric polystyrene spheres are able to enhance the absorption and benefit the generation of charge carriers in the solar cells. Copyright © 2017 SPIE.
    view abstractdoi: 10.1117/12.2253223
  • 2017 • 556 Local delivery of siRNA-loaded calcium phosphate nanoparticles abates pulmonary inflammation
    Frede, A. and Neuhaus, B. and Knuschke, T. and Wadwa, M. and Kollenda, S. and Klopfleisch, R. and Hansen, W. and Buer, J. and Bruder, D. and Epple, M. and Westendorf, A.M.
    Nanomedicine: Nanotechnology, Biology, and Medicine 13 2395-2403 (2017)
    The local interference of cytokine signaling mediated by siRNA-loaded nanoparticles might be a promising new therapeutic approach to dampen inflammation during pulmonary diseases. For the local therapeutic treatment of pulmonary inflammation, we produced multi-shell nanoparticles consisting of a calcium phosphate core, coated with siRNAs directed against pro-inflammatory mediators, encapsulated into poly(lactic-co-glycolic acid), and coated with a final outer layer of polyethylenimine. Nasal instillation of nanoparticles loaded with a mixture of siRNAs directed against different cytokines to mice suffering from TH1 cell-mediated lung inflammation, or of siRNA directed against NS-1 in an influenza infection model led to a significant reduction of target gene expression which was accompanied by distinct amelioration of lung inflammation in both models. Thus, this study provides strong evidence that the specific and local modulation of the inflammatory response by CaP/PLGA nanoparticle-mediated siRNA delivery could be a promising approach for the treatment of inflammatory disorders of the lung. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.nano.2017.08.001
  • 2017 • 555 Long-term thermal stability of nanoclusters in ODS-Eurofer steel: An atom probe tomography study
    Zilnyk, K.D. and Pradeep, K.G. and Choi, P. and Sandim, H.R.Z. and Raabe, D.
    Journal of Nuclear Materials 492 142-147 (2017)
    Oxide-dispersion strengthened materials are important candidates for several high-temperature structural applications in advanced nuclear power plants. Most of the desirable mechanical properties presented by these materials are due to the dispersion of stable nanoparticles in the matrix. Samples of ODS-Eurofer steel were annealed for 4320 h (6 months) at 800 °C. The material was characterized using atom probe tomography in both conditions (prior and after heat treatment). The particles number density, size distribution, and chemical compositions were determined. No significant changes were observed between the two conditions indicating a high thermal stability of the Y-rich nanoparticles at 800 °C. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.jnucmat.2017.05.027
  • 2017 • 554 Mass spectrometric analysis of clusters and nanoparticles during the gas-phase synthesis of tungsten oxide
    Kluge, S. and Wiggers, H. and Schulz, C.
    Proceedings of the Combustion Institute 36 1037-1044 (2017)
    The combustion synthesis of nanoscale tungsten-oxide particles from tungsten hexafluoride is investigated in a low-pressure hydrogen/oxygen flat flame. The reactor is equipped with molecular-beam sampling of post-flame gases at variable height above burner (HAB). Main species of the flame, intermediate tungsten species, and tungsten-oxide clusters are studied with time-of-flight mass spectrometry (TOF-MS) as a function of HAB. Various WO x (OH) y are identified within the flame front. With increasing HAB, (WO3) n clusters with increasing cluster size appear in the burnt gases at the expense of the concentration of W1 species. Clusters with n =3-7 arise at 70mm HAB, followed by larger clusters at even larger heights. Clusters up to (WO3)38 were identified. The subsequent formation of nanoparticles is detected with particle mass spectrometry (PMS) and a quartz crystal microbalance (QCM) from 120mm HAB and the increasing particle size and mass flux have been determined. © 2016.
    view abstractdoi: 10.1016/j.proci.2016.06.165
  • 2017 • 553 Massive nanoprecipitation in an Fe-19Ni-xAl maraging steel triggered by the intrinsic heat treatment during laser metal deposition
    Kürnsteiner, P. and Wilms, M.B. and Weisheit, A. and Barriobero-Vila, P. and Jägle, E.A. and Raabe, D.
    Acta Materialia 129 52-60 (2017)
    Due to the layer-by-layer build-up of additively manufactured parts, the deposited material experiences a cyclic re-heating in the form of a sequence of temperature pulses. In the current work, this “intrinsic heat treatment (IHT)” was exploited to induce the precipitation of NiAl nanoparticles in an Fe-19Ni-xAl (at%) model maraging steel, a system known for rapid clustering. We used Laser Metal Deposition (LMD) to synthesize compositionally graded specimens. This allowed for the efficient screening of effects associated with varying Al contents ranging from 0 to 25 at% and for identifying promising concentrations for further studies. Based on the existence of the desired martensitic matrix, an upper bound for the Al concentration of 15 at% was defined. Owing to the presence of NiAl precipitates as observed by Atom Probe Tomography (APT), a lower bound of 3–5 at% Al was established. Within this concentration window, increasing the Al concentration gave rise to an increase in hardness by 225 HV due to an exceptionally high number density of 1025 NiAl precipitates per m3, as measured by APT. This work demonstrates the possibility of exploiting the IHT of the LMD process for the production of samples that are precipitation strengthened during the additive manufacturing process without need for any further heat treatment. © 2017
    view abstractdoi: 10.1016/j.actamat.2017.02.069
  • 2017 • 552 Metal–Organic Framework Derived Carbon Nanotube Grafted Cobalt/Carbon Polyhedra Grown on Nickel Foam: An Efficient 3D Electrode for Full Water Splitting
    Aijaz, A. and Masa, J. and Rösler, C. and Xia, W. and Weide, P. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    ChemElectroChem 4 188-193 (2017)
    The growth of metal–organic framework (ZIF-67) nanocrystals on nickel foam (NF), followed by carbonization in diluted H2, leads to a nitrogen-doped carbon-nanotube-grafted cobalt/carbon polyhedra film on NF. The obtained material serves as a highly active binder-free electrocatalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), enabling high-performance alkaline (0.1 m KOH) water electrolysis with potentials of 1.62 and 0.24 V, respectively, at OER and HER current densities of 10 mA cm−2. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201600452
  • 2017 • 551 Microstructure and thermoelectric properties of Si-WSi2 nanocomposites
    Stoetzel, J. and Schneider, T. and Mueller, M.M. and Kleebe, H.-J. and Wiggers, H. and Schierning, G. and Schmechel, R.
    Acta Materialia 125 321-326 (2017)
    Nanocomposites of n-doped Si/WSi2 were prepared and morphologically and thermoelectrically investigated. The composites were densified by spark-plasma-sintering of doped Si nanoparticles with WSi2 nanoinclusions. The nanoparticles were synthesized in a gas-phase process. The microstructure of the bulk nanocomposite shows an inhomogeneous distribution of the WSi2 nanoinclusions in form of WSi2-rich and -depleted regions. This inhomogeneity is not present in the starting material and is assigned to a self-organizing process during sintering. The inhomogeneities are in the micrometer range and may act as scattering centers for long-wavelength phonons. The WSi2 nanoinclusions grow during sintering from originally 3–7 nm up to 30–143 nm depending on the total W content and might act as scattering centers for the medium wavelength range of phonons. Further, the growth of Si grains is suppressed by the WSi2 inclusions, which leads to an enhanced grain boundary density. Adding 1 at% W reduces lattice thermal conductivity by almost 35% within the temperature range from 300 K to 1250 K compared to pure, nanocrystalline silicon (doped). By addition of 6 at% W a reduction of 54% in lattice thermal conductivity is achieved. Although little amounts of W slightly reduce the power factor an enhancement of the thermoelectric figure of merit of 50% at 1250 K compared to a tungsten-free reference was realized. © 2016
    view abstractdoi: 10.1016/j.actamat.2016.11.069
  • 2017 • 550 Mobility investigations of magnetic nanoparticles in biocomposites
    Müller, R. and Zhou, M. and Liebert, T. and Landers, J. and Salamon, S. and Webers, S. and Dellith, A. and Borin, D. and Heinze, T. and Wende, H.
    Materials Chemistry and Physics 193 364-370 (2017)
    Biocompatible composites are presented, consisting of magnetite nanoparticles embedded into a matrix of meltable dextran ester, which can be softened under an induced alternating magnetic field and may thereby allow magnetically controlled release applications. Temperature dependent mobility investigations of magnetic nanoparticles in the molten composites were carried out by optical microscopy, magnetometry, AC susceptibility and Mössbauer spectroscopy measurements. Optical microscopy shows a movement of agglomerates and texturing in the micrometer scale, whereas AC-susceptometry and Mössbauer spectroscopy investigations reveal that the particles perform diffusive Brownian motion in the liquid polymer melt as separated particles rather than as large agglomerates. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2017.02.046
  • 2017 • 549 MOF-Templated Assembly Approach for Fe3C Nanoparticles Encapsulated in Bamboo-Like N-Doped CNTs: Highly Efficient Oxygen Reduction under Acidic and Basic Conditions
    Aijaz, A. and Masa, J. and Rösler, C. and Antoni, H. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    Chemistry - A European Journal (2017)
    Developing high-performance non-precious metal catalysts (NPMCs) for the oxygen-reduction reaction (ORR) is of critical importance for sustainable energy conversion. We report a novel NPMC consisting of iron carbide (Fe3C) nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes (b-NCNTs), synthesized by a new metal-organic framework (MOF)-templated assembly approach. The electrocatalyst exhibits excellent ORR activity in 0.1m KOH (0.89V at -1mAcm-2) and in 0.5m H2SO4 (0.73V at -1mAcm-2) with a hydrogen peroxide yield of below 1% in both electrolytes. Due to encapsulation of the Fe3C nanoparticles inside porous b-NCNTs, the reported NPMC retains its high ORR activity after around 70hours in both alkaline and acidic media. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201701389
  • 2017 • 548 Nanoparticle atoms pinpointed
    Farle, M.
    Nature 542 35-36 (2017)
    doi: 10.1038/542035a
  • 2017 • 547 Nanoparticle-based B-cell targeting vaccines: Tailoring of humoral immune responses by functionalization with different TLR-ligands
    Zilker, C. and Kozlova, D. and Sokolova, V. and Yan, H. and Epple, M. and Überla, K. and Temchura, V.
    Nanomedicine: Nanotechnology, Biology, and Medicine 13 173-182 (2017)
    Induction of an appropriate type of humoral immune response during vaccination is essential for protection against viral and bacterial infections. We recently observed that biodegradable calcium phosphate (CaP) nanoparticles coated with proteins efficiently targeted and activated naïve antigen-specific B-cells in vitro. We now compared different administration routes for CaP-nanoparticles and demonstrated that intramuscular immunization with such CaP-nanoparticles induced stronger immune responses than immunization with monovalent antigen. Additional functionalization of the CaP-nanoparticles with TRL-ligands allowed modulating the IgG subtype response and the level of mucosal IgA antibodies. CpG-containing CaP-nanoparticles were as immunogenic as a virus-like particle vaccine. Functionalization of CaP-nanoparticles with T-helper cell epitopes or CpG also allowed overcoming lack of T-cell help. Thus, our results indicate that CaP-nanoparticle-based B-cell targeting vaccines functionalized with TLR-ligands can serve as a versatile platform for efficient induction and modulation of humoral immune responses in vivo. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.nano.2016.08.028
  • 2017 • 546 Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in the freshwater mussel Dreissena polymorpha
    Zimmermann, S. and Ruchter, N. and Loza, K. and Epple, M. and Sures, B.
    Environmental Pollution 222 251-260 (2017)
    Zebra mussels (Dreissena polymorpha) were exposed to polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP; hydrodynamic diameter 80 nm; solid diameter 50 nm) to investigate the behavior of Ag in the tank water with respect to its uptake, bioaccumulation, elimination and subcellular distribution in the mussel soft tissue. Parallel experiments were performed with ionic Ag (AgNO3) to unravel possible differences between the metal forms. The recovery of the applied Ag concentration (500 μg/L) in the tank water was clearly affected by the metal source (AgNP < AgNO3) and water type (reconstituted water < tap water). Filtration (< 0.45 μm) of water samples showed different effects on the quantified metal concentration depending on the water type and Ag form. Ag accumulation in the mussel soft tissue was neither influenced by the metal source nor by the water type. Ag concentrations in the mussel soft tissue did not decrease during 14 days of depuration. For both metal forms the Ag distribution within different subcellular fractions, i.e. metal-rich granules (MRG), cellular debris, organelles, heat-sensitive proteins (HSP) and metallothionein-like proteins (MTLP), revealed time-dependent changes which can be referred to intracellular Ag translocation processes. The results provide clear evidence for the uptake of Ag by the mussel soft tissue in nanoparticulate as well as in ionic form. Thus, zebra mussels could be used as effective accumulation indicators for environmental monitoring of both Ag forms. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.envpol.2016.12.048
  • 2017 • 545 Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane
    Zirehpour, A. and Rahimpour, A. and Ulbricht, M.
    Journal of Membrane Science 531 59-67 (2017)
    In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.02.049
  • 2017 • 544 On the bifunctional nature of Cu/ZrO2 catalysts applied in the hydrogenation of ethyl acetate
    Schittkowski, J. and Tölle, K. and Anke, S. and Stürmer, S. and Muhler, M.
    Journal of Catalysis 352 120-129 (2017)
    The catalytic hydrogenation of ethyl acetate to ethanol was studied at ambient pressure in the temperature range from 463 K to 513 K using Cu/ZrO2 catalysts obtained by co-precipitation as a function of the Cu loading. The hydrogenation was established as a reproducible probe reaction by determining optimal reaction parameters without deactivation or thermodynamic limitations. Power-law kinetics were determined yielding an apparent activation energy of 74 kJ mol−1 and reaction orders of 0.1–0.3 for H2 and −0.4 to 0.1 for ethyl acetate in the temperature range from 473 K to 503 K. Metallic Cu was found to be essential for the hydrogenation, but the catalytic activity was not proportional to the Cu surface area derived from N2O decomposition and temperature-programmed H2 desorption experiments identifying Cu/ZrO2 as bifunctional catalyst. The acidic sites of the ZrO2 matrix were probed by temperature-programmed experiments with ethyl acetate and NH3. Cu0 is assumed to provide atomic hydrogen by dissociative adsorption and spillover, but the reaction rate is more affected by the tight contact between the embedded Cu nanoparticles and the X-ray amorphous ZrO2 matrix. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2017.05.009
  • 2017 • 543 Parasitic Reactions in Nanosized Silicon Anodes for Lithium-Ion Batteries
    Gao, H. and Xiao, L. and Plümel, I. and Xu, G.-L. and Ren, Y. and Zuo, X. and Liu, Y. and Schulz, C. and Wiggers, H. and Amine, K. and Chen, Z.
    Nano Letters 17 1512-1519 (2017)
    When designing nano-Si electrodes for lithium-ion batteries, the detrimental effect of the c-Li15Si4 phase formed upon full lithiation is often a concern. In this study, Si nanoparticles with controlled particle sizes and morphology were synthesized, and parasitic reactions of the metastable c-Li15Si4 phase with the nonaqueous electrolyte was investigated. The use of smaller Si nanoparticles (∼60 nm) and the addition of fluoroethylene carbonate additive played decisive roles in the parasitic reactions such that the c-Li15Si4 phase could disappear at the end of lithiation. This suppression of c-Li15Si4 improved the cycle life of the nano-Si electrodes but with a little loss of specific capacity. In addition, the characteristic c-Li15Si4 peak in the differential capacity (dQ/dV) plots can be used as an early-stage indicator of cell capacity fade during cycling. Our findings can contribute to the design guidelines of Si electrodes and allow us to quantify another factor to the performance of the Si electrodes. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.6b04551
  • 2017 • 542 Peptide Cross-linkers: Immobilization of Platinum Nanoparticles Highly Dispersed on Graphene Oxide Nanosheets with Enhanced Photocatalytic Activities
    Mizutaru, T. and Marzun, G. and Kohsakowski, S. and Barcikowski, S. and Hong, D. and Kotani, H. and Kojima, T. and Kondo, T. and Nakamura, J. and Yamamoto, Y.
    ACS Applied Materials and Interfaces 9 9996-10002 (2017)
    For exerting potential catalytic and photocatalytic activities of metal nanoparticles (MNPs), immobilization of MNPs on a support medium in highly dispersed state is desired. In this Research Article, we demonstrated that surfactant-free platinum nanoparticles (PtNPs) were efficiently immobilized on graphene oxide (GO) nanosheets in a highly dispersed state by utilizing oligopeptide β-sheets as a cross-linker. The fluorenyl-substituted peptides were designed to form β-sheets, where metal-binding thiol groups and protonated and positively charged amino groups are integrated on the opposite sides of the surface of a β-sheet, which efficiently bridge PtNPs and GO nanosheet. In comparison to PtNP/GO composite without the peptide linker, the PtNP/peptide/GO ternary complex exhibited excellent photocatalytic dye degradation activity via electron transfer from GO to PtNP and simultaneous hole transfer from oxidized GO to the dye. Furthermore, the ternary complex showed photoinduced hydrogen evolution upon visible light irradiation using a hole scavenger. This research provides a new methodology for the development of photocatalytic materials by a bottom-up strategy on the basis of self-assembling features of biomolecules. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b16765
  • 2017 • 541 Perspective of laser-prototyping nanoparticle-polymer composites
    Zhang, D. and Gökce, B.
    Applied Surface Science 392 991-1003 (2017)
    Nanoparticle synthesis by laser ablation in liquids has attracted attention from researchers worldwide the past few years and the integration of these nanoparticles in functional materials such as nanoparticle-polymer composites, represents a natural next step. Such “nanointegration” into polymers can be achieved by the ex situ dispersion of laser-synthesized inorganic nanoparticles in polymer matrices and the in situ encapsulation/grafting of nanoparticles with polymers/monomers during synthesis. Because the nanoparticle shell and the polymer matrix may be identical, this method often does not require the use of dispersants or matrix binders and constitutes a new avenue for direct particle-polymer coupling. In this perspective review, we summarize the methodologies for in situ and ex situ laser prototyping of nanoparticle-polymer composites (LaNPC) and downstream bulk-processing techniques. The determinants of polymer-solvent-laser parametrization for aimed physical and chemical properties of the composites are discussed. By highlighting representative works related to a variety of promising applications, the advantageous features of this technique are demonstrated. Finally, the challenges and prospects of LaNPC are outlined and a perspective is given regarding how the recent research findings reviewed changed the research direction in the field. © 2016
    view abstractdoi: 10.1016/j.apsusc.2016.09.150
  • 2017 • 540 Photocatalytic and Magnetic Porous Cellulose-Based Nanocomposite Films Prepared by a Green Method
    Wittmar, A. and Fu, Q. and Ulbricht, M.
    ACS Sustainable Chemistry and Engineering 5 9858-9868 (2017)
    The present work expands our previous studies related to cellulose processing with room-temperature ionic liquids and simultaneous integration of functional nanoparticles toward photocatalytically active and easily recyclable nanocomposite porous films based on a renewable matrix material. Porosity can be tuned by the selection of phase separation conditions for the films obtained from the casting solutions of cellulose in ionic liquids or their mixture with an organic co-solvent. TiO2 nanoparticles confer to the nanocomposite photocatalytic activity, while Fe3O4 nanoparticles make it magnetically active. The photocatalytic activity of the cellulose film containing 10 mg of TiO2 was 1 order of magnitude lower than that of the same amount of pure TiO2 nanopowder, due to the reduction of the active catalytic surface which can be reached by UV irradiation after embedment in the polymer matrix. However, this fixation in a solid polymer support allows facile recovery of the catalyst after use. The rate constant when using the cellulose nanocomposite doped with TiO2 and Fe3O4 (k ≈ 0.0019 min-1) is very close to that for the corresponding composite containing only TiO2 (k ≈ 0.0017 min-1), suggesting that co-doping with Fe3O4 nanoparticles did not diminish the photocatalytic activity of the final composite, which can be easily separated from solution with a magnet. Additionally, by Fe3O4 doping, the composite material's temperature can be homogeneously increased by ∼12 K via exposure to a high-frequency alternating magnetic field (AMF) for 5 min. For an optimal thermal response to AMF, the magnetite nanoparticles have to be homogeneously dispersed within the polymer matrix. The preparation method for the casting solution has been found to play an essential role for the one-step fabrication of multifunctional cellulose-based nanocomposite materials. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acssuschemeng.7b01830
  • 2017 • 539 Probing Oxide Reduction and Phase Transformations at the Au-TiO2 Interface by Vibrational Spectroscopy
    Pougin, A. and Lüken, A. and Klinkhammer, C. and Hiltrop, D. and Kauer, M. and Tölle, K. and Havenith-Newen, M. and Morgenstern, K. and Grünert, W. and Muhler, M. and Strunk, J.
    Topics in Catalysis 60 1744-1753 (2017)
    By a combination of FT-NIR Raman spectroscopy, infrared spectroscopy of CO adsorption under ultrahigh vacuum conditions (UHV-IR) and Raman spectroscopy in the line scanning mode the formation of a reduced titania phase in a commercial Au/TiO2 catalyst and in freshly prepared Au/anatase catalysts was detected. The reduced phase, formed at the Au-TiO2 interface, can serve as nucleation point for the formation of stoichiometric rutile. TinO2n−1 Magnéli phases, structurally resembling the rutile phase, might be involved in this process. The formation of the reduced phase and the rutilization process is clearly linked to the presence of gold nanoparticles and it does not proceed under similar conditions with the pure titania sample. Phase transformations might be both thermally or light induced, however, the colloidal deposition synthesis of the Au/TiO2 catalysts is clearly ruled out as cause for the formation of the reduced phase. © 2017, The Author(s).
    view abstractdoi: 10.1007/s11244-017-0851-8
  • 2017 • 538 Process Chain for the Fabrication of Nanoparticle Polymer Composites by Laser Ablation Synthesis
    Maurer, E. and Barcikowski, S. and Gökce, B.
    Chemical Engineering and Technology 40 1535-1543 (2017)
    Nanoparticle polymer composites are of growing interest due to their unique properties. However, conventional composite synthesis methods usually require several process steps including steps for cleaning and improving the particle-matrix dispersion. As an alternative, laser ablation synthesis can be used to prepare tunable composite materials. This method enables an easy process chain, without the need of additional steps. In this status report, the process chain of laser-based pre-series fabrication of nanocomposites is visualized, and the increase of the method's technology readiness level is demonstrated. The process steps are demonstrated from the synthesis of the colloid to applicable functional products. The advantages of using laser ablation for nanocomposite synthesis are highlighted. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ceat.201600506
  • 2017 • 537 Rock Salt Ni/Co Oxides with Unusual Nanoscale-Stabilized Composition as Water Splitting Electrocatalysts
    Fominykh, K. and Tok, G.C. and Zeller, P. and Hajiyani, H. and Miller, T. and Döblinger, M. and Pentcheva, R. and Bein, T. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 27 (2017)
    The influence of nanoscale on the formation of metastable phases is an important aspect of nanostructuring that can lead to the discovery of unusual material compositions. Here, the synthesis, structural characterization, and electrochemical performance of Ni/Co mixed oxide nanocrystals in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is reported and the influence of nanoscaling on their composition and solubility range is investigated. Using a solvothermal synthesis in tert-butanol ultrasmall crystalline and highly dispersible Ni x Co1− x O nanoparticles with rock salt type structure are obtained. The mixed oxides feature non-equilibrium phases with unusual miscibility in the whole composition range, which is attributed to a stabilizing effect of the nanoscale combined with kinetic control of particle formation. Substitutional incorporation of Co and Ni atoms into the rock salt lattice has a remarkable effect on the formal potentials of NiO oxidation that shift continuously to lower values with increasing Co content. This can be related to a monotonic reduction of the work function of (001) and (111)-oriented surfaces with an increase in Co content, as obtained from density functional theory (DFT+U) calculations. Furthermore, the electrocatalytic performance of the Ni x Co1− x O nanoparticles in water splitting changes significantly. OER activity continuously increases with increasing Ni contents, while HER activity shows an opposite trend, increasing for higher Co contents. The high electrocatalytic activity and tunable performance of the nonequilibrium Ni x Co1− x O nanoparticles in HER and OER demonstrate great potential in the design of electrocatalysts for overall water splitting. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201605121
  • 2017 • 536 Role of Composition and Size of Cobalt Ferrite Nanocrystals in the Oxygen Evolution Reaction
    Chakrapani, K. and Bendt, G. and Hajiyani, H. and Schwarzrock, I. and Lunkenbein, T. and Salamon, S. and Landers, J. and Wende, H. and Schlögl, R. and Pentcheva, R. and Behrens, M. and Schulz, S.
    ChemCatChem 9 2988-2995 (2017)
    Sub-10 nm CoFe2O4 nanoparticles with different sizes and various compositions obtained by (partial) substitution of Co with Ni cations have been synthesized by using a one-pot method from organic solutions by the decomposition of metal acetylacetonates in the presence of oleylamine. The electrocatalytic activity of CoFe2O4 towards the oxygen evolution reaction (OER) is clearly enhanced with a smaller size (3.1 nm) of the CoFe2O4 nanoparticles (compared with 4.5 and 5.9 nm). In addition, the catalytic activity is improved by partial substitution of Co with Ni, which also leads to a higher degree of inversion of the spinel structure. Theoretical calculations attribute the positive catalytic effect of Ni owing to the lower binding energy differences between adsorbed O and OH compared with pure cobalt or nickel ferrites, resulting in higher OER activity. Co0.5Ni0.5Fe2O4 exhibited a low overpotential of approximately 340 mV at 10 mA cm−2, a smaller Tafel slope of 51 mV dec−1, and stability over 30 h. The unique tunability of these CoFe2O4 nanocrystals provides great potential for their application as an efficient and competitive anode material in the field of electrochemical water splitting as well as for systematic fundamental studies aiming at understanding the correlation of composition and structure with performance in electrocatalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201700376
  • 2017 • 535 SiO multi-line laser-induced fluorescence for quantitative temperature imaging in flame-synthesis of nanoparticles
    Chrystie, R.S.M. and Feroughi, O.M. and Dreier, T. and Schulz, C.
    Applied Physics B: Lasers and Optics 123 (2017)
    Silicon monoxide (SiO) is an intermediate in the gas-phase synthesis of SiO2 nanoparticles and coatings. We demonstrate a method for in situ imaging the gas-phase temperature via multi-line laser-induced fluorescence (LIF) using excitation in the A1Π–X1Σ+(0,0) band near 235 nm. A low-pressure lean (3 kPa, φ = 0.39) premixed hydrogen/oxygen flame was seeded with 210 ppm hexamethyldisiloxane (HMDSO) to produce SiO2 nanoparticles. Spectral regions with no interference from other species in the flame were located, and the excitation-spectral range that provides the best temperature sensitivity was determined from numerical experiments. Quenching rates of the selected transitions were also determined from fluorescence lifetime measurements, and found to be independent of the excited rotational state. Upon laser light-sheet excitation, images of fluorescence were recorded for a sequence of excitation wavelengths and pixel-wise multi-line fitting of the spectra yields temperature images. The results were compared against multi-line NO-LIF temperature imaging measurements using the A2Σ+–X2Π(0,0) band near 225 nm from 500 ppm NO added to the gas flow as a thermometry target. Both methods show good qualitative agreement with each other and demonstrate that temperature can be evaluated from the zone in the reactor where SiO is naturally present without adding tracers. SiO LIF exhibited high signal-to-noise ratios of the order of ten times that of NO LIF. © 2017, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00340-017-6692-0
  • 2017 • 534 Site-Specific SERS Assay for Survivin Protein Dimer: From Ensemble Experiments to Correlative Single-Particle Imaging
    Wissler, J. and Bäcker, S. and Feis, A. and Knauer, S.K. and Schlücker, S.
    Small 13 (2017)
    An assay for Survivin, a small dimeric protein which functions as modulator of apoptosis and cell division and serves as a promising diagnostic biomarker for different types of cancer, is presented. The assay is based on switching on surface-enhanced Raman scattering (SERS) upon incubation of the Survivin protein dimer with Raman reporter-labeled gold nanoparticles (AuNP). Site-specificity is achieved by complexation of nickel-chelated N-nitrilo-triacetic acid (Ni-NTA) anchors on the particle surface by multiple histidines (His6-tag) attached to each C-terminus of the centrosymmetric protein dimer. Correlative single-particle analysis using light sheet laser microscopy enables the simultaneous observation of both elastic and inelastic light scattering from the same sample volume. Thereby, the SERS-inactive AuNP-protein monomers can be directly discriminated from the SERS-active AuNP-protein dimers/oligomers. This information, i.e. the percentage of SERS-active AuNP in colloidal suspension, is not accessible from conventional SERS experiments due to ensemble averaging. The presented correlative single-particle approach paves the way for quantitative site-specific SERS assays in which site-specific protein recognition by small chemical and in particular supramolecular ligands can be tested. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201700802
  • 2017 • 533 Size- and density-controlled deposition of Ag nanoparticle films by a novel low-temperature spray chemical vapour deposition method—research into mechanism, particle growth and optical simulation
    Liu, Y. and Plate, P. and Hinrichs, V. and Köhler, T. and Song, M. and Manley, P. and Schmid, M. and Bartsch, P. and Fiechter, S. and Lux-Steiner, M.C. and Fischer, C.-H.
    Journal of Nanoparticle Research 19 (2017)
    Ag nanoparticles have attracted interest for plasmonic absorption enhancement of solar cells. For this purpose, well-defined particle sizes and densities as well as very low deposition temperatures are required. Thus, we report here a new spray chemical vapour deposition method for producing Ag NP films with independent size and density control at substrate temperatures even below 100 °C, which is much lower than for many other techniques. This method can be used on different substrates to deposit Ag NP films. It is a reproducible, low-cost process which uses trimethylphosphine (hexafluoroacetylacetonato) silver as a precursor in alcoholic solution. By systematic variation of deposition parameters and classic experiments, mechanisms of particle growth and of deposition processes as well as the low decomposition temperature of the precursor could be explained. Using the 3D finite element method, absorption spectra of selected samples were simulated, which fitted well with the measured results. Hence, further applications of such Ag NP films for generating plasmonic near field can be predicted by the simulation. © 2017, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-017-3834-6
  • 2017 • 532 Size Quenching during Laser Synthesis of Colloids Happens Already in the Vapor Phase of the Cavitation Bubble
    Letzel, A. and Gökce, B. and Wagener, P. and Ibrahimkutty, S. and Menzel, A. and Plech, A. and Barcikowski, S.
    Journal of Physical Chemistry C 121 5356-5365 (2017)
    Although nanoparticle synthesis by pulsed laser ablation in liquids (PLAL) is gaining wide applicability, the mechanism of particle formation, in particular size-quenching effects by dissolved anions, is not fully understood yet. It is well-known that the size of small primary particles (d ≤ 10 nm), secondary particles (spherical particles d > 10 nm), and agglomerates observed ex situ is effectively reduced by the addition of small amounts of monovalent electrolyte to the liquid prior to laser ablation. In this study, we focus on the particle formation and evolution inside the vapor filled cavitation bubble. This vapor phase is enriched with ions from the afore added electrolyte. By probing the cavitation bubbles' interior by means of small-angle X-ray scattering (SAXS), we are able to examine whether the size quenching reaction between nanoparticles and ions starts already during cavitation bubble confinement or if these reactions are subjected to the liquid phase. We find that particle size quenching occurs already within the first bubble oscillation (approximately 100 μs after laser impact), still inside the vapor phase. Thereby we demonstrate that nanoparticle-ion interactions during PLAL are in fact a gas phase phenomenon. These interactions include size reduction of both primary and secondary particles and a decreased abundance of the latter as shown by in situ SAXS and confirmed by ex situ particle analysis (e.g., static SAXS and TEM). (Figure Presented). © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.6b12554
  • 2017 • 531 Size-dependent reactivity of gold-copper bimetallic nanoparticles during CO2 electroreduction
    Mistry, H. and Reske, R. and Strasser, P. and Roldan Cuenya, B.
    Catalysis Today 288 30-36 (2017)
    New catalysts are needed to achieve lower overpotentials and higher faradaic efficiency for desirable products during the electroreduction of CO2. In this study, we explore the size-dependence of monodisperse gold-copper alloy nanoparticles (NPs) synthesized by inverse micelle encapsulation as catalysts for CO2 electroreduction. X-ray spectroscopy revealed that gold-copper alloys were formed and were heavily oxidized in their initial as prepared state. Current density was found to increase significantly for smaller NPs due to the increasing population of strongly binding low coordinated sites on NPs below 5nm. Product analysis showed formation of H2, CO, and CH4, with faradaic selectivity showing a minor dependence on size. The selectivity trends observed are assigned to reaction-induced segregation of gold atoms to the particle surface and altered electronic or geometric properties due to alloying. © 2016.
    view abstractdoi: 10.1016/j.cattod.2016.09.017
  • 2017 • 530 Solar biosupercapacitor
    González-Arribas, E. and Aleksejeva, O. and Bobrowski, T. and Toscano, M.D. and Gorton, L. and Schuhmann, W. and Shleev, S.
    Electrochemistry Communications 74 9-13 (2017)
    Here we report on an entirely new kind of bioelectronic device – a solar biosupercapacitor, which is built from a dual-feature photobioanode combined with a double-function enzymatic cathode. The self-charging biodevice, based on transparent nanostructured indium tin oxide electrodes modified with biological catalysts, i.e. thylakoid membranes and bilirubin oxidase, is able to capacitively store electricity produced by direct conversion of radiant energy into electric energy. When self-charged during 10 min, using ambient light only, the biosupercapacitor provided a maximum of 6 mW m− 2 at 0.20 V. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.elecom.2016.11.009
  • 2017 • 529 Spectroscopic models for laser-heated silicon and copper nanoparticles
    Daun, K. and Menser, J. and Mansmann, R. and Moghaddam, S.T. and Dreier, T. and Schulz, C.
    Journal of Quantitative Spectroscopy and Radiative Transfer 197 3-11 (2017)
    Interpreting laser-induced incandescence (LII) measurements on aerosolized nanoparticles requires a spectroscopic model that relates the measured spectral incandescence to the temperature of the nanoparticles. We present spectroscopic models for molten silicon and copper nanoparticles, which are evaluated through extinction and incandescence measurements on nanoaerosols. Measurements on molten silicon nanoparticles are consistent with the Drude theory in the Rayleigh limit of Mie theory. The copper nanoparticles were initially assumed to coalesce into spheres, but the observed spectral incandescence does not show a surface plasmon polariton (SPP) peak in the vicinity of 600. nm expected of spheres. A simulation based on the discrete dipole approximation (DDA) suggests that this effect could be explained by the structure of the copper aggregates. © 2016.
    view abstractdoi: 10.1016/j.jqsrt.2016.10.006
  • 2017 • 528 Surface-Enhanced Raman Spectroscopy and Density Functional Theory Calculations of a Rationally Designed Rhodamine with Thiol Groups at the Xanthene Ring
    Brem, S. and Schlücker, S.
    Journal of Physical Chemistry C 121 15310-15317 (2017)
    Rhodamines are widely used dyes in fluorescence and surface-enhanced Raman spectroscopy (SERS). The latter requires adsorption of the dye onto the surface of plasmonic nanostructures, a process which requires attractive molecule-surface interactions. Here, we report an experimental SERS and computational density functional theory (DFT) study investigating the role of thiol functionalization at the xanthene ring of the rhodamine in the adsorption onto gold nanoparticles. For this purpose, a new bisthiolated rhodamine derivative was rationally designed and synthesized via a PPh3/I2 reduction route. The introduction of two thiol moieties directly at the xanthene ring provides the shortest possible distance between the molecular π-system and the metal surface for maximum SERS enhancement combined with the strong Au-S interaction for chemisorption. The comparison of experimental SERS spectra obtained from gold nanostars and a film of gold nanoparticles with results from DFT calculations (molecular electrostatic potential, normal modes) suggests adsorption via the thiol groups at the xanthene moiety. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.7b01504
  • 2017 • 527 Synergistic effect of potassium hydroxide and steam co-treatment on the functionalization of carbon nanotubes applied as basic support in the Pd-catalyzed liquid-phase oxidation of ethanol
    Dong, W. and Xia, W. and Xie, K. and Peng, B. and Muhler, M.
    Carbon 121 452-462 (2017)
    Surface functionalization of carbon nanotubes (CNTs) was achieved by a thermal treatment in the presence of pre-adsorbed potassium hydroxide and steam at 350–550 °C. The generated oxygen-containing functional groups were more basic and thermally stable compared with conventional acid-generated groups. The influence of the KOH-steam co-treatment conditions on the functionalization of CNTs was systematically investigated. Residual K species were found to intercalate in the inner graphene layers of the CNTs providing additional Brønsted basicity. Owing to the favorable basic properties and high thermal stability of the generated functional groups, Pd nanoparticles supported on the co-treated CNTs were found to be strongly anchored leading to a high degree of Pd dispersion and a high resistance to sintering. The Pd nanoparticles on the co-treated CNT support produced at 450 °C and 550 °C showed the highest activity and yields of acetic acid in the aerobic oxidation of aqueous ethanol reaching almost full conversion after 5 h in the absence of additional base. In addition, the KOH-steam co-treatment was found to enhance the recyclability of the Pd/CNT catalysts. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.carbon.2017.06.019
  • 2017 • 526 The Production of Cu Nanoparticles on Large Area Graphene by Sputtering and in-Flight Sintering
    Ünlü, C.G. and Acet, M. and Tekgül, A. and Farle, M. and Atakan, Ş. and Lindner, J.
    Crystal Research and Technology 52 (2017)
    We have developed a simple method to synthesize Cu nanoparticles on graphene, which is a composite that is currently investigated for use as biosensors. Firstly, large area graphene (2 × 2 cm2) was prepared by chemical vapor deposition on Cu foils and then transferred onto SiO2 substrates by a transfer process. The Cu nanoparticles were collected on graphene/SiO2 by magnetron sputtering. The presence of graphene was verified by optical microscopy and Raman spectroscopy. The structure of graphene decorated with Cu nanoparticles was determined by scanning and transmission electron microscopy. The results show that the Cu nanoparticles acquire a cubic structure on graphene. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/crat.201700149
  • 2017 • 525 Time-resolved impact electrochemistry for quantitative measurement of single-nanoparticle reaction kinetics
    Saw, E.N. and Kratz, M. and Tschulik, K.
    Nano Research 1-10 (2017)
    Single-nanoparticle electrochemistry has been established as a tool to characterize various nanomaterials based on the charge passed during their random impact at an electrode. Here it is demonstrated that the duration and shape of the resulting current peak can be used to quantify the reaction kinetics on a single-particle basis. Both the chemical rate constant and reaction mechanism for oxidation of single nanoparticles in different electrolytes can be determined directly from the duration of the current signal recorded in high-speed, highsensitivity current measurements. Using 29-nm-sized Ag particles in four different electrolytes as a proof of concept for this general approach, hitherto inaccessible insights into single-particle reactivity are provided. While comparable rate constants were measured for the four electrolytes at low overpotentials, transport-limited impacts at high overpotentials were found to depend strongly on the type and quantity of anions present in solution. [Figure not available: see fulltext.] © 2017 Tsinghua University Press and Springer-Verlag GmbH Germany
    view abstractdoi: 10.1007/s12274-017-1578-3
  • 2017 • 524 Transparent, mediator- and membrane-free enzymatic fuel cell based on nanostructured chemically modified indium tin oxide electrodes
    González-Arribas, E. and Bobrowski, T. and Di Bari, C. and Sliozberg, K. and Ludwig, R. and Toscano, M.D. and De Lacey, A.L. and Pita, M. and Schuhmann, W. and Shleev, S.
    Biosensors and Bioelectronics 97 46-52 (2017)
    We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67 V and power output of up to 1.4 µW/cm2 at an operating voltage of 0.35 V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2017.05.040
  • 2017 • 523 Uptake of the proteins HTRA1 and HTRA2 by cells mediated by calcium phosphate nanoparticles
    Rotan, O. and Severin, K.N. and Pöpsel, S. and Peetsch, A. and Merdanovic, M. and Ehrmann, M. and Epple, M.
    Beilstein Journal of Nanotechnology 8 381-393 (2017)
    The efficient intracellular delivery of (bio)molecules into living cells remains a challenge in biomedicine. Many biomolecules and synthetic drugs are not able to cross the cell membrane, which is a problem if an intracellular mode of action is desired, for example, with a nuclear receptor. Calcium phosphate nanoparticles can serve as carriers for small and large biomolecules as well as for synthetic compounds. The nanoparticles were prepared and colloidally stabilized with either polyethyleneimine (PEI; cationic nanoparticles) or carboxymethyl cellulose (CMC; anionic nanoparticles) and loaded with defined amounts of the fluorescently labelled proteins HTRA1, HTRA2, and BSA. The nanoparticles were purified by ultracentrifugation and characterized by dynamic light scattering and scanning electron microscopy. Various cell types (HeLa, MG-63, THP-1, and hMSC) were incubated with fluorescently labelled proteins alone or with protein-loaded cationic and anionic nanoparticles. The cellular uptake was followed by light and fluorescence microscopy, confocal laser scanning microscopy (CLSM), and flow cytometry. All proteins were readily transported into the cells by cationic calcium phosphate nanoparticles. Notably, only HTRA1 was able to penetrate the cell membrane of MG-63 cells in dissolved form. However, the application of endocytosis inhibitors revealed that the uptake pathway was different for dissolved HTRA1 and HTRA1-loaded nanoparticles. © 2017 Rotan et al.
    view abstractdoi: 10.3762/bjnano.8.40
  • 2017 • 522 Upconversion Nanoparticles Synthesized by Ultrashort Pulsed Laser Ablation in Liquid: Effect of the Stabilizing Environment
    Gemini, L. and Schmitz, T. and Kling, R. and Barcikowski, S. and Gökce, B.
    ChemPhysChem 18 1210-1216 (2017)
    The distinctive feature of upconverting compounds to absorb and emit light in the near-infrared region has made upconverting nanoparticles of great interest in various application fields. Nevertheless, these colloids show a highly hydrophobic behavior, and therefore, the use of a proper stabilizing agent is necessary in most cases. Although few chemical techniques for colloid stabilization are available, it is still difficult to achieve a fully reproducible synthesis method for stable upconverting nanoparticle colloids. In this work, upconversion 18 %Yb:1 %Er:NaYF4 nanoparticles were produced by ultrafast pulsed laser ablation in a water and 2-[2-(2-methoxyethoxy)- ethoxy]acetic acid (MEEAA) environment to assess the stabilization effect of the surfactant on the nanoparticle colloid properties. The effects of the laser fluence and MEEAA concentration on the nanoparticles′ properties were investigated by TEM, EDS, and emission spectra analyses. The results show that ultrashort pulsed laser ablation in liquid allows generating highly spherical nanoparticles with conserved stoichiometry and optical properties. Moreover, it is possible to obtain colloids with significantly higher stability and preserved optical properties by one-step PLAL processes directly in the MEEAA environment. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cphc.201601266
  • 2017 • 521 Water-free synthesis of ZnO quantum dots for application as an electron injection layer in light-emitting electrochemical cells
    Daumann, S. and Andrzejewski, D. and Di Marcantonio, M. and Hagemann, U. and Wepfer, S. and Vollkommer, F. and Bacher, G. and Epple, M. and Nannen, E.
    Journal of Materials Chemistry C 5 2344-2351 (2017)
    Large-area light emitters like organic (OLEDs) or quantum dot light-emitting devices (QLEDs) and light-emitting electrochemical cells (LECs) have gained increasing interest due to their cost-effective fabrication on various even flexible substrates. The implementation of ZnO nanoparticles as an electron injection layer in large-area emitters leads to efficient solution-based devices. However, ZnO support layers are frequently in direct contact with water-sensitive emitter materials, which requires ZnO nanoparticles with minimum water content. A water-free synthesis route (except for the small amount of water formed during the synthesis) of ligand-free ZnO nanoparticles is presented. The spherical ZnO nanoparticles have a diameter of 3.4 nm, possess a high crystallinity, and form stable dispersions in ethanol or 1-hexanol. Their application together with a transition metal complex (iTMC)-LEC as an additional electron injection layer resulted in an increase of the device efficiency from 1.6 to 2.4 lm W−1 as well as the reduction of the run-up time to one fifth, compared to the same system without ZnO nanoparticles. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6tc05571k
  • 2016 • 520 A novel magnetically-separable porous iron-oxide nanocomposite as an adsorbent for methylene blue (MB) dye
    Sehlleier, Y.H. and Hardt, S. and Schulz, C. and Wiggers, H.
    Journal of Environmental Chemical Engineering 4 3779-3787 (2016)
    In this study, efficient and magnetically separable adsorbents for the removal of organic pollutants from water are developed, which are both, environmental friendly and cheap to produce. A new type of porous iron-oxide/polymer nanocomposite was synthesized by a two-step process utilizing surface modification of gas-phase synthesized iron-oxide nanoparticles and a subsequent polymerization process. The potential of iron-oxide/polymer composite adsorbents with a large surface area for the removal of organic components was studied using methylene blue (MB) as a test substance. Adsorption isotherms fitted well with the Langmuir isotherm model and the adsorption capacity of MB on this adsorbent was found to be as high as 298 mg/g which is several times higher than the adsorption capacity of a number of recently reported potential adsorbents. Owing to its magnetic properties, the polluted adsorbent can be easily separated from aqueous solutions. © 2016 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jece.2016.08.018
  • 2016 • 519 A versatile large-scale and green process for synthesizing magnetic nanoparticles with tunable magnetic hyperthermia features
    Simeonidis, K. and Liébana-Viñas, S. and Wiedwald, U. and Ma, Z. and Li, Z.-A. and Spasova, M. and Patsia, O. and Myrovali, E. and Makridis, A. and Sakellari, D. and Tsiaoussis, I. and Vourlias, G. and Farle, M. and Angelakeris, M.
    RSC Advances 6 53107-53117 (2016)
    This work proposes a large-scale synthesis methodology for engineered and functional magnetic nanoparticles (i.e. ferrites, sulfides) designed towards the principles of green and sustainable production combined with biomedical applicability. The experimental setup consists of a two-stage continuous-flow reactor in which single-crystalline nanoparticles are formed by the coprecipitation of metal salts in an aqueous environment. A series of optimized iron-based nanocrystals (Fe3O4, Fe3S4, CoFe2O4 and MnFe2O4) with diameters between 18 and 38 nm has been obtained. The samples were validated as potential magnetic hyperthermia agents by their heating efficiency as determined by specific loss power (SLP) in calorimetric experiments. In an effort to enhance colloidal stability and surface functionality, nanoparticles were coated by typical molecules of biomedical interest in a single step process. Finally, two-phase particle systems have been produced by a two-stage procedure to enhance the heating rate by the effective combination of different magnetic features. Results indicate relatively high SLP values for uncoated nanoparticles (420 W g-1 for Fe3O4) and a reduction of 20-60% in the heat dissipation rate upon covering by functional groups. Eventually, such effect was more than counterbalanced by the magnetic coupling of different phases in binary systems, since SLP was multiplied up to ∼1700 W g-1 for MnFe2O4/Fe3O4 suggesting a novel route to tune the efficiency of magnetic hyperthermia agents. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra09362k
  • 2016 • 518 Alternative Precursors for the Synthesis of Binary Sb2E3and Bi2E3(E = S, Se, Te) Nanoparticles by the Hot Injection Method
    Rusek, M. and Bendt, G. and Wölper, C. and Schulz, S.
    European Journal of Inorganic Chemistry 2016 3673-3679 (2016)
    Intramolecularly stabilized Sb(OCH2CH2NMe2)3(1) and Bi(OCH2CH2NMe2)3(2) readily react with (Me3Si)2S and (Et3Si)2E (E = Se, Te) at moderate temperatures (hot injection method) with elimination of the corresponding silyl ether and subsequent formation of the group 15 chalcogenides Sb2E3and Bi2E3, which were characterized by XRD, SEM, and energy-dispersive X-ray spectroscopy (EDX). In addition, the solid-state structure of 1 was determined by single-crystal XRD. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ejic.201600490
  • 2016 • 517 Atomic layer deposition and high-resolution electron microscopy characterization of nickel nanoparticles for catalyst applications
    Dashjav, E. and Lipińska-Chwałek, M. and Grüner, D. and Mauer, G. and Luysberg, M. and Tietz, F.
    Surface and Coatings Technology 307 428-435 (2016)
    Ni nanoparticles (diameter <  10 nm) are deposited on Si and ceramic substrates of porous lanthanum-substituted strontium titanate/yttrium-stabilized zirconia (LST/YSZ) composites by a two-step process. First, NiO films are produced by atomic layer deposition at 200 °C using bis(methylcyclopentadienyl)nickel(II) (Ni(MeCp)2) and H2O as precursors. In the second step, the NiO films are reduced in H2 atmosphere at 400–800 °C. The size of the resulting Ni nanoparticles is controlled by the temperature. The largest particles with a diameter of about 7 nm are obtained at 800 °C. NiO film and Ni nanoparticles deposited on Si substrates are characterized by high-resolution electron microscopy. It was found that the Ni(MeCp)2 precursor reacts with the substrate, leading to the formation of NiSi2 precipitates beneath the surface of the Si wafer and amorphization of the surrounding area, resulting in a 10 nm thick top layer of the Si wafer. After reductive annealing, NiSi2 precipitates are preserved but Si recrystallizes and the amorphous NiO film transforms into crystalline Ni nanoparticles well distributed on the wafer surface. Process parameters were optimized for Si substrates and transfer of the process to ceramic LST/YSZ substrates is possible in principle. However, a much higher number of ALD cycles (1200 compared to 100 for Si) are necessary to obtain Ni nanoparticles of similar size and the number density of particles is lower than observed for Si substrates. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.08.074
  • 2016 • 516 Barium sulfate micro- and nanoparticles as bioinert reference material in particle toxicology
    Loza, K. and Föhring, I. and Bünger, J. and Westphal, G.A. and Köller, M. and Epple, M. and Sengstock, C.
    Nanotoxicology 10 1492-1502 (2016)
    The inhalation of particles and their exposure to the bronchi and alveoli constitute a major public health risk. Chemical as well as particle-related properties are important factors for the biological response but are difficult to separate from each other. Barium sulfate is a completely inert chemical compound, therefore it is ideally suited to separate these two factors. The biological response of rat alveolar macrophages (NR8383) was analyzed after exposure to barium sulfate particles with three different diameters (40 nm, 270 nm, and 1.3 μm, respectively) for 24 h in vitro (particle concentrations from 12.5 to 200 μg mL− 1). The particles were colloidally stabilized as well as fluorescently-labeled by carboxymethylcellulose, conjugated with 6-aminofluorescein. All kinds of barium sulfate particles were efficiently taken up by NR8383 cells and found inside endo-lysosomes, but never in the cell nucleus. Neither an inflammatory nor a cytotoxic response was detected by the ability of dHL-60 and NR8383 cells to migrate towards a chemotactic gradient (conditioned media of NR8383 cells) and by the release of inflammatory mediators (CCL2, TNF-α, IL-6). The particles neither caused apoptosis (up to 200 μg mL− 1) nor necrosis (up to 100 μg mL− 1). As only adverse reaction, necrosis was found at a concentration of 200 μg mL− 1 of the largest barium sulfate particles (1.3 μm). Barium sulfate particles are ideally suited as bioinert control to study size-dependent effects such as uptake mechanisms of intracellular distributions of pure particles, especially in nanotoxicology. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/17435390.2016.1235740
  • 2016 • 515 Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study
    Jendrzej, S. and Gökce, B. and Amendola, V. and Barcikowski, S.
    Journal of Colloid and Interface Science 463 299-307 (2016)
    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50 days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1. day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. © 2015.
    view abstractdoi: 10.1016/j.jcis.2015.10.032
  • 2016 • 514 Characterization of the oleic acid/iron oxide nanoparticle interface by magnetic resonance
    Masur, S. and Zingsem, B. and Marzi, T. and Meckenstock, R. and Farle, M.
    Journal of Magnetism and Magnetic Materials 415 8-12 (2016)
    The synthesis of colloidal nanoparticles involves surfactant molecules, which bind to the particle surface and stabilize nanoparticles against aggregation. In many cases these protecting shells also can be used for further functionalization. In this study, we investigated monodisperse single crystalline iron oxide core/shell nanoparticles (FexOy-NPs) in situ covered with an oleic acid layer which showed two electron spin resonance (ESR) signals. The nanoparticles with the ligands attached were characterized by transmission electron microscopy (TEM) and ferro- and paramagnetic resonance (FMR, EPR). Infrared spectroscopy confirmed the presence of the functional groups and revealed that the oleic acid (OA) is chemisorbed as a carboxylate on the iron oxide and is coordinated symmetrically to the oxide atoms. We show that the EPR signal of the OA ligand molecule can be used as a local probe to determine the temperature changes at the surface of the nanoparticle. © 2016 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2016.03.045
  • 2016 • 513 Characterizing the Effect of Multivalent Conjugates Composed of Aβ-Specific Ligands and Metal Nanoparticles on Neurotoxic Fibrillar Aggregation
    Streich, C. and Akkari, L. and Decker, C. and Bormann, J. and Rehbock, C. and Müller-Schiffmann, A. and Niemeyer, F.C. and Nagel-Steger, L. and Willbold, D. and Saccà, B. and Korth, C. and Schrader, T. and Barcikowski, S.
    ACS Nano 10 7582-7597 (2016)
    Therapeutically active small molecules represent promising nonimmunogenic alternatives to antibodies for specifically targeting disease-relevant receptors. However, a potential drawback compared to antibody-antigen interactions may be the lower affinity of small molecules toward receptors. Here, we overcome this low-affinity problem by coating the surface of nanoparticles (NPs) with multiple ligands. Specifically, we explored the use of gold and platinum nanoparticles to increase the binding affinity of Aβ-specific small molecules to inhibit Aβ peptide aggregation into fibrils in vitro. The interactions of bare NPs, free ligands, and NP-bound ligands with Aβ are comprehensively studied via physicochemical methods (spectroscopy, microscopy, immunologic tests) and cell assays. Reduction of thioflavin T fluorescence, as an indicator for β-sheet content, and inhibition of cellular Aβ excretion are even more effective with NP-bound ligands than with the free ligands. The results from this study may have implications in the development of therapeutics for treating Alzheimer's disease. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.6b02627
  • 2016 • 512 Co@Co3O4 Encapsulated in Carbon Nanotube-Grafted Nitrogen-Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode
    Aijaz, A. and Masa, J. and Rösler, C. and Xia, W. and Weide, P. and Botz, A.J.R. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    Angewandte Chemie - International Edition 55 4087-4091 (2016)
    Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal-air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core-shell Co@Co3O4 nanoparticles embedded in CNT-grafted N-doped carbon-polyhedra obtained by the pyrolysis of cobalt metal-organic framework (ZIF-67) in a reductive H2 atmosphere and subsequent controlled oxidative calcination. The catalysts afford 0.85 V reversible overvoltage in 0.1 m KOH, surpassing Pt/C, IrO2, and RuO2 and thus ranking them among one of the best non-precious-metal electrocatalysts for reversible oxygen electrodes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201509382
  • 2016 • 511 Co3O4 Nanoparticles Supported on Mesoporous Carbon for Selective Transfer Hydrogenation of α,β-Unsaturated Aldehydes
    Wang, G.-H. and Deng, X. and Gu, D. and Chen, K. and Tüysüz, H. and Spliethoff, B. and Bongard, H.-J. and Weidenthaler, C. and Schmidt, W. and Schüth, F.
    Angewandte Chemie - International Edition 55 11101-11105 (2016)
    A simple and scalable method for synthesizing Co3O4nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3O4nanoparticles (ca. 3 nm) supported on MC (Co3O4/MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3O4/MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3O4/MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201604673
  • 2016 • 510 Colonic gene silencing using siRNA-loaded calcium phosphate/PLGA nanoparticles ameliorates intestinal inflammation in vivo
    Frede, A. and Neuhaus, B. and Klopfleisch, R. and Walker, C. and Buer, J. and Müller, W. and Epple, M. and Westendorf, A.M.
    Journal of Controlled Release 222 86-96 (2016)
    Cytokines and chemokines are predominant players in the progression of inflammatory bowel diseases. While systemic neutralization of these players with antibodies works well in some patients, serious contraindications and side effects have been reported. Therefore, the local interference of cytokine signaling mediated by siRNA-loaded nanoparticles might be a promising new therapeutic approach. In this study, we produced multi-shell nanoparticles consisting of a calcium phosphate (CaP) core coated with siRNA directed against pro-inflammatory mediators, encapsulated into poly(d,l-lactide-co-glycolide acid) (PLGA), and coated with a final outer layer of polyethyleneimine (PEI), for the local therapeutic treatment of colonic inflammation. In cell culture, siRNA-loaded CaP/PLGA nanoparticles exhibited a rapid cellular uptake, almost no toxicity, and an excellent in vitro gene silencing efficiency. Importantly, intrarectal application of these nanoparticles loaded with siRNA directed against TNF-α, KC or IP-10 to mice suffering from dextran sulfate sodium (DSS)-induced colonic inflammation led to a significant decrease of the target genes in colonic biopsies and mesenteric lymph nodes which was accompanied with a distinct amelioration of intestinal inflammation. Thus, this study provides evidence that the specific and local modulation of the inflammatory response by CaP/PLGA nanoparticle-mediated siRNA delivery could be a promising approach for the treatment of intestinal inflammation. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jconrel.2015.12.021
  • 2016 • 509 Combination of nanoparticle-based therapeutic vaccination and transient ablation of regulatory T cells enhances anti-viral immunity during chronic retroviral infection
    Knuschke, T. and Rotan, O. and Bayer, W. and Sokolova, V. and Hansen, W. and Sparwasser, T. and Dittmer, U. and Epple, M. and Buer, J. and Westendorf, A.M.
    Retrovirology 13 (2016)
    Background: Regulatory T cells (Tregs) have been shown to limit anti-viral immunity during chronic retroviral infection and to restrict vaccine-induced T cell responses. The objective of the study was to assess whether a combinational therapy of nanoparticle-based therapeutic vaccination and concomitant transient ablation of Tregs augments anti-viral immunity and improves virus control in chronically retrovirus-infected mice. Therefore, chronically Friend retrovirus (FV)-infected mice were immunized with calcium phosphate (CaP) nanoparticles functionalized with TLR9 ligand CpG and CD8+ or CD4+ T cell epitope peptides (GagL85-93 or Env gp70123-141) of FV. In addition, Tregs were ablated during the immunization process. Reactivation of CD4+ and CD8+ effector T cells was analysed and the viral loads were determined. Results: Therapeutic vaccination of chronically FV-infected mice with functionalized CaP nanoparticles transiently reactivated cytotoxic CD8+ T cells and significantly reduced the viral loads. Transient ablation of Tregs during nanoparticle-based therapeutic vaccination strongly enhanced anti-viral immunity and further decreased viral burden. Conclusion: Our data illustrate a crucial role for CD4+ Foxp3+ Tregs in the suppression of anti-viral T cell responses during therapeutic vaccination against chronic retroviral infection. Thus, the combination of transient Treg ablation and therapeutic nanoparticle-based vaccination confers robust and sustained anti-viral immunity. © 2016 Knuschke et al.
    view abstractdoi: 10.1186/s12977-016-0258-9
  • 2016 • 508 Concentrating light in Cu(In,Ga)Se2 solar cells
    Schmid, M. and Yin, G. and Song, M. and Duan, S. and Heidmann, B. and Sancho-Martinez, D. and Kämmer, S. and Köhler, T. and Manley, P. and Lux-Steiner, M.C.
    Proceedings of SPIE - The International Society for Optical Engineering 9937 (2016)
    Light concentration has proven beneficial for solar cells, most notably for highly efficient but expensive absorber materials using high concentrations and large scale optics. Here we investigate light concentration for cost efficient thinfilm solar cells which show nano-or microtextured absorbers. Our absorber material of choice is Cu(In,Ga)Se2 (CIGSe) which has a proven stabilized record efficiency of 22.6% and which-despite being a polycrystalline thin-film material-is very tolerant to environmental influences. Taking a nanoscale approach, we concentrate light in the CIGSe absorber layer by integrating photonic nanostructures made from dielectric materials. The dielectric nanostructures give rise to resonant modes and field localization in their vicinity. Thus when inserted inside or adjacent to the absorber layer, absorption and efficiency enhancement are observed. In contrast to this internal absorption enhancement, external enhancement is exploited in the microscale approach: mm-sized lenses can be used to concentrate light onto CIGSe solar cells with lateral dimensions reduced down to the micrometer range. These micro solar cells come with the benefit of improved heat dissipation compared to the large scale concentrators and promise compact high efficiency devices. Both approaches of light concentration allow for reduction in material consumption by restricting the absorber dimension either vertically (ultra-thin absorbers for dielectric nanostructures) or horizontally (micro absorbers for concentrating lenses) and have significant potential for efficiency enhancement. © 2016 SPIE.
    view abstractdoi: 10.1117/12.2238056
  • 2016 • 507 Conjugation of thiol-terminated molecules to ultrasmall 2 nm-gold nanoparticles leads to remarkably complex 1H-NMR spectra
    Schuetze, B. and Mayer, C. and Loza, K. and Gocyla, M. and Heggen, M. and Epple, M.
    Journal of Materials Chemistry B 4 2179-2189 (2016)
    Gold nanoparticles, functionalized by aliphatic and aromatic mercapto-functionalized carboxylic acids and by two small peptides (CG and CGGRGD), respectively, were synthesized by the reduction of HAuCl4 with NaBH4 in the presence of the above ligands. After purification by centrifugation or filtration and redispersion, the dispersed nanoparticles were analysed by differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and a variety of NMR spectroscopic techniques: 1H-NMR, 1H,1H-COSY and 1H-DOSY. The hydrodynamic diameter of the particles was between 1.8 and 4.4 nm, as determined by DOSY, in good agreement with the DCS and HRTEM results. Diffusion ordered spectroscopy (DOSY) turned out to be a valuable and non-destructive tool to determine the hydrodynamic diameter of dispersed nanoparticles and to control the purity of the final particles. The coordination of the organic molecules to the gold nanoparticles resulted in distinct and complex changes in the 1H-NMR spectra. These were only partially explainable but clearly caused by the vicinity of the molecules to the gold nanoparticle. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5tb02443a
  • 2016 • 506 Continuous multigram nanoparticle synthesis by high-power, high-repetition-rate ultrafast laser ablation in liquids
    Streubel, R. and Barcikowski, S. and Gökce, B.
    Optics Letters 41 1486-1489 (2016)
    Utilizing a novel laser system consisting of a 500 W, 10 MHz, 3 ps laser source which is fully synchronized with a polygon scanner reaching scanning speeds up to 500 m/s, we explore the possibilities to increase the productivity of nanoparticle synthesis by laser ablation in liquids. By exploiting the high scanning speed, laser-induced cavitation bubbles are spatially bypassed at high repetition rates and continuous multigram ablation rates up to 4 g/h are demonstrated for platinum, gold, silver, aluminum, copper, and titanium. Furthermore, the applicable, ablation-effective repetition rate is increased by two orders ofmagnitude.The ultrafast ablation mechanisms are investigated for different laser fluences, repetition rates, interpulse distances, and ablation times, while the resulting trends are successfully described by validating a model developed for ultrafast laser ablation in air to hold in liquids as well. © 2016 Optical Society of America.
    view abstractdoi: 10.1364/OL.41.001486
  • 2016 • 505 Controlling the Photocorrosion of Zinc Sulfide Nanoparticles in Water by Doping with Chloride and Cobalt Ions
    Weide, P. and Schulz, K. and Kaluza, S. and Rohe, M. and Beranek, R. and Muhler, M.
    Langmuir 32 12641-12649 (2016)
    Photodegradation under UV light irradiation is a major drawback in photocatalytic applications of sulfide semiconductors. ZnS nanoparticles were doped with very low amounts of chloride or cobalt ions in the ppm range and codoped with chloride and cobalt ions during their synthesis by precipitation in aqueous solution followed by calcination. The high-temperature wurtzite phase annealed at 800 °C had a high susceptibility to UV irradiation in water, while the low-temperature zincblende phase annealed at 400 °C was found to be stable. Chlorine doping increased the rate of photocorrosion in water, whereas cobalt doping led to a stabilization of the ZnS nanoparticles. Based on photochemical and spectroscopic investigations applying UV/vis, X-ray photoelectron, and photoluminescence spectroscopy, the increased susceptibility of Cl-doped ZnS is ascribed to a higher number of surface point defects, whereas the stabilization by Co2+ is caused by additional recombination pathways for the charge carriers in the bulk, thus avoiding photocorrosion processes at the surface. Additional doping of Cl-doped ZnS with cobalt ions was found to counteract the detrimental effect of the chloride ions efficiently. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.6b03385
  • 2016 • 504 Controlling the shape of Janus nanostructures through supramolecular modification of ABC terpolymer bulk morphologies
    Hiekkataipale, P. and Löbling, T.I. and Poutanen, M. and Priimagi, A. and Abetz, V. and Ikkala, O. and Gröschel, A.H.
    Polymer (United Kingdom) 107 456-465 (2016)
    Block copolymers microphase separate into a variety of bulk morphologies that serve as scaffolds, templates, masks and source for polymeric nano-particles. While supramolecular additives are common to complex within diblock copolymers to modify the morphology, the subtle effects of complexation on ABC triblock terpolymer morphologies are less explored. Here, we describe the manipulation of polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or S4VT) triblock terpolymer bulk morphologies through supramolecular complexation with rod-like 4-(4-pentylphenylazo)phenol (5PAP). The 5PAP molecule hydrogen bonds by phenolic groups to the 4VP repeating units and with increasing molar fraction of 5PAP, initially observed P4VP cylinders flatten into elliptic cylinders until a morphological transition occurs into a third (P4VP/5PAP) lamella. At sufficient 5PAP loadings, the cylinders can even merge into a perforated P4VP lamella located at the PS/PT interface. Quaternization of the P4VP phase and re-dispersion in organic solvent allows liberating S4VT Janus nanostructures from the bulk, including Janus cylinders, nanoporous Janus membranes and Janus sheets. The manipulation of “sandwiched” microphases through supramolecular binding motifs could allow the preparation of previously inaccessible terpolymer bulk morphologies and, in case of cross-linkable phases, lead to a larger library of Janus nano-objects. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.polymer.2016.05.076
  • 2016 • 503 Cr2O3 Nanoparticles on Ba5Ta4O15 as a Noble-Metal-Free Oxygen Evolution Co-Catalyst for Photocatalytic Overall Water Splitting
    Soldat, J. and Busser, G.W. and Muhler, M. and Wark, M.
    ChemCatChem 8 153-156 (2016)
    The (1 1 1)-layered perovskite material Ba5Ta4O15 represents a suitable photoabsorber with remarkable photocatalytic activity in overall water splitting. We are the first to demonstrate overall water splitting without the presence of a noble-metal-based co-catalyst over this catalyst. The photocatalytic activity of Ba5Ta4O15 was investigated by overall water splitting after reductive photodeposition of amorphous Cr2O3. The formation of Cr2O3 nanoparticles for water splitting was evidenced by X-ray photoelectron spectroscopy and transmission electron microscopy. The reductive photodeposition of very low amounts of Cr2O3 on Ba5Ta4O15 induces stable rates in overall water splitting up to 465 μmol h-1 H2 and 228 μmol h-1 O2. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201500977
  • 2016 • 502 Deagglomeration testing of airborne nanoparticle agglomerates: Stability analysis under varied aerodynamic shear and relative humidity conditions
    Ding, Y. and Stahlmecke, B. and Kaminski, H. and Jiang, Y. and Kuhlbusch, T.A.J. and Riediker, M.
    Aerosol Science and Technology 50 1253-1263 (2016)
    Occupational exposure to nanomaterial aerosols poses potential health risks to workers at nanotechnology workplaces. Understanding the mechanical stability of airborne nanoparticle agglomerates under varied mechanical forces and environmental conditions is important for estimating their emission potential and the released particle size distributions, which in consequence alters their transport and human uptake probability. In this study, two aerosolization and deagglomeration systems were used to investigate the potential for deagglomeration of nanopowder aerosols with different surface hydrophilicity under a range of shear forces and relative humidity conditions. Critical orifices were employed to subject airborne agglomerates to the shear forces induced by a pressure drop. Increasing applied pressure drop was found to be associated with decreased mean particle size and increased particle number concentrations. Rising humidity decreased the deagglomeration tendency as expressed by larger modal particle sizes and lower number concentrations compared to dry conditions. Hydrophilic aerosols exhibited higher sensitivities to changes in humidity than hydrophobic particles. However, the test systems themselves also differed in generated particle number concentrations and size distributions, which in turn altered the responses of created aerosols to humidity changes. The results of the present study clearly demonstrate that (a) humidity control is essential for dustiness and deagglomeration testing, (b) that (industrial) deagglomeration, for example, for preparation of aerosol suspensions, can be manipulated by subjecting airborne particles to external energies, and (c) that the humidity of workplace air may be relevant when assessing occupational exposure to nanomaterial aerosols. Copyright © 2016 American Association for Aerosol Research © 2016 American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2016.1216072
  • 2016 • 501 Detection of individual nanoparticle impacts using etched carbon nanoelectrodes
    Clausmeyer, J. and Wilde, P. and Löffler, T. and Ventosa, E. and Tschulik, K. and Schuhmann, W.
    Electrochemistry Communications 73 67-70 (2016)
    A rapid and reliable nanofabrication route produces electrodes with beneficial properties for electrochemistry based on stochastic nanoparticle collision events. Carbon nanoelectrodes are etched to expose conical carbon tips which present an increased surface area for the detection of nanoparticle impacts. The tuneable electrode size as well as the conical geometry allow to increase the observed particle impact frequency while maintaining low background noise. Moreover, anodic particle coulometry for the sizing of silver nanoparticles shows that the detected impacts are representative of the polydisperse particle population. © 2016
    view abstractdoi: 10.1016/j.elecom.2016.11.003
  • 2016 • 500 Effect of pH on the spontaneous synthesis of palladium nanoparticles on reduced graphene oxide
    Zhang, X. and Ooki, W. and Kosaka, Y.R. and Okonogi, A. and Marzun, G. and Wagener, P. and Barcikowski, S. and Kondo, T. and Nakamura, J.
    Applied Surface Science 389 911-915 (2016)
    Palladium (Pd) nanoparticles were spontaneously deposited on reduced graphene oxide (rGO) without any external reducing agents. The prepared Pd/rGO composites were then characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Spontaneous deposition occurred because of a redox reaction between the Pd precursor and rGO, which involved reduction of bivalent Pd to metallic Pd0 and oxidation of the sp2 carbon of rGO to oxygen-containing functional groups. The amount of Pd deposited on rGO varied with pH, and this was attributed to electrostatic interactions between the Pd precursor and rGO based on the results of zeta potential measurements. The importance of the redox reaction in the spontaneous deposition was demonstrated in the experiment with Zn, Ni, Cu, Ag, Pt, Pd, and Au. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2016.08.014
  • 2016 • 499 Efficient synthesis of polyoxazoline-silica hybrid nanoparticles by using the "grafting-onto" approach
    Bissadi, G. and Weberskirch, R.
    Polymer Chemistry 7 1271-1280 (2016)
    Well-defined silica poly(2-methyl-2-oxazoline) nanoparticles were prepared via the "grafting to" method employing either click chemistry or silane coupling using different reaction conditions. In the first approach, alkyne-functionalized poly(2-methyl-2-oxazoline), P1, was prepared by ring opening cationic polymerization and clicked on azide-functionalized silica nanoparticles (SNPs), which led to the fabrication of hybrid nanoparticles. In the second approach, trimethoxysilane-functionalized poly(2-methyl-2-oxazoline), P2, was prepared similar to P1 and grafted on the surface of SNPs using coupling reactions between trimethoxysilane and hydroxyl groups of the silica nanoparticle. Hybrid particles were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and elemental analysis (EA). The grafting density ranged from 0.183 chains per nm2 for the click chemistry approach up to 0.45 chains per nm2 when using trimethoxysilane-functionalized P2 in acetonitrile at 80 °C. The water-in-oil microemulsion approach resulted still in a relatively high grafting density of 0.353 chains per nm2 and has the advantage of a one-step process and mild reaction conditions. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5py01775k
  • 2016 • 498 Electrophoretic deposition of ligand-free platinum nanoparticles on neural electrodes affects their impedance in vitro and in vivo with no negative effect on reactive gliosis
    Angelov, S.D. and Koenen, S. and Jakobi, J. and Heissler, H.E. and Alam, M. and Schwabe, K. and Barcikowski, S. and Krauss, J.K.
    Journal of Nanobiotechnology 14 (2016)
    Background: Electrodes for neural stimulation and recording are used for the treatment of neurological disorders. Their features critically depend on impedance and interaction with brain tissue. The effect of surface modification on electrode impedance was examined in vitro and in vivo after intracranial implantation in rats. Electrodes coated by electrophoretic deposition with platinum nanoparticles (NP; <10 and 50 nm) as well as uncoated references were implanted into the rat's subthalamic nucleus. After postoperative recovery, rats were electrostimulated for 3 weeks. Impedance was measured before implantation, after recovery and then weekly during stimulation. Finally, local field potential was recorded and tissue-to-implant reaction was immunohistochemically studied. Results: Coating with NP significantly increased electrode's impedance in vitro. Postoperatively, the impedance of all electrodes was temporarily further increased. This effect was lowest for the electrodes coated with particles <10 nm, which also showed the most stable impedance dynamics during stimulation for 3 weeks and the lowest total power of local field potential during neuronal activity recording. Histological analysis revealed that NP-coating did not affect glial reactions or neural cell-count. Conclusions: Coating with NP <10 nm may improve electrode's impedance stability without affecting biocompatibility. Increased impedance after NP-coating may improve neural recording due to better signal-to-noise ratio. © 2016 Angelov et al.
    view abstractdoi: 10.1186/s12951-015-0154-9
  • 2016 • 497 Exploring the mineral-water interface: Reduction and reaction kinetics of single hematite (α-Fe2O3) nanoparticles
    Shimizu, K. and Tschulik, K. and Compton, R.G.
    Chemical Science 7 1408-1414 (2016)
    In spite of their natural and technological importance, the intrinsic electrochemical properties of hematite (α-Fe2O3) nanoparticles are not well understood. In particular, particle agglomeration, the presence of surface impurities, and/or inadequate proton concentrations are major obstacles to uncover the fundamental redox activities of minerals in solution. These are particularly problematic when samples are characterized in common electrochemical analyses such as cyclic voltammetry in which nanoparticles are immobilized on a stationary electrode. In this work, the intrinsic reaction kinetics and thermodynamics of individual hematite nanoparticles are investigated by particle impact chronoamperometry. The particle radius derived from the integrated area of spikes recorded in a chronoamperogram is in excellent agreement with electron microscopy results, indicating that the method provides a quantitative analysis of the reduction of the nanoparticles to the ferrous ion. A key finding is that the suspended individual nanoparticles undergo electrochemical reduction at potentials much more positive than those immobilized on a stationary electrode. The critical importance of the solid/water interface on nanoparticle activity is further illustrated by a kinetic model. It is found that the first electron transfer process is the rate determining step of the reductive dissolution of hematite nanoparticles, while the overall process is strongly affected by the interfacial proton concentration. This article highlights the effects of the interfacial proton and ferrous ion concentrations on the reductive dissolution of hematite nanoparticles and provides a highly effective method that can be readily applied to study a wide range of other mineral nanoparticles. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5sc03678j
  • 2016 • 496 Formation of polyoxazoline-silica nanoparticles: Via the surface-initiated cationic polymerization of 2-methyl-2-oxazoline
    Bissadi, G. and Weberskirch, R.
    Polymer Chemistry 7 5157-5168 (2016)
    Well-defined polyoxazoline-silica hybrid nanoparticles were prepared by coating silica nanoparticles (SNPs) with poly(2-methyl-2-oxazoline) using a surface-initiated cationic ring-opening polymerization process. First, reverse microemulsion was used to synthesize monodisperse SNPs followed by immobilizing (chloromethyl)phenylethyl)trimethoxysilane on the surface of the nanoparticles acting as an initiator. The grafting density of the polymeric shell was controlled by varying the polymerization time, PSNPs-A, and the monomer/initiator ratio concentration, PSNPs-B. Hybrid nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The molecular weight and polydispersity indices of the polymer chains were determined by size exclusion chromatography (SEC) after etching the silica core. The hybrid nanoparticles were further functionalized with fluorescein isothiocyanate (FITC) and folic acid (FA) as a fluorescence imaging molecule and a cancer-targeting ligand, respectively. Moreover, hybrid nanoparticles with Rubpy as a fluorophore encapsulated in the silica core and the poly(2-methyl-2-oxazoline) shell were prepared. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6py01034b
  • 2016 • 495 Formation of Well-Defined Polymer Particles in the Sub-100 nm Size Range by Using Amphiphilic Block Copolymer Surfactants and a Microemulsion Approach
    Kampmann, A.-L. and Luksin, M. and Pretzer, I. and Weberskirch, R.
    Macromolecular Chemistry and Physics 217 1704-1711 (2016)
    Here, the formation of nanoparticles based on a microemulsion approach and the use of polymer surfactants are described. Therefore, two amphiphilic poly(2-oxazoline) block copolymers P1 and P2 with alkyne groups in their hydrophobic block have been synthesized by ring-opening, cationic polymerization. The polymers P1 and P2 are employed in a microemulsion process to stabilize the particle core by core cross-linking of 1,6-hexanediol diacrylate (HDDA) using either AIBN as azo-initiator or 2-propanethiol as a photo-initiator for the polymerization reaction. The results show that particle size can be controlled by sonication time, the hydrophilic–hydrophobic balance of the polymer surfactant, and the ratio of polymer surfactant versus HDDA giving access to water-soluble nanoparticles in a size range of 10–70 nm. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/macp.201600108
  • 2016 • 494 Gas-phase synthesis of Fe-Bi metastable and dumbbell particles
    Ünlü, C.G. and Li, Z.-A. and Acet, M. and Farle, M.
    Crystal Research and Technology 51 333-336 (2016)
    Fe-Bi nanoparticles were prepared in the gas-phase by DC magnetron sputtering and in-fight annealing. The morphological, structural and compositional properties were investigated by High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and scanning transmission electron microscopy. High-resolution microscopy studies show that primary particles produced without in-flight annealing are spherical with a diameter of about 50 nm. Particles sintered at 773 K acquire a dumbbell structure with Fe-FeO and Bi sections. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/crat.201500329
  • 2016 • 493 Gold on Different Manganese Oxides: Ultra-Low-Temperature CO Oxidation over Colloidal Gold Supported on Bulk-MnO2 Nanomaterials
    Gu, D. and Tseng, J.-C. and Weidenthaler, C. and Bongard, H.-J. and Spliethoff, B. and Schmidt, W. and Soulimani, F. and Weckhuysen, B.M. and Schüth, F.
    Journal of the American Chemical Society 138 9572-9580 (2016)
    Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nanosized gold particles (2-3 nm) were supported on α-MnO2 nanowires and mesoporous β-MnO2 nanowire arrays. The materials were extremely active at very low temperature (-80 °C) and also highly stable at 25 °C (70 h) under normal conditions for CO oxidation. The specific reaction rate of 2.8 molCO·h-1·gAu -1 at a temperature as low as -85 °C is almost 30 times higher than that of the most active Au/Mn2O3 catalyst. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/jacs.6b04251
  • 2016 • 492 High temperature stability study of carbon supported high surface area catalysts—Expanding the boundaries of ex-situ diagnostics
    Polymeros, G. and Baldizzone, C. and Geiger, S. and Grote, J.P. and Knossalla, J. and Mezzavilla, S. and Keeley, G.P. and Cherevko, S. and Zeradjanin, A.R. and Schüth, F. and Mayrhofer, K.J.J.
    Electrochimica Acta 211 744-753 (2016)
    The performance of proton-exchange membrane fuel cells (PEMFCs) is defined by the equally important parameters of the intrinsic activity and stability of the electrocatalysts. This work focuses on the stability of carbon supported high surface area oxygen reduction reaction catalysts at potentials and temperatures similar to the operating conditions of PEMFCs. The catalysts used for this investigation consist of Pt nanoparticles of the same particle size supported on two types of carbon support having different textural properties, i.e., Vulcan and Hollow Graphitic Spheres (HGS). A broad toolbox of characterization techniques is utilized at 60 °C in order to resolve the contribution of the different degradation mechanisms, namely nanoparticle coalescence, metal dissolution and the corrosion of carbon support, to the total active surface area loss. The results obtained by investigating the impact of temperature, potential treatment and catalyst layer morphology on the aging behavior lead to a deeper understanding of the aging mechanisms and their interrelation at application-relevant conditions. Moreover, the previously reported improved performance of the Pt/HGS catalyst is confirmed also under higher temperatures. The experimental approach introduced in this work, highlights new challenges for high-temperature degradation investigations with supported PEMFC catalyst. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2016.06.105
  • 2016 • 491 High-Temperature Stable Ni Nanoparticles for the Dry Reforming of Methane
    Mette, K. and Kühl, S. and Tarasov, A. and Willinger, M.G. and Kröhnert, J. and Wrabetz, S. and Trunschke, A. and Scherzer, M. and Girgsdies, F. and Düdder, H. and Kähler, K. and Ortega, K.F. and Muhler, M. and Schlögl, R. an...
    ACS Catalysis 6 7238-7248 (2016)
    Dry reforming of methane (DRM) has been studied for many years as an attractive option to produce synthesis gas. However, catalyst deactivation by coking over nonprecious-metal catalysts still remains unresolved. Here, we study the influence of structural and compositional properties of nickel catalysts on the catalytic performance and coking propensity in the DRM. A series of bulk catalysts with different Ni contents was synthesized by calcination of hydrotalcite-like precursors NixMg0.67-xAl0.33(OH)2(CO3)0.17·mH2O prepared by constant-pH coprecipitation. The obtained Ni/MgAl oxide catalysts contain Ni nanoparticles with diameters between 7 and 20 nm. High-resolution transmission electron microscopy (HR-TEM) revealed a nickel aluminate overgrowth on the Ni particles, which could be confirmed by Fourier transform infrared (FTIR) spectroscopy. In particular, catalysts with low Ni contents (5 mol %) exhibit predominantly oxidic surfaces dominated by Ni2+ and additionally some isolated Ni0 sites. These properties, which are determined by the overgrowth, effectively diminish the formation of coke during the DRM, while the activity is preserved. A large (TEM) and dynamic (microcalorimetry) metallic Ni surface at high Ni contents (50 mol %) causes significant coke formation during the DRM. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b01683
  • 2016 • 490 High-yield and scalable synthesis of a Silicon/Aminosilane-functionalized Carbon NanoTubes/Carbon (Si/A-CNT/C) composite as a high-capacity anode for lithium-ion batteries
    Sehlleier, Y.H. and Dobrowolny, S. and Plümel, I. and Xiao, L. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Applied Electrochemistry 46 229-239 (2016)
    In this study, we present a novel anode architecture for high-performance lithium-ion batteries based on a Silicon/3-aminosilane-functionalized CNT/Carbon (Si/A-CNT/C) composite. A high-yield, low-cost approach has been developed to stabilize and support silicon as an active anode material. Silicon (Si) nanoparticles synthesized in a hot-wall reactor and aminosilane-functionalized carbon nanotubes (A-CNT) were dispersed in styrene and divinylbenzene (DVB) and subsequently polymerized forming a porous Si/A-CNT/C composite. Transmission electron microscopy showed that this method enables the interconnection and a uniform encapsulation of Si nanoparticles within a porous carbon matrix especially using aminosilane-functionalized CNT (A-CNT). Electrochemical characterization shows that this material can deliver a delithiation capacity of 2293 mAh g−1 with a capacity retention of more than 90 % after 200 cycles at lithiation and delithiation rate of 0.5 C. We conclude that the porous Si/A-CNT/C composite material can accommodate sufficient space for Si volume expansion and extraction and improve the electronic and ionic conduction. Excellent electrochemical performance during repeated cycling can thus be achieved. © 2015, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s10800-015-0897-x
  • 2016 • 489 Hollow Zn/Co Zeolitic Imidazolate Framework (ZIF) and Yolk-Shell Metal@Zn/Co ZIF Nanostructures
    Rösler, C. and Aijaz, A. and Turner, S. and Filippousi, M. and Shahabi, A. and Xia, W. and Van Tendeloo, G. and Muhler, M. and Fischer, R.A.
    Chemistry - A European Journal 22 3304-3311 (2016)
    Metal-organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well-defined hollow Zn/Co-based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn-MOF (ZIF-8) on preformed Co-MOF (ZIF-67) nanocrystals that involve in situ self-sacrifice/excavation of the Co-MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co-ZIF shells to generate yolk-shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co-ZIF with dominance of the Zn-MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201503619
  • 2016 • 488 Improved photoelectrochemical performance of electrodeposited metal-doped BiVO4 on Pt-nanoparticle modified FTO surfaces
    Gutkowski, R. and Peeters, D. and Schuhmann, W.
    Journal of Materials Chemistry A 4 7875-7882 (2016)
    The recombination of photogenerated electron-hole pairs is one of the main limiting factors of photoelectrocatalysts absorbing in the visible part of the solar spectrum. Especially for BiVO4 the slow electron transport to the back contact facilitates charge recombination. Hence, thin layers have to be used to obtain higher photocurrents which are concomitantly only allow low absorption of the incident light. To address this limitation we have modified FTO substrates with Pt-nanoparticles before electrodepositing BiVO4. The Pt-nanoparticles decrease the overpotential for the electrodeposition of BiVO4, but more importantly they provide the basis for decreased charge recombination. Electrodeposited Mo-doped BiVO4 on Pt-nanoparticle modified FTO exhibits a substantially decreased recombination of photogenerated charge carriers during frontside illumination. Simultaneous co-doping of BiVO4 with two different metals leads to a substantial enhancement of the incident-photon-to-current efficiency (IPCE) during light driven oxygen evolution reaction. Highest IPCE (&gt;30% at 1.2 V vs. RHE) values were obtained for Mo/Zn- and Mo/B-doped BiVO4. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ta01340f
  • 2016 • 487 In Situ Investigations of Laser-Generated Ligand-Free Platinum Nanoparticles by X-ray Absorption Spectroscopy: How Does the Immediate Environment Influence the Particle Surface?
    Fischer, M. and Hormes, J. and Marzun, G. and Wagener, P. and Hagemann, U. and Barcikowski, S.
    Langmuir 32 8793-8802 (2016)
    Pulsed laser ablation in liquid (PLAL) has proven its usefulness as a nanoparticle (NP) synthesis method alternative to traditional chemical reduction methods, where the absence of any molecular ligands or residual reactants makes laser-generated nanoparticles ideal reference materials for charge-transfer experiments. We synthesized additive-free platinum nanoparticles by PLAL and in-situ characterized their interaction with H2O, sodium phosphate buffer, and sodium citrate as well as a TiO2 support by X-ray absorption fine structure (XAFS), i.e., X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Differences in the white-line intensity among the colloidal particles in the three liquids indicate that the respective NP-solvent interaction varies in strength. The ions added ex situ diffuse through the particles' electric double layer and interact electrostatically with the Stern plane. Consequently, these ions weaken the interaction of the functional OH groups that are bound to the partially oxidized platinum surfaces and cause their partial reduction. Comparing XAFS spectra of laser-generated Pt NPs in citrate with wet-chemically synthesized ones (both ligand-covered) indicates different types of Pt-O bonds: a Pt(IV)O2 type in the case of wet-chemical NPs and a Pt(II)O type in the case of laser-generated NPs. A comparison of unsupported laser-generated platinum NPs in H2O with TiO2-supported ones shows no white-line intensity differences and also an identical number of Pt-O bonds in both cases. This suggests that in the deposition process at least part of the double-layer coating stays intact and that the ligand-free Pt particle properties are preserved in the TiO2-supported Pt particles, relevant for heterogeneous catalysis. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.6b00685
  • 2016 • 486 Influence of agglomeration and specific lung lining lipid/protein interaction on short-term inhalation toxicity
    Wohlleben, W. and Driessen, M.D. and Raesch, S. and Schaefer, U.F. and Schulze, C. and Vacano, B.V. and Vennemann, A. and Wiemann, M. and Ruge, C.A. and Platsch, H. and Mues, S. and Ossig, R. and Tomm, J.M. and Schnekenburger, J. ...
    Nanotoxicology 10 970-980 (2016)
    Abstract: Lung lining fluid is the first biological barrier nanoparticles (NPs) encounter during inhalation. As previous inhalation studies revealed considerable differences between surface functionalized NPs with respect to deposition and toxicity, our aim was to investigate the influence of lipid and/or protein binding on these processes. Thus, we analyzed a set of surface functionalized NPs including different SiO2 and ZrO2 in pure phospholipids, CuroSurfTM and purified native porcine pulmonary surfactant (nS). Lipid binding was surprisingly low for pure phospholipids and only few NPs attracted a minimal lipid corona. Additional presence of hydrophobic surfactant protein (SP) B in CuroSurfTM promoted lipid binding to NPs functionalized with Amino or PEG residues. The presence of the hydrophilic SP A in nS facilitated lipid binding to all NPs. In line with this the degree of lipid and protein affinities for different surface functionalized SiO2 NPs in nS followed the same order (SiO2 Phosphate ∼ unmodified SiO2 < SiO2 PEG < SiO2 Amino NPs). Agglomeration and biomolecule interaction of NPs in nS was mainly influenced by surface charge and hydrophobicity. Toxicological differences as observed in short-term inhalation studies (STIS) were mainly influenced by the core composition and/or surface reactivity of NPs. However, agglomeration in lipid media and lipid/protein affinity appeared to play a modulatory role on short-term inhalation toxicity. For instance, lipophilic NPs like ZrO2, which are interacting with nS to a higher extent, exhibited a far higher lung burden than their hydrophilic counterparts, which deserves further attention to predict or model effects of respirable NPs. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.3109/17435390.2016.1155671
  • 2016 • 485 Influence of the liquid on femtosecond laser ablation of iron
    Kanitz, A. and Hoppius, J.S. and Gurevich, E.L. and Ostendorf, A.
    Physics Procedia 83 114-122 (2016)
    Ultrashort pulse laser ablation has become a very important industrial method for highly precise material removal ranging from sensitive thin film processing to drilling and cutting of metals. Over the last decade, a new method to produce pure nanoparticles emerged from this technique: Pulsed Laser Ablation in Liquids (PLAL). By this method, the ablation of material by a laser beam is used to generate a metal vapor within the liquid in order to obtain nanoparticles from its recondensation process. It is well known that the liquid significantly alters the ablation properties of the substrate, in our case iron. For example, the ablation rate and crater morphology differ depending on the used liquid. We present our studies on the efficiency and quality of ablated grooves in water, methanol, acetone, ethanol and toluene. The produced grooves are investigated by means of white-light interferometry, EDX and SEM. © 2016 The Authors.
    view abstractdoi: 10.1016/j.phpro.2016.08.022
  • 2016 • 484 Kinetics of chemotaxis, cytokine, and chemokine release of NR8383 macrophages after exposure to inflammatory and inert granular insoluble particles
    Schremmer, I. and Brik, A. and Weber, D.G. and Rosenkranz, N. and Rostek, A. and Loza, K. and Brüning, T. and Johnen, G. and Epple, M. and Bünger, J. and Westphal, G.A.
    Toxicology Letters 263 68-75 (2016)
    Accumulation of macrophages and neutrophil granulocytes in the lung are key events in the inflammatory response to inhaled particles. The present study aims at the time course of chemotaxis in vitro in response to the challenge of various biopersistent particles and its functional relation to the transcription of inflammatory mediators. NR8383 rat alveolar macrophages were challenged with particles of coarse quartz, barium sulfate, and nanosized silica for one, four, and 16 h and with coarse and nanosized titanium dioxide particles (rutile and anatase) for 16 h only. The cell supernatants were used to investigate the chemotaxis of unexposed NR8383 macrophages. The transcription of inflammatory mediators in cells exposed to quartz, silica, and barium sulfate was analyzed by quantitative real-time PCR. Challenge with quartz, silica, and rutile particles induced significant chemotaxis of unexposed NR8383 macrophages. Chemotaxis caused by quartz and silica was accompanied by an elevated transcription of CCL3, CCL4, CXCL1, CXCL3, and TNFα. Quartz exposure showed an earlier onset of both effects compared to the nanosized silica. The strength of this response roughly paralleled the cytotoxic effects. Barium sulfate and anatase did not induce chemotaxis and barium sulfate as well caused no elevated transcription. In conclusion, NR8383 macrophages respond to the challenge with inflammatory particles with the release of chemotactic compounds that act on unexposed macrophages. The kinetics of the response differs between the various particles. © 2016 Elsevier Ireland Ltd
    view abstractdoi: 10.1016/j.toxlet.2016.08.014
  • 2016 • 483 Laser-based diagnostics in the gas-phase synthesis of inorganic nanoparticles
    Dreier, T. and Schulz, C.
    Powder Technology 287 226-238 (2016)
    As gas-phase methods for the synthesis of tailored nanomaterials become increasingly sophisticated, the need for in situ diagnostics of reaction conditions and particle properties grows correspondingly. Laser-based methods provide a wide range of capabilities which are reviewed in this article. © 2015.
    view abstractdoi: 10.1016/j.powtec.2015.10.015
  • 2016 • 482 Laser-based in situ embedding of metal nanoparticles into bioextruded alginate hydrogel tubes enhances human endothelial cell adhesion
    Blaeser, A. and Million, N. and Campos, D.F.D. and Gamrad, L. and Köpf, M. and Rehbock, C. and Nachev, M. and Sures, B. and Barcikowski, S. and Fischer, H.
    Nano Research 9 3407-3427 (2016)
    Alginate is a widely used hydrogel in tissue engineering owing to its simple and non-cytotoxic gelation process, ease of use, and abundance. However, unlike hydrogels derived from mammalian sources such as collagen, alginate does not contain cell adhesion ligands. Here, we present a novel laser ablation technique for the in situ embedding of gold and iron nanoparticles into hydrogels. We hypothesized that integration of metal nanoparticles in alginate could serve as an alternative material because of its chemical biofunctionalization ability (coupling of RGD ligands) to favor cell adhesion. Cytocompatibility and biofunctionality of the gels were assessed by cell culture experiments using fibroblasts and endothelial cells. Nanoparticles with an average particle size of 3 nm (gold) and 6 nm (iron) were generated and stably maintained in alginate for up to 6 months. Using an extrusion system, several centimeter-long alginate tubes with an outer diameter of approximately 3 mm and a wall thickness of approximately 150 μm were manufactured. Confocal microscopy revealed homogeneously distributed nanoparticle agglomerates over the entire tube volume. Endothelial cells seeded on iron-loaded gels showed significantly higher viability and an increased degree of spreading, and the number of attached cells was also elevated in comparison to the control and gold-loaded alginates. We conclude that laser-based in situ integration of iron nanoparticles (&le; 0.01 wt.%) in alginate is a straightforward method to generate composite materials that favor the adhesion of endothelial cells. In addition, we show that nanoparticle integration does not impair the alginate’s gelation and 3D biofabrication properties. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s12274-016-1218-3
  • 2016 • 481 Laser-induced incandescence from laser-heated silicon nanoparticles
    Menser, J. and Daun, K. and Dreier, T. and Schulz, C.
    Applied Physics B: Lasers and Optics 122 (2016)
    This work describes the application of temporally and spectrally resolved laser-induced incandescence to silicon nanoparticles synthesized in a microwave plasma reactor. Optical properties for bulk silicon presented in the literature were extended for nanostructured particles analyzed in this paper. Uncertainties of parameters in the evaporation submodel, as well as measurement noise, are incorporated into the inference process by Bayesian statistics. The inferred nanoparticle sizes agree with results from transmission electron microscopy, and the determined accommodation coefficient matches the values of the preceding study. © 2016, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00340-016-6551-4
  • 2016 • 480 Laser-synthesized ligand-free Au nanoparticles for contrast agent applications in computed tomography and magnetic resonance imaging
    Simão, T. and Chevallier, P. and Lagueux, J. and Côté, M.-F. and Rehbock, C. and Barcikowski, S. and Fortin, M.-A. and Guay, D.
    Journal of Materials Chemistry B 4 6413-6427 (2016)
    In recent years, pulsed laser ablation in liquids (PLAL) has emerged as a new green chemistry method to produce different types of nanoparticles (NPs). It does not require the use of reducing or stabilizing agents, therefore enabling the synthesis of NPs with highly-pure surfaces. In this study, pure Au NPs were produced by PLAL in aqueous solutions, sterically stabilized using minimal PEG excess, and functionalized with manganese chelates to produce a dual CT/MRI contrast agent. The small hydrodynamic size (36.5 nm), low polydispersity (0.2) and colloidal stability of Au NPs@PEG-Mn2+ were demonstrated by DLS. The particles were further characterized by TEM, XPS, FTIR and 1H NMR to confirm the purity of the Au surfaces (i.e. free from the common residual chemicals found after NP synthesis) and the presence of the different surface molecules. The potential of these particles as contrast agents for CT/MRI was assessed in vivo (e.g. chicken embryo). Au NPs@PEG-Mn2+ also demonstrated strong blood retention for at least 90 minutes following intravenous injection in mouse models. The promising performance of PEGylated PLAL-synthesized Au NPs containing manganese chelates could open new possibilities for the production of purer dual imaging contrast agents based on Au colloids. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6tb01162d
  • 2016 • 479 Magnetic Mesoporous Photonic Cellulose Films
    Giese, M. and Blusch, L.K. and Schlesinger, M. and Meseck, G.R. and Hamad, W.Y. and Arjmand, M. and Sundararaj, U. and MacLachlan, M.J.
    Langmuir 32 9329-9334 (2016)
    Novel hybrid materials of cellulose and magnetic nanoparticles (NPs) were synthesized and characterized. The materials combine the chiral nematic structural features of mesoporous photonic cellulose (MPC) with the magnetic properties of cobalt ferrite (CoFe2O4). The photonic, magnetic, and dielectric properties of the hybrid materials were investigated during the dynamic swelling and deswelling of the MPC films. It was observed that the dielectric properties of the generated MPC films increased tremendously following swelling in water, endorsing efficient swelling ability of the generated mesoporous films. The high magnetic permeability of the developed MPC films in conjunction with their superior dielectric properties, predominantly in the swollen state, makes them interesting for electromagnetic interference shielding applications. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.6b02974
  • 2016 • 478 Magnetoresponsive Poly(ether sulfone)-Based Iron Oxide cum Hydrogel Mixed Matrix Composite Membranes for Switchable Molecular Sieving
    Lin, X. and Nguyen Quoc, B. and Ulbricht, M.
    ACS Applied Materials and Interfaces 8 29001-29014 (2016)
    Stimuli-responsive membranes that can adjust mass transfer and interfacial properties "on demand" have drawn large interest over the last few decades. Here, we designed and prepared a novel magnetoresponsive separation membrane with remote switchable molecular sieving effect by simple one-step and scalable nonsolvent induced phase separation (NIPS) process. Specifically, poly(ether sulfone) (PES) as matrix for an anisotropic membrane, prefabricated poly(N-isopropylacrylamide) (PNIPAAm) nanogel (NG) particles as functional gates, and iron oxide magnetic nanoparticles (MNP) as localized heaters were combined in a synergistic way. Before membrane casting, the properties of the building blocks, including swelling property and size distribution for NG, and magnetic property and heating efficiency for MNP, were investigated. Further, to identify optimal film casting conditions for membrane preparation by NIPS, in-depth rheological study of the effects of composition and temperature on blend dope solutions was performed. At last, a composite membrane with 10% MNP and 10% NG blended in a porous PES matrix was obtained, which showed a large, reversible, and stable magneto-responsivity. It had 9 times higher water permeability at the "on" state of alternating magnetic field (AMF) than at the "off"-state. Moreover, the molecular weight cutoff of such membrane could be reversibly shifted from ∼70 to 1750 kDa by switching off or on the external AMF, as demonstrated in dextran ultrafiltration tests. Overall, it has been proved that the molecular sieving performance of the novel mixed matrix composite membrane can be controlled by the swollen/shrunken state of PNIPAAm NG embedded in the nanoporous barrier layer of a PES-based anisotropic porous matrix, via the heat generation of nearby MNP. And the structure of such membrane can be tailored by the NIPS process conditions. Such membrane has potential as enabling material for remote-controlled drug release systems or devices for tunable fractionations of biomacromolecule/-particle mixtures. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b09369
  • 2016 • 477 Membrane-based purification of proteins from nanoparticle dispersions: Influences of membrane type and ultrafiltration conditions
    Alele, N. and Ulbricht, M.
    Separation and Purification Technology 158 171-182 (2016)
    The combination of nanoparticles with proteins to form functional hybrid systems is receiving undiminished attention because of its many biotechnological and medical applications. The separation of these hybrid materials from unbound free biomolecules has posed difficult challenges to fractionation and purification. Here, a model study has been carried out by removing proteins (bovine serum albumin (BSA) or lysozyme (LYS)) from the dispersion mixtures with silica nanoparticles (nominal size 20 nm) using ultrafiltration (UF) membranes. Regenerated cellulose (RC) and polyethersulfone (PES) membranes with nominal molecular weight cut-off (NMWCO) of 100 kDa, and a PES UF membrane (NMWCO 300 kDa) functionalized with UV-grafted amphoteric polymer hydrogel layer consisting of N-[3-(dimethylamino)propyl]-acrylamide (DMAPAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and having an experimentally determined cut-off of 180 kDa (identical with the experimental data for PES 100 kDa) were studied. Membrane properties and filtration conditions, in particular pH value and flux, were selected or adapted based on data for single component feeds to achieve maximum protein transmission, complete silica retention and, hence, maximum silica/protein selectivity. Batch dead-end and continuous diafiltration processes were used for fractionation and purification. Overall, the performance of PES UF membranes was inferior compared to the other membranes because of too strong fouling. With membrane RC 100, the transmission data of LYS and BSA from the mixture with silica were 80% and 30%, respectively. With the hydrogel-functionalized PES membrane, the respective transmissions from the mixture were ∼35% and ∼15% for LYS and BSA, respectively. In both cases, quantitative rejection of silica could be achieved. Using continuous diafiltration, membrane RC 100 had better purification efficiency, removing a total of 91% of LYS using 6 diavolumes (DV) in 2.4 h and 84% of BSA using 10 DV in 5.5 h. With the hydrogel-functionalized PES membrane, 82% of LYS and 74% of BSA were removed using 6 and 10 DV within larger time, i.e. 4.0 and 6.8 h, respectively. Importantly, the retained silica nanoparticles remained stable in the dispersion, without any indication of aggregation. Overall, this study will add valuable knowledge to the most efficient use of ultrafiltration sieving properties for the removal or purification of proteins from systems comprising other colloidal particles having a size which is larger by a factor of only 3-10. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2015.11.031
  • 2016 • 476 Metal-semiconductor pair nanoparticles by a physical route based on bipolar mixing
    Kala, S. and Theissmann, R. and Rouenhoff, M. and Kruis, F.E.
    Nanotechnology 27 (2016)
    In this report a methodology is described and demonstrated for preparing Au-Ge pair nanoparticles with known compositions by extending and modifying the basic steps normally used to synthesize nanoparticles in carrier gas. For the formation of pair nanoparticles by bipolar mixing, two oppositely charged aerosols of nanoparticles having the desired size are produced with the help of two differential mobility analyzers. Then both are allowed to pass through a tube, which provides sufficient residence time to result in nanoparticle pair formation due to Brownian collisions influenced by Coulomb forces. The effect of residence time on the formation of nanoparticle pairs as well as the influence of diffusion and discharging is described. Subsequently, necessary modifications to the experimental setup are demonstrated systematically. The kinetics of nanoparticles pair formation in a carrier gas is also calculated and compared with measurements made with the help of an online aerosol size analysis technique. This synthesis of nanoparticle pairs can be seen as a possible route towards Janus-type nanoparticles. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/12/125604
  • 2016 • 475 Nanoelectrodes: Applications in electrocatalysis, single-cell analysis and high-resolution electrochemical imaging
    Clausmeyer, J. and Schuhmann, W.
    TrAC - Trends in Analytical Chemistry 79 46-59 (2016)
    High sensitivity and high spatial resolution in localized electrochemical measurements are the key advantages of electroanalysis using nanometer-sized electrodes. Due to recent progress in nanoelectrode fabrication and electrochemical instrument development, nanoelectrochemical methods are becoming more widespread. We summarize different protocols for the fabrication of needle-type nanoelectrodes and discuss their properties with regard to various applications. We discuss the limits of conventional theory to describe electrochemistry at the nanoscale and point out technical aspects for characterization and handling of nanometric electrodes. Different applications are highlighted: i) Nanoelectrodes are powerful tools for non-ensemble studies of electrocatalysis at single nanoparticles at high mass transport rates. ii) Electrochemical nanosensors are employed for highly localized non-invasive analysis of single living cells and intracellular detection of neurotransmitters and metabolites. iii) Used in scanning electrochemical probe techniques, nanoprobes afford topographical and truly chemical imaging of samples with high spatial resolution. © 2016 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.trac.2016.01.018
  • 2016 • 474 Nanoparticles as transfection agents: A comprehensive study with ten different cell lines
    Neuhaus, B. and Tosun, B. and Rotan, O. and Frede, A. and Westendorf, A.M. and Epple, M.
    RSC Advances 6 18102-18112 (2016)
    The performance of transfection agents to deliver nucleic acids into cells strongly depends on the cell type. In a comprehensive study, nine different cell lines and primary human mesenchymal stem cells were transfected with DNA encoding for enhanced green fluorescent protein (eGFP). As transfection agents, two kinds of cationic multi-shell calcium phosphate nanoparticles and the commercially available transfection agent Lipofectamine were used. The transfection efficiency was measured by fluorescence microscopy by counting the percentage of green fluorescent cells which expressed eGFP as well as qPCR. Furthermore, the uptake of fluorescent calcium phosphate nanoparticles was measured by fluorescence microscopy. The cell viability was measured by the MTT test after incubation with nanoparticles and Lipofectamine. All cell types took up nanoparticles (with different efficiency), but the expression of eGFP was strongly different, demonstrating that the uptake not necessarily leads to processing of a gene. A clear correlation was found between the transfection efficiency and the cell viability that was independent on the transfection agent: a high transfection efficiency was clearly correlated with a low cell viability and vice versa. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5ra25333k
  • 2016 • 473 Nanoparticles for light management in ultrathin chalcopyrite solar cells
    Schmid, M. and Manley, P. and Ott, A. and Song, M. and Yin, G.
    Journal of Materials Research 31 3273-3289 (2016)
    We evaluate the potential of inserting metallic, metal-dielectric core-shell, and fully dielectric nanoparticles in ultrathin chalcopyrite solar cells to enhance absorption which experiences a significant drop for absorber thicknesses below 500 nm. For different integration positions at the front or at the rear of the solar cell structure theoretical expectations and potential benefits originating from light scattering, near-field enhancement and coupling into waveguide modes by the nanoparticles are presented. These benefits are always balanced against experimental challenges arising for particular geometries due to the very specific fabrication processes of chalcopyrite solar cells. In particular high absorber deposition temperatures as well as contact layers that are relatively thick compared to other devices need to be considered. Based on this, we will need to go beyond some geometries that have proven beneficial for other types of solar cells and identify the most promising configurations for chalcopyrite-based devices. © 2016 Materials Research Society.
    view abstractdoi: 10.1557/jmr.2016.382
  • 2016 • 472 Nitrogen-Doped Ordered Mesoporous Carbon Supported Bimetallic PtCo Nanoparticles for Upgrading of Biophenolics
    Wang, G.-H. and Cao, Z. and Gu, D. and Pfänder, N. and Swertz, A.-C. and Spliethoff, B. and Bongard, H.-J. and Weidenthaler, C. and Schmidt, W. and Rinaldi, R. and Schüth, F.
    Angewandte Chemie - International Edition 55 8850-8855 (2016)
    Hydrodeoxygenation (HDO) is an attractive route for the upgrading of bio-oils produced from lignocellulose. Current catalysts require harsh conditions to effect HDO, decreasing the process efficiency in terms of energy and carbon balance. Herein we report a novel and facile method for synthesizing bimetallic PtCo nanoparticle catalysts (ca. 1.5 nm) highly dispersed in the framework of nitrogen-doped ordered mesoporous carbon (NOMC) for this reaction. We demonstrate that NOMC with either 2D hexagonal (p6m) or 3D cubic (Im3m) structure can be easily synthesized by simply adjusting the polymerization temperature. We also demonstrate that PtCo/NOMC (metal loading: Pt 9.90 wt %; Co 3.31 wt %) is a highly effective catalyst for HDO of phenolic compounds and “real-world” biomass-derived phenolic streams. In the presence of PtCo/NOMC, full deoxygenation of phenolic compounds and a biomass-derived phenolic stream is achieved under conditions of low severity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201511558
  • 2016 • 471 Novel back-reflector architecture with nanoparticle based buried light-scattering microstructures for improved solar cell performance
    Desta, D. and Ram, S.K. and Rizzoli, R. and Bellettato, M. and Summonte, C. and Jeppesen, B.R. and Jensen, P.B. and Tsao, Y.-C. and Wiggers, H. and Pereira, R.N. and Balling, P. and Larsen, A.N.
    Nanoscale 8 12035-12046 (2016)
    A new back-reflector architecture for light-management in thin-film solar cells is proposed that includes a morphologically smooth top surface with light-scattering microstructures buried within. The microstructures are pyramid shaped, fabricated on a planar reflector using TiO2 nanoparticles and subsequently covered with a layer of Si nanoparticles to obtain a flattened top surface, thus enabling growth of good quality thin-film solar cells. The optical properties of this back-reflector show high broadband haze parameter and wide angular distribution of diffuse light-scattering. The n-i-p amorphous silicon thin-film solar cells grown on such a back-reflector show enhanced light absorption resulting in improved external quantum efficiency. The benefit of the light trapping in those solar cells is evidenced by the gains in short-circuit current density and efficiency up to 15.6% and 19.3% respectively, compared to the reference flat solar cells. This improvement in the current generation in the solar cells grown on the flat-topped (buried pyramid) back-reflector is observed even when the irradiation takes place at large oblique angles of incidence. Finite-difference-time-domain simulation results of optical absorption and ideal short-circuit current density values agree well with the experimental findings. The proposed approach uses a low cost and simple fabrication technique and allows effective light manipulation by utilizing the optical properties of micro-scale structures and nanoscale constituent particles. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6nr00259e
  • 2016 • 470 Novel magneto-responsive membrane for remote control switchable molecular sieving
    Lin, X. and Huang, R. and Ulbricht, M.
    Journal of Materials Chemistry B 4 867-879 (2016)
    Stimuli-responsive separation membranes with tunable molecular scale pore size, which are desirable for on-demand sieving of targeted macromolecules, have attracted increasing attention in recent years. In this study, novel magneto-hydrogel pore-filled composite membranes with excellent magneto-responsivity and tunability for molecular sieving have been developed. Such membranes comprising magnetic nanoparticles (MNPs) as localized heater which can be excited by high frequency alternating magnetic field (AMF), poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network as the sieving medium and actuator, and polyethylene terephthalate (PET) track-etched membrane as robust support, have been prepared via in situ reactive pore-filling functionalization. Rheological study has been carried out first to investigate the influence of MNPs and initiation methods on gelation kinetics and microstructure of the MNP-PNIPAAm composite hydrogels, and to identify proper conditions for further pore-filling functionalization. Then AMF distribution of chosen field condition and its heating effectiveness for MNPs and MNP-PNIPAMm composite hydrogel were studied. Pre-functionalization of the PET membranes with linear polymer chains with different composition were compared with respect to their effects for achieving desired MNP loading and fixation of the hydrogel network in the pores. At last, in situ reactive pore-filling functionalization was carried out to immobilize robust magneto-hydrogel in the pores of the membranes. Conditions were investigated and optimized to obtain functionalized membranes with high MNP loading and suited PNIPAM network properties, i.e. good stimuli-responsivity and sieving in the ultrafiltration range. The excellent thermo- and magneto-responsivity of obtained pore-filled membranes was proved by its large and reversible change of water permeability in response to switching on and off the AMF. Finally, it was demonstrated by filtration of dextrans with different molecular weights that the membranes had ultrafiltration properties and that large changes of their molecular sieving performance could be obtained by "remote control" with the external AMF. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5tb02368h
  • 2016 • 469 On Local Phase Equilibria and the Appearance of Nanoparticles in the Microstructure of Single-Crystal Ni-Base Superalloys
    Yardley, V. and Povstugar, I. and Choi, P.-P. and Raabe, D. and Parsa, A.B. and Kostka, A. and Somsen, C. and Dlouhy, A. and Neuking, K. and George, E.P. and Eggeler, G.
    Advanced Engineering Materials 18 1556-1567 (2016)
    High-resolution characterization techniques are combined with thermodynamic calculations (CALPHAD) to rationalize microstructural features of single crystal Ni-base superalloys. Considering the chemical compositions of dendritic and interdendritic regions one can explain differences in γ′-volume fractions. Using thermodynamic calculations one can explain, why γ-nanoparticles are observed in the central regions of large cuboidal γ′-particles and why tertiary γ′-nanoparticles form in the γ-channels. The chemical compositions of the γ-channels and of the newly formed γ-particles differ because of the Gibbs–Thomson pressure which acts on the small particles. With increasing size of secondary γ′-particles, their shape changes from spherical to cuboidal. Some general thermodynamic aspects including the temperature dependencies of the Gibbs free energy G, the enthalpy H, and the entropy S and site occupancies in the ordered L12 (γ′) phase are considered. The importance of cooling rate after homogenization is discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201600237
  • 2016 • 468 On the Crystallography of Silver Nanoparticles with Different Shapes
    Helmlinger, J. and Prymak, O. and Loza, K. and Gocyla, M. and Heggen, M. and Epple, M.
    Crystal Growth and Design 16 3677-3687 (2016)
    The crystallographic properties of silver nanoparticles with different morphologies (two different kinds of spheres, cubes, platelets, and rods) were derived from X-ray powder diffraction and electron microscopy. The size of the metallic particle core was determined by scanning electron microscopy, and the colloidal stability and the hydrodynamic particle diameter were analyzed by dynamic light scattering. The preferred crystallographic orientation (texture) as obtained by X-ray powder diffraction, including pole figure analysis, and high resolution transmission electron microscopy showed the crystallographic nature of the spheres (almost no texture), the cubes (terminated by {100} faces), the platelets (terminated by {111} faces), and the rods (grown from pentagonal twins along [110] and terminated by {100} faces). The crystallite size was determined by Rietveld refinement of X-ray powder diffraction data and agreed well with the transmission electron microscopic data. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.6b00178
  • 2016 • 467 On the role of the stability of functional groups in multi-walled carbon nanotubes applied as support in iron-based high-temperature Fischer-Tropsch synthesis
    Chew, L.M. and Xia, W. and Düdder, H. and Weide, P. and Ruland, H. and Muhler, M.
    Catalysis Today 270 85-92 (2016)
    The role of the stability of surface functional groups in oxygen- and nitrogen-functionalized multi-walled carbon nanotubes (CNTs) applied as support for iron catalysts in high-temperature Fischer-Tropsch synthesis was studied in a fixed-bed U-tube reactor at 340°C and 25 bar with a H2:CO ratio of 1. Iron oxide nanoparticles supported on untreated oxygen-functionalized CNTs (OCNTs) and nitrogen-functionalized CNTs (NCNTs) as well as thermally treated OCNTs were synthesized by the dry impregnation method using ammonium ferric citrate as iron precursor. The properties of all catalysts were examined using X-ray diffraction, temperature-programmed reduction in H2, X-ray photoelectron spectroscopy and temperature-programmed oxidation in O2. The activity loss for iron nanoparticles supported on untreated OCNTs was found to originate from severe sintering and carbon encapsulation of the iron carbide nanoparticles under reaction conditions. Conversely, the sintering of the iron carbide nanoparticles on thermally treated OCNTs and untreated NCNTs during reaction was far less pronounced. The presence of more stable surface functional groups in both thermally treated OCNTs and untreated NCNTs is assumed to be responsible for the less severe sintering of the iron carbide nanoparticles during reaction. As a result, no activity loss for iron nanoparticles supported on thermally treated OCNTs and untreated NCNTs was observed, which even became gradually more active under reaction conditions. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.cattod.2015.09.023
  • 2016 • 466 Optical and electron microscopy study of laser-based intracellular molecule delivery using peptide-conjugated photodispersible gold nanoparticle agglomerates
    Krawinkel, J. and Richter, U. and Torres-Mapa, M.L. and Westermann, M. and Gamrad, L. and Rehbock, C. and Barcikowski, S. and Heisterkamp, A.
    Journal of Nanobiotechnology 14 (2016)
    Background: Cell-penetrating peptides (CPPs) can act as carriers for therapeutic molecules such as drugs and genetic constructs for medical applications. The triggered release of the molecule into the cytoplasm can be crucial to its effective delivery. Hence, we implemented and characterized laser interaction with defined gold nanoparticle agglomerates conjugated to CPPs which enables efficient endosomal rupture and intracellular release of molecules transported. Results: Gold nanoparticles generated by pulsed laser ablation in liquid were conjugated with CPPs forming agglomerates and the intracellular release of molecules was triggered via pulsed laser irradiation (λ = 532 nm, τpulse = 1 ns). The CPPs enhance the uptake of the agglomerates along with the cargo which can be co-incubated with the agglomerates. The interaction of incident laser light with gold nanoparticle agglomerates leads to heat deposition and field enhancement in the vicinity of the particles. This highly precise effect deagglomerates the nanoparticles and disrupts the enclosing endosomal membrane. Transmission electron microscopy images confirmed this rupture for radiant exposures of 25 mJ/cm2 and above. Successful intracellular release was shown using the fluorescent dye calcein. For a radiant exposure of 35 mJ/cm2 we found calcein delivery in 81 % of the treated cells while maintaining a high percentage of cell viability. Furthermore, cell proliferation and metabolic activity were not reduced 72 h after the treatment. Conclusion: CPPs trigger the uptake of the gold nanoparticle agglomerates via endocytosis and co-resident molecules in the endosomes are released by applying laser irradiation, preventing their intraendosomal degradation. Due to the highly localized effect, the cell membrane integrity is not affected. Therefore, this technique can be an efficient tool for spatially and temporally confined intracellular release. The utilization of specifically designed photodispersible gold nanoparticle agglomerates (65 nm) can open novel avenues in imaging and molecule delivery. Due to the induced deagglomeration the primary, small particles (~5 nm) are more likely to be removed from the body. © 2016 Krawinkel et al.
    view abstractdoi: 10.1186/s12951-015-0155-8
  • 2016 • 465 Optimization of a transferred arc reactor for metal nanoparticle synthesis
    Stein, M. and Kruis, F.E.
    Journal of Nanoparticle Research 18 (2016)
    The demand for metal nanoparticles is increasing strongly. Transferred arc synthesis is a promising process in this respect, as it shows high production rates, good quality particles and the ability of up-scaling. The influence of several process parameters on the performance of the process in terms of production rate and particle size is investigated. These parameters are the electrode design and adjustment, the gas flow rate and power input. A novel feeding mechanism allows process operation over an extended time period. It is shown that the process is capable of producing pure metal nanoparticles with variable primary particle sizes and comparatively high production rates. Optimal process conditions for a single transferred arc electrode pair are found, which allow further scale-up by numbering up. © 2016, The Author(s).
    view abstractdoi: 10.1007/s11051-016-3559-y
  • 2016 • 464 Optimum nanoscale design in ferrite based nanoparticles for magnetic particle hyperthermia
    Liébana-Viñas, S. and Simeonidis, K. and Wiedwald, U. and Li, Z.-A. and Ma, Zh. and Myrovali, E. and Makridis, A. and Sakellari, D. and Vourlias, G. and Spasova, M. and Farle, M. and Angelakeris, M.
    RSC Advances 6 72918-72925 (2016)
    The study demonstrates the multiplex enhancement of the magnetic hyperthermia response in ferrites by nanoscale design and tuning without sparing the biocompatibility of iron-oxide. We propose core/shell nanoparticles with a 7-9 nm ferrite core, either magnetically soft MnFe2O4 or hard CoFe2O4, encapsulated by a 2-3 nm Fe3O4 shell providing a core/shell interface. In this case, the exchange interaction between core and shell dramatically affects the macroscopic magnetic behavior and, at the same time, a biocompatible shell prevents interactions of the toxic cores with their environment. The tunable, yet superior, magnetic hyperthermia response is proven by an increase of the specific loss power by a factor of 24 for CoFe2O4-Fe3O4 core/shell particles. This gain is directly connected with the magnetic coupling strength at the core/shell interface and opens the possibility of further optimization. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra17892h
  • 2016 • 463 Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): Effect of thermal treatments and influence of substrate and particle size
    Schilling, M. and Ziemann, P. and Zhang, Z. and Biskupek, J. and Kaiser, U. and Wiedwald, U.
    Beilstein Journal of Nanotechnology 7 591-604 (2016)
    Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min. © 2016 Schilling et al.
    view abstractdoi: 10.3762/bjnano.7.52
  • 2016 • 462 Palladium Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as a Release-and-Catch Catalytic System in Aerobic Liquid-Phase Ethanol Oxidation
    Dong, W. and Chen, P. and Xia, W. and Weide, P. and Ruland, H. and Kostka, A. and Köhler, K. and Muhler, M.
    ChemCatChem 8 1269-1273 (2016)
    Pd nanoparticles supported on carbon nanotubes were applied in the selective oxidation of ethanol in the liquid phase. The characterization of the surface and bulk properties combined with the catalytic tests indicated the dissolution and redeposition of Pd under the reaction conditions. A dynamic interplay within the Pd life cycle was identified to be responsible for the overall reactivity. Nitrogen-doped carbon nanotubes were found to act as an excellent support for the Pd catalyst system by efficiently stabilizing and recapturing the Pd species, which resulted in high activity and selectivity to acetic acid. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201501379
  • 2016 • 461 Pd deposited on functionalized carbon nanotubes for the electrooxidation of ethanol in alkaline media
    Hiltrop, D. and Masa, J. and Maljusch, A. and Xia, W. and Schuhmann, W. and Muhler, M.
    Electrochemistry Communications 63 30-33 (2016)
    Large scale commercialization of direct ethanol fuel cells is hampered by the high cost and scarcity of noble metal electrocatalysts employed at both the anode and cathode. We demonstrate improved utilization of palladium as anode catalyst for ethanol oxidation by exploiting the strong interaction between Pd nanoparticles and nitrogen-doped carbon nanotubes (NCNTs) as support. 0.85 wt% Pd supported on NCNTs achieved a specific current density of 517 A gPd - 1 compared with 421 A gPd - 1 for 0.86 wt% Pd on oxygen-functionalized carbon nanotubes. The electrocatalytic performance deteriorated only gradually and catalysis was sustained for at least 80 h. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2015.11.010
  • 2016 • 460 Pilot-scale synthesis of metal nanoparticles by high-speed pulsed laser ablation in liquids
    Streubel, R. and Bendt, G. and Gökce, B.
    Nanotechnology 27 (2016)
    The synthesis of catalysis-relevant nanoparticles such as platinum and gold is demonstrated with productivities of 4 g h-1 for pulsed laser ablation in liquids (PLAL). The major drawback of low productivity of PLAL is overcome by utilizing a novel ultrafast high-repetition rate laser system combined with a polygon scanner that reaches scanning speeds up to 500 m s-1. This high scanning speed is exploited to spatially bypass the laser-induced cavitation bubbles at MHz-repetition rates resulting in an increase of the applicable, ablation-effective, repetition rate for PLAL by two orders of magnitude. The particle size, morphology and oxidation state of fully automated synthesized colloids are analyzed while the ablation mechanisms are studied for different laser fluences, repetition rates, interpulse distances, ablation times, volumetric flow rates and focus positions. It is found that at high scanning speeds and high repetition rate PLAL the ablation process is stable in crystallite size and decoupled from shielding and liquid effects that conventionally occur during low-speed PLAL. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/20/205602
  • 2016 • 459 Plasmon assisted 3D microstructuring of gold nanoparticle-doped polymers
    Jonušauskas, L. and Lau, M. and Gruber, P. and Gökce, B. and Barcikowski, S. and Malinauskas, M. and Ovsianikov, A.
    Nanotechnology 27 (2016)
    3D laser lithography of a negative photopolymer (zirconium/silicon hybrid solgel SZ2080) doped with gold nanoparticles (Au NPs) is performed with a 515 nm and 300 fs laser system and the effect of doping is explored. By varying the laser-generated Au NP doping concentration from 4.8 • 10-6 wt% to 9.8 • 10-3 wt% we find that the fabricated line widths are enlarged by up to 14.8% compared to structures achieved in pure SZ2080. While implicating a positive effect on the photosensitivity, the doping has no adverse impact on the mechanical quality of intricate 3D microstructures produced from the doped nanocompound. Additionally, we found that SZ2080 increases the long term (∼months) colloidal stability of Au NPs in isopropanol. By discussing the nanoparticle-light interaction in the 3D polymer structures we provide implications that our findings might have on other fields, such as biomedicine and photonics. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/15/154001
  • 2016 • 458 Plasmonic Au/TiO2 nanostructures for glycerol oxidation
    Dodekatos, G. and Tüysüz, H.
    Catalysis Science and Technology 6 7307-7315 (2016)
    Au nanoparticles supported on P25 TiO2 (Au/TiO2) were prepared by a facile deposition-precipitation method with urea and investigated for surface plasmon-assisted glycerol oxidation under base-free conditions. Au/TiO2 samples were characterized in detail by X-ray diffraction, UV-vis spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The adopted synthetic methodology permits deposition of Au nanoparticles with similar mean particle sizes up to 12.5 wt% loading that allows for the evaluation of the influence of the Au amount (without changing the particle size) on its photocatalytic performance for glycerol oxidation. The reaction conditions were optimized by carrying out a systematic study with different Au loadings on TiO2, reaction times, temperatures, catalyst amounts, O2 pressures and Au particle sizes for photocatalytic reactions as well as traditional heterogeneous catalysis. It has been shown that visible light irradiation during the reaction has a beneficial effect on the conversion of glycerol where the best catalytic results were observed for 7.5 wt% Au loading with an average particle size of around 3 nm. The main product observed, with selectivities up to 63%, was high-value dihydroxyacetone that has important industrial applications, particularly in the cosmetic industry. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6cy01192f
  • 2016 • 457 Precise synthesis of discrete and dispersible carbon-protected magnetic nanoparticles for efficient magnetic resonance imaging and photothermal therapy
    Lu, A.-H. and Zhang, X.-Q. and Sun, Q. and Zhang, Y. and Song, Q. and Schüth, F. and Chen, C. and Cheng, F.
    Nano Research 9 1460-1469 (2016)
    Carbon-protected magnetic nanoparticles exhibit long-term stability in acid or alkaline medium, good biocompatibility, and high saturation magnetization. As a result, they hold great promise for magnetic resonance imaging, photothermal therapy, etc. However, since pyrolysis, which is often required to convert the carbon precursors to carbon, typically leads to coalescence of the nanoparticles, the obtained carbon-protected magnetic nanoparticles are usually sintered as a non-dispersible aggregation. We have successfully synthesized discrete, dispersible, and uniform carbon-protected magnetic nanoparticles via a precise surface/interface nano-engineering approach. Remarkably, the nanoparticles possess excellent water-dispersibility, biocompatibility, a high T2 relaxivity coefficient (384 mM–1·s–1), and a high photothermal heating effect. Furthermore, they can be used as multifunctional core components suited for future extended investigation in early diagnosis, detection and therapy, catalysis, separation, and magnetism. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s12274-016-1042-9
  • 2016 • 456 Probing the Dynamic Structure and Chemical State of Au Nanocatalysts during the Electrochemical Oxidation of 2-Propanol
    Choi, Y. and Sinev, I. and Mistry, H. and Zegkinoglou, I. and Roldan Cuenya, B.
    ACS Catalysis 6 3396-3403 (2016)
    A size-dependent trend was observed for the electrochemical total oxidation of 2-propanol to CO2 over Au nanoparticles (NPs), with increasing activity (increased current density and lower overpotential) for decreasing NP size. Furthermore, an enhanced stability against poisoning by the unreacted acetone intermediate was also obtained for NPs smaller than ∼2 nm. Operando X-ray absorption fine structure (XAFS) measurements provided insight into the dynamic evolution of the NP structure and chemical state under reaction conditions, shedding light on the nature of the most catalytically active species and catalyst deactivation phenomena via chemically driven sintering. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b00057
  • 2016 • 455 Resonant laser processing of nanoparticulate Au/TiO2 films on glass supports: Photothermal modification of a photocatalytic nanomaterial
    Schade, L. and Franzka, S. and Thomas, M. and Hagemann, U. and Hartmann, N.
    Surface Science 650 57-63 (2016)
    Resonant laser processing at λ = 532 nm is used to modify thin Au/TiO2 nanoparticle films on soda lime glass plates. A microfocused continuous-wave laser is employed for local patterning at distinct laser powers. In conjunction with microscopic techniques this approach allows for reproducible high-throughput screening of laser-induced material modifications. Optical microscopy and microspectroscopy reveal laser darkening, i.e. a significantly increased optical absorbance. Scanning electron microscopy and X-ray photoelectron spectroscopy show laser-induced film growth and roughening along with the integration of SiO2 from the glass supports. Raman spectroscopy displays a phase transition from anatase to rutile. Au evaporation and/or integration only takes place at high laser powers. All these modifications provide promising perspectives in view of photocatalytic applications. Data from complementary laser experiments with unblended pure TiO2 coatings at λ = 532 nm and λ = 355 nm point to a photothermal process, in which the optical energy is selectively deposited in the Au nanoparticles and transformed into heat. As a result, thermally activated modifications take place. General prospects of laser processing in targeted modification of nanomaterials for photocatalysis are emphasized. © 2016 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.susc.2016.01.006
  • 2016 • 454 Scalable and Environmentally Benign Process for Smart Textile Nanofinishing
    Feng, J. and Hontañón, E. and Blanes, M. and Meyer, J. and Guo, X. and Santos, L. and Paltrinieri, L. and Ramlawi, N. and Smet, L.C.P.M.D. and Nirschl, H. and Kruis, F.E. and Schmidt-Ott, A. and Biskos, G.
    ACS Applied Materials and Interfaces 8 14756-14765 (2016)
    A major challenge in nanotechnology is that of determining how to introduce green and sustainable principles when assembling individual nanoscale elements to create working devices. For instance, textile nanofinishing is restricted by the many constraints of traditional pad-dry-cure processes, such as the use of costly chemical precursors to produce nanoparticles (NPs), the high liquid and energy consumption, the production of harmful liquid wastes, and multistep batch operations. By integrating low-cost, scalable, and environmentally benign aerosol processes of the type proposed here into textile nanofinishing, these constraints can be circumvented while leading to a new class of fabrics. The proposed one-step textile nanofinishing process relies on the diffusional deposition of aerosol NPs onto textile fibers. As proof of this concept, we deposit Ag NPs onto a range of textiles and assess their antimicrobial properties for two strains of bacteria (i.e., Staphylococcus aureus and Klebsiella pneumoniae). The measurements show that the logarithmic reduction in bacterial count can get as high as ca. 5.5 (corresponding to a reduction efficiency of 99.96%) when the Ag loading is 1 order of magnitude less (10 ppm; i.e., 10 mg Ag NPs per kg of textile) than that of textiles treated by traditional wet-routes. The antimicrobial activity does not increase in proportion to the Ag content above 10 ppm as a consequence of a "saturation" effect. Such low NP loadings on antimicrobial textiles minimizes the risk to human health (during textile use) and to the ecosystem (after textile disposal), as well as it reduces potential changes in color and texture of the resulting textile products. After three washes, the release of Ag is in the order of 1 wt %, which is comparable to textiles nanofinished with wet routes using binders. Interestingly, the washed textiles exhibit almost no reduction in antimicrobial activity, much as those of as-deposited samples. Considering that a realm of functional textiles can be nanofinished by aerosol NP deposition, our results demonstrate that the proposed approach, which is universal and sustainable, can potentially lead to a wide number of applications. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b03632
  • 2016 • 453 Silicon-based nanocomposites for thermoelectric application
    Schierning, G. and Stoetzel, J. and Chavez, R. and Kessler, V. and Hall, J. and Schmechel, R. and Schneider, T. and Petermann, N. and Wiggers, H. and Angst, S. and Wolf, D.E. and Stoib, B. and Greppmair, A. and Stutzmann, M. and B...
    Physica Status Solidi (A) Applications and Materials Science 213 497-514 (2016)
    Here we present the realization of efficient and sustainable silicon-based thermoelectric materials from nanoparticles. We employ a gas phase synthesis for the nanoparticles which is capable of producing doped silicon (Si) nanoparticles, doped alloy nanoparticles of silicon and germanium (Ge), SixGe1-x, and doped composites of Si nanoparticles with embedded metal silicide precipitation phases. Hence, the so-called "nanoparticle in alloy" approach, theoretically proposed in the literature, forms a guideline for the material development. For bulk samples, a current-activated pressure-assisted densification process of the nanoparticles was optimized in order to obtain the desired microstructure. For thin films, a laser annealing process was developed. Thermoelectric transport properties were characterized on nanocrystalline bulk samples and laser-sintered-thin films. Devices were produced from nanocrystalline bulk silicon in the form of p-n junction thermoelectric generators, and their electrical output data were measured up to hot side temperatures of 750°C. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D-Onsager network model was developed. This model was extended further to study the p-n junction thermoelectric generator and understand the fundamental working principle of this novel device architecture. Gas phase synthesis of composite nanoparticles; nanocrystalline bulk with optimized composite microstructure; laser-annealed thin film. The authors fabricated thermoelectric nanomaterials from doped silicon and silicon and germanium alloy nanoparticles, as well as composites of Si nanoparticles with embedded metal silicide nanoparticles. Processing was performed applying a current-activated pressure-assisted densification process for bulk samples and a laser annealing process for thin film samples. Devices were produced in the form of pn junction thermoelectric generators. A 3D-Onsager network model was used to understand the fundamental working principle of this novel device architecture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201532602
  • 2016 • 452 Silver nanoparticles with different size and shape: Equal cytotoxicity, but different antibacterial effects
    Helmlinger, J. and Sengstock, C. and Groß-Heitfeld, C. and Mayer, C. and Schildhauer, T.A. and Köller, M. and Epple, M.
    RSC Advances 6 18490-18501 (2016)
    The influence of silver nanoparticle morphology on the dissolution kinetics in ultrapure water as well as the biological effect on eukaryotic and prokaryotic cells was examined. Silver nanoparticles with different shapes but comparable size and identical surface functionalisation were prepared, i.e. spheres (diameter 40-80 and 120-180 nm; two different samples), platelets (20-60 nm), cubes (140-180 nm), and rods (diameter 80-120 nm, length &gt; 1000 nm). All particles were purified by ultracentrifugation and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Their colloidal dispersion in ultrapure water and cell culture medium was demonstrated by dynamic light scattering. Size, shape, and colloidal stability were analysed by scanning electron microscopy, atomic force microscopy, dynamic light scattering, and differential centrifugal sedimentation. The dissolution in ultrapure water was proportional to the specific surface area of the silver nanoparticles. The averaged release rate for all particle morphologies was 30 ± 13 ng s-1 m-2 in ultrapure water (T = 25 ± 1°C; pH 4.8; oxygen saturation 93%), i.e. about 10-20 times larger than the release of silver from a macroscopic silver bar (1 oz), possibly due to the presence of surface defects in the nanoparticulate state. All particles were taken up by human mesenchymal stem cells and were cytotoxic in concentrations of &gt;12.5 μg mL-1, but there was no significant influence of the particle shape on the cytotoxicity towards the cells. Contrary to that, the toxicity towards bacteria increased with a higher dissolution rate, suggesting that the toxic species against bacteria are dissolved silver ions. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5ra27836h
  • 2016 • 451 Simultaneous Study of Brownian and Néel Relaxation Phenomena in Ferrofluids by Mössbauer Spectroscopy
    Landers, J. and Salamon, S. and Remmer, H. and Ludwig, F. and Wende, H.
    Nano Letters 16 1150-1155 (2016)
    We demonstrate the ability of Mössbauer spectroscopy to simultaneously investigate Brownian motion and Néel relaxation in ferrofluidic samples. For this purpose, Mössbauer spectra of coated iron oxide nanoparticles with core diameters of 6.0-26.4 nm dissolved in 70 vol % glycerol solution were recorded in the temperature range of 234-287 K and compared to low-temperature spectra without Brownian motion. By comparison to theory, we were able to determine the particle coating thickness and the dynamic viscosity of the fluid from the broadening of the absorption lines (Brownian motion), as well as the state of Néel relaxation. Results from Mössbauer spectroscopy were crosschecked by AC-susceptometry at several temperatures for Brownian motion and in the high-frequency regime (100 Hz-1 MHz) for Néel relaxation. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.5b04409
  • 2016 • 450 Single Nanoparticle Voltammetry: Contact Modulation of the Mediated Current
    Li, X. and Batchelor-Mcauley, C. and Whitby, S.A.I. and Tschulik, K. and Shao, L. and Compton, R.G.
    Angewandte Chemie - International Edition 55 4296-4299 (2016)
    The cyclic voltammetric responses of individual palladium-coated carbon nanotubes are reported. Upon impact - from the solution phase - with the electrified interface, the nanoparticles act as individual nanoelectrodes catalyzing the hydrogen-oxidation reaction. At high overpotentials the current is shown to reach a quasi-steady-state diffusion limit, allowing determination of the tube length. The electrochemical response of the individual nanotubes also reveals the system to be modulated by the electrical contact between the electrode and carbon nanotube. This modulation presents itself as fluctuations in the recorded Faradaic current. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201509017
  • 2016 • 449 Size matters - The phototoxicity of TiO2 nanomaterials
    Wyrwoll, A.J. and Lautenschläger, P. and Bach, A. and Hellack, B. and Dybowska, A. and Kuhlbusch, T.A.J. and Hollert, H. and Schäffer, A. and Maes, H.M.
    Environmental Pollution 208 859-867 (2016)
    Under solar radiation several titanium dioxide nanoparticles (nano-TiO2) are known to be phototoxic for daphnids. We investigated the influence of primary particle size (10, 25, and 220 nm) and ionic strength (IS) of the test medium on the acute phototoxicity of anatase TiO2 particles to Daphnia magna. The intermediate sized particles (25 nm) showed the highest phototoxicity followed by the 10 nm and 220 nm sized particles (median effective concentrations (EC50): 0.53, 1.28, 3.88 mg/L). Photoactivity was specified by differentiating free OH radicals (therephthalic acid method) and on the other hand surface adsorbed, as well as free OH, electron holes, and O2- (electron paramagnetic resonance spectroscopy, EPR). We show that the formation of free OH radicals increased with a decrease in primary particle size (terephthalic acid method), whereas the total measured ROS content was highest at an intermediate particle size of 25 nm, which consequently revealed the highest photoxicity. The photoactivities of the 10 and 220 nm particles as measured by EPR were comparable. We suggest that phototoxicity depends additionally on the particle-daphnia interaction area, which explains the higher photoxicity of the 10 nm particles compared to the 220 nm particles. Thus, phototoxicity is a function of the generation of different ROS and the particle-daphnia interaction area, both depending on particle size. Phototoxicity of the 10 nm and 25 nm sized nanoparticles decreased as IS of the test medium increased (EC50: 2.9 and 1.1 mg/L). In conformity with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory we suggest that the precipitation of nano-TiO2 was more pronounced in high than in low IS medium, causing a lower phototoxicity. In summary, primary particle size and IS of the medium were identified as factors influencing phototoxicity of anatase nano-TiO2 to D. magna. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.envpol.2015.10.035
  • 2016 • 448 Size-dependent adhesion energy of shape-selected Pd and Pt nanoparticles
    Ahmadi, M. and Behafarid, F. and Cuenya, B.R.
    Nanoscale 8 11635-11641 (2016)
    Thermodynamically stable shape-selected Pt and Pd nanoparticles (NPs) were synthesized via inverse micelle encapsulation and a subsequent thermal treatment in vacuum above 1000 °C. The majority of the Pd NPs imaged via scanning tunneling microscopy (STM) had a truncated octahedron shape with (111) top and interfacial facets, while the Pt NPs were found to adopt a variety of shapes. For NPs of identical shape for both material systems, the NP-support adhesion energy calculated based on STM data was found to be size-dependent, with large NPs (e.g. ∼6 nm) having lower adhesion energies than smaller NPs (e.g. ∼1 nm). This phenomenon was rationalized based on support-induced strain that for larger NPs favors the formation of lattice dislocations at the interface rather than a lattice distortion that may propagate through the smaller NPs. In addition, identically prepared Pt NPs of the same shape were found to display a lower adhesion energy compared to Pd NPs. While in both cases, a transition from a lattice distortion to interface dislocations is expected to occur with increasing NP size, the higher elastic energy in Pt leads to a lower transition size, which in turn lowers the adhesion energy of Pt NPs compared to Pd. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6nr02166b
  • 2016 • 447 Spectra library: An assumption-free in situ method to access the kinetics of catechols binding to colloidal ZnO quantum dots
    Lin, W. and Haderlein, M. and Walter, J. and Peukert, W. and Segets, D.
    Angewandte Chemie - International Edition 55 932-935 (2016)
    Assumption-free and in situ resolving of the kinetics of ligand binding to colloidal nanoparticles (NPs) with high time resolution is still a challenge in NP research. A unique concept of using spectra library and stopped-flow together with a "search best-match" Matlab algorithm to access the kinetics of ligand binding in colloidal systems is reported. Instead of deconvoluting superimposed spectra using assumptions, species absorbance contributions (ligand@ZnO NPs and ligand in solution) are obtained by offline experiments. Therefrom, a library of well-defined targets with known ligand distribution between particle surface and solution is created. Finally, the evolution of bound ligand is derived by comparing in situ spectra recorded by stopped-flow and the library spectra with the algorithm. Our concept is a widely applicable strategy for kinetic studies of ligand adsorption to colloidal NPs and a big step towards deep understanding of surface functionalization kinetics. Well-established libraries of target spectra that are derived by means of careful offline analysis and identification of equilibrium data within larger kinetic datasets can be used for any particle-ligand system. Kinetics of ligand binding to nanoparticles can be derived free of assumption, in situ, and with high time resolution. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201508252
  • 2016 • 446 Spray Deposition of Titania Films with Incorporated Crystalline Nanoparticles for All-Solid-State Dye-Sensitized Solar Cells Using P3HT
    Song, L. and Wang, W. and Körstgens, V. and Moseguí González, D. and Yao, Y. and Minar, N.K. and Feckl, J.M. and Peters, K. and Bein, T. and Fattakhova-Rohlfing, D. and Santoro, G. and Roth, S.V. and Müller-Buschbaum, P.
    Advanced Functional Materials 26 1498-1506 (2016)
    Spray coating, a simple and low-cost technique for large-scale film deposition, is employed to fabricate mesoporous titania films, which are electron-transporting layers in all-solid-state dye-sensitized solar cells (DSSCs). To optimize solar cell performance, presynthesized crystalline titania nanoparticles are introduced into the mesoporous titania films. The composite film morphology is examined with scanning electron microscopy, grazing incidence small-angle X-ray scattering, and nitrogen adsorption-desorption isotherms. The crystal phase and crystallite sizes are verified by X-ray diffraction measurements. The photovoltaic performance of all-solid-state DSSCs is investigated. The findings reveal that an optimal active layer of the all-solid-state DSSC is obtained by including 50 wt% titania nanoparticles, showing a foam-like morphology with an average pore size of 20 nm, featuring an anatase phase, and presenting a surface area of 225.2 m2 g-1. The optimized morphology obtained by adding 50 wt% presynthesized crystalline titania nanoparticles yields, correspondingly, the best solar cell efficiency of 2.7 ± 0.1%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201504498
  • 2016 • 445 Strong competition between electromagnetic enhancement and surface-energy-transfer induced quenching in plasmonic dye-sensitized solar cells: A generic yet controllable effect
    Yip, C.T. and Liu, X. and Hou, Y. and Xie, W. and He, J. and Schlücker, S. and Lei, D.Y. and Huang, H.
    Nano Energy 26 297-304 (2016)
    Light harvesting strategy using plasmonic metal nanostructures as subwavelength light concentrators provides a highly attractive solution to enhancing the performance of dye-sensitized solar cells (DSSCs). Through comprehensive optical spectroscopy and electrical characterizations together with a theoretical analysis, we demonstrate a strong competition between the surface energy transfer induced non-radiative quenching and the plasmonic electromagnetic enhancement effect in metal-dielectric-semiconductor core-shell-shell nanoparticle doped DSSCs, a generic yet unavoidable phenomenon in all types of plasmonic solar cells. The competition of the two effects results in a non-monotonic relationship between the device efficiency and the thickness of the dielectric shell covering the metal nanoparticles, and leads to an optimal thickness for the highest power conversion efficiency. This observation is further corroborated by photoluminescence spectroscopic measurements. Our experimental results are in good agreement with the Persson model that predicts a strong energy quenching effect when the distance between the photogenerated charge carrier and the metal core is short enough. Both experiment and theory show that the localized surface plasmon resonance enhanced light harvesting efficiency is suppressed by the surface energy transfer to the metal cores for the dielectric shell thickness shorter than a characteristic value (~7 nm in our study). Our work sheds new insights into the fundamental understanding of the photophysics mechanisms of plasmonic DSSCs and could push forward the study of plasmonic solar cells in terms of device design and fabrication. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.nanoen.2016.05.016
  • 2016 • 444 Structure-Activity-Stability Relationships for Space-Confined PtxNiy Nanoparticles in the Oxygen Reduction Reaction
    Mezzavilla, S. and Baldizzone, C. and Swertz, A.-C. and Hodnik, N. and Pizzutilo, E. and Polymeros, G. and Keeley, G.P. and Knossalla, J. and Heggen, M. and Mayrhofer, K.J.J. and Schüth, F.
    ACS Catalysis 6 8058-8068 (2016)
    This study focuses on the synthesis and electrochemical performance (i.e, activity and stability) of advanced electrocatalysts for the oxygen reduction reaction (ORR), made of Pt-Ni nanoparticles embedded in hollow graphitic spheres (HGS). The mechanism of the confined space alloying, that is, the controlled alloying of bimetallic precursors with different compositions (i.e., Pt3Ni, PtNi, and PtNi3) within the HGS mesoporous shell, was examined in detail. It was found that the presence of platinum during the reduction step, as well as the application of high annealing temperatures (at least 850°C for 3.5h in Ar), are necessary conditions to achieve the complete encapsulation and the full stability of the catalysts. The evolution of the activity, the electrochemical surface area, and the residual alloy composition of the Pt-Ni@HGS catalysts was thoroughly monitored (at the macro- and nanoscale level) under different degradation conditions. After the initial activation, the embedded Pt-Ni nanoparticles (3-4 nm in size) yield mass activities that are 2- to 3.5-fold higher than that of pure Pt@HGS (depending on the alloy composition). Most importantly, it is demonstrated that under the normal operation range of an ORR catalyst in PEM-FCs (potential excursions between 0.4 and 1.0 VRHE) both the nanoparticle-related degradation pathways (particle agglomeration) and dealloying phenomena are effectively suppressed, irrespectively of the alloy composition. Thus, the initial enhanced activity is completely maintained over an extended degradation protocol. In addition, owing to the peculiar configuration of the catalysts consisting of space-confined nanoparticles, it was possible to elucidate the impact of the dealloying process (as a function of alloy composition and severity of the degradation protocols) separately from other parallel phenomena, providing valuable insight into this elusive degradation mechanism. (Graph Presented). © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b02221
  • 2016 • 443 Synthesis of Bi2Te3 and (Bi: XSb1- x)2Te3 nanoparticles using the novel IL [C4mim]3[Bi3I12]
    Loor, M. and Bendt, G. and Hagemann, U. and Wölper, C. and Assenmacher, W. and Schulz, S.
    Dalton Transactions 45 15326-15335 (2016)
    The novel Bi-containing reactive ionic liquid [C4mim]3[Bi3I12], which was synthesized in quantitative yield by equimolar reaction of BiI3 and [C4mim]I, was used as a novel Bi-source for the ionothermal synthesis of Bi2Te3 nanoparticles by reaction with (Et3Si)2Te in the ionic liquid [C4mim]I. The solid state structure of [C4mim]3[Bi3I12] was determined by single crystal X-ray diffraction. In addition, the ionothermal synthesis of the single source precursor (Et2Sb)2Te and [C4mim]3[Bi3I12] yielded the ternary (BixSb1-x)2Te3 (x = 0.25, 0.5, 0.75) nanoparticles. The chemical composition and phase purity of the tetradymite-type materials were determined by EDX and XRD and the surface composition of the nanoparticles was further investigated by IR and XPS. In addition, the morphology of the nanoparticles was investigated by SEM and TEM. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6dt02361d
  • 2016 • 442 Synthesis of well-defined core-shell nanoparticles based on bifunctional poly(2-oxazoline) macromonomer surfactants and a microemulsion polymerization process
    Kampmann, A.-L. and Grabe, T. and Jaworski, C. and Weberskirch, R.
    RSC Advances 6 99752-99763 (2016)
    Particles in the sub-100 nm range have attracted widespread attention in the past few years due to their application in drug delivery and diagnostics. Here we describe the synthesis of two bifunctional, amphiphilic poly(2-oxazoline) macromonomers with multiple acrylate groups in their hydrophobic block and azide or primary amino end groups. The amphiphilic macromonomers were applied in a microemulsion polymerization to form well-defined core-crosslinked nanoparticles with surface functional azide or amine groups. Therefore, an amphiphilic poly(2-oxazoline) was prepared by cationic ring-opening polymerization of 2-methyl-2-oxazoline to form the hydrophilic block and a mixture of 2-heptyl-2-oxazoline and 2-(5-pentyl-[(1,2,3-triazol)-4-yl-methacrylat)]-oxazoline to form the hydrophobic block and was terminated with an azide moiety as end group. The introduction of multiple methacrylate groups into the poly(2-oxazoline) macromonomers serve as a stabilizer in the microemulsion process to covalently link the polymer to the particle core. Variable particle sizes of 20-75 nm have been prepared by encapsulating different amounts of 1,6-hexanedioldimethacrylate (HDDMA) to swell the micellar core before subsequent crosslinking takes place. Finally, particle surface functionalization was achieved by converting the terminal azide group via Staudinger-reaction to a primary amine group. Nanoparticles with surface primary amine groups were functionalized with folic acid (FA), a GRGDS-peptide derivative and fluorescein isothiocyanate (FITC) by simple amidation reaction (FA, RGD-peptide) or thiourea formation (FITC). © 2016 Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra22896h
  • 2016 • 441 The Electrochemical Characterization of Single Core-Shell Nanoparticles
    Holt, L.R. and Plowman, B.J. and Young, N.P. and Tschulik, K. and Compton, R.G.
    Angewandte Chemie - International Edition 55 397-400 (2016)
    We report the direct solution-phase characterization of individual gold-core silver-shell nanoparticles through an electrochemical means, with selectivity achieved between the core and shell components based on their different redox activities. The electrochemically determined core-shell sizes are in excellent agreement with electron microscopy-based results, successfully demonstrating the electrochemical characterization of individual core-shell nanoparticles. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201509008
  • 2016 • 440 Tuning Catalytic Selectivity at the Mesoscale via Interparticle Interactions
    Mistry, H. and Behafarid, F. and Reske, R. and Varela, A.S. and Strasser, P. and Roldan Cuenya, B.
    ACS Catalysis 6 1075-1080 (2016)
    The selectivity of heterogeneously catalyzed chemical reactions is well-known to be dependent on nanoscale determinants, such as surface atomic geometry and composition. However, principles to control the selectivity of nanoparticle (NP) catalysts by means of mesoscopic descriptors, such as the interparticle distance, have remained largely unexplored. We used well-defined copper catalysts to deconvolute the effect of NP size and distance on product selectivity during CO2 electroreduction. Corroborated by reaction-diffusion modeling, our results reveal that mesoscale phenomena such as interparticle reactant diffusion and readsorption of intermediates play a defining role in product selectivity. More importantly, this study uncovers general principles of tailoring NP activity and selectivity by carefully engineering size and distance. These principles provide guidance for the rational design of mesoscopic catalyst architectures in order to enhance the production of desired reaction products. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.5b02202
  • 2016 • 439 Tuning the magnetism of ferrite nanoparticles
    Viñas, S.L. and Simeonidis, K. and Li, Z.-A. and Ma, Z. and Myrovali, E. and Makridis, A. and Sakellari, D. and Angelakeris, M. and Wiedwald, U. and Spasova, M. and Farle, M.
    Journal of Magnetism and Magnetic Materials 415 20-23 (2016)
    The importance of magnetic interactions within an individual nanoparticle or between adjacent ones is crucial not only for the macroscopic collective magnetic behavior but for the AC magnetic heating efficiency as well. On this concept, single-(MFe2O4 where M=Fe, Co, Mn) and core-shell ferrite nanoparticles consisting of a magnetically softer (MnFe2O4) or magnetically harder (CoFe2O4) core and a magnetite (Fe3O4) shell with an overall size in the 10 nm range were synthesized and studied for their magnetic particle hyperthermia efficiency. Magnetic measurements indicate that the coating of the hard magnetic phase (CoFe2O4) by Fe3O4 provides a significant enhancement of hysteresis losses over the corresponding single-phase counterpart response, and thus results in a multiplication of the magnetic hyperthermia efficiency opening a novel pathway for high-performance, magnetic hyperthermia agents. At the same time, the existence of a biocompatible Fe3O4 outer shell, toxicologically renders these systems similar to iron-oxide ones with significantly milder side-effects. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2016.02.098
  • 2016 • 438 Ultrafiltration membrane-based purification of bioconjugated gold nanoparticle dispersions
    Alele, N. and Streubel, R. and Gamrad, L. and Barcikowski, S. and Ulbricht, M.
    Separation and Purification Technology 157 120-130 (2016)
    Functionalization of nanoparticles (NP) with biomolecules to form bioconjugated systems has received large attention in biomedical applications. However, purification of these nanoparticle bioconjugates from unbound free biofunctional ligands (e.g., peptides) remains a significant challenge in the production of well-defined materials. The conventional separation methods often compromise the product's properties and recovery. In this work, removal of excess of unbound peptides after the bioconjugation step to yield functionalized gold nanoparticles (AuNP) was achieved by exploiting the sieving properties of commercial regenerated cellulose (RC) ultrafiltration (UF) membranes. The RC membrane with nominal molecular weight cut-off (NMWCO) of 30 kDa precisely fractionated the mixtures and purified gold nanoparticle-peptide bioconjugates in a pressure driven semi-continuous diafiltration process. The RC 30 kDa membrane showed absolute rejection of the bioconjugated AuNP and the recovery of AuNP-peptide bioconjugate in the retentate was >87% relative to the initial amount in the mixture. In addition, the separation efficiency and throughput results were much better compared to the centrifugal membrane filtration method using an analogous membrane. All results indicate that by choice of an appropriate membrane type and barrier pore size, and with optimized solution chemistry and filtration parameters, ultrafiltration membranes, and in particular RC membranes, can be very well suited for the purification of bioconjugated nanoparticle dispersions, and the diafiltration mode is very well suited for upscaling. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2015.11.033
  • 2016 • 437 Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods
    Castro, M. and Haouas, M. and Lim, I. and Bongard, H.J. and Schüth, F. and Taulelle, F. and Karlsson, G. and Alfredsson, V. and Breyneart, E. and Kirschhock, C.E.A. and Schmidt, W.
    Chemistry - A European Journal 22 15307-15319 (2016)
    The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state29Si,27Al,14N, and1H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs.1H and14N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate–template interactions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201600511
  • 2015 • 436 A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO
    Schindler, T. and Schmiele, M. and Schmutzler, T. and Kassar, T. and Segets, D. and Peukert, W. and Radulescu, A. and Kriele, A. and Gilles, R. and Unruh, T.
    Langmuir 31 10130-10136 (2015)
    ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (d<inf>core</inf>) the surrounding shell (d<inf>shell</inf>) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Thus, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient μ between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b02198
  • 2015 • 435 A rapid, high-yield and large-scale synthesis of uniform spherical silver nanoparticles by a microwave-assisted polyol process
    Helmlinger, J. and Heise, M. and Heggen, M. and Ruck, M. and Epple, M.
    RSC Advances 5 92144-92150 (2015)
    Silver nanoparticles are often employed in medical devices and consumer products due to their antibacterial action. For this, reliable syntheses with quantitative yield are required. Uniform spherical silver nanoparticles with a diameter of about 180 nm were synthesized by carrying out the polyol synthesis in a microwave. Silver nitrate was dissolved in ethylene glycol and poly(N-vinyl pyrrolidone) (PVP) was added as capping agent. The particles were characterized by SEM, HRTEM, XRD, and DLS. The results are compared with the classical method where silver nitrate is reduced by glucose in aqueous solution, heated with an oil-bath. The microwave-assisted synthesis leads to an almost quantitative yield of uniform silver nanoparticles after 20 min reaction time and gives exclusively spherical particles without other shapes like triangles, rods or prisms. Diethylene glycol as solvent gave a more homogeneous particle size distribution than ethylene glycol. For both kinds of particles, dissolution in ultrapure water was examined over a period of 29 days in the presence of oxygen. The dissolution was comparable in both cases (about 50% after 4 weeks), indicating the same antibacterial action for particles from the microwave and from the glucose synthesis. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5ra20446a
  • 2015 • 434 Amorphous and Crystalline Sodium Tantalate Composites for Photocatalytic Water Splitting
    Grewe, T. and Tüysüz, H.
    ACS Applied Materials and Interfaces 7 23153-23162 (2015)
    A facile hydrothermal synthesis protocol for the fabrication of sodium tantalates for photocatalytic water splitting is presented. Mixtures of tantalum and sodium ethoxide precursors were dispersed in ethanol, and ammonium hydroxide solution was used as mineralizer. By adjusting the amount of mineralizer, a variety of sodium tantalates with various morphologies, textural parameters, band gaps, crystal phases, and degrees of crystallinity were fabricated. The reaction was carefully monitored with a pressure sensor inside the autoclave reactor, and the obtained samples were characterized using X-ray diffraction, transmission electron microscopy, N2-physisorption, and ultraviolet-visible light spectroscopy. Among the series, the amorphous sample and the composite sample that consists of amorphous and crystalline phases showed superior activity toward photocatalytic hydrogen production than highly crystalline samples. Particularly, an amorphous sodium tantalate with a small fraction of crystalline nanoparticles with perovskite structure was found to be the most active sample, reaching a hydrogen rate of 3.6 mmol h-1 from water/methanol without the use of any cocatalyst. Despite its amorphous nature, this photocatalyst gave an apparent photocatalyst activity of 1200 μmol g-1 L-1 h-1 W1-, which is 4.5-fold higher than highly crystalline NaTaO3. In addition, the most active sample gave promising activity for overall water splitting with a hydrogen production rate of 94 μmol h-1, which is superior to highly crystalline NaTaO3 prepared by conventional solid-solid state route. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b06965
  • 2015 • 433 An approach for transparent and electrically conducting coatings: A transparent plastic varnish with nanoparticulate magnetic additives
    Beck, G. and Barcikowski, S. and Chakravadhanula, V.S.K. and Comesaña-Hermo, M. and Deng, M. and Farle, M. and Hilgendorff, M. and Jakobi, J. and Janek, J. and Kienle, L. and Mogwitz, B. and Schubert, T. and Stiemke, F.
    Thin Solid Films 595 96-107 (2015)
    For the purpose of preparing TCCs (= transparent and electrical conducting coatings), metallic and ferromagnetic nano-additives were dispersed into a transparent varnish and the obtained dispersions were coated on transparent plastic substrates. During hardening of the dispersion the magnetic nano-additives were aligned by a magnetic field. The resulting coatings have electrical pathways along lines of nano-additive chains and are highly transparent in the areas between the lines. Therefore, the electrical conductivity is anisotropic, and it depends on the alignment of the nano-additives (i.e. on the distance between the nano-additives within the chains and the length of the lines) as well as on the thickness of an oxide and/or solvent shell around the nano-additives. The transparency depends also on the alignment and here especially on the thickness and the distance between the formed lines. The quality of the alignment in turn, depends on the magnetic properties and on the size of the particles. We used commercial plastic varnishes, which form electrically isolating (≥ 10− 12 S/m) and transparent (about 90% transparency) coatings, and the following magnetic additives: Co-, Fe-, CoPt3, CoPt3@Au- and Fe@Au-nanoparticles as well as CoNi-nanowires. Coatings with Fe@Au-nanoparticles show the best results in terms of the electrical conductivity (10− 5 S/m–10− 6 S/m) at transparencies above 70%. Furthermore, in addition to the magnetic nano-additives, transparent additives (Al2O3-particles) and non-magnetic, but better conducting additives (carbon-nanotubes) were added to the varnish to increase the transparency and the electrical conductivity, respectively. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2015.10.059
  • 2015 • 432 An efficient method for calculating the absorption enhancement in solar cells with integrated plasmonic and photonic nanoparticles
    Manley, P. and Schmidt, F. and Schmid, M.
    2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, METAMATERIALS 2015 193-195 (2015)
    We present a method for calculating the plasmonic and photonic enhancement of the absorption in solar cells. The method involves coupling between a transfer matrix method to describe light propagation in the layered stack and Mie theory for calculating the absorption and angular scattered field distribution from the nanoparticles. We also compare the method to rigorous simulations. © 2015 IEEE.
    view abstractdoi: 10.1109/MetaMaterials.2015.7342570
  • 2015 • 431 Are Nanoparticles Spherical or Quasi-Spherical?
    Sokolov, S.V. and Batchelor-Mcauley, C. and Tschulik, K. and Fletcher, S. and Compton, R.G.
    Chemistry - A European Journal 21 10741-10746 (2015)
    The geometry of quasi-spherical nanoparticles is investigated. The combination of SEM imaging and electrochemical nano-impact experiments is demonstrated to allow sizing and characterization of the geometry of single silver nanoparticles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201500807
  • 2015 • 430 Assembling Paramagnetic Ceruloplasmin at Electrode Surfaces Covered with Ferromagnetic Nanoparticles. Scanning Electrochemical Microscopy in the Presence of a Magnetic Field
    Matysiak, E. and Botz, A.J.R. and Clausmeyer, J. and Wagner, B. and Schuhmann, W. and Stojek, Z. and Nowicka, A.M.
    Langmuir 31 8176-8183 (2015)
    Adsorption of ceruloplasmin (Cp) at a gold electrode modified with ferromagnetic iron nanoparticles encapsulated in carbon (Fe@C Nps) leads to a successful immobilization of the enzyme in its electroactive form. The proper placement of Cp at the electrode surface on top of the nanocapsules containing an iron core allowed a preorientation of the enzyme, hence allowing direct electron transfer between the electrode and the enzyme. Laser ablation coupled with inductively coupled plasma mass spectrometry indicated that Cp was predominantly located at the paramagnetic nanoparticles. Scanning electrochemical microscopy measurements in the sample-generation/tip-collection mode proved that Cp was ferrooxidative inactive if it was immobilized on the bare gold surface and reached the highest activity if it was adsorbed on Fe@C Nps in the presence of a magnetic field. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b01155
  • 2015 • 429 Bifunctional redox tagging of carbon nanoparticles
    Poon, J. and Batchelor-McAuley, C. and Tschulik, K. and Palgrave, R.G. and Compton, R.G.
    Nanoscale 7 2069-2075 (2015)
    Despite extensive work on the controlled surface modification of carbon with redox moieties, to date almost all available methodologies involve complex chemistry and are prone to the formation of polymerized multi-layer surface structures. Herein, the facile bifunctional redox tagging of carbon nanoparticles (diameter 27 nm) and its characterization is undertaken using the industrial dye Reactive Blue 2. The modification route is demonstrated to be via exceptionally strong physisorption. The modified carbon is found to exhibit both well-defined oxidative and reductive voltammetric redox features which are quantitatively interpreted. The method provides a generic approach to monolayer modifications of carbon and carbon nanoparticle surfaces. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4nr06058j
  • 2015 • 428 Biocompatible microgel-modified electrospun fibers for zinc ion release
    Wilke, P. and Coger, V. and Nachev, M. and Schachschal, S. and Million, N. and Barcikowski, S. and Sures, B. and Reimers, K. and Vogt, P.M. and Pich, A.
    Polymer (United Kingdom) 61 163-173 (2015)
    We present a novel and facile method for the design of biocompatible microgel-modified microfibers loaded with ZnO nanoparticles capable of zinc ion release under physiological conditions. The microfibers consist of three materials hierarchically assembled in a controlled and reproducible way. We synthesized poly(N-vinylcaprolactam-co-itaconic acid) aqueous microgels with carboxylic groups located in the microgel core. The obtained microgels can be loaded with various amounts of ZnO nanoparticles by in-situ growth of ZnO in microgels. As shown by electrophoretic mobility and TEM measurements, ZnO nanoparticles are selectively loaded in the microgel core and stabilized by itaconic acid groups bearing strong negative charges. ZnO-loaded microgels were used as functional additive to produce poly(ε-caprolactone) (PCL) microfibers using the electrospinning process. The resulting microfibers consist of a PCL core coated with the microgels located at the surface of the fibers. The variation of the ZnO amount loaded into microgels allows regulating the ZnO content in microfibers and gives the possibility to tune the released amount of zinc ions in aqueous medium at pH 7.5 and 37 °C. We demonstrate that the obtained functional microfibers are biocompatible and non-toxic, thus being good candidates for biomedical applications like scaffolds for tissue engineering, biointerface coatings or wound closing dressings. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2015.01.078
  • 2015 • 427 Bioconjugated gold nanoparticles penetrate into spermatozoa depending on plasma membrane status
    Barchanski, A. and Taylor, U. and Sajti, C.L. and Gamrad, L. and Kues, W.A. and Rath, D. and Barcikowski, S.
    Journal of Biomedical Nanotechnology 11 1597-1607 (2015)
    Spermatozoa are not only essential for animal reproduction they also represent important tools for the manipulation of animal genetics. For instance, the genetic labeling and analysis of spermatozoa could provide a prospective complementation of pre-fertilization diagnosis and could help to prevent the inheritance of defective alleles during artificial insemination or to select beneficial traits in livestock. Spermatozoa feature extremely specialized membrane organization and restricted transport mechanisms making the labeling of genetically interesting DNA-sequences, e.g., with gold nanoparticles, a particular challenge. Here, we present a systematic study on the size-related internalization of ligand-free, monovalent and bivalent polydisperse gold nanoparticles, depending on spermatozoa membrane status. While monovalent conjugates were coupled solely to either negatively-charged oligonucleotides or positively-charged cell-penetrating peptides, bivalent conjugates were functionalized with both molecules simultaneously. The results clearly indicate that the cell membrane of acrosome-intact, bovine spermatozoa was neither permeable to ligand-free or oligonucleotide-conjugated nanoparticles, nor responsive to the mechanisms of cell-penetrating peptides. Interestingly, after acrosome reaction, which comprises major changes in sperm membrane composition, fluidity and charge, high numbers of monovalent and bivalent nanoparticles were found in the postequatorial segment, depicting a close and complex correlation between particle internalization and membrane organization. Additionally, depending on the applied peptide and for nanoparticle sizes <10 nm even a successive nuclear penetration was observed, making the bivalent conjugates promising for future genetic delivery and sorting issues. Copyright © 2015 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jbn.2015.2094
  • 2015 • 426 Calcium phosphate nanoparticles carrying BMP-7 plasmid DNA induce an osteogenic response in MC3T3-E1 pre-osteoblasts
    Hadjicharalambous, C. and Kozlova, D. and Sokolova, V. and Epple, M. and Chatzinikolaidou, M.
    Journal of Biomedical Materials Research - Part A 103 3834-3842 (2015)
    Functionalized calcium phosphate nanoparticles with osteogenic activity were prepared. Polyethyleneimine-stabilized calcium phosphate nanoparticles were coated with a shell of silica and covalently functionalized by silanization with thiol groups. Between the calcium phosphate surface and the outer silica shell, plasmid DNA which encoded either for bone morphogenetic protein 7 (BMP-7) or for enhanced green fluorescent protein was incorporated as cargo. The plasmid DNA-loaded calcium phosphate nanoparticles were used for the transfection of the pre-osteoblastic MC3T3-E1 cells. The cationic nanoparticles showed high transfection efficiency together with a low cytotoxicity. Their potential to induce an osteogenic response by transfection was demonstrated by measuring the alkaline phosphatase (ALP) activity and calcium deposition with alizarin red staining. The expression of the osteogenic markers Alp, Runx2, ColIa1 and Bsp was investigated by means of real-time quantitative polymerase chain reaction. It was shown that phBMP-7-loaded nanoparticles can provide a means of transient transfection and localized production of BMP-7 in MC3T3-E1 cells, with a subsequent increase of two osteogenic markers, specifically ALP activity and calcium accumulation in the extracellular matrix. Future strategies to stimulate bone regeneration focus into enhancing transfection efficiency and achieving higher levels of BMP-7 produced by the transfected cells. © 2015 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/jbm.a.35527
  • 2015 • 425 Carbon Monoxide-Induced Stability and Atomic Segregation Phenomena in Shape-Selected Octahedral PtNi Nanoparticles
    Ahmadi, M. and Cui, C. and Mistry, H. and Strasser, P. and Roldan Cuenya, B.
    ACS Nano 9 10686-10694 (2015)
    The chemical and morphological stability of size- and shape-selected octahedral PtNi nanoparticles (NP) were investigated after different annealing treatments up to a maximum temperature of 700 °C in a vacuum and under 1 bar of CO. Atomic force microscopy was used to examine the mobility of the NPs and their stability against coarsening, and X-ray photoelectron spectroscopy to study the surface composition, chemical state of Pt and Ni in the NPs, and thermally and CO-induced atomic segregation trends. Exposing the samples to 1 bar of CO at room temperature before annealing in a vacuum was found to be effective at enhancing the stability of the NPs against coarsening. In contrast, significant coarsening was observed when the sample was annealed in 1 bar of CO, most likely as a result of Ni(CO)4 formation and their enhanced mobility on the support surface. Sample exposure to CO at room temperature prior to annealing led to the segregation of Pt to the NP surface. Nevertheless, oxidic PtOx and NiOx species still remained at the NP surface, and, irrespective of the initial sample pretreatment, Ni surface segregation was observed upon annealing in a vacuum at moderate temperature (T < 300 °C). Interestingly, a distinct atomic segregation trend was detected between 300 and 500 °C for the sample pre-exposed to CO; namely, Ni surface segregation was partially hindered. This might be attributed to the higher bonding energy of CO to Pt as compared to Ni. Annealing in the presence of 1 bar CO also resulted in the initial surface segregation of Ni (T < 400 °C) as long as PtOx and NiOx species were available on the surface as a result of the higher affinity of Ni for oxygen. Above 500 °C, and regardless of the sample pretreatment, the diffusion of Pt atoms to the NP surface and the formation of a Ni-Pt alloy are observed. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.5b01807
  • 2015 • 424 Charge storage in β -FeSi2 nanoparticles
    Theis, J. and Bywalez, R. and Küpper, S. and Lorke, A. and Wiggers, H.
    Journal of Applied Physics 117 (2015)
    We report on the observation of a surprisingly high specific capacitance of β-FeSi2 nanoparticle layers. Lateral, interdigitated capacitor structures were fabricated on thermally grown silicon dioxide and covered with β-FeSi2 particles by drop or spin casting. The β-FeSi2-nanoparticles, with crystallite sizes in the range of 10-30nm, were fabricated by gas phase synthesis in a hot wall reactor. Compared to the bare electrodes, the nanoparticle-coated samples exhibit a 3-4 orders of magnitude increased capacitance. Time-resolved current voltage measurements show that for short times (seconds to minutes), the material is capable of storing up to 1 As/g at voltages of around 1V. The devices are robust and exhibit long-term stability under ambient conditions. The specific capacitance is highest for a saturated relative humidity, while for a relative humidity below 40% the capacitance is almost indistinguishable from a nanoparticle-free reference sample. The devices work without the need of a fluid phase, the charge storing material is abundant and cost effective, and the sample design is easy to fabricate. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4906500
  • 2015 • 423 Co3O4-MnO2-CNT Hybrids Synthesized by HNO3 Vapor Oxidation of Catalytically Grown CNTs as OER Electrocatalysts
    Xie, K. and Masa, J. and Madej, E. and Yang, F. and Weide, P. and Dong, W. and Muhler, M. and Schuhmann, W. and Xia, W.
    ChemCatChem 7 3027-3035 (2015)
    An efficient two-step gas-phase method was developed for the synthesis of Co<inf>3</inf>O<inf>4</inf>-MnO<inf>2</inf>-CNT hybrids used as electrocatalysts in the oxygen evolution reaction (OER). Spinel Co-Mn oxide was used for the catalytic growth of multiwalled carbon nanotubes (CNTs) and the amount of metal species remaining in the CNTs was adjusted by varying the growth time. Gas-phase treatment in HNO<inf>3</inf> vapor at 200 °C was performed to 1)open the CNTs, 2)oxidize encapsulated Co nanoparticles to Co<inf>3</inf>O<inf>4</inf> as well as MnO nanoparticles to MnO<inf>2</inf>, and 3)to create oxygen functional groups on carbon. The hybrid demonstrated excellent OER activity and stability up to 37.5h under alkaline conditions, with longer exposure to HNO<inf>3</inf> vapor up to 72h beneficial for improved electrocatalytic properties. The excellent OER performance can be assigned to the high oxidation states of the oxide nanoparticles, the strong electrical coupling between these oxides and the CNTs as well as favorable surface properties rendering the hybrids a promising alternative to noble metal based OER catalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201500469
  • 2015 • 422 Conductivity Mechanisms in Sb-Doped SnO2 Nanoparticle Assemblies: DC and Terahertz Regime
    Skoromets, V. and Němec, H. and Kopeček, J. and Kužel, P. and Peters, K. and Fattakhova-Rohlfing, D. and Vetushka, A. and Müller, M. and Ganzerová, K. and Fejfar, A.
    Journal of Physical Chemistry C 119 19485-19495 (2015)
    Assemblies of undoped and antimony-doped tin oxide nanoparticles synthesized via a nonaqueous sol-gel procedure, pressed into pellets, and annealed under various conditions were investigated using time-domain terahertz spectroscopy, scanning electron microscopy, atomic force microscopy, and dc conductivity measurements. Combination of these methods made it possible to resolve the conductivity limitations imposed by intrinsic properties of the material and by the morphology of the samples. Percolation of the nanoparticles was confirmed in all samples. The undoped samples exhibit a weak hopping conductivity, whereas bandlike conduction of charges partially confined in the nanoparticles dominates in the doped samples. The conductivity of nanoparticles and their connectivity can be greatly controlled during the sample preparation, namely by the calcination temperature and by the order of technological steps. A substantial increase of the conductivity inside nanoparticles and of the charge transport between them is achieved upon calcination at 500 °C. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b05091
  • 2015 • 421 Continuous electrophoretic deposition and electrophoretic mobility of ligand-free, metal nanoparticles in liquid flow
    Koenen, S. and Streubel, R. and Jakobi, J. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
    Journal of the Electrochemical Society 162 D174-D179 (2015)
    Direct current electrophoretic deposition (DC-EPD) of ligand-free metal nanoparticles in a flow-through reactor is studied by analyzing the educt colloid and the outflow of the flow through chamber while the concentration of the colloid and the strength of the electric field is varied.Metal nanoparticles synthesized by pulsed laser ablation in liquid (PLAL) are used to ensure that the colloidal nanoparticle surface is free of any ligands and that the colloid's stability and movement in an electric field is solely influenced by electrostatic forces. Electrophoretic mobility and deposition kinetics of these ligand-free nanoparticles on plain surfaces are examined for different electric field strengths. Additionally, a continuous liquid flow DC-EPD process is presented and optimized regarding deposition rate, colloid stability, and liquid flow rate. The reported parameter window for high deposition rates of nanoparticles without a negative impact on the colloid, allows to define an efficient stationary EPD process suitable for high throughput applications. © 2015 The Electrochemical Society.
    view abstractdoi: 10.1149/2.0811504jes
  • 2015 • 420 Controllable Synthesis of Mesoporous Peapod-like Co3O4@Carbon Nanotube Arrays for High-Performance Lithium-Ion Batteries
    Gu, D. and Li, W. and Wang, F. and Bongard, H. and Spliethoff, B. and Schmidt, W. and Weidenthaler, C. and Xia, Y. and Zhao, D. and Schüth, F.
    Angewandte Chemie - International Edition 54 7060-7064 (2015)
    Abstract Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li+ insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co<inf>3</inf>O<inf>4</inf> nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co<inf>3</inf>O<inf>4</inf> nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201501475
  • 2015 • 419 Core-Shell Nanoparticles: Characterizing Multifunctional Materials beyond Imaging - Distinguishing and Quantifying Perfect and Broken Shells
    Tschulik, K. and Ngamchuea, K. and Ziegler, C. and Beier, M.G. and Damm, C. and Eychmueller, A. and Compton, R.G.
    Advanced Functional Materials 25 5149-5158 (2015)
    Core-shell nanoparticles (NPs) are amongst the most promising candidates in the development of new functional materials. Their fabrication and characterization are challenging, in particular when thin and intact shells are needed. To date no technique has been available that differentiates between intact and broken or cracked shells. Here a method is presented to distinguish and quantify these types of shells in a single cyclic voltammetry experiment by using the different electrochemical reactivities of the core and the shell material. A simple comparison of the charge measured during the stripping of the core material before and after the removal of the shell makes it possible to determine the quality of the shells and to estimate their thickness. As a proof-of-concept two multifunctional examples of core-shell NPs, Fe<inf>3</inf>O<inf>4</inf>@Au and Au@SnO<inf>2</inf>, are used. This general and original method can be applied whenever core and shell materials show different redox properties. Because billions of NPs are probed simultaneously and at a low cost, this method is a convenient new screening tool for the development of new multifunctional core-shell materials and is hence a powerful complementary technique or even an alternative to the state-of-the-art characterization of core-shell NPs by TEM. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201501556
  • 2015 • 418 Covalently bonded compounds of heavy group 15/16 elements - Synthesis, structure and potential application in material sciences
    Schulz, S.
    Coordination Chemistry Reviews 297-298 49-76 (2015)
    Our understanding on the nature of weak intermolecular metal-metal interactions as well as of multiple bonding in group 15/16 chemistry, in particular of compounds containing the heaviest elements of both groups - Sb, Bi, Se, and Te - is still scarce. These types of interactions are particularly important for the chemical and physical properties of such main group element compounds. For instance, the formation and disruption of weak intermolecular metal-metal interactions are the origin of the so-called thermochroism. The structural characterization of compounds containing sterically less demanding organic substituents is therefore of particular interest, since the capability of small substituents to kinetically stabilize the respective metal centers - and hence to suppress intermolecular interactions - is expected to be rather less pronounced. We will herein summarize the most recent results reported for the synthesis and structural characterization of group 15/16 compounds containing a direct (polar-covalent) element-element bond including compounds containing a terminal, formally double bond. In addition, the capability of selected compounds to serve as single-source precursor for the synthesis of the corresponding nanomaterials, in particular Sb<inf>2</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf>, by using wet chemical methods as well as gas phase approaches such as metal organic chemical vapor deposition (MOCVD) processes will be demonstrated. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.ccr.2014.11.003
  • 2015 • 417 Cysteine-containing oligopeptide β-sheets as redispersants for agglomerated metal nanoparticles
    Mizutaru, T. and Sakuraba, T. and Nakayama, T. and Marzun, G. and Wagener, P. and Rehbock, C. and Barcikowski, S. and Murakami, K. and Fujita, J. and Ishii, N. and Yamamoto, Y.
    Journal of Materials Chemistry A 3 17612-17619 (2015)
    Oligopeptide β-sheets comprising a fluorenyl methoxy carbonyl (Fmoc) group on its N-terminus and five amino acid residues of cysteine, lysine and valine displays redispersive properties with respect to agglomerated metal nanoparticles (MNPs, M = Au, Cu, Pt and Pd). The ligand-free MNPs prepared by a laser ablation technique in liquid maintain a high dispersion state due to the inherent surface charges delivered by anionic species present in solution, but may agglomerate after the preparation depending on concentration or salinity. We show how the agglomerated MNPs can be returned to the dispersed state by adding the Fmoc-oligopeptide β-sheets in methanol, as characterized by photoabsorption spectroscopy and transmission electron microscopy. Systematic studies in which we vary the concentration, the amino acid sequences and the secondary structures of a series of the oligopeptides clarify that the β-sheet structure is essential for the redispersion of the MNPs, where metal-binding thiol groups are integrated on one side and positively charged amino groups are located on the other side of the β-sheet. A possible mechanism for the redispersion may be that the agglomerated MNPs are subsequently enwrapped by the flexible β-sheets and gradually separated due to the reconstruction of peptide β-sheets under the assembly/disassembly equilibrium. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5ta02098k
  • 2015 • 416 Diffusional impacts of nanoparticles on microdisc and microwire electrodes: The limit of detection and first passage statistics
    Eloul, S. and Kätelhön, E. and Batchelor-McAuley, C. and Tschulik, K. and Compton, R.G.
    Journal of Electroanalytical Chemistry 755 136-142 (2015)
    We derive approximate expressions for the average number of diffusive impacts/hits of nanoparticles on microdisc and microwire electrodes for the case where the impact leads to the loss of the nanoparticles from solution either via irreversible adsorption or complete electro-dissolution. The theory can also be applied to sub-micrometre size electrodes (nano-electrodes). The resulting equations can be utilised to analyse the number of impacts and its variance in the 'nano-impact' experiment. We also provide analytical expressions for the first passage time of an impact for dilute nanoparticle solutions in the continuum limit of Fickian diffusion. The expressions for the first passage times are used to estimate the lower limit of detection in ultra-dilute nanoparticle solutions for typical nano-impact experiments, and show the advantage of using microwire electrodes in ultra-dilute solutions or solutions containing larger nano-particles. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jelechem.2015.07.042
  • 2015 • 415 Effect of process parameters on the formation of laser-induced nanoparticles during material processing with continuous solid-state lasers
    Scholz, T. and Dickmann, K. and Ostendorf, A. and Uphoff, H. and Michalewicz, M.
    Journal of Laser Applications 27 (2015)
    During laser material processing with high laser beam intensities, a laser-induced vapor formation can occur. Due to the shockwave behavior of the vapor plume and the associated rapid cooling, a significant particle formation can be initiated by nucleation. The laser radiation interacts with the particles which can result in a dynamic change of the intensity distribution on the surface. Especially in the field of laser remote processing, the attenuation of laser radiation by nanoparticles can influence the process stability and reduce the processing quality. The presented work is focused on the particle formation at a height of 10 mm above the material surface during the laser welding of stainless steel with a fiber laser. The laser beam intensity on the surface was varied between 1.3 and 5.1 MW/cm2. Transmission electron microscopy images of the nanoparticles and high speed images of the vapor propagation in the ambient atmosphere were analyzed. The attenuation of a probe beam in the vapor plume was evaluated in dependence on the wavelength. The results indicate a linear connection between the laser beam power and the particle formation rate. © 2015 Laser Institute of America.
    view abstractdoi: 10.2351/1.4916081
  • 2015 • 414 Effect of the specific surface area on thermodynamic and kinetic properties of nanoparticle anatase TiO2 in lithium-ion batteries
    Madej, E. and Klink, S. and Schuhmann, W. and Ventosa, E. and La Mantia, F.
    Journal of Power Sources 297 140-148 (2015)
    Anatase TiO<inf>2</inf> nanoparticles with a specific surface area of 100 m2 g-1 and 300 m2 g-1 have been investigated as negative insertion electrode material for lithium-ion batteries. Galvanostatic intermittent titration (GITT) and electrochemical impedance spectroscopy (EIS) were used to investigate the effect of the specific surface area on the performance of the material. GITT was performed at C/10 rate, followed by an EIS measurement after each relaxation step. Separation of kinetic and thermodynamic contributions to the overpotential of the phase transformation on Li+ (de-)insertion allowed revealing a dependency of both terms on the specific surface area. The material with higher surface area undergoes intrinsic transformation during the initial cycles affecting the thermodynamics of (de-)insertion while the sample with lower surface area shows large and asymmetric kinetic hindrances. For the material with 15 nm particles, Li+ de-insertion appears to have a higher resistance than lithium insertion. © 2015, Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jpowsour.2015.07.079
  • 2015 • 413 Electrochemical detection of single E. coli bacteria labeled with silver nanoparticles
    Sepunaru, L. and Tschulik, K. and Batchelor-McAuley, C. and Gavish, R. and Compton, R.G.
    Biomaterials Science 3 816-820 (2015)
    A proof-of-concept for the electrochemical detection of single Escherichia coli bacteria decorated with silver nanoparticles is reported. Impacts of bacteria with an electrode - held at a suitably oxidizing potential - lead to an accompanying burst of current with each collision event. The frequency of impacts scales with the concentration of bacteria and the charge indicates the extent of decoration. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5bm00114e
  • 2015 • 412 Enhanced biomedical heat-triggered carriers via nanomagnetism tuning in ferrite-based nanoparticles
    Angelakeris, M. and Li, Z.-A. and Hilgendorff, M. and Simeonidis, K. and Sakellari, D. and Filippousi, M. and Tian, H. and Van Tendeloo, G. and Spasova, M. and Acet, M. and Farle, M.
    Journal of Magnetism and Magnetic Materials 381 179-187 (2015)
    Biomedical nanomagnetic carriers are getting a higher impact in therapy and diagnosis schemes while their constraints and prerequisites are more and more successfully confronted. Such particles should possess a well-defined size with minimum agglomeration and they should be synthesized in a facile and reproducible high-yield way together with a controllable response to an applied static or dynamic field tailored for the specific application. Here, we attempt to enhance the heating efficiency in magnetic particle hyperthermia treatment through the proper adjustment of the core-shell morphology in ferrite particles, by controlling exchange and dipolar magnetic interactions at the nanoscale. Thus, core-shell nanoparticles with mutual coupling of magnetically hard (CoFe2O4) and soft (MnFe2O4) components are synthesized with facile synthetic controls resulting in uniform size and shell thickness as evidenced by high resolution transmission electron microscopy imaging, excellent crystallinity and size monodispersity. Such a magnetic coupling enables the fine tuning of magnetic anisotropy and magnetic interactions without sparing the good structural, chemical and colloidal stability. Consequently, the magnetic heating efficiency of CoFe2O4 and MnFe2O4 core-shell nanoparticles is distinctively different from that of their counterparts, even though all these nanocrystals were synthesized under similar conditions. For better understanding of the AC magnetic hyperthermia response and its correlation with magnetic-origin features we study the effect of the volume ratio of magnetic hard and soft phases in the bimagnetic core-shell nanocrystals. Eventually, such particles may be considered as novel heating carriers that under further biomedical functionalization may become adaptable multifunctional heat-triggered nanoplatforms. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jmmm.2014.12.069
  • 2015 • 411 Formation and stabilization of ZnO nanoparticles inside MCM-48 porous support via post-synthetic organometallic route
    Bandyopadhyay, M. and Gies, H. and Grünert, W. and Van Den Berg, M. and Birkner, A.
    Advanced Materials Letters 6 978-983 (2015)
    The interpenetrating 3-dimensional channel system of silica MCM-48 has been selected for the deposition of ZnO nanoparticles. The post-synthetic organometallic route was employed to load the mesoporous silica with ZnO-precursor molecule. Calcination of the composite transformed the organometallic sorbate to the corresponding metal oxide. X-ray powder diffraction, N2-Adsorption and TEM measurement have supported the efficient loading and growth of ZnO particles in the channels of mesoporous silica matrix. EXAFS analysis (ZnK-edges) also complemented the metal uptake. Presence of nano-dispersed and nanosized ZnO particles confined by the mesoporous pore system was established by TEM and EXAFS analysis. © 2015 VBRI Press.
    view abstractdoi: 10.5185/amlett.2015.5963
  • 2015 • 410 From in situ characterization to process control of quantum dot systems
    Segets, D. and Peukert, W.
    Procedia Engineering 102 575-581 (2015)
    Quantum confined semiconductor nanoparticles (quantum dots, QDs) are promising candidates for various applications in emerging fields like electronics, solar cells, sensors and diagnostics. However, a larger scale production of QDs at high product quality is still missing. One of the key requirements to address this issue in the near future was identified to be a fast and in situ applicable characterization method. Suitable characterization requires knowledge on the full shape of the particle size distributions (PSDs) under investigation. Thus, determination of a mean particle size together with the width of the PSD is not sufficient. In the following, a method will be presented that allows the derivation of arbitrary shaped PSDs for QDs with direct band gap based on their optical absorbance spectra. After validation of the technique by means of ZnO nanoparticles the transfer of the concept to other QD materials like PbS and PbSe will be proven. Therefore we will extend our methodology and show how our approach can be used to derive spectral properties like the size dependent band gap energy. This is realized by proper calibration of the calculation results against PSDs determined by an independent analysis technique like transmission electron microscopy (TEM). © 2015 The Authors.
    view abstractdoi: 10.1016/j.proeng.2015.01.129
  • 2015 • 409 Gene silencing of the pro-inflammatory cytokine TNF-α with siRNA delivered by calcium phosphate nanoparticles, quantified by different methods
    Neuhaus, B. and Frede, A. and Westendorf, A.M. and Epple, M.
    Journal of Materials Chemistry B 3 7186-7193 (2015)
    The pro-inflammatory cytokine TNF-α was silenced by treating MODE-K cells with triple-shell calcium phosphate nanoparticles. These consisted of a core of calcium phosphate, followed by a shell of siRNA, then a shell of calcium phosphate to protect the siRNA from nucleases and finally a shell of poly(ethyleneimine) for colloidal stabilization and to give the particles a positive charge. First, the gene silencing efficiency was demonstrated with HeLa-eGFP cells and determined by manually counting the green fluorescent cells, by quantitative FACS analysis of the green fluorescence per cell, and by qPCR at the RNA level. Cell counting gave the highest degrees of eGFP expression, but FACS and qPCR gave more accurate data as they are not probing the cell colour (green or not green) only as yes/no property. This was transposed to the inflammatory relevant mouse cell line MODE-K that was previously stimulated with LPS to induce the expression of TNF-α. By application of the nanoparticles, the TNF-α expression was reduced almost to the original level, as shown by qPCR. Thus, calcium phosphate nanoparticles are well suited to reduce inflammatory reactions by silencing the corresponding cytokines, e.g. TNF-α. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5tb01377a
  • 2015 • 408 How electrophoretic deposition with ligand-free platinum nanoparticles affects contact angle
    Heinemann, A. and Koenen, S. and Schwabe, K. and Rehbock, C. and Barcikowski, S.
    Key Engineering Materials 654 218-223 (2015)
    Electrophoretic deposition of ligand-free platinum nanoparticles has been studied to elucidate how wettability, indicated by contact angle measurements, is linked to vital parameters of the electrophoretic deposition process. These parameters, namely the colloid concentration, electric field strength and deposition time, have been systematically varied in order to determine their influence on the contact angle. Additionally, scanning electron microscopy has been used to confirm the homogeneity of the achieved coatings. © (2015) Trans Tech Publications, Switzerland.
    view abstractdoi: 10.4028/www.scientific.net/KEM.654.218
  • 2015 • 407 Hybrid biocomposite with a tunable antibacterial activity and bioactivity based on RF magnetron sputter deposited coating and silver nanoparticles
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Loza, K. and Prymak, O. and Epple, M.
    Applied Surface Science 329 212-218 (2015)
    In this work, we describe fabrication techniques used to prepare a multifunctional biocomposite based on a hydroxyapatite (HA) coating and silver nanoparticles (AgNPs). AgNPs synthesized by a wet chemical reduction method were deposited on Ti substrates using a dripping/drying method followed by deposition of calcium phosphate (CaP) coating via radio-frequency (RF) magnetron sputter-deposition. The negatively charged silver nanoparticles (zeta potential -21 mV) have a spherical shape with a metallic core diameter of 50 ± 20 nm. The HA coating was deposited as a dense nanocrystalline film over a surface of AgNPs. The RF-magnetron sputter deposition of HA films on the AgNPs layer did not affect the initial content of AgNPs on the substrate surface as well as NPs size and shape. SEM cross-sectional images taken using the backscattering mode revealed a homogeneous layer of AgNPs under the CaP layer. The diffraction patterns from the coatings revealed reflexes of crystalline HA and silver. The concentration of Ag ions released from the biocomposites after 7 days of immersion in phosphate and acetate buffers was estimated. The obtained results revealed that the amount of silver in the solutions was 0.27 ± 0.02 μg mL-1 and 0.54 ± 0.02 μg mL-1 for the phosphate and acetate buffers, respectively, which corresponded well with the minimum inhibitory concentration range known for silver ions in literature. Thus, this work establishes a new route to prepare a biocompatible layer using embedded AgNPs to achieve a local antibacterial effect. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2014.12.153
  • 2015 • 406 Impact of ambient pressure on titania nanoparticle formation during spray-flame synthesis
    Hardt, S. and Wlokas, I. and Schulz, C. and Wiggers, H.
    Journal of Nanoscience and Nanotechnology 15 9449-9456 (2015)
    Nanocrystalline titania was synthesized via liquid-fed spray-flame synthesis in a hermetically closed system at various pressures. Titanium tetraisopropoxide dissolved in isopropanol was used as precursor. The size, crystal structure, degree of agglomeration, morphology and the band gap of the as-prepared particles were investigated ex situ by nitrogen adsorption, transmission electron microscopy, X-ray diffraction, and UV-VIS absorption spectroscopy. In comparison to synthesis at atmospheric pressure it was found that decreasing pressure has a significant influence on the particle size distribution leading to smaller particles with reduced geometric standard deviation while particle morphology and crystal structure are not affected. Computational fluid dynamics simulations support the experimental findings also indicating a significant decrease in particle size at reduced pressure. Although it is well known that decreasing pressure leads to smaller particle sizes, it is (to our knowledge) the first time that this relation was investigated for spray-flame synthesis. Copyright © 2015 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jnn.2015.10607
  • 2015 • 405 Influence of gold, silver and gold-silver alloy nanoparticles on germ cell function and embryo development
    Taylor, U. and Tiedemann, D. and Rehbock, C. and Kues, W.A. and Barcikowski, S. and Rath, D.
    Beilstein Journal of Nanotechnology 6 651-664 (2015)
    The use of engineered nanoparticles has risen exponentially over the last decade. Applications are manifold and include utilisation in industrial goods as well as medical and consumer products. Gold and silver nanoparticles play an important role in the current increase of nanoparticle usage. However, our understanding concerning possible side effects of this increased exposure to particles, which are frequently in the same size regime as medium sized biomolecules and accessorily possess highly active surfaces, is still incomplete. That particularly applies to reproductive aspects, were defects can be passed onto following generations. This review gives a brief overview of the most recent findings concerning reprotoxicological effects. The here presented data elucidate how composition, size and surface modification of nanoparticles influence viablility and functionality of reproduction relevant cells derived from various animal models. While in vitro cultured embryos displayed no toxic effects after the microinjection of gold and silver nanoparticles, sperm fertility parameters deteriorated after co-incubation with ligand free gold nanoparticles. However, the effect could be alleviated by bio-coating the nanoparticles, which even applies to silver and silver-rich alloy nanoparticles. The most sensitive test system appeared to be in vitro oocyte maturation showing a dose-dependent response towards protein (BSA) coated gold-silver alloy and silver nanoparticles leading up to complete arrest of maturation. Recent biodistribution studies confirmed that nanoparticles gain access to the ovaries and also penetrate the blood-testis and placental barrier. Thus, the design of nanoparticles with increased biosafety is highly relevant for biomedical applications. © 2015 Taylor et al.
    view abstractdoi: 10.3762/bjnano.6.66
  • 2015 • 404 Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se2 solar cells
    Yin, G. and Steigert, A. and Andrae, P. and Goebelt, M. and Latzel, M. and Manley, P. and Lauermann, I. and Christiansen, S. and Schmid, M.
    Applied Surface Science 355 800-804 (2015)
    Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se2 (CIGSe) solar cells is investigated. X-ray photoelectron spectroscopy results show that Ag nanoparticles underneath a Sn:In2O3 back contact could not be thermally passivated even at a low substrate temperature of 440 °C during CIGSe deposition. It is shown that a 50 nm thick Al2O3 film prepared by atomic layer deposition is able to block the diffusion of Ag, clearing the thermal obstacle in utilizing Ag nanoparticles as a back reflector in ultra-thin CIGSe solar cells. Via 3-D finite element optical simulation, it is proved that the Ag nanoparticles show the potential to contribute the effective absorption in CIGSe solar cells. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.07.195
  • 2015 • 403 Iron-doped nickel oxide nanocrystals as highly efficient electrocatalysts for alkaline water splitting
    Fominykh, K. and Chernev, P. and Zaharieva, I. and Sicklinger, J. and Stefanic, G. and Döblinger, M. and Müller, A. and Pokharel, A. and Böcklein, S. and Scheu, C. and Bein, T. and Fattakhova-Rohlfing, D.
    ACS Nano 9 5180-5188 (2015)
    Efficient electrochemical water splitting to hydrogen and oxygen is considered a promising technology to overcome our dependency on fossil fuels. Searching for novel catalytic materials for electrochemical oxygen generation is essential for improving the total efficiency of water splitting processes. We report the synthesis, structural characterization, and electrochemical performance in the oxygen evolution reaction of Fe-doped NiO nanocrystals. The facile solvothermal synthesis in tert-butanol leads to the formation of ultrasmall crystalline and highly dispersible Fe<inf>x</inf>Ni<inf>1-x</inf>O nanoparticles with dopant concentrations of up to 20%. The increase in Fe content is accompanied by a decrease in particle size, resulting in nonagglomerated nanocrystals of 1.5-3.8 nm in size. The Fe content and composition of the nanoparticles are determined by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy measurements, while Mössbauer and extended X-ray absorption fine structure analyses reveal a substitutional incorporation of Fe(III) into the NiO rock salt structure. The excellent dispersibility of the nanoparticles in ethanol allows for the preparation of homogeneous ca. 8 nm thin films with a smooth surface on various substrates. The turnover frequencies (TOF) of these films could be precisely calculated using a quartz crystal microbalance. Fe<inf>0.1</inf>Ni<inf>0.9</inf>O was found to have the highest electrocatalytic water oxidation activity in basic media with a TOF of 1.9 s-1 at the overpotential of 300 mV. The current density of 10 mA cm-2 is reached at an overpotential of 297 mV with a Tafel slope of 37 mV dec-1. The extremely high catalytic activity, facile preparation, and low cost of the single crystalline Fe<inf>x</inf>Ni<inf>1-x</inf>O nanoparticles make them very promising catalysts for the oxygen evolution reaction. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.5b00520
  • 2015 • 402 Large scale Molecular Dynamics simulation of microstructure formation during thermal spraying of pure copper
    Wang, T. and Begau, C. and Sutmann, G. and Hartmaier, A.
    Surface and Coatings Technology 280 72-80 (2015)
    Thermal spray processes are widely used for the manufacture of advanced coating systems, e.g. metallic coatings for wear and corrosion protection. The desired coating properties are closely related to the microstructure, which is highly influenced by the processing parameters, such as temperature, size and velocity of the sprayed particles. In this paper, large scale Molecular Dynamics simulations are conducted to investigate the microstructure formation mechanisms during the spraying process of hot nano-particles onto a substrate at room temperature using pure copper as a benchmark material representing for a wider class of face-centered-cubic metals. To evaluate the influence of processing parameters on the coating morphology, a number of simulations are performed in which the initial temperature, size and velocity of copper particles are systematically varied in order to investigate the thermal and microstructural evolution during impaction. Two distinct types of microstructural formation mechanisms, resulting in different coating morphologies, are observed in the present investigation, which are either governed by plastic deformation or by the process of melting and subsequent solidification. Furthermore, a thermodynamically motivated model as a function of the particle temperature and velocity is developed, which predicts the microstructural mechanisms observed in the simulations. The results provide an elementary insight into the microstructure formation mechanisms on an atomistic scale, which can serve as basic input for continuum modeling of thermal spray process. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2015.08.034
  • 2015 • 401 Laser-based in situ measurement and simulation of gas-phase temperature and iron atom concentration in a pilot-plant nanoparticle synthesis reactor
    Feroughi, O.M. and Hardt, S. and Wlokas, I. and Hülser, T. and Wiggers, H. and Dreier, T. and Schulz, C.
    Proceedings of the Combustion Institute 35 2299-2306 (2015)
    A scaled-up flame reactor for nanoparticle synthesis was investigated through a combination of in-situ laser-induced fluorescence (LIF) measurements and computational fluid dynamics (CFD) simulations with detailed chemistry. Multi-line NO-LIF was used for imaging gas-temperature and Fe-LIF for measurement of iron atom concentration. Despite the challenging environment of production reactors in an industrial environment, various conditions for stable flames with different gas flows with and without adding Fe(CO)5 as precursor for the synthesis of iron-oxide nanoparticles were investigated. In contrast to previous measurements in laminar lab-scale flames, a second mechanism for forming iron oxide nanoparticles was found via intermediate formation of iron clusters and elemental iron particles in hot, oxygen-free gas streams followed by subsequent oxidation. © 2014 Published by Elsevier Inc. on behalf of The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2014.05.039
  • 2015 • 400 Laser-induced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications
    Michelsen, H.A. and Schulz, C. and Smallwood, G.J. and Will, S.
    Progress in Energy and Combustion Science 51 2-48 (2015)
    The understanding of soot formation in combustion processes and the optimization of practical combustion systems require in situ measurement techniques that can provide important characteristics, such as particle concentrations and sizes, under a variety of conditions. Of equal importance are techniques suitable for characterizing soot particles produced from incomplete combustion and emitted into the environment. Additionally, the production of engineered nanoparticles, such as carbon blacks, may benefit from techniques that allow for online monitoring of these processes. In this paper, we review the fundamentals and applications of laser-induced incandescence (LII) for particulate diagnostics in a variety of fields. The review takes into account two variants of LII, one that is based on pulsed-laser excitation and has been mainly used in combustion diagnostics and emissions measurements, and an alternate approach that relies on continuous-wave lasers and has become increasingly popular for measuring black carbon in environmental applications. We also review the state of the art in the determination of physical parameters central to the processes that contribute to the non-equilibrium nanoscale heat and mass balances of laser-heated particles; these parameters are important for LII-signal analysis and simulation. Awareness of the significance of particle aggregation and coatings has increased recently, and the effects of these characteristics on the LII technique are discussed. Because of the range of experimental constraints in the variety of applications for which laser-induced incandescence is suited, many implementation approaches have been developed. This review discusses considerations for selection of laser and detection characteristics to address application-specific needs. The benefits of using LII for measurements of a range of nanoparticles in the fields mentioned above are demonstrated with some typical examples, covering simple flames, internal-combustion engines, exhaust emissions, the ambient atmosphere, and nanoparticle production. We also remark on less well-known studies employing LII for particles suspended in liquids. An important aspect of the paper is to critically assess the improvement in the understanding of the fundamental physical mechanisms at the nanoscale and the determination of underlying parameters; we also identify further research needs in these contexts. Building on this enhanced capability in describing the underlying complex processes, LII has become a workhorse of particulate measurement in a variety of fields, and its utility continues to be expanding. When coupled with complementary methods, such as light scattering, probe-sampling, molecular-beam techniques, and other nanoparticle instrumentation, new directions for research and applications with LII continue to materialize. © 2015 Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.pecs.2015.07.001
  • 2015 • 399 Ligand-free Gold Nanoparticles as a Reference Material for Kinetic Modelling of Catalytic Reduction of 4-Nitrophenol
    Gu, S. and Kaiser, J. and Marzun, G. and Ott, A. and Lu, Y. and Ballauff, M. and Zaccone, A. and Barcikowski, S. and Wagener, P.
    Catalysis Letters 145 1105-1112 (2015)
    The reduction of 4-nitrophenol by sodium borohydride is a common model reaction to test the catalytic activity of metal nanoparticles. As all reaction steps proceed solely on the surface of the metal nanoparticles (Langmuir-Hinshelwood model), ligand-coverage of metal nanoparticles impedes the merging of theory and experiment. Therefore we analyzed the catalytic activity of bare gold nanoparticles prepared by laser ablation in liquid without any stabilizers or ligands. The catalytic reaction is characterized by a full kinetic analysis including 4-hydroxylaminophenol as an intermediate species. Excellent agreement between theory and experiment is found. Moreover, the suspension of the nanoparticles remains stable. Hence, ligand-free nanoparticles can be used as a reference material for mechanistic studies of catalytic reactions. In addition, the analysis shows that gold nanoparticles synthesized by laser ablation are among the most active catalysts for this reaction. (Graph Presented). © 2015 Springer Science+Business Media.
    view abstractdoi: 10.1007/s10562-015-1514-7
  • 2015 • 398 Light Coupling and Trapping in Ultrathin Cu(In,Ga)Se2 Solar Cells Using Dielectric Scattering Patterns
    Van Lare, C. and Yin, G. and Polman, A. and Schmid, M.
    ACS Nano 9 9603-9613 (2015)
    We experimentally demonstrate photocurrent enhancement in ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells with absorber layers of 460 nm by nanoscale dielectric light scattering patterns printed by substrate conformal imprint lithography. We show that patterning the front side of the device with TiO2 nanoparticle arrays results in a small photocurrent enhancement in almost the entire 400-1200 nm spectral range due to enhanced light coupling into the cell. Three-dimensional finite-difference time-domain simulations are in good agreement with external quantum efficiency measurements. Patterning the Mo/CIGSe back interface using SiO2 nanoparticles leads to strongly enhanced light trapping, increasing the efficiency from 11.1% for a flat to 12.3% for a patterned cell. Simulations show that optimizing the array geometry could further improve light trapping. Including nanoparticles at the Mo/CIGSe interface leads to substantially reduced parasitic absorption in the Mo back contact. Parasitic absorption in the back contact can be further reduced by fabricating CIGSe cells on top of a SiO2-patterned In2O3:Sn (ITO) back contact. Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitransparent geometry. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.5b04091
  • 2015 • 397 Light Induced H2 Evolution from a Biophotocathode Based on Photosystem 1 - Pt Nanoparticles Complexes Integrated in Solvated Redox Polymers Films
    Zhao, F. and Conzuelo, F. and Hartmann, V. and Li, H. and Nowaczyk, M.M. and Plumeré, N. and Rögner, M. and Schuhmann, W.
    Journal of Physical Chemistry B 119 13726-13731 (2015)
    We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)2Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 ± 0.4 μA cm-2) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H2 evolution. Direct evidence for the latter process is provided by monitoring the H2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.5b03511
  • 2015 • 396 Magneto-responsive alginate capsules
    Degen, P. and Zwar, E. and Schulz, I. and Rehage, H.
    Journal of Physics Condensed Matter 27 (2015)
    Upon incorporation of magnetic nanoparticles (mNPs) into gels, composite materials called ferrogels are obtained. These magneto-responsive systems have a wide range of potential applications including switches and sensors as well as drug delivery systems. In this article, we focus on the properties of calcium alginate capsules, which are widely used as carrier systems in medicine and technology. We studied the incorporation of different kinds of mNPs in matrix capsules and in the core and the shell of hollow particles. We found out that not all particle-alginate or particle-CaCl<inf>2</inf> solution combinations were suitable for a successful capsule preparation on grounds of a destabilization of the nanoparticles or the polymer. For those systems allowing the preparation of switchable beads or capsules, we systematically studied the size and microscopic structure of the capsules, their magnetic behavior and mechanical resistance. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/27/19/194105
  • 2015 • 395 Mapping near-field plasmonic interactions of silver particles with scanning near-field optical microscopy measurements
    Andrae, P. and Song, M. and Haggui, M. and Fumagalli, P. and Schmid, M.
    Proceedings of SPIE - The International Society for Optical Engineering 9547 (2015)
    A scanning near-field optical microscope (SNOM) is a powerful tool to investigate optical effects that are smaller than Abbe's limit. Its greatest strength is the simultaneous measurement of high-resolution topography and optical nearfield data that can be correlated to each other. However, the resolution of an aperture SNOM is always limited by the probe. It is a technical challenge to fabricate small illumination tips with a well-defined aperture and high transmission. The aperture size and the coating homogeneity will define the optical resolution and the optical image whereas the tip size and shape influence the topographic accuracy. Although the technique has been developing for many years, the correlation between simulated near-field data and measurement is still not convincing. To overcome this challenge, the mapping of near-field plasmonic interactions of silver nanoparticles is investigated. Different nanocluster samples with diverse distributions of silver particles are characterized via SNOM in illumination and collection mode. This will lead to topographical and optical images that can be used as an input for SNOM simulations with the aim of estimating optical artifacts. Including tip, particles, and substrate, our finite-elementmethod (FEM) simulations are based on the realistic geometry. Correlating the high-precision SNOM measurement and the detailed simulation of a full image scan will enable us to draw conclusions regarding near-field enhancements caused by interacting particles. © 2015 SPIE.
    view abstractdoi: 10.1117/12.2187358
  • 2015 • 394 Measurements of nanoscale TiO2 and Al2O3 in industrial workplace environments – Methodology and results
    Kaminski, H. and Beyer, M. and Fissan, H. and Asbach, C. and Kuhlbusch, T.A.J.
    Aerosol and Air Quality Research 15 129-141 (2015)
    The possible release of engineered nanomaterials was investigated based on a previously developed but now refined methodology. Data from altogether eight industrial work areas in production plants of nanostructured TiO2 and Al2O3 particles were obtained and used to test the methodology and to derive a first assessment of possible exposure of workers. Particle size distributions were determined in work area environments with concurrent measurements at a comparison site. Data from the comparison site were used to estimate the particle background level in the work area and distinguish it from potentially released nanomaterial. The analysis is based on the comparison of time resolved data from the work area and the comparison site as well as data determined during periods with and without work activities in the work area. The data analysis method introduced delivers size-resolved information on the potential nanoparticle exposure of workers. A significant release of particles in the size range 100–562 nm was observed in the work area of bagging aluminum oxide and is stemming from damaging or overfilling of bags, and the necessary activities during the cleaning of the work area. The maximum particle diameter of these particles was around 340 nm. At all other investigated locations no significant releases of particles in the size range 100–562 nm were determined. Also, no significant release of particles < 100 nm was observed in all work areas. The average PM10 exposure during the work activities varied from 48 to 1,330 µg/m3 in the different work areas. The maximum concentrations of aluminum were 118 µg/m3 and 58 µg/m3 for PM10 and PM1, respectively, during the bagging of Al2O3 in small bags. In comparison, the maximum concentrations of titanium were 550 µg/m3 and 434 µg/m3 for PM10 and PM1, respectively, during the bagging of TiO2 and indicate a significant release of coarser particles. © Taiwan Association for Aerosol Research.
    view abstractdoi: 10.4209/aaqr.2014.03.0065
  • 2015 • 393 Mesoporous Silica Supported Au and AuCu Nanoparticles for Surface Plasmon Driven Glycerol Oxidation
    Schünemann, S. and Dodekatos, G. and Tüysüz, H.
    Chemistry of Materials 27 7743-7750 (2015)
    Herein, we report for the first time the visible-light-assisted rate enhancement for glycerol oxidation using direct plasmonic photocatalysis. Au nanoparticles were loaded on various mesoporous SiO2 supports, and the catalytic performance was investigated with and without visible-light illumination. Monodispersed mesoporous silica spheres loaded with Au nanoparticles demonstrated a superior photoassisted catalytic rate enhancement compared to Au loaded ordered mesoporous silica (SBA-15, KIT-6, and MCM-41). The enhancement is attributed to the particle size of the Au nanoparticles and better light interaction resulting from the small SiO2 domains. Au loaded monodispersed mesoporous silica spheres exhibit a constant and remarkably small particle diameter of 2 nm at Au loadings of up to 15 wt % as a result of the support's small domain size and efficient pore confinement. The performance of the Au catalyst could be further improved by preparing bimetallic AuCu nanoparticles. Synergistic effects between Au and Cu improved the glycerol conversion by a factor of 2.5 and the dihydroxyacetone selectivity from 80% to 90% compared to monometallic Au catalysts. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.5b03520
  • 2015 • 392 Metal-halide Nanoparticle Formation: Electrolytic and Chemical Synthesis of Mercury(I) Chloride Nanoparticles
    Bartlett, T.R. and Batchelor-Mcauley, C. and Tschulik, K. and Jurkschat, K. and Compton, R.G.
    ChemElectroChem 2 522-528 (2015)
    Mercury(I) chloride (Hg<inf>2</inf>Cl<inf>2</inf>) nanoparticles (NPs) are synthesised for the first time by using two different techniques. First, particles are formed by implosion of a calomel nanolayer, induced by partial electrolysis at a mercury hemisphere microelectrode. The resulting NPs are then characterised by the nanoimpact method, demonstrating the first time metal chloride NPs have been sized by this technique and showing the ability to form and study NPs insitu. Second, Hg<inf>2</inf>Cl<inf>2</inf> NPs are synthesised by using the precipitation reaction of Hg<inf>2</inf>(NO<inf>3</inf>)<inf>2</inf> with KCl. The NPs are characterised on both mercury and carbon microelectrodes and their size is found to agree with TEM results. Sizable studies: Mercury(I) chloride (Hg<inf>2</inf>Cl<inf>2</inf>) nanoparticles (NPs) are synthesised for the first time by using two different techniques. First, particles are formed by implosion of a calomel nanolayer, induced by partial electrolysis at a mercury hemisphere microelectrode. Second, Hg<inf>2</inf>Cl<inf>2</inf> NPs are synthesised by the precipitation reaction between Hg<inf>2</inf>(NO<inf>3</inf>)<inf>2</inf> and KCl. The NPs are characterised on both mercury and carbon microelectrodes by using the nanoimpact method and their size is found to agree with TEM results. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201402401
  • 2015 • 391 Microwave plasma synthesis of Si/Ge and Si/WSi2 nanoparticles for thermoelectric applications
    Petermann, N. and Schneider, T. and Stötzel, J. and Stein, N. and Weise, C. and Wlokas, I. and Schierning, G. and Wiggers, H.
    Journal of Physics D: Applied Physics 48 (2015)
    The utilization of microwave-based plasma systems enables a contamination-free synthesis of highly specific nanoparticles in the gas phase. A reactor setup allowing stable, long-term operation was developed with the support of computational fluid dynamics. This paper highlights the prospects of gas-phase plasma synthesis to produce specific materials for bulk thermoelectrics. Taking advantage of specific plasma reactor properties such as Coulomb repulsion in combination with gas temperatures considerably higher than 1000 K, spherical and non-aggregated nanoparticles of multiple compositions are accessible. Different strategies towards various nanostructured composites and alloys are discussed. It is shown that, based on doped silicon/germanium alloys and composites, thermoelectric materials with zT values up to almost unity can be synthesized in one step. First experimental results concerning silicon/tungsten silicide thermoelectrics applying the nanoparticle-in-alloy idea are presented indicating that this concept might work. However, it is found that tungsten silicides show a surprising sinter activity more than 1000 K below their melting temperature. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/48/31/314010
  • 2015 • 390 miR-542-3p exerts tumor suppressive functions in neuroblastoma by downregulating survivin
    Althoff, K. and Lindner, S. and Odersky, A. and Mestdagh, P. and Beckers, A. and Karczewski, S. and Molenaar, J.J. and Bohrer, A. and Knauer, S. and Speleman, F. and Epple, M. and Kozlova, D. and Yoon, S. and Baek, K. and Vandesom...
    International Journal of Cancer 136 1308-1320 (2015)
    MicroRNAs (miRNAs) are deregulated in a variety of human cancers, including neuroblastoma, the most common extracranial tumor of childhood. We previously reported a signature of 42 miRNAs to be highly predictive of neuroblastoma outcome. One miRNA in this signature, miR-542, was downregulated in tumors from patients with adverse outcome. Reanalysis of quantitative PCR and next-generation sequencing transcript data revealed that miR-542-5p as well as miR-542-3p expression is inversely correlated with poor prognosis in neuroblastoma patients. We, therefore, analyzed the function of miR-542 in neuroblastoma tumor biology. Ectopic expression of miR-542-3p in neuroblastoma cell lines reduced cell viability and proliferation, induced apoptosis and downregulated Survivin. Survivin expression was also inversely correlated with miR-542-3p expression in primary neuroblastomas. Reporter assays confirmed that miR-542-3p directly targeted Survivin. Downregulating Survivin using siRNA copied the phenotype of miR-542-3p expression in neuroblastoma cell lines, while cDNA-mediated ectopic expression of Survivin partially rescued the phenotype induced by miR-542-3p expression. Treating nude mice bearing neuroblastoma xenografts with miR-542-3p-loaded nanoparticles repressed Survivin expression, decreased cell proliferation and induced apoptosis in the respective xenograft tumors. We conclude that miR-542-3p exerts its tumor suppressive function in neuroblastoma, at least in part, by targeting Survivin. Expression of miR-542-3p could be a promising therapeutic strategy for treating aggressive neuroblastoma. © 2014 UICC.
    view abstractdoi: 10.1002/ijc.29091
  • 2015 • 389 Multifunctional calcium phosphate nanoparticles for combining near-infrared fluorescence imaging and photodynamic therapy
    Haedicke, K. and Kozlova, D. and Gräfe, S. and Teichgräber, U. and Epple, M. and Hilger, I.
    Acta Biomaterialia 14 197-207 (2015)
    Photodynamic therapy (PDT) of tumors causes skin photosensitivity as a result of unspecific accumulation behavior of the photosensitizers. PDT of tumors was improved by calcium phosphate nanoparticles conjugated with (i) Temoporfin as a photosensitizer, (ii) the RGDfK peptide for favored tumor targeting and (iii) the fluorescent dye molecule DY682-NHS for enabling near-infrared fluorescence (NIRF) optical imaging in vivo. The nanoparticles were characterized with regard to size, spectroscopic properties and uptake into CAL-27 cells. The nanoparticles had a hydrodynamic diameter of approximately 200 nm and a zeta potential of around +22 mV. Their biodistribution at 24 h after injection was investigated via NIRF optical imaging. After treating tumor-bearing CAL-27 mice with nanoparticle-PDT, the therapeutic efficacy was assessed by a fluorescent DY-734-annexin V probe at 2 days and 2 weeks after treatment to detect apoptosis. Additionally, the contrast agent IRDye® 800CW RGD was used to assess tumor vascularization (up to 4 weeks after PDT). After nanoparticle-PDT in mice, apoptosis in the tumor was detected after 2 days. Decreases in tumor vascularization and tumor volume were detected in the next few days. Calcium phosphate nanoparticles can be used as multifunctional tools for NIRF optical imaging, PDT and tumor targeting as they exhibited a high therapeutic efficacy, being capable of inducing apoptosis and destroying tumor vascularization. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actbio.2014.12.009
  • 2015 • 388 Nano- And microlenses as concepts for enhanced performance of solar cells
    Schmid, M. and Manley, P.
    Journal of Photonics for Energy 5 (2015)
    Both metallic nanoparticles exhibiting plasmonic effects and dielectric nanoparticles coupling the light into resonant modes have shown successful applications to photovoltaics. On a larger scale, microconcentrator optics promise to enhance solar cell efficiency and to reduce material consumption. Here, we want to create a link between the concentrators on the nano- and on the microscale. From metallic nanospheres, we turn to dielectric ones and then look at increasing radii to approach the microscale. The lenses are investigated with respect to their interaction with light using three-dimensional simulations with the finite-element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations, which give ray distributions in agreement with electric field intensities, can be applied. Calculations of back focal lengths in geometrical optics coincide with ray tracing results and allow insight into how the focal length can be tuned as a function of particle size, substrate refractive index, and the shape of the microlens. Despite the similarities we find for the nano- and the microlenses, integration into solar cells needs to be carefully adjusted, depending on the goals of material saving, concentration level, focal distance, and lens size. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
    view abstractdoi: 10.1117/1.JPE.5.057003
  • 2015 • 387 Nanocellulose-Templated Porous Titania Scaffolds Incorporating Presynthesized Titania Nanocrystals
    Ivanova, A. and Fravventura, M.C. and Fattakhova-Rohlfing, D. and Rathouský, J. and Movsesyan, L. and Ganter, P. and Savenije, T.J. and Bein, T.
    Chemistry of Materials 27 6205-6212 (2015)
    Nanocrystalline cellulose (NCC) is an abundant biogenic nanomaterial with unique properties that enables the efficient synthesis of mesoporous crystalline titania. We significantly enhance the photocatalytic activity of titania thin films by introducing solvothermally synthesized preformed anatase nanoparticles into a sol-gel based biotemplated titania scaffold. The resulting dual source titania thin films containing different amounts of preformed crystalline species were investigated by time-resolved microwave conductivity (TRMC) measurements and tested in the photocatalytic conversion of 4-chlorophenol. The gradual addition of preformed nanoparticles leads to a consistent increase of the mean size of titania crystalline domains, whereas the porosity of the composite is well-preserved due to the shape-persistent nature of the NCC template. Microwave conductivity studies establish increased photoconductivity of the films containing preformed anatase nanoparticles in comparison to that of films made without the nanoparticles. The synergistic features of the dual source titania, namely the improved crystalline properties brought by the preformed nanocrystals in combination with the high surface area provided by the NCC-templated sol-gel titania, result in a very high photocatalytic activity of the films in the photocatalytic decomposition of 4-chlorophenol. In quantitative terms, the dual source titania films prepared with 75% nanoparticles exhibit a first order degradation rate constant of 0.53 h-1 (1.47 × 10-4 sec-1), which strongly outperforms the activity of commercial P90 nanopowder showing a rate constant of 0.17 h-1 (0.47 × 10-4 sec-1) under the same conditions. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.5b00770
  • 2015 • 386 Nano-optical concept design for light management
    Schmid, M. and Tsakanikas, S. and Mangalgiri, G. and Andrae, P. and Song, M. and Yin, G. and Riedel, W. and Manley, P.
    Proceedings of SPIE - The International Society for Optical Engineering 9626 (2015)
    Efficient light management in optoelectronic devices requires nanosystems where high optical qualities coincide with suitable device integration. The requirement of chemical and electrical passivation for integrating nanostrutures in e.g.Thin film solar cells points towards the use of insulating and stable dielectric material, which however has to provide high scattering and near-fields as well. We investigate metal@dielectric core-shell nanoparticles and dielectric nanorods. Whereas core-shell nanoparticles can be simulated using Mie theory, nanorods of finite length are studied with the finite element method. We reveal that a metallic core within a thin dielectric shell can help to enhance scattering and near-field cross sections compared to a bare dielectric nanoparticle of the same radius. A dielectric nanorod has the benefit over a dielectric nanosphere in that it can generate much higher scattering cross sections and also give rise to a high near-field enhancement along its whole length. Electrical benefits of e.g. Ag@oxide nanoparticles in thin-film solar cells and ZnO nanorods in hybrid devices lie in reduction of recombination centers or close contact of the nanorod material with the surrounding organics, respectively. The optical benefit of dielectric shell material and elongated dielectric nanostructures is highlighted in this paper. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2191081
  • 2015 • 385 Nanoparticle Capping Agent Dynamics and Electron Transfer: Polymer-Gated Oxidation of Silver Nanoparticles
    Tanner, E.E.L. and Tschulik, K. and Tahany, R. and Jurkschat, K. and Batchelor-McAuley, C. and Compton, R.G.
    Journal of Physical Chemistry C 119 18808-18815 (2015)
    Capping agent-controlled stability of nanoparticles tailors them for different applications, but the associated particle-solvent dynamics are poorly understood. Herein, previously unseen capping agent-gated nanoparticle redox activity is observed for poly(ethylene glycol)-coated silver nanoparticles. This is revealed by stochastic nanoparticle stripping, probing one individual nanoparticle at a time, from an ensemble of surface-immobilized nanoparticles. Thus, new and previously inaccessible understanding is gained on the crucial role of capping agent dynamics on nanoparticle reactivity. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b05789
  • 2015 • 384 Nanostructure of wet-chemically prepared, polymer-stabilized silver-gold nanoalloys (6 nm) over the entire composition range
    Ristig, S. and Prymak, O. and Loza, K. and Gocyla, M. and Meyer-Zaika, W. and Heggen, M. and Raabe, D. and Epple, M.
    Journal of Materials Chemistry B 3 4654-4662 (2015)
    Bimetallic silver-gold nanoparticles were prepared by co-reduction using citrate and tannic acid in aqueous solution and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). The full composition range of silver:gold from 0:100 to 100:0 (n:n) was prepared with steps of 10 mol%. The nanoparticles were spherical, monodispersed, and had a diameter of ∼6 nm, except for Ag:Au 90:10 nanoparticles and pure Ag nanoparticles which were slightly larger. The size of the nanoalloys was determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). By means of X-ray powder diffraction (XRD) together with Rietveld refinement, precise lattice parameters, crystallite size and microstrain were determined. Scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) showed that the particles consisted of a gold-rich core and a silver-rich shell. XRD and DCS indicated that the nanoparticles were not twinned, except for pure Ag and Ag:Au 90:10, although different domains were visible in the TEM. A remarkable negative deviation from Vegard's linear rule of alloy mixtures was observed (isotropic contraction of the cubic unit cell with a minimum at a 50:50 composition). This effect was also found for Ag:Au bulk alloys, but it was much more pronounced for the nanoalloys. Notably, it was much less pronounced for pure silver and gold nanoparticles. The microstrain was increased along with the contraction of the unit cell with a broad maximum at a 50:50 composition. The synthesis is based on aqueous solvents and can be easily scaled up to a yield of several mg of a well dispersed nanoalloy with application potential due to its tuneable antibacterial action (silver) and its optical properties for bioimaging. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5tb00644a
  • 2015 • 383 New approaches to nanoparticle sample fabrication for atom probe tomography
    Felfer, P. and Li, T. and Eder, K. and Galinski, H. and Magyar, A.P. and Bell, D.C. and Smith, G.D.W. and Kruse, N. and Ringer, S.P. and Cairney, J.M.
    Ultramicroscopy 159 413-419 (2015)
    Due to their unique properties, nano-sized materials such as nanoparticles and nanowires are receiving considerable attention. However, little data is available about their chemical makeup at the atomic scale, especially in three dimensions (3D). Atom probe tomography is able to answer many important questions about these materials if the challenge of producing a suitable sample can be overcome. In order to achieve this, the nanomaterial needs to be positioned within the end of a tip and fixed there so the sample possesses sufficient structural integrity for analysis. Here we provide a detailed description of various techniques that have been used to position nanoparticles on substrates for atom probe analysis. In some of the approaches, this is combined with deposition techniques to incorporate the particles into a solid matrix, and focused ion beam processing is then used to fabricate atom probe samples from this composite. Using these approaches, data has been achieved from 10-20 nm core-shell nanoparticles that were extracted directly from suspension (i.e. with no chemical modification) with a resolution of better than ±1 nm. © 2015 Elsevier B.V..
    view abstractdoi: 10.1016/j.ultramic.2015.04.014
  • 2015 • 382 New possibilities of accurate particle characterisation by applying direct boundary models to analytical centrifugation
    Walter, J. and Thajudeen, T. and Süß, S. and Segets, D. and Peukert, W.
    Nanoscale 7 6574-6587 (2015)
    Analytical centrifugation (AC) is a powerful technique for the characterisation of nanoparticles in colloidal systems. As a direct and absolute technique it requires no calibration or measurements of standards. Moreover, it offers simple experimental design and handling, high sample throughput as well as moderate investment costs. However, the full potential of AC for nanoparticle size analysis requires the development of powerful data analysis techniques. In this study we show how the application of direct boundary models to AC data opens up new possibilities in particle characterisation. An accurate analysis method, successfully applied to sedimentation data obtained by analytical ultracentrifugation (AUC) in the past, was used for the first time in analysing AC data. Unlike traditional data evaluation routines for AC using a designated number of radial positions or scans, direct boundary models consider the complete sedimentation boundary, which results in significantly better statistics. We demonstrate that meniscus fitting, as well as the correction of radius and time invariant noise significantly improves the signal-to-noise ratio and prevents the occurrence of false positives due to optical artefacts. Moreover, hydrodynamic non-ideality can be assessed by the residuals obtained from the analysis. The sedimentation coefficient distributions obtained by AC are in excellent agreement with the results from AUC. Brownian dynamics simulations were used to generate numerical sedimentation data to study the influence of diffusion on the obtained distributions. Our approach is further validated using polystyrene and silica nanoparticles. In particular, we demonstrate the strength of AC for analysing multimodal distributions by means of gold nanoparticles. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5nr00995b
  • 2015 • 381 Non-Invasive Probing of Nanoparticle Electrostatics
    Tschulik, K. and Cheng, W. and Batchelor-Mcauley, C. and Murphy, S. and Omanović, D. and Compton, R.G.
    ChemElectroChem 2 112-118 (2015)
    Electrostatic interactions between surface-charged nanoparticles (NPs) and electrodes studied using existing techniques unavoidably and significantly alter the system being analyzed. Here we present a methodology that allows the probing of unperturbed electrostatic interactions between individual NPs and charged surfaces. The uniqueness of this approach is that stochastic NP impact events are used as the probe. During a single impact, only an attomole of the redox species reacts and is released at the interface during each sensing event. As an example, the effect of electrostatic screening on the reduction of negatively charged indigo NPs at a mercury microelectrode is explored at potentials positive and negative of the potential of zero charge. At suitable overpotentials fully driven electron transfer is seen for all but very low (<0.005M) ionic strengths. The loss of charge transfer in such dilute electrolytes is unambiguously shown to arise from a reduced driving force for the reaction rather than a reduced population of NPs near the electrode, contradicting popular perceptions. Electrostatics were found not to significantly affect the reactivity of the studied NPs. Importantly, the presented technique is general and can be applied to a wide variety of NPs, including metals, metal oxides and organic compounds. Not what you might think: A new and non-invasive technique to probe the electrostatic interaction between surface-charged nanoparticles and a charged metal/solution interface shows that electrostatic effects are insignificant in all but very dilute electrolytes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201402285
  • 2015 • 380 NOx conversion properties of a novel material: Iron nanoparticles stabilized in carbon
    Busch, M. and Kompch, A. and Suleiman, S. and Notthoff, C. and Bergmann, U. and Theissmann, R. and Atakan, B. and Winterer, M.
    Applied Catalysis B: Environmental 166-167 211-216 (2015)
    Nitrogen oxides (NOx) belong to the most common pollutants from combustion processes and are a major threat to human health. Carbon-based catalysts exhibit strong advantages for NOx removal like low-toxic application and easy handling. However, gasification of the carbon matrix at elevated temperatures is still one of the greatest concerns. Hence, we have directed our focus on especially low temperature NOx-removal using a novel material, iron nanoparticles stabilized in a carbon matrix (nano-Fe/C). The investigations included NO2 uptake properties and catalytic conversion of NO2 in recycle flow at 425K and 328K, scanning transmission electron microscopy and 77K-N2-adsorption. Nano-Fe/C exhibits superior NOx-removal properties compared with untreated or iron-infiltrated activated carbon or magnetite reference catalysts. No severe catalyst deactivation or catalyst aging at 425K is observed. Even at 328K nano-Fe/C still exhibits NO2-conversion, although without converting the product NO. NO2 adsorption at 297K is suggested to occur in three stages with different kinetics: (1) NO2 adsorption and reduction to NO, (2) physisorption on the oxidized catalyst surface and (3) saturation of the catalyst and diffusion into the substrate matrix. At 425K, NO2 is quickly reduced to NO and the resulting NO is further converted to N2O. After complete consumption of NO, the residual NO2 is also converted to N2O. A possible reaction mechanism is suggested based on the conversion kinetics. © 2014 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.apcatb.2014.11.013
  • 2015 • 379 Numerical investigation of the process steps in a spray flame reactor for nanoparticle synthesis
    Weise, C. and Menser, J. and Kaiser, S.A. and Kempf, A. and Wlokas, I.
    Proceedings of the Combustion Institute 35 2259-2266 (2015)
    The synthesis of titanium dioxide nanoparticles from titanium tetraisopropoxide (TTIP) in a nanoparticle spray flame reactor was investigated. The nanoparticle properties are affected by different processes: (a) the break-up of the liquid jet from the spray nozzle, (b) the combustion of the spray and in the pilot flame and (c) the formation and growth of the nanoparticles. The spray process of the injected liquid was analyzed by volume of fluid (VOF) calculations and validated by shadowgraphy imaging which provided the size distribution and the mean velocity of the droplets. The spray angle was determined by a side illuminated long exposure image of the spray. The resulting spray properties (droplet sizes, velocity, and spray angle) served as injector boundary conditions for the downstream combustion simulations. Spray and gas phase of the flame were simulated using an Euler-Lagrange approach, turbulence was modeled by the RNG k-epsilon model, and turbulent combustion was described as a partially stirred reactor (PaSR). For the formation and growth of the nanoparticles within the synthesis reactor, the population balance equation was solved coupled to the spray combustion using a monodisperse model. The findings from experiment and simulation are discussed in terms of flow, species, temperature, and nanoparticle formation inside the reactor. The effect of the spray droplet properties as droplet size, angle, mean velocity and the dispersion behavior on the nanoparticle synthesis process are investigated and discussed, confirming the observation that this type of spray reactor is a robust design overall. © 2014 Published by Elsevier Inc. on behalf of The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2014.05.037
  • 2015 • 378 On the mechanism of nanoparticle formation in a flame doped by iron pentacarbonyl
    Poliak, M. and Fomin, A. and Tsionsky, V. and Cheskis, S. and Wlokas, I. and Rahinov, I.
    Physical Chemistry Chemical Physics 17 680-685 (2015)
    In this work we have investigated the mechanism of nanoparticle synthesis in a low pressure, premixed, laminar flat flame of CH4-O2, doped with iron pentacarbonyl using a combined quartz-crystal-microbalance-particle-mass-spectrometry apparatus. We have unambiguously demonstrated that the formation of nanoparticles in iron pentacarbonyl-doped flames occurs very early, in close proximity to the burner surface, prior to the flame front. This early rise of nanoparticle mass concentration is followed by a sharp drop in nanoparticle concentration at the high temperature flame front. This "prompt" nanoparticle generation is consistent with kinetic models describing iron cluster formation. The observation of this phenomenon in a quasi-one-dimensional premixed flat flame strengthens our previous findings and points out that the "prompt" nanoparticle formation is a general phenomenon, not limited to diffusion flames. It presents a challenge and a trigger for further development of the existing mechanisms for gas phase synthesis of iron oxide particles in flames. This journal is © the Owner Societies 2015.
    view abstractdoi: 10.1039/c4cp04454a
  • 2015 • 377 Particle-induced cell migration assay (PICMA): A new in vitro assay for inflammatory particle effects based on permanent cell lines
    Westphal, G.A. and Schremmer, I. and Rostek, A. and Loza, K. and Rosenkranz, N. and Brüning, T. and Epple, M. and Bünger, J.
    Toxicology in Vitro 29 997-1005 (2015)
    Inflammation is a decisive pathophysiologic mechanism of particle toxicity and accumulation of neutrophils in the lung is believed to be a crucial step in this process. This study describes an in vitro model for investigations of the chemotactic attraction of neutrophils in response to particles using permanent cell lines. We challenged NR8383 rat macrophages with particles that were characterized concerning chemical nature, crystallinity, and size distribution in the dry state and in the culture medium. The cell supernatants were used to investigate migration of differentiated human leukemia cells (dHL-60 cells). The dose range for the tests was determined using an impedance-based Real-Time Cell Analyzer. The challenge of NR8383 cells with 32-96μgcm-2 coarse and nanosized particles resulted in cell supernatants which induced strong and dose-dependent migration of dHL-60 cells. Quartz caused the strongest effects - exceeding the positive control "fetal calf serum" (FCS) several-fold, followed by silica, rutile, carbon black, and anatase. BaSO<inf>4</inf> served as inert control and induced no cell migration. Particles caused NR8383 cells to secrete chemotactic compounds. The assay clearly distinguished between the particles of different inflammatory potential in a highly reproducible way. Specificity of the test is suggested by negative results with BaSO<inf>4</inf>. © 2015 The Authors.
    view abstractdoi: 10.1016/j.tiv.2015.04.005
  • 2015 • 376 Particle-Matrix Interaction in Cross-Linked PAAm-Hydrogels Analyzed by Mössbauer Spectroscopy
    Landers, J. and Roeder, L. and Salamon, S. and Schmidt, A.M. and Wende, H.
    Journal of Physical Chemistry C 119 20642-20648 (2015)
    The constrained motion of spindle-shaped hematite nanoparticles of about 400 nm in PAAm-hydrogels with different degrees of cross-link density is measured utilizing the line broadening observable in Mössbauer spectra at 265-293 K. A slight decrease of nanoparticle mobility is observed upon increasing cross-link density. Mössbauer spectra of the same nanoparticles in 60 wt % sucrose solution, used as reference material, display line broadening of the same magnitude as the hydrogel samples, indicating a similar degree of motion at the atomic scale and the time scale of the Mössbauer experiment. AC (alternating current) susceptibility data indicate that the magnetic relaxation of the nanoparticles in sucrose solution mainly occurs by Brownian motion, while the absence of magnetic loss within the investigated frequency range observed in measurements on hydrogel samples reveals very limited particle mobility. This apparent contradiction between results on particle dynamics in hydrogels by Mössbauer spectroscopy and AC susceptibility measurements is explained in terms of constrained particle mobility at atomic scales. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b03697
  • 2015 • 375 Phase transitions during formation of Ag nanoparticles on In2S3 precursor layers
    Liu, Y. and Fu, Y. and Dittrich, T. and Sáez-Araoz, R. and Schmid, M. and Hinrichs, V. and Lux-Steiner, M.C. and Fischer, C.-H.
    Thin Solid Films 590 54-59 (2015)
    Phase transitions have been investigated for silver deposition onto In<inf>2</inf>S<inf>3</inf> precursor layers by spray chemical vapor deposition from a trimethylphosphine (hexafluoroacetylacetonato) silver (Ag(hfacac)(PMe<inf>3</inf>)) solution. The formation of Ag nanoparticles (Ag NPs) on top of the semiconductor layer set on concomitant with the formation of AgIn<inf>5</inf>S<inf>8</inf>. The increase of the diameter of Ag NPs was accompanied by the evolution of orthorhombic AgInS<inf>2</inf>. The formation of Ag<inf>2</inf>S at the interface between Ag NPs and the semiconductor layer was observed. Surface photovoltage spectroscopy indicated charge separation and electronic transitions in the ranges of corresponding band gaps. The phase transition approach is aimed to be applied for the formation of plasmonic nanostructures on top of extremely thin semiconducting layers. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2015.07.021
  • 2015 • 374 Plasma synthesis of titanium nitride, carbide and carbonitride nanoparticles by means of reactive anodic arc evaporation from solid titanium
    Kiesler, D. and Bastuck, T. and Theissmann, R. and Kruis, F.E.
    Journal of Nanoparticle Research 17 (2015)
    Plasma methods using the direct evaporation of a transition metal are well suited for the cost-efficient production of ceramic nanoparticles. In this paper, we report on the development of a simple setup for the production of titanium-ceramics by reactive anodic arc evaporation and the characterization of the aerosol as well as the nanopowder. It is the first report on TiCXN1 − X synthesis in a simple anodic arc plasma. By means of extensive variations of the gas composition, it is shown that the composition of the particles can be tuned from titanium nitride over a titanium carbonitride phase (TiCXN1 − X) to titanium carbide as proven by XRD data. The composition of the plasma gas especially a very low concentration of hydrocarbons around 0.2 % of the total plasma gas is crucial to tune the composition and to avoid the formation of free carbon. Examination of the particles by HR-TEM shows that the material consists mostly of cubic single crystalline particles with mean sizes between 8 and 27 nm. © 2015, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-015-2967-8
  • 2015 • 373 Process engineering of nanoparticles below 20 nm—a fundamental discussion of characterization, particle formation, stability and post processing
    Segets, D. and Peukert, W.
    Colloid Process Engineering 279-305 (2015)
    In the following chapter fundamental aspects that have to be considered during the processing of small nanoparticles will be addressed. We investigated quantum confined manganese doped ZnS, ZnO, PbS and PbSe semiconductor nanoparticles, so-called quantum dots (QDs) and silver noble metal nanorods. All materials were chosen due to their technical relevance for future applications in the emerging fields of solar cells, sensors and diagnostics as well as due to the possibility of their in situ characterization by UV/Vis absorbance spectroscopy. After a brief introduction to the specific prospects and challenges of these materials we will focus on the important processing issues that need to be solved for producing these particles at high quality on a larger scale: (i) the modelling of particle formation including nucleation, growth and ripening based on a mechanistic understanding and on experimentally derived data on solubility and surface energies, (ii) the stabilization of nanoparticles not only against agglomeration but also against shape changes and (iii) classification. The latter is realized by size selective precipitation which allows surprisingly sharp separations (κ= 0.75) of particles with only a few nm in diameter. Although the extremely small particle sizes (feed PSD between 1.5 and 3 nm), classification results were successfully analyzed by well-known concepts from particle technology. Our results are seen to be an essential contribution to colloidal processing. They enable a future optimization of process parameters by a knowledge-based design strategy that can be applied within continuous as well as automatized batch reactor concepts. © Springer International Publishing Switzerland 2015.
    view abstractdoi: 10.1007/978-3-319-15129-8_12
  • 2015 • 372 Proteomic analysis of protein carbonylation: A useful tool to unravel nanoparticle toxicity mechanisms
    Driessen, M.D. and Mues, S. and Vennemann, A. and Hellack, B. and Bannuscher, A. and Vimalakanthan, V. and Riebeling, C. and Ossig, R. and Wiemann, M. and Schnekenburger, J. and Kuhlbusch, T.A.J. and Renard, B. and Luch, A. and Haase, A.
    Particle and Fibre Toxicology 12 (2015)
    Background: Oxidative stress, a commonly used paradigm to explain nanoparticle (NP)-induced toxicity, results from an imbalance between reactive oxygen species (ROS) generation and detoxification. As one consequence, protein carbonyl levels may become enhanced. Thus, the qualitative and quantitative description of protein carbonylation may be used to characterize how biological systems respond to oxidative stress induced by NPs. Methods: We investigated a representative panel of 24 NPs including functionalized amorphous silica (6), zirconium dioxide (4), silver (4), titanium dioxide (3), zinc oxide (2), multiwalled carbon nanotubes (3), barium sulfate and boehmite. Surface reactivities of all NPs were studied in a cell-free system by electron spin resonance (ESR). NRK-52E cells were treated with all NPs, analyzed for viability (WST-1 assay) and intracellular ROS production (DCFDA assay). Carbonylated proteins were assessed by 1D and/or 2D immunoblotting and identified by matrix assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF/TOF). In parallel, tissue homogenates from rat lungs intratracheally instilled with silver NPs were studied. Results: Eleven NPs induced elevated levels of carbonylated proteins. This was in good agreement with the surface reactivity of the NPs as obtained by ESR and the reduction in cell viability as assessed by WST-1 assay. By contrast, results obtained by DCFDA assay were deviating. Each NP induced an individual pattern of protein carbonyls on 2D immunoblots. Affected proteins comprised cytoskeletal components, proteins being involved in stress response, or cytoplasmic enzymes of central metabolic pathways such as glycolysis and gluconeogenesis. Furthermore, induction of carbonyls upon silver NP treatment was also verified in rat lung tissue homogenates. Conclusions: Analysis of protein carbonylation is a versatile and sensitive method to describe NP-induced oxidative stress and, therefore, can be used to identify NPs of concern. Furthermore, detailed information about compromised proteins may aid in classifying NPs according to their mode of action. © 2015 Driessen et al.
    view abstractdoi: 10.1186/s12989-015-0108-2
  • 2015 • 371 Pseudomorphic Generation of Supported Catalysts for Glycerol Oxidation
    Deng, X. and Dodekatos, G. and Pupovac, K. and Weidenthaler, C. and Schmidt, W. and Schüth, F. and Tüysüz, H.
    ChemCatChem 7 3832-3837 (2015)
    A catalyst consisting of copper nanoparticles (15-20 nm in size) supported on ordered mesoporous cobalt monoxide was synthesized by the one-step reduction of ethanol from nanocast copper cobalt spinel oxides. The small-angle X-ray scattering patterns showed that the ordered mesostructure was maintained after post-treatment, and the cross-section scanning electron microscopy images showed that the Cu nanoparticles were distributed homogeneously throughout the mesoporous CoO framework. The materials were tested as noble-metal-free catalysts for the oxidation of glycerol under alkaline conditions. The catalytic data showed that the presence of Cu nanoparticles greatly enhanced the catalytic performance. Nothing noble: A catalyst consisting of copper nanoparticles (NPs, 15-20 nm in size) supported on ordered mesoporous cobalt monoxide is synthesized by the one-step reduction with ethanol from nanocast copper cobalt spinel oxides. As a noble-metal-free catalyst for the oxidation of glycerol, the presence of Cu NPs greatly enhances the catalytic performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201500703
  • 2015 • 370 Quantitative replacement of citrate by phosphane on silver nanoparticle surfaces monitored by Surface-Enhanced Raman Spectroscopy (SERS)
    Grass, S. and Diendorf, J. and Gebauer, J.S. and Epple, M. and Treuel, L.
    Journal of Nanoscience and Nanotechnology 15 1591-1596 (2015)
    Chemical approaches to metal NP synthesis commonly use capping agents to achieve a desired NP size and shape. Frequently, such NPs require chemically different surface ligands after synthesis to generate desired NP properties (e.g., charge or hydrophilicity) and to increase their long term colloidal stability. Here, we prepared SERS active citrate-stabilized silver NPs (d = 38 ± 4 nm), purified them from remaining reactants by ultracentrifugation and redispersion, and immersed them into solutions containing different concentrations of Tris(sodium-m-sulfonatophenyl)phosphine (TPPTS), which is often used in such ligand replacement approaches to increase colloidal stability. After equilibration, SERS spectra were acquired, elucidating the concentration dependence of the ligand replacement reaction. SERS data were complemented by concentration dependent size measurements and relations between ligand exchange and colloidal stability are discussed. Copyright © 2015 American Scientific Publishers
    view abstractdoi: 10.1166/jnn.2015.9143
  • 2015 • 369 Raman-encoded microbeads for spectral multiplexing with SERS detection
    Lai, Y. and Sun, S. and He, T. and Schlücker, S. and Wang, Y.
    RSC Advances 5 13762-13767 (2015)
    Simultaneous detection of multiple molecular targets can greatly facilitate early diagnosis and drug discovery. Encoding micron-sized beads with optically active tags is one of the most popular methods to achieve multiplexing. Noble metal nanoparticle labels for optical detection by surface-enhanced Raman spectroscopy (SERS) exhibit narrow bandwidths, high photostability and intense Raman signals. In this study, we demonstrate the feasibility of spectral multiplexing by SERS using micron-sized polystyrene (PS) beads loaded with SERS-active nanoparticles. The silica-encapsulated SERS nanotags comprise gold nanocrystals with a self-assembled monolayer (SAM) of aromatic thiols as Raman reporter molecules for spectral identification. SERS microspectroscopic images of single Raman-encoded PS microbeads indicate the homogeneous spatial distribution of the SERS-active nanoparticles on the surface of the beads. By using up to five different Raman reporters, 31 spectrally distinct micron-sized beads were encoded and characterized spectroscopically at the single-bead level. This journal is © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4ra16163g
  • 2015 • 368 Resonant photothermal laser processing of hybrid gold/titania nanoparticle films
    Schade, L. and Franzka, S. and Dzialkowski, K. and Hardt, S. and Wiggers, H. and Reichenberger, S. and Wagener, P. and Hartmann, N.
    Applied Surface Science 336 48-52 (2015)
    Photothermal processing of thin anatase TiO2 and hybrid Au/anatase TiO2 nanoparticle films on glass supports is investigated using continuous-wave microfocused lasers at λ = 355 nm and λ = 532 nm. UV/Vis spectroscopy, Raman spectroscopy, optical microscopy, atomic force microscopy and scanning electron microscopy are used for characterization. Processing of TiO2 nanoparticle films is feasible at λ = 355 nm only. In contrast, the addition of Au nanoparticles enhances the overall absorbance of the material in the visible range and enables processing at both wavelengths, i.e. at λ = 355 nm and λ = 532 nm. Generally, laser heating induces a transition from anatase to rutile. The modification degree increases with increasing laser power and laser irradiation time. Resonant laser processing of hybrid Au/TiO2-mesoporous films provide promising perspectives in various applications, e.g. in photovoltaics, where embedded nanoparticulate Au could be exploited to enhance light trapping. © 2014 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2014.09.118
  • 2015 • 367 Reversible or Not? Distinguishing Agglomeration and Aggregation at the Nanoscale
    Sokolov, S.V. and Tschulik, K. and Batchelor-McAuley, C. and Jurkschat, K. and Compton, R.G.
    Analytical Chemistry 87 10033-10039 (2015)
    Nanoparticles are prone to clustering either via aggregation (irreversible) or agglomeration (reversible) processes. It is exceedingly difficult to distinguish the two via conventional techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), or electron microscopy imaging (scanning electron microscopy (SEM), transmission electron microscopy (TEM)) as such techniques only generally confirm the presence of large particle clusters. Herein we develop a joint approach to tackle the issue of distinguishing between nanoparticle aggregation vs agglomeration by characterizing a colloidal system of Ag NPs using DLS, NTA, SEM imaging and the electrochemical nanoimpacts technique. In contrast to the conventional techniques which all reveal the presence of large clusters of particles, electrochemical nanoimpacts provide information regarding individual nanoparticles in the solution phase and reveal the presence of small nanoparticles (<30 nm) even in high ionic strength (above 0.5 M KCl) and allow a more complete analysis. The detection of small nanoparticles in high ionic strength media evidence the clustering to be a reversible process. As a result it is concluded that agglomeration rather than irreversible aggregation takes place. This observation is of general importance for all colloids as it provides a feasible analysis technique for a wide range of systems with an ability to distinguish subtly different processes. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.5b02639
  • 2015 • 366 Ripening kinetics of laser-generated plasmonic nanoparticles in different solvents
    Gökce, B. and Van't Zand, D.D. and Menéndez-Manjón, A. and Barcikowski, S.
    Chemical Physics Letters 626 96-101 (2015)
    Abstract Pulsed laser ablation in liquid is considered to be a fast nanoparticle-synthesis method taking place on ps to μs timescale. Here, we report the comparably slow ripening kinetics of laser-generated plasmonic nanoparticles (copper, silver, and gold) immediately after ablation. The growth dynamics is studied in situ by following the surface plasmon resonance and correlated to known models. We thereby identify a two-step diffusion-controlled coalescence and growth mechanism, quantify their kinetic constants and show the effect of different solvents (water, acetone, ethanol, and ethyl acetate). © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.cplett.2015.03.010
  • 2015 • 365 Routes towards catalytically active TiO2 doped porous cellulose
    Wittmar, A. and Thierfeld, H. and Köcher, S. and Ulbricht, M.
    RSC Advances 5 35866-35873 (2015)
    Cellulose-TiO<inf>2</inf> nanocomposites have been successfully prepared by non-solvent induced phase separation, either from cellulose solutions in ionic liquids or from cellulose acetate solutions in classical organic solvents followed by deacetylation ("regeneration"). Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as dispersions in the respective polymer solution. The used TiO<inf>2</inf> nanoparticles have been characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD), and their dispersions in ionic liquids and organic solvents have been evaluated by dynamic light scattering (DLS) and advanced rheology. The intermediate polymer solutions used in the phase separation process have been studied by advanced rheology. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Special attention has been given to the complex relationship between the characteristics of the phase separation process and the porous structure of the formed nanocomposites. Two catalytic tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the characterization of the TiO<inf>2</inf> doped nanocomposites. The proof-of-concept experiments demonstrated the feasibility of photocatalyst immobilization in porous cellulose via phase separation of nanoparticle dispersions in polymer solutions, as indicated by UV-activated dye degradation in aqueous solution. © The Royal Society of Chemistry.2015.
    view abstractdoi: 10.1039/c5ra03707g
  • 2015 • 364 Sample temperature profile during the excimer laser annealing of silicon nanoparticles
    Caninenberg, M. and Verheyen, E. and Kiesler, D. and Stoib, B. and Brandt, M.S. and Benson, N. and Schmechel, R.
    Optics and Laser Technology 74 132-137 (2015)
    Based on the heat diffusion equation we describe the temperature profile of a silicon nanoparticle thin film on silicon during excimer laser annealing using COMSOL Multiphysics. For this purpose system specific material parameters are determined such as the silicon nanoparticle melting point at 1683 K, the surface reflectivity at 248 nm of 20% and the nanoparticle thermal conductivity between 0.3 and 1.2 W/m K. To validate our model, the simulation results are compared to experimental data obtained by Raman spectroscopy, SEM microscopy and electrochemical capacitance-voltage measurements (ECV). The experimental data are in good agreement with our theoretical findings and support the validity of the model. © 2015, Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.optlastec.2015.05.020
  • 2015 • 363 Sex-Sorted Boar Sperm - An Update on Related Production Methods
    Rath, D. and Tiedemann, D. and Gamrad, L. and Johnson, L.A. and Klein, S. and Kues, W. and Mancini, R. and Rehbock, C. and Taylor, U. and Barcikowski, S.
    Reproduction in domestic animals = Zuchthygiene 50 56-60 (2015)
    As in other mammals, sex sorting of pig sperm is based on quantitative flow cytometry. A major disadvantage of the technique is the relatively low efficiency to produce enough sorted sperm for artificial insemination. However, several approaches are on the way to make sexed pig sperm available for commercial application. In this context, for example, the growing field of nanotechnology may significantly contribute to these developments, as it provides highly efficient bio-nanoprobes, for example, based on plasmonic nanoparticles. Independent of the method, further development requires enormous investments and set-up of logistics to get the technology into the practical pig market. Only global players will be able to establish the necessary research projects, but in the end, a significant shift of sex ratios will be available for pig producers as it is already the case for the dairy industry. © 2015 Blackwell Verlag GmbH.
    view abstractdoi: 10.1111/rda.12572
  • 2015 • 362 Shape-Selection of Thermodynamically Stabilized Colloidal Pd and Pt Nanoparticles Controlled via Support Effects
    Ahmadi, M. and Behafarid, F. and Holse, C. and Nielsen, J.H. and Roldan Cuenya, B.
    Journal of Physical Chemistry C 119 29178-29185 (2015)
    Colloidal chemistry, in combination with nanoparticle (NP)/support epitaxial interactions is used here to synthesize shape-selected and thermodynamically stable metallic NPs over a broad range of NP sizes. The morphology of three-dimensional palladium and platinum NPs supported on TiO2(110) was investigated using scanning tunneling microscopy. Well-defined Pd and Pt NPs were synthesized via inverse micelle encapsulation. The initially spherical NPs were found to become faceted and form an epitaxial relationship with the support after high-temperature annealing (e.g., 1100 °C). Shape selection was achieved for almost all Pd NPs, namely, a truncated octahedron shape with (111) top and interfacial facets. The Pt NPs were however found to adopt a variety of shapes. The epitaxial relationship of the NPs with the support was evidenced by the alignment of the cluster's edges with TiO2(110)-[001] atomic rows and was found to be responsible for the shape control. The ability of synthesizing thermally stable shape-selected metal NPs demonstrated here is expected to be of relevance for applications in the field of catalysis, since the activity and selectivity of NP catalysts has been shown to strongly depend on the NP shape. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b09980
  • 2015 • 361 Si-CNT/rGO Nanoheterostructures as High-Performance Lithium-Ion-Battery Anodes
    Xiao, L. and Sehlleier, Y.H. and Dobrowolny, S. and Orthner, H. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    ChemElectroChem 2 1983-1990 (2015)
    A robust and electrochemically stable 3D nanoheterostructure consisting of Si nanoparticles (NPs), carbon nanotubes (CNTs) and reduced graphene oxide (rGO) is developed as an anode material (Si-CNT/rGO) for lithium-ion batteries (LIBs). It integrates the benefits from its three building blocks of Si NPs, CNTs, and rGO; Si NPs offer high capacity, CNTs act as a mechanical, electrically conductive support to connect Si NPs, and highly electrically conductive and flexible rGO provides a robust matrix with enough void space to accommodate the volume changes of Si NPs upon lithiation/delithiation and to simultaneously assure good electric contact. The composite material shows a high reversible capacity of 1665mAhg-1 with good capacity retention of 88.6% over 500 cycles when cycled at 0.5C, that is, a 0.02% capacity decay per cycle. The high-power capability is demonstrated at 10C (16.2Ag-1) where 755mAhg-1 are delivered, thus indicating promising characteristics of this material for high-performance LIBs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201500323
  • 2015 • 360 Size control and supporting of palladium nanoparticles made by laser ablation in saline solution as a facile route to heterogeneous catalysts
    Marzun, G. and Nakamura, J. and Zhang, X. and Barcikowski, S. and Wagener, P.
    Applied Surface Science 348 75-84 (2015)
    In the literature many investigations on colloidal stability and size control of gold nanoparticles are shown but less for ligand-free palladium nanoparticles, which can be promising materials in various applications. Palladium nanoparticles are perspective materials for a manifold of energy application like photo- and electrocatalysis or hydrogen storage. For this purpose, size-controlled nanoparticles with clean surfaces and facile immobilization on catalyst supports are wanted. Laser ablation in saline solution yields ligand-free, charged colloidal palladium nanoparticles that are supported by titania and graphene nanosheets as model systems for photo- and electrocatalysis, respectively. By adjusting the ionic strength during laser ablation in liquid, it is possible to control stability and particle size without compromising subsequent nanoparticle adsorption of supporting materials. A quantitative deposition of nearly 100% yield with up to 18 wt% nanoparticle load was achieved. The average size of the laser-generated nanoparticles remains the same after immobilization on a support material, in contrast to other preparation methods of catalysts. The characterization by X-ray photoelectron spectroscopy reveals a redox reaction between the immobilized nanoparticles and the graphene support. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.01.108
  • 2015 • 359 Soft Nanocomposites-From Interface Control to Interphase Formation
    Pihan, S.A. and Emmerling, S.G.J. and Butt, H.-J. and Berger, R. and Gutmann, J.S.
    ACS Applied Materials and Interfaces 7 12380-12386 (2015)
    We report measurements of structure, mechanical properties, glass transition temperature, and contact angle of a novel nanocomposite material consisting of swellable silsesquioxane nanoparticles with grafted poly(ethyl methacrylate) (PEMA) brushes and PEMA matrices with varying molecular weight. We measured the interparticle distance at the surface of the composites using scanning probe microscopy (SPM) and in the bulk of ∼0.5 μm thick films by grazing incidence small angle X-ray scattering (GISAXS). For a given molecular weight of the brush unstable dispersions at high molecular weight of the matrix indicate an intrinsic incompatibility between polymer-grafted-nanoparticles and homopolymer matrices. This incompatibility is affirmed by a high contact angle between the polymer-grafted-nanoparticles and the high molecular weight matrix as measured by SPM. For unstable dispersions, we measured a decreased glass transition temperature along with a decreased plateau modulus by dynamic mechanical thermal analysis (DMTA) which indicates the formation of a liquid-like layer at the brush-matrix interface. This proves the ability to decouple the structural and mechanical properties from the potential to be swollen with small molecules. It opens a new area of use of these soft nanocomposites as slow release materials with tailored mechanical properties. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/am507572q
  • 2015 • 358 Stability of Dealloyed Porous Pt/Ni Nanoparticles
    Baldizzone, C. and Gan, L. and Hodnik, N. and Keeley, G.P. and Kostka, A. and Heggen, M. and Strasser, P. and Mayrhofer, K.J.J.
    ACS Catalysis 5 5000-5007 (2015)
    We provide a comprehensive durability assessment dedicated to a promising class of electrocatalysts for the oxygen reduction reaction (i.e., porous platinum nanoparticles). The stability of these nanoengineered open structures is tested under two accelerated degradation test conditions (ADT), particularly selected to mimic the potential regimes experienced by the catalyst during the operative life of a fuel cell (i.e., load cycles (up to 1.0 V<inf>RHE</inf>) and start-up cycles (up to 1.4 V<inf>RHE</inf>)). To understand the evolution of the electrochemical performance, the catalyst properties are investigated by means of fundamental rotating disc electrode studies, identical location-transmission electron microscopy (IL-TEM) coupled with electron energy loss spectroscopy chemical mapping (IL-EELS), and post-use chemical analysis and online highly sensitive potential resolved dissolution concentration monitoring by scanning flow cell inductively coupled plasma-mass spectrometry (SFC-ICP-MS). The experimental results on the nanoporous Pt revealed distinctive degradation mechanisms that could potentially affect a wide range of other nanoengineered open structures. The study concludes that, although providing promising activity performance, under the relevant operational conditions of fuel cells, the nanoporosity is only metastable and subjected to a progressive reorganization toward the minimization of the nanoscale curvature. The rate and pathways of this specific degradation mechanism together with other well-known degradation mechanisms like carbon corrosion and platinum dissolution are strongly dependent on the selected upper limit potential, leading to distinctly different durability performance. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.5b01151
  • 2015 • 357 Structure-activity relationships of Co-modified Cu/ZnO/Al2O3 catalysts applied in the synthesis of higher alcohols from synthesis gas
    Anton, J. and Nebel, J. and Song, H. and Froese, C. and Weide, P. and Ruland, H. and Muhler, M. and Kaluza, S.
    Applied Catalysis A: General 505 326-333 (2015)
    Cu-Co-based catalysts were synthesized by co-precipitation using Cu, Co, Zn and Al nitrates and applied in higher alcohol synthesis (HAS) at 280 °C, 60 bar and a ratio of H<inf>2</inf>/CO = 1. The catalyst exhibiting a Cu/Co ratio of 2.5 was found to provide the best trade-off between product distribution and degree of CO conversion. After activation and 40 h time on stream reaching steady-state conditions the bulk and surface properties of the catalyst were thoroughly investigated without exposing it to air during the transfer and the measurements. The conditions during activation and HAS led to a significant enrichment of Zn in the surface composition of the catalysts. The XRD pattern of the catalyst after reaction compared with the reduced catalyst revealed further sintering of the metallic Cu nanoparticles and the growth of crystalline ZnO nanoparticles, but there were no indications for the presence of bulk metallic Co or for bulk alloying. With increasing time on stream the product distribution shifted favorably towards higher alcohols presumably due to an increased intimate interface contact between the large metallic Cu0 particles detected by XRD and the X-ray amorphous metallic Co surface species probed by XPS. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.apcata.2015.07.002
  • 2015 • 356 Synthesis and characterization of antimicrobial textile finishing based on Ag:ZnO nanoparticles/chitosan biocomposites
    Buşilə, M. and Muşat, V. and Textor, T. and Mahltig, B.
    RSC Advances 5 21562-21571 (2015)
    ZnO and Ag:ZnO nanoparticles were prepared by hydrolysis of zinc acetate in the presence of lithium hydroxide (LiOH). In combination with binders based on hybrid polymer sols, these metal oxide materials were applied for textile treatment. Hybrid coatings based on ZnO, Ag:ZnO/CS, chitosan (CS), 3-glycidyloxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) prepared by sol-gel method were applied on cotton 100% and cotton/polyester (50/50%) textiles using "pad-dry-cure" technique. The obtained nanoparticles incorporated within chitosan matrix were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), UV-Vis spectroscopy and field emission scanning electron microscopy (FE-SEM). The antimicrobial activity of Ag/CS, ZnO/CS and Ag:ZnO/CS composite coatings was investigated in comparison to that of the pure chitosan using the paper disc method on Mueller-Hinton agar, against the Gram-negative E. coli and the Gram-positive S. aureus bacteria. For the same composite coatings applied on textile, the antimicrobial activity was investigated by UV-Vis absorption spectroscopy using TTC method, against the bacteria E. coli and M. luteus. The investigated nanocomposite materials showed good antimicrobial activity and are promising materials for use as medical applications. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c4ra13918f
  • 2015 • 355 Synthesis of Binary Sb2E3 (E = S, Se) and Ternary Sb2(S,Se)3 Nanowires Using Tailor-Made Single-Source Precursors
    Heimann, S. and Assenmacher, W. and Prymak, O. and Schulz, S.
    European Journal of Inorganic Chemistry 2015 2407-2415 (2015)
    Thermal decomposition of four single-source precursors of the type (Et<inf>2</inf>Sb)<inf>2</inf>E and Et<inf>3</inf>SbE (E = S, Se) at 170 °C in the presence of suitable capping agents yielded binary Sb<inf>2</inf>S<inf>3</inf> and Sb<inf>2</inf>Se<inf>3</inf> nanowires. In addition, simultaneous decomposition of (Et<inf>2</inf>Sb)<inf>2</inf>S and(Et<inf>2</inf>Sb)<inf>2</inf>Se gave the ternary phase Sb<inf>2</inf>(S,Se)<inf>3</inf> with almost equal S and Se concentrations. The materials were characterized by XRD, REM, EDX, ED and HRTEM. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201500325
  • 2015 • 354 Synthesis, characterization and in vitro effects of 7 nm alloyed silver-gold nanoparticles
    Ristig, S. and Chernousova, S. and Meyer-Zaika, W. and Epple, M.
    Beilstein Journal of Nanotechnology 6 1212-1220 (2015)
    Alloyed silver-gold nanoparticles were prepared in nine different metal compositions with silver/gold molar ratios of ranging from 90:10 to 10:90. The one-pot synthesis in aqueous medium can easily be modified to gain control over the final particle diameter and the stabilizing agents. The purification of the particles to remove synthesis by-products (which is an important factor for subsequent in vitro experiments) was carried out by multiple ultracentrifugation steps. Characterization by transmission electron microscopy (TEM), differential centrifugal sedimentation (DCS), dynamic light scattering (DLS), UV-vis spectroscopy and atomic absorption spectroscopy (AAS) showed spherical, monodisperse, colloidally stable silver-gold nanoparticles of ≈7 nm diameter with measured molar metal compositions very close to the theoretical values. The examination of the nanoparticle cytotoxicity towards HeLa cells and human mesenchymal stem cells (hMSCs) showed that the toxicity is not proportional to the silver content. Nanoparticles with a silver/gold molar composition of 80:20 showed the highest toxicity. © 2015 Ristig et al.
    view abstractdoi: 10.3762/bjnano.6.124
  • 2015 • 353 The fate of nano-silver in aqueous media
    Plowman, B.J. and Tschulik, K. and Walport, E. and Young, N.P. and Compton, R.G.
    Nanoscale 7 12361-12364 (2015)
    Silver nanoparticles offer highly attractive properties for many applications, however concern has been raised over the possible toxicity of this material in environmental systems. While it is thought that the release of Ag+ can play a crucial role in this toxicity, the mechanism by which the oxidative dissolution of nano-silver occurs is not yet understood. Here we address this through the electrochemical analysis of gold-core silver-shell nanoparticles in various solutions. This novel method allows the direct quantification of silver dissolution by normalisation to the gold core signal. This is shown to be highly effective at discriminating between silver dissolution and the loss of nanoparticles from the electrode surface. We evidence through this rigorous approach that the reduction of O<inf>2</inf> drives the dissolution of nano-silver, while in the presence of Cl- this dissolution is greatly inhibited. This work is extended to the single nanoparticle level using nano-impact experiments. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5nr02995c
  • 2015 • 352 The potential of nanoparticles for the immunization against viral infections
    Sokolova, V. and Westendorf, A.M. and Buer, J. and Überla, K. and Epple, M.
    Journal of Materials Chemistry B 3 4767-4779 (2015)
    Vaccination has a great impact on the prevention and control of infectious diseases. However, there are still many infectious diseases for which an effective vaccine is missing. Thirty years after the discovery of the AIDS-pathogen (human immunodeficiency virus, HIV) and intensive research, there is still no protective immunity against the HIV infection. Over the past decade, nanoparticulate systems such as virus-like particles, liposomes, polymers and inorganic nanoparticles have received attention as potential delivery vehicles which can be loaded or functionalized with active biomolecules (antigens and adjuvants). Here we compare the properties of different nanoparticulate systems and assess their potential for the development of new vaccines against a range of viral infections. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5tb00618j
  • 2015 • 351 Thermoelectrics from silicon nanoparticles: the influence of native oxide
    Petermann, N. and Stötzel, J. and Stein, N. and Kessler, V. and Wiggers, H. and Theissmann, R. and Schierning, G. and Schmechel, R.
    European Physical Journal B 88 (2015)
    Thermoelectric materials were synthesized by current-assisted sintering of doped silicon nanoparticles produced in a microwave-plasma reactor. Due to their affinity to oxygen, the nanoparticles start to oxidize when handled in air and even a thin surface layer of native silicon oxide leads to a significant increase in the oxide volume ratio. This results in a considerable incorporation of oxygen into the sintered pellets, thus affecting the thermoelectric performance. To investigate the necessity of inert handling of the raw materials, the thermoelectric transport properties of sintered nanocrystalline silicon samples were characterized with respect to their oxygen content. An innovative method allowing a quantitative silicon oxide analysis by means of electron microscopy was applied: the contrast between areas of high and low electrical conductivity was attributed to the silicon matrix and silicon oxide precipitates, respectively. Thermoelectric characterization revealed that both, electron mobility and thermal conductivity decrease with increasing silicon oxide content. A maximum figure of merit with zT = 0.45 at 950 °C was achieved for samples with a silicon oxide mass fraction of 9.5 and 21.4% while the sample with more than 25% of oxygen clearly indicates a negative impact of the oxygen on the electron mobility. © 2015, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1140/epjb/e2015-50594-7
  • 2015 • 350 Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship
    Guo, Y. and Gu, D. and Jin, Z. and Du, P.-P. and Si, R. and Tao, J. and Xu, W.-Q. and Huang, Y.-Y. and Senanayake, S. and Song, Q.-S. and Jia, C.-J. and Schüth, F.
    Nanoscale 7 4920-4928 (2015)
    Uniform Au nanoparticles (∼2 nm) with narrow size-distribution (standard deviation: 0.5-0.6 nm) supported on both hydroxylated (Fe-OH) and dehydrated iron oxide (Fe-O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed high homogeneity in the supported Au nanoparticles. The ex situ and in situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H<inf>2</inf>-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe-OH < Au/Fe-O) and CD (Au/Fe-OH > Au/Fe-O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe-OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO<inf>x</inf> catalysts with very similar structural characteristics in CO oxidation. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4nr06967f
  • 2015 • 349 Unveiling the correlation between nanometer-thick molecular monolayer sensitivity and near-field enhancement and localization in coupled plasmonic oligomers
    König, M. and Rahmani, M. and Zhang, L. and Lei, D.Y. and Roschuk, T.R. and Giannini, V. and Qiu, C.-W. and Hong, M. and Schlücker, S. and Maier, S.A.
    ACS Nano 8 9188-9198 (2015)
    Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic hot spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nn5028714
  • 2015 • 348 Water-dispersible small monodisperse electrically conducting antimony doped tin oxide nanoparticles
    Peters, K. and Zeller, P. and Stefanic, G. and Skoromets, V. and Němec, H. and Kužel, P. and Fattakhova-Rohlfing, D.
    Chemistry of Materials 27 1090-1099 (2015)
    We describe the fabrication of crystalline electrically conducting antimony-doped tin oxide (ATO) nanoparticles highly dispersible in polar solvents such as water and ethanol without any stabilizing agents. Nonagglomerated monodisperse ATO nanoparticles with different doping levels are obtained by a facile solvothermal reaction in tert-butanol, leading to the formation of monodisperse nanocrystals with a size of about 3 nm directly after synthesis. Electrical conductivity of ATO nanoparticles strongly increases due to the substitutional doping with antimony, reaching 6.8 × 10-2 S cm-1 for the as-synthesized nanoparticles prepared with 3-5 mol % Sb. This increase stems from transition from hopping in the undoped samples to band-like conduction in the doped samples as revealed by terahertz (THz) spectroscopy measurements describing transport on nanometer distances. The dc conductivity of the doped nanoparticles increases by about 3 orders of magnitude up to 62 S cm-1 after annealing in air at 500 °C. The electrical conductivity, crystallinity, small size, and high dispersibility in polar solvents make the obtained ATO nanoparticles promising building blocks for the direct assembly of more complex conducting architectures using polymer templates that could be damaged in organic solvents. We illustrate the benefits of the water-dispersible ATO nanoparticles by their assembly to periodic macroporous electrodes using poly(methyl methacrylate) (PMMA) beads as the porosity templates. Aqueous dispersion of ATO nanoparticles can be directly combined with PMMA beads that are easily removed by calcination, enabling a facile deposition of 3D-macroporous ATO electrodes featuring optical transparency and a large periodically ordered conducting interface. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/cm504409k
  • 2015 • 347 Wet-chemical synthesis of different bismuth telluride nanoparticles using metal organic precursors-single source vs. dual source approach
    Bendt, G. and Weber, A. and Heimann, S. and Assenmacher, W. and Prymak, O. and Schulz, S.
    Dalton Transactions 44 14272-14280 (2015)
    Thermolysis of the single source precursor (Et<inf>2</inf>Bi)<inf>2</inf>Te 1 in DIPB at 80 °C yielded phase-pure Bi<inf>4</inf>Te<inf>3</inf> nanoparticles, while mixtures of Bi<inf>4</inf>Te<inf>3</inf> and elemental Bi were formed at higher temperatures. In contrast, cubic Bi<inf>2</inf>Te particles were obtained by thermal decomposition of Et<inf>2</inf>BiTeEt 2 in DIPB. Moreover, a dual source approach (hot injection method) using the reaction of Te(SiEt<inf>3</inf>)<inf>2</inf> and Bi(NMe<inf>2</inf>)<inf>3</inf> was applied for the synthesis of different pure Bi-Te phases including Bi<inf>2</inf>Te, Bi<inf>4</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf>, which were characterized by PXRD, REM, TEM and EDX. The influence of reaction temperature, precursor molar ratio and thermolysis conditions on the resulting material phase was verified. Moreover, reactions of alternate bismuth precursors such as Bi(NEt<inf>2</inf>)<inf>3</inf>, Bi(NMeEt)<inf>3</inf> and BiCl<inf>3</inf> with Te(SiEt<inf>3</inf>)<inf>2</inf> were investigated. © 2015 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5dt02072g
  • 2014 • 346 A polyphenylene support for pd catalysts with exceptional catalytic activity
    Wang, F. and Mielby, J. and Richter, F.H. and Wang, G. and Prieto, G. and Kasama, T. and Weidenthaler, C. and Bongard, H.-J. and Kegnæs, S. and Fürstner, A. and Schüth, F.
    Angewandte Chemie - International Edition 53 8645-8648 (2014)
    We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201404912
  • 2014 • 345 A radial differential mobility analyzer for the size-classification of gas-phase synthesized nanoparticles at low pressures
    Nanda, K.K. and Kruis, F.E.
    Measurement Science and Technology 25 (2014)
    Differential mobility analyzers (DMAs) are commonly used to generate monodisperse nanoparticle aerosols. Commercial DMAs operate at quasi-atmospheric pressures and are therefore not designed to be vacuum-tight. In certain particle synthesis methods, the use of a vacuum-compatible DMA is a requirement as a process step for producing high-purity metallic particles. A vacuum-tight radial DMA (RDMA) has been developed and tested at low pressures. Its performance has been evaluated by using a commercial NANO-DMA as the reference. The performance of this low-pressure RDMA (LP-RDMA) in terms of the width of its transfer function is found to be comparable with that of other NANO-DMAs at atmospheric pressure and is almost independent of the pressure down to 30 mbar. It is shown that LP-RDMA can be used for the classification of nanometer-sized particles (5-20nm) under low pressure condition (30 mbar) and has been successfully applied to nanoparticles produced by ablating FeNi at low pressures. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-0233/25/7/075605
  • 2014 • 344 Adsorption of Colloidal Platinum Nanoparticles to Supports: Charge Transfer and Effects of Electrostatic and Steric Interactions
    Marzun, G. and Streich, C. and Jendrzej, S. and Barcikowski, S. and Wagener, P.
    Langmuir 30 11928-11936 (2014)
    Adsorption of colloidal nanoparticles to surfaces and supports is a convenient approach to heterogeneous catalysts, polymer additives, or wastewater treatment. We investigated the adsorption efficiency of laser-generated and initially ligand-free platinum nanoparticles to TiO<inf>2</inf> supports as a function of pH, ionic strength, and ligand surface coverage. The nanoparticle adsorption is dominantly controlled by electrostatic interactions: if the pH of the suspension is between the isoelectric point of the nanoparticles and the support, nanoparticles are adsorbed and transfer a net charge to the support. This charge-driven adsorption is not affected by steric repulsion due to various ligands attached to the nanoparticle surface. In addition to electrostatic interactions, colloidal stability given by moderate ionic strengths and pH values above the isoelectric point of nanoparticles are prerequisites for colloidal deposition. (Chemical Equation Presented). © 2014 American Chemical Society.
    view abstractdoi: 10.1021/la502588g
  • 2014 • 343 Aluminum-doped ZnO nanoparticles: Gas-phase synthesis and dopant location
    Schilling, C. and Zähres, M. and Mayer, C. and Winterer, M.
    Journal of Nanoparticle Research 16 (2014)
    Aluminum-doped ZnO (AZO) nanoparticles are studied widely as transparent conducting alternatives for indium tin oxide. However, the properties of AZO vary in different investigations not only with the amount of dopant and the particle size, but also with other parameters such as synthesis method and conditions. Hence, AZO nanoparticles, synthesized in the gas phase, were investigated to study the influence of the synthesis parameters dopant level, reactor temperature and residence time in the reaction zone on the particle characteristics. The local structure of the dopant in semiconductors determines whether the doping is functional, i.e., whether mobile charge carriers are generated. Therefore, information obtained from 27Al solid-state NMR spectroscopy, X-ray diffraction, photoluminescence and UV-Vis spectroscopy was used to understand how the local structure influences particles characteristics and how the local structure itself can be influenced by the synthesis parameters. In addition to AZO particles of different Al content, pure ZnO, Al2O3, ZnAl2O4 and core-shell particles of ZnO and Al2O3 were synthesized for comparison and aid to a deeper understanding of the formation of AZO nanoparticles in the gas phase. © 2014 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-014-2506-z
  • 2014 • 342 Antibacterial AgNPs/CaP biocomposites
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Sharonova, A.A. and Grubova, I.Y. and Loza, K. and Chernousova, S. and Prymak, O. and Epple, M.
    2014 9th International Forum on Strategic Technology, IFOST 2014 472-474 (2014)
    The modification of implant surface is in the focus of many scientists worldwide. In this study, multifunctional biocomposite on the basis of calcium phosphate coating and silver nanoparticles has been fabricated through the use of nanofabrication techniques. Dense nanocrystalline HA film was deposited over AgNPs. The properties as well as the in vitro behavior of the developed biocomposites have been studied. The diffraction patterns of the biocomposites revealed the peaks of crystalline HA and silver (Ag). The release of Ag from the developed biocomposites was evaluated. The concentration of the released silver ions for 7 days of dissolution was 0.27±0.02 μg/mL and 0.54±0.02 μg/mL for phosphate and acetate buffers, respectively. In order to estimate the cytotoxicity of the samples the functional activity of osteoclasts, in particular, cell morphology, multinuclearity, actin ring and resorption pit on the substrates coated with HA and AgNPs-HA have been evaluated. © 2014 IEEE.
    view abstractdoi: 10.1109/IFOST.2014.6991166
  • 2014 • 341 Assessment of a cylindrical and a rectangular plate differential mobility analyzer for size fractionation of nanoparticles at high-aerosol flow rates
    Hontañón, E. and Rouenhoff, M. and Azabal, A. and Ramiro, E. and Kruis, F.E.
    Aerosol Science and Technology 48 333-339 (2014)
    An existing differential mobility analyzer (DMA) of cylindrical electrodes and a novel DMA of rectangular plate electrodes are demonstrated for size fractionation of nanoparticles at high-aerosol flow rates in this work. The two DMAs are capable of delivering monodisperse size selected nanoparticles (SMPS σg < 1.1) at gas flow rates ranging from 200 slm to 500 slm. At an aerosol flow rate of 200 slm, the maximum attainable particle mean size is of about 20 nm for the cylindrical DMA and of nearly 50 nm for the rectangular plate DMA. The number concentration of the monodisperse nanoparticles delivered by the high-flow DMAs spans from 104 cm-3 to 10 6 cm-3 depending upon the particle mean size and particle size dispersion. Copyright © 2014 American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2013.875116
  • 2014 • 340 Atomic imaging of carbon-supported Pt, Pt/Co, and Ir@Pt nanocatalysts by atom-probe tomography
    Li, T. and Bagot, P.A.J. and Christian, E. and Theobald, B.R.C. and Sharman, J.D.B. and Ozkaya, D. and Moody, M.P. and Tsang, S.C.E. and Smith, G.D.W.
    ACS Catalysis 4 695-702 (2014)
    Atom probe tomography (APT) has been used to characterize commercially prepared Pt, Pt/Co alloy, and Ir@Pt core-shell nanoparticles supported on high-surface-area carbon black. Concentration profiles and 3D atom maps revealing the detailed internal structures and compositions of Pt, Pt/Co alloy, and Ir@Pt core-shell particles have been generated, and the distribution of trace impurity elements, including Na and Cl, has been examined. The observation of retained Na on the support, especially in the Pt nanoparticle system, indicates a more rigorous washing procedure is required. In the Pt/Co alloyed carbon-supported nanoparticle system, a marked variation in both compositions and particle sizes is observed. In the case of Ir@Pt, significant intermixing of the Ir core and Pt shell atoms takes place, which would be very difficult to measure by other techniques. All such observations will likely impact the catalytic performance of these materials. We envisage that the single nanoparticle analysis capability of APT, providing atomic-scale structures and chemical mapping, can also act as a means of quality control, identifying differences in the final product compared with the intended specification. Although the catalytic activity of these nanoparticles was not part of current study, the detailed information offered by such studies will permit knowledge-based improvements in nanoscale catalyst preparation methods and will also provide new ways of investigating structure and activity relationships at the nanometer scale. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/cs401117e
  • 2014 • 339 Behavior of nanoscale titanium dioxide in laboratory wastewater treatment plants according to OECD 303 A
    Gartiser, S. and Flach, F. and Nickel, C. and Stintz, M. and Damme, S. and Schaeffer, A. and Erdinger, L. and Kuhlbusch, T.A.J.
    Chemosphere 104 197-204 (2014)
    The fate assessment of nanomaterials in municipal sewage treatment plants (STP) is a crucial step for their environmental risk assessment and may be assessed by monitoring full scale STP, dosage to medium scale pilot STP or by laboratory testing. For regulatory purposes preferably standardised test protocols such as the OECD guidelines for testing of chemicals should be used. However, these test protocols have not yet been specifically designed for nanoparticles. Therefore, the fate and behavior of a TiO2 nanomaterial (P25, average hydrodynamic diameter < 250nm) was investigated in laboratory sewage treatment plants according to the OECD Guideline for the Testing of Chemicals 303 A. It is concluded that this guideline is applicable for the testing of nanomaterials if modifications regarding the dosage, nitrifying conditions, and a characterisation of the nanoparticles in the effluent are applied. A compilation of the cumulative mass balance by comparison of the total dosage added with the amount in the outflow and in the activated sludge is recommended. In this study, the majority of the TiO2 nanomaterial (&gt;95%) was retained in the sewage sludge and only 3-4% was found in the effluent. No effect of the TiO2 nanomaterials on the biodegradation or nitrification was observed. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.chemosphere.2013.11.015
  • 2014 • 338 Calcium phosphate nanoparticles show an effective activation of the innate immune response in vitro and in vivo after functionalization with flagellin
    Kozlova, D. and Sokolova, V. and Zhong, M. and Zhang, E. and Yang, J. and Li, W. and Yang, Y. and Buer, J. and Westendorf, A.M. and Epple, M. and Yan, H.
    Virologica Sinica 29 33-39 (2014)
    For subunit vaccines, adjuvants play a key role in shaping the magnitude, persistence and form of targeted antigen-specific immune response. Flagellin is a potent immune activator by bridging innate inflammatory responses and adaptive immunity and an adjuvant candidate for clinical application. Calcium phosphate nanoparticles are efficient carriers for different biomolecules like DNA, RNA, peptides and proteins. Flagellin-functionalized calcium phosphate nanoparticles were prepared and their immunostimulatory effect on the innate immune system, i.e. the cytokine production, was studied. They induced the production of the proinflammatory cytokines IL-8 (Caco-2 cells) and IL-1β (bone marrow-derived macrophages; BMDM) in vitro and IL-6 in vivo after intraperitoneal injection in mice. The immunostimulation was more pronounced than with free flagellin. © 2014 Wuhan Institute of Virology, CAS and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s12250-014-3379-0
  • 2014 • 337 Carbon monoxide-assisted size confinement of bimetallic alloy nanoparticles
    Cui, C. and Gan, L. and Neumann, M. and Heggen, M. and Roldan Cuenya, B. and Strasser, P.
    Journal of the American Chemical Society 136 4813-4816 (2014)
    Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 °C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of ∼4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/ja4124658
  • 2014 • 336 Charge balancing of model gold-nanoparticle-peptide conjugates controlled by the peptide's net charge and the ligand to nanoparticle ratio
    Gamrad, L. and Rehbock, C. and Krawinkel, J. and Tumursukh, B. and Heisterkamp, A. and Barcikowski, S.
    Journal of Physical Chemistry C 118 10302-10313 (2014)
    Gold nanoparticles (AuNPs) covalently bound to biomolecules, termed bioconjugates,1 are highly relevant for biological applications like drug targeting or bioimaging. Here, the net charge of the bioconjugate is one key parameter affecting biocompatibility and cell membrane interaction. However, when negatively charged AuNPs are conjugated to positively charged biomolecules, resulting charge compensation compromises the stability of the conjugates. In this work, laser-generated negatively charged AuNPs exhibiting a bare surface were used as a model and separately conjugated to cell penetrating peptides (CPPs) carrying different positive net charges. Occurring charge compensation leads to two regimes where stable bioconjugates are obtained on both sides of the bioconjugate's isoelectric point. These regimes can be controlled by the peptide's net charge. Generally, increasing the peptide's net charges yields stable positively charged bioconjugates with decreased surface coverages. To demonstrate the compatibility of the bioconjugates in bioapplications, long-term stability measurements were performed. Furthermore, the uptake by live mammalian cells was investigated with multiphoton microscopy using the luminescence of the AuNP-peptide conjugates. The results for our model system of laser-generated AuNPs and CPPs show that a precise tuning of conjugate properties is possible. They can be transferred to other oppositely charged nanoparticle-ligand systems, avoiding occurrence of charge compensation with defined ligand load. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp501489t
  • 2014 • 335 Chemical interactions between silver nanoparticles and thiols: A comparison of mercaptohexanol against cysteine
    Toh, H.S. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    Science China Chemistry 57 1199-1210 (2014)
    The interaction between citrate capped silver nanoparticles and two different thiols, mercaptohexanol (MH) and cysteine, was investigated. The thiols interacted with silver nanoparticles in a significantly contrasting manner. With MH, a sparingly soluble silver(I) thiolate complex AgSRm (Rm = -(CH2)6OH) was formed on the silver nanoparticle surface. Cyclic voltammograms and UV-vis spectra were used to infer that the AgSRm complex on the nanoparticle surface undergoes a phase transition to give a mixture of AgSRm and Ag2S-like complexes. In contrast, when silver nanoparticles were exposed to cysteine, the citrate capping agent on the silver nanoparticles was replaced by cysteine to give cysteine capped nanoparticles. As cysteine capped nanoparticles form, the electrochemical data displayed a decrease in oxidative peak charge but the UV-vis spectra showed a constant signal. Therefore, cysteine capped nanoparticles were suggested to have either inactivated the silver surface or else promoted detachment from the electrode surface. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s11426-014-5141-8
  • 2014 • 334 CO 2 hydrogenation to hydrocarbons over iron nanoparticles supported on oxygen-functionalized carbon nanotubes
    Chew, L.M. and Ruland, H. and Schulte, H.J. and Xia, W. and Muhler, M.
    Journal of Chemical Sciences 126 481-486 (2014)
    Hydrogenation of CO2 to hydrocarbons over iron nanoparticles supported on oxygen-functionalized multi-walled carbon nanotubes was studied in a fixed-bed U-tube reactor at 25 bar with a H2:CO2 ratio of 3. Conversion of CO2 was approximately 35% yielding C 1-C5 products at 360°C with methane and CO as major products. The CO2 equilibrium conversion for temperatures in the range of 320° to 420°C was analysed by using CHEMCAD simulation software. Comparison between experimental and simulated degrees of CO 2 conversion shows that reverse water gas shift equilibrium had been achieved in the investigated temperature range and that less than 47% of CO 2 can be converted to CO at 420°C. © 2014 Indian Academy of Sciences.
    view abstractdoi: 10.1007/s12039-014-0591-2
  • 2014 • 333 Comparison of different characterization methods for nanoparticle dispersions before and after aerosolization
    Fissan, H. and Ristig, S. and Kaminski, H. and Asbach, C. and Epple, M.
    Analytical Methods 6 7324-7334 (2014)
    A well-known and accepted aerosol measurement technique, the scanning mobility particle sizer (SMPS), is applied to characterize colloidally dispersed nanoparticles. To achieve a transfer from dispersed particles to aerosolized particles, a newly developed nebulizer (N) is used that, unlike commonly used atomizers, produces significantly smaller droplets and therefore reduces the problem of the formation of residual particles. The capabilities of this new instrument combination (N + SMPS) for the analysis of dispersions were investigated, using three different dispersions, i.e. gold-PVP nanoparticles (∼20 nm), silver-PVP nanoparticles (∼70 nm) and their 1:1 (m:m) mixture. The results are compared to scanning electron microscopy (SEM) measurements and two frequently applied techniques for characterizing colloidal systems: Dynamic light scattering (DLS) and analytical disc centrifugation (ADC). The differences, advantages and disadvantages of each method are discussed, especially with respect to the size resolution of the techniques and their ability to distinguish the particle sizes of the mixed dispersion. While DLS is, as expected, unable to resolve the binary dispersion, SEM, ADC and SMPS are able to give quantitative information on the two particle sizes. However, while the high-resolving ADC is limited due to the dependency on a predefined density of the investigated system, the transfer of dispersed particles into an aerosol and subsequent analysis with SMPS are an adequate way to characterize binary systems, independent of the density of concerned particles, but matching the high resolution of the ADC. We show that it is possible to use the well-established aerosol measurement technique (N + SMPS) in colloid science with all its advantages concerning size resolution and accuracy. © the Partner Organisations 2014.
    view abstractdoi: 10.1039/c4ay01203h
  • 2014 • 332 Comparison of silver nanoparticles stored under air or argon with respect to the induction of intracellular free radicals and toxic effects toward keratinocytes
    Ahlberg, S. and Meinke, M.C. and Werner, L. and Epple, M. and Diendorf, J. and Blume-Peytavi, U. and Lademann, J. and Vogt, A. and Rancan, F.
    European Journal of Pharmaceutics and Biopharmaceutics 88 651-657 (2014)
    Bacterial infections decreased considerably after the discovery of antibiotics. Nevertheless, because of the rising rate of infections caused by antibiotic-resistant bacteria strains, the search for new bactericidal agents has again become a crucial topic in clinical medicine. Silver nanoparticles (AgNP) have a huge potential in dermatology and wound care management because of their ability to release silver ions (Ag+ ions) in a prolonged and sustained way. However, negative effects of silver on the patient's cells should not be underestimated. Furthermore, it has been controversially discussed whether AgNP are responsible for nanoparticle-specific outcomes or not. In this study, we investigated the effects of AgNP on human skin keratinocytes (HaCaT) in order to better understand the mechanisms of cytotoxicity and to improve the use of this highly reactive biocide in wound healing. We found that most of the cells with internalized AgNP displayed the typical morphological signs of apoptosis. The cell viability assay (XTT) showed concentration-dependent toxic effects of the AgNP toward HaCaT cells. The generation of reactive oxygen species (ROS) induced by AgNP was investigated in cell suspensions by means of electron paramagnetic resonance (EPR) spectroscopy. In order to distinguish between the effects of Ag+ ions released during AgNP storage and those of Ag+ ions released after nanoparticle application, we compared AgNP stored under air (O2) with AgNP stored under argon (Ar). Dispersions of AgNP stored under Ar have a low content of Ag+ ions because of the absence of oxygen which is needed for oxidative dissolution. The results show that Ag+ ions released during particle storage are responsible for most of the ROS produced during 1 h incubation with the cells. AgNP (Ar) also induced intracellular ROS but to a much smaller extent compared to AgNP (O2). These findings highlight the complexity of experiments to assess the toxicity of AgNP and suggest the possibility of reducing AgNP toxic effects by storing AgNP formulations and even silver-containing wound dressing under an inert gas atmosphere. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.ejpb.2014.07.012
  • 2014 • 331 Confined-space alloying of nanoparticles for the synthesis of efficient PtNi fuel-cell catalysts
    Baldizzone, C. and Mezzavilla, S. and Carvalho, H.W.P. and Meier, J.C. and Schuppert, A.K. and Heggen, M. and Galeano, C. and Grunwaldt, J.-D. and Schüth, F. and Mayrhofer, K.J.J.
    Angewandte Chemie - International Edition 53 14250-14254 (2014)
    The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nano-structured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 AmgPt -1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined space alloying of the nanoparticles in a controlled manner in the pores of the support. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201406812
  • 2014 • 330 Correlation of superparamagnetic relaxation with magnetic dipole interaction in capped iron-oxide nanoparticles
    Landers, J. and Stromberg, F. and Darbandi, M. and Schöppner, C. and Keune, W. and Wende, H.
    Journal of Physics Condensed Matter 27 (2014)
    Six nanometer sized iron-oxide nanoparticles capped with an organic surfactant and/or silica shell of various thicknesses have been synthesized by a microemulsion method to enable controllable contributions of interparticle magnetic dipole interaction via tunable interparticle distances. Bare particles with direct surface contact were used as a reference to distinguish between interparticle interaction and surface effects by use of Mössbauer spectroscopy. Superparamagnetic relaxation behaviour was analyzed by SQUID-magnetometry techniques, showing a decrease of the blocking temperature with decreasing interparticle interaction energies kBT 0 obtained by AC susceptibility. A many-state relaxation model enabled us to describe experimental Mössbauer spectra, leading to an effective anisotropy constant Keff ≈ 45 kJm-3 in case of weakly interacting particles, consistent with results from ferromagnetic resonance. Our unique multi-technique approach, spanning a huge regime of characteristic time windows from about 10 s to 5 ns, provides a concise picture of the correlation of superparamagnetic relaxation with interparticle magnetic dipole interaction. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/27/2/026002
  • 2014 • 329 Design criteria for stable Pt/C fuel cell catalysts
    Meier, J.C. and Galeano, C. and Katsounaros, I. and Witte, J. and Bongard, H.J. and Topalov, A.A. and Baldizzone, C. and Mezzavilla, S. and Schüth, F. and Mayrhofer, K.J.J.
    Beilstein Journal of Nanotechnology 5 44-67 (2014)
    Platinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3-4 nm and two Pt@HGS catalysts with different particle size, 1-2 nm and 3-4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS). All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested.& copy 2014 Meier et al.
    view abstractdoi: 10.3762/bjnano.5.5
  • 2014 • 328 Dipole-dipole interaction in arrays of Fe/FexOy Core/shell nanocubes probed by ferromagnetic resonance
    Sukhov, A. and Horley, P.P. and Berakdar, J. and Terwey, A. and Meckenstock, R. and Farle, M.
    IEEE Transactions on Magnetics 50 (2014)
    This paper represents a detailed theoretical study of the role of the long-range magnetic dipole-dipole interaction (DDI) evidenced by the ferromagnetic resonance (FMR) spectra for the ordered arrays of cubic nanoparticles. We show that the size of the array essentially controls the stability of the system, allowing us to suppress the intermittent low-field excitations starting from the arrays formed by 6 × 6 nanoparticles. Our numerical simulations allow us to determine the threshold inter-particle distance (around 80/100 nm), after which the DDI becomes negligible so that the FMR spectrum of the nanoparticle arrays becomes the same as the spectrum featured by a single nanoparticle.We also compare our simulations with experimental FMR-spectra of 24 Fe/FexOy-nanocubes irregularly placed on a substrate. © 2014 IEEE.
    view abstractdoi: 10.1109/TMAG.2014.2329814
  • 2014 • 327 Dose-dependent surface endothelialization and biocompatibility of polyurethane noble metal nanocomposites
    Hess, C. and Schwenke, A. and Wagener, P. and Franzka, S. and Laszlo Sajti, C. and Pflaum, M. and Wiegmann, B. and Haverich, A. and Barcikowski, S.
    Journal of Biomedical Materials Research - Part A 102 1909-1920 (2014)
    Surface pre-endothelialization is a promising approach to improve the hemocompatibility of implants, medical devices, and artificial organs. To promote the adhesive property of thermoplastic polyurethane (TPU) for endothelial cells (ECs), up to 1 wt % of gold (Au) or platinum (Pt) nanoparticles, fabricated by pulsed laser ablation in polymer solution, were embedded into the polymer matrix. The analysis of these nanocomposites showed a homogenous dispersion of the nanoparticles, with average diameters of 7 nm for Au or 9 nm for Pt. A dose-dependent effect was found when ECs were seeded onto nanocomposites comprising different nanoparticle concentrations, resulting in a fivefold improvement of proliferation at 0.1 wt % nanoparticle load. This effect was associated with a nanoparticle concentration-dependent hydrophilicity and negative charge of the nanocomposite. In dynamic flow tests, nanocomposites containing 0.1 wt % Au or Pt nanoparticles allowed for the generation of a confluent and resistant EC layer. Real-time polymerase chain reaction quantification of specific markers for EC activation indicated that ECs cultivated on nanocomposites remain in an inactivated, nonthrombogenic and noninflammatory state; however, maintain the ability to trigger an inflammatory response upon stimulation. These findings were confirmed by a platelet and leukocyte adhesion assay. The results of this study suggest the possible applicability of TPU nanocomposites, containing 0.1 wt % Au or Pt nanoparticles, for the generation of pre-endothelialized surfaces of medical devices. © 2013 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/jbm.a.34860
  • 2014 • 326 Dynamic surface processes of nanostructured Pd2Ga catalysts derived from hydrotalcite-like precursors
    Ota, A. and Kröhnert, J. and Weinberg, G. and Kasatkin, I. and Kunkes, E.L. and Ferri, D. and Girgsdies, F. and Hamilton, N. and Armbrüster, M. and Schlögl, R. and Behrens, M.
    ACS Catalysis 4 2048-2059 (2014)
    The stability of the surface termination of intermetallic Pd2Ga nanoparticles and its effect on the hydrogenation of acetylene was investigated. For this purpose, a precursor synthesis approach was applied to synthesize supported intermetallic Pd2Ga nanoparticles. A series of Pd-substituted MgGa-hydrotalcite (HT)-like compounds with different Pd loading was prepared by coprecipitation and studied in terms of loading, phase formation, stability and catalytic performance in the selective hydrogenation of acetylene. Higher Pd loadings than 1 mol % revealed an incomplete incorporation of Pd into the HT lattice, as evidenced by XANES and TPR measurements. Upon thermal reduction in hydrogen, Pd2Ga nanoparticles were obtained with particle sizes varying with the Pd loading, from 2 nm to 6 nm. The formation of intermetallic Pd2Ga nanoparticles led to a change of the CO adsorption properties as was evidenced by IR spectroscopy. Dynamic changes of the surface were noticed at longer exposure times to CO and higher coverage at room temperature as a first indication of surface instability. These were ascribed to the decomposition into a Ga-depleted Pd phase and Ga 2O3, which is a process that was suppressed at liquid nitrogen temperature. The reduction of the Pd precursor at 473 K is not sufficient to form the Pd2Ga phase and yielded a poorly selective catalyst (26% selectivity to ethylene) in the semihydrogenation of acetylene. In accordance with the well-known selectivity-promoting effect of a second metal, the selectivity was increased to 80% after reduction at 773 K due to a change from the elemental to the intermetallic state of palladium in our catalysts. Interestingly, if air contact was avoided after reduction, the conversion slowly rose from initially 22% to 94% with time on stream. This effect is interpreted in the light of chemical response of Pd and Pd2Ga to the chemical potential of the reactive atmosphere. Conversely to previous interpretations, we attribute the initial low active state to the clean intermetallic surface, while the increase in conversion is related to the surface decomposition of the Pd2Ga particles. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/cs500465r
  • 2014 • 325 Dynamical behavior of laser-induced nanoparticles during remote processing
    Scholz, T. and Dickmann, K. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 8963 (2014)
    Laser remote processing is used in a wide field of industrial applications. Among other things, it is characterized by flexible beam guidance in combination with high processing velocities. But in most cases process gas support in the interaction zone is omitted. Consequently, interaction mechanism between the vapor plume and the incident laser radiation can dynamically affect the process stability. Referring to remote welding with high brilliant laser sources having a wavelength around 1 μm, the interaction between the incident laser radiation and formed particles plays an important role. The presented work shows results of the investigation of the laser-induced particle formation during the laser welding of stainless steel with a 2 kW fiber laser under remote conditions. It is therefore concentrated on the dynamical behavior of the laser-induced particle formation and the dependence of the particle formation on the laser beam power. TEM images of formed particles were analyzed. In addition, the radiation of a LED was directed through the vapor plume. On the one hand, the dynamic of the attenuation was considered. On the other hand, the Rayleigh approximation was used in order to evaluate the detected signals. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2035197
  • 2014 • 324 Effect of a side reaction involving structural changes of the surfactants on the shape control of cobalt nanoparticles
    Comesaña-Hermo, M. and Estivill, R. and Ciuculescu, D. and Li, Z.-A. and Spasova, M. and Farle, M. and Amiens, C.
    Langmuir 30 4474-4482 (2014)
    Cobalt nanoparticles with different sizes and morphologies including spheres, rods, disks, and hexagonal prisms have been synthesized through the decomposition of the olefinic precursor [Co(η3-C 8H13)(η4-C8H12)] under dihydrogen, in the presence of hexadecylamine and different rhodamine derivatives, or aromatic carboxylic acids. UV-vis spectroscopy, X-ray diffraction, low and high resolution transmission electron microscopy, and electron tomography have been used to characterize the nanomaterials. Especially, the Co nanodisks formed present characteristics that make them ideal nanocrystals for applications such as magnetic data storage. Focusing on their growth process, we have evidenced that a reaction between hexadecylamine and rhodamine B occurs during the formation of these Co nanodisks. This reaction limits the amount of free acid and amine, usually at the origin of the formation of single crystal Co rods and wires, in the growth medium of the nanocrystals. As a consequence, a growth mechanism based on the structure of the preformed seeds rather than oriented attachment or template assisted growth is postulated to explain the formation of the nanodisks. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/la5005165
  • 2014 • 323 Effect of silver nanoparticles on human mesenchymal stem cell differentiation
    Sengstock, C. and Diendorf, J. and Epple, M. and Schildhauer, T.A. and Köller, M.
    Beilstein Journal of Nanotechnology 5 2058-2069 (2014)
    Background: Silver nanoparticles (Ag-NP) are one of the fastest growing products in nano-medicine due to their enhanced antibacterial activity at the nanoscale level. In biomedicine, hundreds of products have been coated with Ag-NP. For example, various medical devices include silver, such as surgical instruments, bone implants and wound dressings. After the degradation of these materials, or depending on the coating technique, silver in nanoparticle or ion form can be released and may come into close contact with tissues and cells. Despite incorporation of Ag-NP as an antibacterial agent in different products, the toxicological and biological effects of silver in the human body after long-term and low-concentration exposure are not well understood. In the current study, we investigated the effects of both ionic and nanoparticulate silver on the differentiation of human mesenchymal stem cells (hMSCs) into adipogenic, osteogenic and chondrogenic lineages and on the secretion of the respective differentiation markers adiponectin, osteocalcin and aggrecan. Results: As shown through laser scanning microscopy, Ag-NP with a size of 80 nm (hydrodynamic diameter) were taken up into hMSCs as nanoparticulate material. After 24 h of incubation, these Ag-NP were mainly found in the endo-lysosomal cell compartment as agglomerated material. Cytotoxicity was observed for differentiated or undifferentiated hMSCs treated with high silver concentrations (≥20 μg·mL-1 Ag-NP; ≥1.5 μg·mL-1 Ag+ ions) but not with low-concentration treatments (≤10 μg·mL-1 Ag-NP; ≤1.0 μg·mL-1 Ag+ ions). Subtoxic concentrations of Ag-NP and Ag+ ions impaired the adipogenic and osteogenic differentiation of hMSCs in a concentration-dependent manner, whereas chondrogenic differentiation was unaffected after 21 d of incubation. In contrast to aggrecan, the inhibitory effect of adipogenic and osteogenic differentiation was confirmed by a decrease in the secretion of specific biomarkers, including adiponectin (adipocytes) and osteocalcin (osteoblasts). Conclusion: Aside from the well-studied antibacterial effect of silver, little is known about the influence of nano-silver on cell differentiation processes. Our results demonstrate that ionic or nanoparticulate silver attenuates the adipogenic and osteogenic differentiation of hMSCs even at non-toxic concentrations. Therefore, more studies are needed to investigate the effects of silver species on cells at low concentrations during long-term treatment. © 2014 Sengstock et al.
    view abstractdoi: 10.3762/bjnano.5.214
  • 2014 • 322 Electrochemical detection and characterisation of polymer nanoparticles
    Zhou, X.-F. and Cheng, W. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    Electroanalysis 26 248-253 (2014)
    We report the detection and characterisation of polymer nanoparticles using electrochemistry using poly(N-vinylcarbazole) nanoparticles (PVK NPs) as a model system. These were synthesised using the reprecipitation method. The number of electrons (n=2) transferred per PVK monomer was characterised by drop-casting method. Sticking and sensing experiments were then conducted, which involve PVK nanoparticle immobilisation on the electrode surface and subsequent oxidative sensing, to enable rapid detection of polymer nanoparticles in aqueous solution. It is shown for the first time, that using this "stick and sense" method, polymer nanoparticles in aqueous solution can be immobilised, preconcentrated and quantified. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/elan.201300438
  • 2014 • 321 Electrochemical observation of single collision events: Fullerene nanoparticles
    Stuart, E.J.E. and Tschulik, K. and Batchelor-Mcauley, C. and Compton, R.G.
    ACS Nano 8 7648-7654 (2014)
    Individual fullerene nanoparticles are detected and sized in a non-aqueous solution via cathodic particle coulometry where the direct, quantitative reduction of single nanoparticles is achieved upon collision with a potentiostated gold electrode. This is the first time that the nanoparticle impact technique has been shown to work in a non-aqueous electrolyte and utilized to coulometrically size carbonaceous nanoparticles. Contrast is drawn between single-nanoparticle electrochemistry and that seen using nanoparticle ensembles via modified electrodes. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nn502634n
  • 2014 • 320 Enhancing solar cell efficiency by lenses on the nano- And microscale
    Schmid, M. and Manley, P.
    Proceedings of SPIE - The International Society for Optical Engineering 9178 (2014)
    Metallic nanoparticles exhibiting plasmonic effects as well as dielectric nanoparticles coupling the light into resonant modes have both shown successful application to photovoltaics. On the larger scale, microconcentrator optics promise to enhance solar cell efficiency and reduce material consumption. Here we want to make the link between concentrators on the nano- And on the microscale. From metallic nanospheres we turn to dielectric ones and then look at increasing radii to approach concentrator optics on the mircoscale. The nano- And microlenses are investigated with respect to their interaction with light using 3D simulations with the finite element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations can be applied which give ray distributions in agreement with areas of high electric field intensities. Calculations of back focal lengths using ray tracing coincide with results from geometrical optics simulations. They give us insight into how the focal length can be tuned as a function of particle size, but also depending on the substrate refractive index and the shape of the microlens. Turning from spherical to segment-shaped lenses allows us to approach the realistic case of microconcentrator optics and to draw conclusions about focus tuning and system design. Despite the similarities of focusing behavior we find for the nano- And the microlenses, the integration into solar cells needs to be carefully adjusted, depending on the ambition of material saving, concentration level, focal distance and lens size, all being closely related. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2061132
  • 2014 • 319 Exceptional size-dependent activity enhancement in the electroreduction of CO2 over Au nanoparticles
    Mistry, H. and Reske, R. and Zeng, Z. and Zhao, Z.-J. and Greeley, J. and Strasser, P. and Cuenya, B.R.
    Journal of the American Chemical Society 136 16473-16476 (2014)
    The electrocatalytic reduction of CO2 to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but it is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. We report here the size-dependent catalytic activity of micelle-synthesized Au nanoparticles (NPs) in the size range of ∼1-8 nm for the electroreduction of CO2 to CO in 0.1 M KHCO3. A drastic increase in current density was observed with decreasing NP size, along with a decrease in Faradaic selectivity toward CO. Density functional theory calculations showed that these trends are related to the increase in the number of low-coordinated sites on small NPs, which favor the evolution of H2 over CO2 reduction to CO. We show here that the H2/CO product ratio can be specifically tailored for different industrial processes by tuning the size of the catalyst particles. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/ja508879j
  • 2014 • 318 Fetuin-A and albumin alter cytotoxic effects of calcium phosphate nanoparticles on human vascular smooth muscle cells
    Dautova, Y. and Kozlova, D. and Skepper, J.N. and Epple, M. and Bootman, M.D. and Proudfoot, D.
    PLoS ONE 9 (2014)
    Calcification is a detrimental process in vascular ageing and in diseases such as atherosclerosis and arthritis. In particular, small calcium phosphate (CaP) crystal deposits are associated with inflammation and atherosclerotic plaque de-stabilisation. We previously reported that CaP particles caused human vascular smooth muscle cell (VSMC) death and that serum reduced the toxic effects of the particles. Here, we found that the serum proteins fetuin-A and albumin (≥1 μM) reduced intracellular Ca2+ elevations and cell death in VSMCs in response to CaP particles. In addition, CaP particles functionalised with fetuin-A, but not albumin, were less toxic than naked CaP particles. Electron microscopic studies revealed that CaP particles were internalised in different ways; via macropinocytosis, membrane invagination or plasma membrane damage, which occurred within 10 minutes of exposure to particles. However, cell death did not occur until approximately 30 minutes, suggesting that plasma membrane repair and survival mechanisms were activated. In the presence of fetuin-A, CaP particle-induced damage was inhibited and CaP/plasma membrane interactions and particle uptake were delayed. Fetuin-A also reduced dissolution of CaP particles under acidic conditions, which may contribute to its cytoprotective effects after CaP particle exposure to VSMCs. These studies are particularly relevant to the calcification observed in blood vessels in patients with kidney disease, where circulating levels of fetuin-A and albumin are low, and in pathological situations where CaP crystal formation outweighs calcification-inhibitory mechanisms. © 2014 Dautova et al.
    view abstractdoi: 10.1371/journal.pone.0097565
  • 2014 • 317 Generation of NiTi nanoparticles by femtosecond laser ablation in liquid
    Chakif, M. and Essaidi, A. and Gurevich, E. and Ostendorf, A. and Prymak, O. and Epple, M.
    Journal of Materials Engineering and Performance 23 2482-2486 (2014)
    NiTi was investigated as a model system for a binary alloy where the properties strongly depend on the relative proportion of the two elements and on the grain size. The NiTi nanoparticles were generated by laser ablation in water. For the analysis of the particle size distribution, we used transmission electron microscopy and dynamic light scattering. Here, we found a broad particle size distribution (10-200 nm). Furthermore, the temperature-resolved x-ray powder diffraction and differential scanning calorimetry (DSC) were used to evaluate the phase transition behavior of the generated NiTi nanoparticles. Here, we found an interesting effect. During the heating by DSC, an austenite phase transition and a weak martensite phase transition in the NiTi nanoparticles appeared. Moreover, the phase transformation temperature was about 40 K lower than that of the bulk target. © 2014 ASM International.
    view abstractdoi: 10.1007/s11665-014-1007-7
  • 2014 • 316 Gold electrodes from recordable CDs for the sensitive, semi-quantitative detection of commercial silver nanoparticles in seawater media
    Stuart, E.J.E. and Tschulik, K. and Lowinsohn, D. and Cullen, J.T. and Compton, R.G.
    Sensors and Actuators, B: Chemical 195 223-229 (2014)
    We report the use of homemade disposable gold electrodes fabricated from commercial recordable CDs for the detection and quantification of silver nanoparticles from a consumer product in a seawater sample. The "CDtrode" is immersed in a seawater sample containing silver nanoparticles for a certain amount of time during which the silver nanoparticles adsorb onto the CDtrode surface under open circuit conditions. The CDtrode is then transferred to an aqueous electrolyte and oxidative stripping is used to determine the amount of silver nanoparticles that have become stuck to the electrode surface. Depending on immersion time and silver nanoparticle concentration, up to a full monolayer coverage of silver nanoparticles on the CDtrode surface has been achieved. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.snb.2014.01.040
  • 2014 • 315 Hidden structural features of multicompartment micelles revealed by cryogenic transmission electron tomography
    Löbling, T.I. and Haataja, J.S. and Synatschke, C.V. and Schacher, F.H. and Müller, M. and Hanisch, A. and Gröschel, A.H. and Müller, A.H.E.
    ACS Nano 8 11330-11340 (2014)
    The demand for ever more complex nanostructures in materials and soft matter nanoscience also requires sophisticated characterization tools for reliable visualization and interpretation of internal morphological features. Here, we address both aspects and present synthetic concepts for the compartmentalization of nanoparticle peripheries as well as their in situ tomographic characterization. We first form negatively charged spherical multicompartment micelles from ampholytic triblock terpolymers in aqueous media, followed by interpolyelectrolyte complex (IPEC) formation of the anionic corona with bis-hydrophilic cationic/neutral diblock copolymers. At a 1:1 stoichiometric ratio of anionic and cationic charges, the so-formed IPECs are charge neutral and thus phase separate from solution (water). The high chain density of the ionic grafts provides steric stabilization through the neutral PEO corona of the grafted diblock copolymer and suppresses collapse of the IPEC; instead, the dense grafting results in defined nanodomains oriented perpendicular to the micellar core. We analyze the 3D arrangements of the complex and purely organic compartments, in situ, by means of cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET). We study the effect of block lengths of the cationic and nonionic block on IPEC morphology, and while 2D cryo-TEM projections suggest similar morphologies, cryo-ET and computational 3D reconstruction reveal otherwise hidden structural features, e.g., planar IPEC brushes emanating from the micellar core. (Figure Presented). © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nn504197y
  • 2014 • 314 Highly luminescent ZnO quantum dots made in a nonthermal plasma
    Felbier, P. and Yang, J. and Theis, J. and Liptak, R.W. and Wagner, A. and Lorke, A. and Bacher, G. and Kortshagen, U.
    Advanced Functional Materials 24 1988-1993 (2014)
    Nonthermal plasmas allow the preparation of ligand-free quantum dots combining high production rates with superior crystalline quality and luminescence properties. Here, ZnO quantum dots are produced in a radiofrequency capacitively-coupled plasma, exhibiting size dependent photoluminescent quantum yields up to 60% after air exposure - the highest reported to date for any compound semiconductor quantum dots prepared in the gas phase. Systematic studies indicate the importance of the surface for the observed luminescence behavior. The high luminescent quantum yields in the visible range of the spectrum and the ligand-free, scalable synthesis make these quantum dots good candidates for light emitting applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201303449
  • 2014 • 313 High-throughput fabrication of Au-Cu nanoparticle libraries by combinatorial sputtering in ionic liquids
    König, D. and Richter, K. and Siegel, A. and Mudring, A.-V. and Ludwig, Al.
    Advanced Functional Materials 24 2049-2056 (2014)
    Materials libraries of binary alloy nanoparticles (NPs) are synthesized by combinatorial co-sputter deposition of Cu and Au into the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 1C4im][Tf2N]), which is contained in a micromachined cavity array substrate. The resulting NPs and NP-suspensions are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis measurements (UV-Vis), and attenuated total reflection Fourier transformed infrared (ATR-FTIR) spectroscopy. Whereas the NPs can be directly observed in the IL using TEM, for XRD measurements the NP concentration is too low to lead to satisfactory results. Thus, a new NP isolation process involving capping agents is developed which enables separation of NPs from the IL without changing their size, morphology, composition, and state of aggregation. The results of the NP characterization show that next to the unary Cu and Au NPs, both stoichiometric and non-stoichiometric Cu-Au NPs smaller than 7 nm can be readily obtained. Whereas the size and shape of the alloy NPs change with alloy composition, for a fixed composition the NPs have a small size distribution. The measured lattice constants of all capped NPs show unexpected increased values, which could be related to the NP/surfactant interactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201303140
  • 2014 • 312 Impact of process parameters on the laser-induced nanoparticle formation during keyhole welding under remote conditions
    Scholz, T. and Dickmann, K. and Ostendorf, A.
    Physics Procedia 56 477-486 (2014)
    The interaction between the vapor plume and the incident laser radiation affects remote laser welding. Relating to laser systems with an emitted wavelength around 1 μm, a significant loss mechanism can be traced back to the extinction by laser-induced particle formation. Due to the tight coupling between the particle formation and the evaporation rate inside the keyhole, the particle formation shows a strong dependence on the keyhole geometry and thus on process parameters (e.g. feed rate and laser beam power). In order to verify the relationship between particle formation and process parameters, the beam of a broadband LED was guided through the vapor plume during the welding processes with a fiber laser. The attenuated probe beam was analyzed in dependence on the wavelength. In addition, the propagation of the vapor plume was investigated by using high speed imaging. © 2014 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.phpro.2014.08.151
  • 2014 • 311 Impact of solvent mixture on iron nanoparticles generated by laser ablation
    Chakif, M. and Prymak, O. and Slota, M. and Heintze, E. and Gurevich, E.L. and Esen, C. and Bogani, L. and Epple, M. and Ostendorf, A.
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8955 (2014)
    The present work reveals the structural and magnetic properties of iron oxide (FexOy) nanoparticles (NPs) prepared by femtosecond laser ablation. The FexOy-NPs were produced in solutions consisting of different ratios of water and acetone. Laser ablation in water yields agglomerates and that in acetone yields chain structures whereas that in water/acetone show a mixture of both. We observe significant fabrication dependent properties such as different crystallinities and magnetic behaviors. The structural characterization shows a change from iron (Fe) to a Fe xOy state of the NPs which depends on the solution composition. Furthermore, transmission electron microscopy measurements exhibit a broad particle size distribution in all samples but with significant differences in the mean sizes. Using magnetic measurements we show that nanoparticles fabricated in pure acetone have lower coercive fields which come along with a smaller mean particle size and therefore increasing superparamagnetic behavior. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2037682
  • 2014 • 310 In situ nanoparticle size measurements of gas-borne silicon nanoparticles by time-resolved laser-induced incandescence
    Sipkens, T.A. and Mansmann, R. and Daun, K.J. and Petermann, N. and Titantah, J.T. and Karttunen, M. and Wiggers, H. and Dreier, T. and Schulz, C.
    Applied Physics B: Lasers and Optics 116 623-636 (2014)
    This paper describes the application of time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used mainly for measuring soot primary particles, to size silicon nanoparticles formed within a plasma reactor. Inferring nanoparticle sizes from TiRe-LII data requires knowledge of the heat transfer through which the laser-heated nanoparticles equilibrate with their surroundings. Models of the free molecular conduction and evaporation are derived, including a thermal accommodation coefficient found through molecular dynamics. The model is used to analyze TiRe-LII measurements made on silicon nanoparticles synthesized in a low-pressure plasma reactor containing argon and hydrogen. Nanoparticle sizes inferred from the TiRe-LII data agree with the results of a Brunauer-Emmett-Teller analysis. © 2013 Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00340-013-5745-2
  • 2014 • 309 In Situ Particle Size Measurements of Gas-borne Silicon Nanoparticles by Time-resolved Laser-induced Incandescence
    Sipkens, T. A. and Petermann, N. and Daun, K. J. and Titantah, J. and Karttunen, M. and Wiggers, H. and Dreier, T. and Schulz, C.
    Proceedings of the Asme Summer Heat Transfer Conference - 2013, Vol 1 V001T03A001 (2014)
    The functionality of silicon nanoparticles is strongly size-dependent, so there is a pressing need for laser diagnostics that can characterize aerosolized silicon nanoparticles. The present work is the first attempt to extend time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used for sizing soot, to size silicon nanoparticles. TiRe-LII measurements are made on silicon nanoparticles synthesized in a low-pressure plasma reactor containing argon. Molecular dynamics (MD) is used to predict the accommodation coefficient between silicon nanoparticles and argon and helium, which is needed to interpret the TiRe-LII data. The MD-derived thermal accommodation coefficients will be validated by comparing them to experimentally-derived values found using transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis.
    view abstractdoi: 10.1115/HT2013-17246
  • 2014 • 308 In vitro and in vivo interactions of selected nanoparticles with rodent serum proteins and their consequences in biokinetics
    Kreyling, W.G. and Fertsch-Gapp, S. and Schäffler, M. and Johnston, B.D. and Haberl, N. and Pfeiffer, C. and Diendorf, J. and Schleh, C. and Hirn, S. and Semmler-Behnke, M. and Epple, M. and Parak, W.J.
    Beilstein Journal of Nanotechnology 5 1699-1711 (2014)
    When particles incorporated within a mammalian organism come into contact with body fluids they will bind to soluble proteins or those within cellular membranes forming what is called a protein corona. This binding process is very complex and highly dynamic due to the plethora of proteins with different affinities and fractions in different body fluids and the large variation of compounds and structures of the particle surface. Interestingly, in the case of nanoparticles (NP) this protein corona is well suited to provide a guiding vehicle of translocation within body fluids and across membranes. This NP translocation may subsequently lead to accumulation in various organs and tissues and their respective cell types that are not expected to accumulate such tiny foreign bodies. Because of this unprecedented NP accumulation, potentially adverse biological responses in tissues and cells cannot be neglected a priori but require thorough investigations. Therefore, we studied the interactions and protein binding kinetics of blood serum proteins with a number of engineered NP as a function of their physicochemical properties. Here we show by in vitro incubation tests that the binding capacity of different engineered NP (polystyrene, elemental carbon) for selected serum proteins depends strongly on the NP size and the properties of engineered surface modifications. In the following attempt, we studied systematically the effect of the size (5, 15, 80 nm) of gold spheres (AuNP), surface-modified with the same ionic ligand; as well as 5 nm AuNP with five different surface modifications on the binding to serum proteins by using proteomics analyses. We found that the binding of numerous serum proteins depended strongly on the physicochemical properties of the AuNP. These in vitro results helped us substantially in the interpretation of our numerous in vivo biokinetics studies performed in rodents using the same NP. These had shown that not only the physicochemical properties determined the AuNP translocation from the organ of intake towards blood circulation and subsequent accumulation in secondary organs and tissues but also the the transport across organ membranes depended on the route of AuNP application. Our in vitro protein binding studies support the notion that the observed differences in in vivo biokinetics are mediated by the NP protein corona and its dynamical change during AuNP translocation in fluids and across membranes within the organism. © 2014 Kreyling et al.
    view abstractdoi: 10.3762/bjnano.5.180
  • 2014 • 307 Influence of the inter-electrode distance on the production of nanoparticles by means of atmospheric pressure inert gas dc glow discharge
    Hontañón, E. and Palomares, J.M. and Guo, X. and Engeln, R. and Nirschl, H. and Kruis, F.E.
    Journal of Physics D: Applied Physics 47 (2014)
    This work is aimed at investigating the influence of the inter-electrode spacing on the production rate and size of nanoparticles generated by evaporating a cathode on an atmospheric pressure dc glow discharge. Experiments are conducted in the configuration of two vertically aligned cylindrical electrodes in upward coaxial flow with copper as a consumable cathode and nitrogen as a carrier gas. A constant current of 0.5 A is delivered to the electrodes and the inter-electrode distance spanned from 0.5 to 10 mm. Continuous stable nanoparticle production is attained by optimal coaxial flow convection cooling of the cathode. Both the particle production rate and the primary particle size increase with the inter-electrode spacing up to nearly 5 mm and strongly decrease with an increasing inter-electrode distance beyond 5 mm. Production rates in the range of 1 mg h-1of very small nanoparticles (< 10 nm) are attained by a micro glow discharge (< 1 mm); while glow discharges of intermediate sizes (< 5 mm) result in production rates of up to 10 mg h-1and primary particles of sizes between 10 and 20 nm. No correlation is found between the measured spatially averaged plasma parameters and nanoparticle production. Since the latter is largely determined by the properties of the cathode surface, spatially resolved spectrometric measurements are needed to discern between the positive column and the cathode region of the glow discharge plasma. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/47/41/415201
  • 2014 • 306 Injection of ligand-free gold and silver nanoparticles into murine embryos does not impact pre-implantation development
    Taylor, U. and Garrels, W. and Barchanski, A. and Peterson, S. and Sajti, L. and Lucas-Hahn, A. and Gamrad, L. and Baulain, U. and Klein, S. and Kues, W.A. and Barcikowski, S. and Rath, D.
    Beilstein Journal of Nanotechnology 5 677-688 (2014)
    Intended exposure to gold and silver nanoparticles has increased exponentially over the last decade and will continue to rise due to their use in biomedical applications. In particular, reprotoxicological aspects of these particles still need to be addressed so that the potential impacts of this development on human health can be reliably estimated. Therefore, in this study the toxicity of gold and silver nanoparticles on mammalian preimplantation development was assessed by injecting nanoparticles into one blastomere of murine 2 cell-embryos, while the sister blastomere served as an internal control. After treatment, embryos were cultured and embryo development up to the blastocyst stage was assessed. Development rates did not differ between microinjected and control groups (gold nanoparticles: 67.3%, silver nanoparticles: 61.5%, sham: 66.2%, handling control: 79.4%). Real-time PCR analysis of six developmentally important genes (BAX, BCL2L2, TP53, OCT4, NANOG, DNMT3A) did not reveal an influence on gene expression in blastocysts. Contrary to silver nanoparticles, exposure to comparable Ag+-ion concentrations resulted in an immediate arrest of embryo development. In conclusion, the results do not indicate any detrimental effect of colloidal gold or silver nanoparticles on the development of murine embryos. © 2014 Taylor et al; licensee Beilstein-Institut.
    view abstractdoi: 10.3762/bjnano.5.80
  • 2014 • 305 Interaction of cobalt nanoparticles with oxygen- and nitrogen- functionalized carbon nanotubes and impact on nitrobenzene hydrogenation catalysis
    Chen, P. and Yang, F. and Kostka, A. and Xia, W.
    ACS Catalysis 4 1478-1486 (2014)
    The type and the amount of functional groups on the surface of carbon nanotubes (CNTs) were tuned to improve the activity of supported Co nanoparticles in hydrogenation catalysis. Surface nitrogen species on CNTs significantly promoted the decomposition of the cobalt precursor and the reduction of cobalt oxide, and improved the resistance of metallic Co against oxidation in ambient atmosphere. In the selective hydrogenation of nitrobenzene in the gas phase, Co supported on CNTs with the highest surface nitrogen content showed the highest activity, which is ascribed to the higher reducibility and the lower oxidation state of the Co nanoparticles under reaction conditions. For Co nanoparticles supported on CNTs with a smaller amount of surface nitrogen groups, a repeated reduction at 350 °C was essential to achieve a comparable high catalytic activity reaching 90% conversion at 250 °C, pointing to the importance of nitrogen species for the supported Co nanoparticles in nitrobenzene hydrogenation. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/cs500173t
  • 2014 • 304 Interaction of colloidal nanoparticles with their local environment: The (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles
    Pfeiffer, C. and Rehbock, C. and Hühn, D. and Carrillo-Carrion, C. and De Aberasturi, D.J. and Merk, V. and Barcikowski, S. and Parak, W.J.
    Journal of the Royal Society Interface 11 (2014)
    The physico-chemical properties of colloidal nanoparticles (NPs) are influenced by their local environment, as, in turn, the local environment influences the physico-chemical properties of the NPs. In other words, the local environment around NPs has a profound impact on the NPs, and it is different from bulk due to interaction with the NP surface. So far, this important effect has not been addressed in a comprehensive way in the literature. The vicinity of NPs can be sensitively influenced by local ions and ligands, with effects already occurring at extremely low concentrations. NPs in the Hückel regime are more sensitive to fluctuations in the ionic environment, because of a larger Debye length. The local ion concentration hereby affects the colloidal stability of the NPs, as it is different from bulk owing to Debye Hückel screening caused by the charge of the NPs. This can have subtle effects, now caused by the environment to the performance of the NP, such as for example a buffering effect caused by surface reaction on ultrapure ligandfree nanogold, a size quenching effect in the presence of specific ions and a significant impact on fluorophore-labelled NPs acting as ion sensors. Thus, the aim of this review is to clarify and give an unifying view of the complex interplay between the NP's surface with their nanoenvironment. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
    view abstractdoi: 10.1098/rsif.2013.0931
  • 2014 • 303 Interaction of dermatologically relevant nanoparticles with skin cells and skin
    Vogt, A. and Rancan, F. and Ahlberg, S. and Nazemi, B. and Choe, C.S. and Darvin, M.E. and Hadam, S. and Blume-Peytavi, U. and Loza, K. and Diendorf, J. and Epple, M. and Graf, C. and Ruhl, E. and Meinke, M.C. and Lademann, J.
    Beilstein Journal of Nanotechnology 5 2363-2373 (2014)
    The investigation of nanoparticle interactions with tissues is complex. High levels of standardization, ideally testing of different material types in the same biological model, and combinations of sensitive imaging and detection methods are required. Here, we present our studies on nanoparticle interactions with skin, skin cells, and biological media. Silica, titanium dioxide and silver particles were chosen as representative examples for different types of skin exposure to nanomaterials, e.g., unintended environmental exposure (silica) versus intended exposure through application of sunscreen (titanium dioxide) or antiseptics (silver). Because each particle type exhibits specific physicochemical properties, we were able to apply different combinations of methods to examine skin penetration and cellular uptake, including optical microscopy, electron microscopy, X-ray microscopy on cells and tissue sections, flow cytometry of isolated skin cells as well as Raman microscopy on whole tissue blocks. In order to assess the biological relevance of such findings, cell viability and free radical production were monitored on cells and in whole tissue samples. The combination of technologies and the joint discussion of results enabled us to look at nanoparticle-skin interactions and the biological relevance of our findings from different angles. © 2014 Vogt et al.
    view abstractdoi: 10.3762/bjnano.5.245
  • 2014 • 302 Interplay of hydrogen treatment and nitrogen doping in ZnO nanoparticles: A first-principles study
    Gutjahr, J. and Sakong, S. and Kratzer, P.
    Nanotechnology 25 (2014)
    With the help of density functional calculations using the HSE and PBE functionals, it is shown that incorporation of nitrogen into ZnO nanoparticles is energetically less costly compared to ZnO bulk, due to charge transfer between Zn dangling bonds and the NO impurity. Neutral NO results after full passivation of the doped nanoparticles by a treatment with atomic hydrogen. A nanocomposite made from such ZnO particles could show thermally activated p-type hopping conductivity. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/25/14/145204
  • 2014 • 301 Iron oxide/polymer-based nanocomposite material for hydrogen sulfide adsorption applications
    Blatt, O. and Helmich, M. and Steuten, B. and Hardt, S. and Bathen, D. and Wiggers, H.
    Chemical Engineering and Technology 37 1938-1944 (2014)
    The processing of iron oxide nanoparticles derived from spray flame synthesis for specific adsorption applications is described. After the as-prepared particles proved the ability for H2S removal in pure gas treatment, two different nanoparticle- based composite materials were prepared. While impregnation of activated carbon with the as-prepared nanoparticles showed the expected increase in H2S adsorption capacities, a significant enhancement in desulfurization performance was observed for a novel iron oxide nanoparticle composite material. H2S adsorption was tested in fixed-bed breakthrough curve measurements. The H2S removal efficiency of the novel material under ambient conditions indicates highly promising properties for potential use in industrial and air pollution control applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ceat.201400303
  • 2014 • 300 Koutecky-Levich analysis applied to nanoparticle modified rotating disk electrodes: Electrocatalysis or misinterpretation
    Masa, J. and Batchelor-McAuley, C. and Schuhmann, W. and Compton, R.G.
    Nano Research 7 71-78 (2014)
    The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate constant kapp o, equal to the true rate constant k o describing the redox reaction of interest on the surface of the nanoparticles and the ratio, ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I -1 versus ω -1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof kapp o, not k o. Thus, for ψ &gt; 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ < 1 the deduced electrochemical rate constant will be less than k o. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s12274-013-0372-0
  • 2014 • 299 Mimicking exposures to acute and lifetime concentrations of inhaled silver nanoparticles by two different in vitro approaches
    Herzog, F. and Loza, K. and Balog, S. and Clift, M.J.D. and Epple, M. and Gehr, P. and Petri-Fink, A. and Rothen-Rutishauser, B.
    Beilstein Journal of Nanotechnology 5 1357-1370 (2014)
    In the emerging market of nano-sized products, silver nanoparticles (Ag NPs) are widely used due to their antimicrobial properties. Human interaction with Ag NPs can occur through the lung, skin, gastrointestinal tract, and bloodstream. However, the inhalation of Ag NP aerosols is a primary concern. To study the possible effects of inhaled Ag NPs, an in vitro triple cell co-culture model of the human alveolar/airway barrier (A549 epithelial cells, human peripheral blood monocyte derived dendritic and macrophage cells) together with an air-liquid interface cell exposure (ALICE) system was used in order to reflect a real-life exposure scenario. Cells were exposed at the air-liquid interface (ALI) to 0.03, 0.3, and 3 μg Ag/cm2 of Ag NPs (diameter 100 nm; coated with polyvinylpyrrolidone: PVP). Ag NPs were found to be highly aggregated within ALI exposed cells with no impairment of cell morphology. Furthermore, a significant increase in release of cytotoxic (LDH), oxidative stress (SOD-1, HMOX-1) or pro-inflammatory markers (TNF-α, IL-8) was absent. As a comparison, cells were exposed to Ag NPs in submerged conditions to 10, 20, and 30 μg Ag/mL. The deposited dose per surface area was estimated by using a dosimetry model (ISDD) to directly compare submerged vs ALI exposure concentrations after 4 and 24 h. Unlike ALI exposures, the two highest concentrations under submerged conditions promoted a cytotoxic and pro-inflammatory response after 24 h. Interestingly, when cell cultures were co-incubated with lipopolysaccharide (LPS), no synergistic inflammatory effects were observed. By using two different exposure scenarios it has been shown that the ALI as well as the suspension conditions for the lower concentrations after 4 h, reflecting reallife concentrations of an acute 24 h exposure, did not induce any adverse effects in a complex 3D model mimicking the human alveolar/airway barrier. However, the highest concentrations used in the ALI setup, as well as all concentrations under submerged conditions after 24 h, reflecting more of a chronic lifetime exposure concentration, showed cytotoxic as well as pro-inflammatory effects. In conclusion, more studies need to address long-term and chronic Ag NP exposure effects. © 2014 Herzog et al.
    view abstractdoi: 10.3762/bjnano.5.149
  • 2014 • 298 MnxOy/NC and CoxOy/NC nanoparticles embedded in a nitrogen-doped carbon matrix for high-performance bifunctional oxygen electrodes
    Masa, J. and Xia, W. and Sinev, I. and Zhao, A. and Sun, Z. and Grützke, S. and Weide, P. and Muhler, M. and Schuhmann, W.
    Angewandte Chemie - International Edition 53 8508-8512 (2014)
    Reversible interconversion of water into H2 and O2, and the recombination of H2 and O2 to H2O thereby harnessing the energy of the reaction provides a completely green cycle for sustainable energy conversion and storage. The realization of this goal is however hampered by the lack of efficient catalysts for water splitting and oxygen reduction. We report exceptionally active bifunctional catalysts for oxygen electrodes comprising Mn3O4 and Co 3O4 nanoparticles embedded in nitrogen-doped carbon, obtained by selective pyrolysis and subsequent mild calcination of manganese and cobalt N4 macrocyclic complexes. Intimate interaction was observed between the metals and nitrogen suggesting residual M-Nx coordination in the catalysts. The catalysts afford remarkably lower reversible overpotentials in KOH (0.1M) than those for RuO2, IrO2, Pt, NiO, Mn3O4, and Co3O4, thus placing them among the best non-precious-metal catalysts for reversible oxygen electrodes reported to date. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201402710
  • 2014 • 297 Mössbauer study of temperature-dependent cycloidal ordering in BiFeO3 nanoparticles
    Landers, J. and Salamon, S. and Escobar Castillo, M. and Lupascu, D.C. and Wende, H.
    Nano Letters 14 6061-6065 (2014)
    To study the effects of different temperatures and particle sizes on the anharmonic cycloidal spin structure in BiFeO3 nanoparticles, Mössbauer spectroscopy was applied to three sets of particles with different mean diameters in the range of 54 nm to 1.6 μm at temperatures between 4.2 and 800 K. The paramagnetic transition showed a distinct broadening upon decreasing particle size with Néel temperatures decreasing from 652 to 631 K. The anharmonicity of the long-range cycloidal structure, calculated from experimental Mössbauer spectra, is revealed to decrease upon rising temperature, starting at 150-200 K and reaching the harmonic state at about 400 K. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nl5031375
  • 2014 • 296 Multidiagnostic analysis of silicate speciation in clear solutions/sols for zeolite synthesis
    Castro, M. and Haouas, M. and Taulelle, F. and Lim, I. and Breynaert, E. and Brabants, G. and Kirschhock, C.E.A. and Schmidt, W.
    Microporous and Mesoporous Materials 189 158-162 (2014)
    The formation of zeolites in presence of tetraalkylammonium cations from so-called clear solutions using silicon alkoxides is a highly complex process which challenges experimental chemistry. Most clear solutions are better described as clear sols as they contain nanosized silicate particles, which are formed during hydrolysis of the Si source before self-assembly into the zeolite framework. This process spans multiple time- and length-scales and only a combination of different analysis methods allows revelation of molecular level zeolite formation mechanisms. On the example of the early stages of the formation of zeolite beta from clear solutions/sols the different windows of observation of liquid-state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy, small angle X-ray scattering (SAXS), dynamic light scattering (DLS) and mass spectrometry (MS) are demonstrated. Each diagnostic means by itself needs to be carefully assessed for its window of temporal and spatial resolution which can be achieved by exploiting the overlapping information available from their combination. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2013.08.027
  • 2014 • 295 Nanoparticle release from dental composites
    Van Landuyt, K.L. and Hellack, B. and Van Meerbeek, B. and Peumans, M. and Hoet, P. and Wiemann, M. and Kuhlbusch, T.A.J. and Asbach, C.
    Acta Biomaterialia 10 365-374 (2014)
    Dental composites typically contain high amounts (up to 60 vol.%) of nanosized filler particles. There is a current concern that dental personnel (and patients) may inhale nanosized dust particles (< 100 nm) during abrasive procedures to shape, finish or remove restorations but, so far, whether airborne nanoparticles are released has never been investigated. In this study, composite dust was analyzed in real work conditions. Exposure measurements of dust in a dental clinic revealed high peak concentrations of nanoparticles in the breathing zone of both dentist and patient, especially during aesthetic treatments or treatments of worn teeth with composite build-ups. Further laboratory assessment confirmed that all tested composites released very high concentrations of airborne particles in the nanorange (&gt;106 cm-3). The median diameter of airborne composite dust varied between 38 and 70 nm. Electron microscopic and energy dispersive X-ray analysis confirmed that the airborne particles originated from the composite, and revealed that the dust particles consisted of filler particles or resin or both. Though composite dust exhibited no significant oxidative reactivity, more toxicological research is needed. To conclude, on manipulation with the bur, dental composites release high concentrations of nanoparticles that may enter deeply into the lungs. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actbio.2013.09.044
  • 2014 • 294 Nanoparticle-Impact Experiments are Highly Sensitive to the Presence of Adsorbed Species on Electrode Surfaces
    Kätelhön, E. and Cheng, W. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    ChemElectroChem 1 1057-1062 (2014)
    We theoretically and experimentally investigate the influence of partial surface blocking on the electrochemistry of nanoparticles impacting at an electrode. To this end, we introduce an analytical model for the adsorption of single blocking molecules on the electrode and calculate the resulting fractional electrode coverage. We find that even small amounts of adsorbed molecules can fully suppress detection of impacts of nanoparticles while the electrode characteristics in the detection of electroactive molecules hardly change. Our findings are supported by experimental data on the indigo nanoparticle electroreduction at a carbon microelectrode (radius 5.5μm) in aqueous solution. We find that nanoimpacts are fully suppressed in the presence of acetone at concentrations of 250nm, which have a negligible effect on the electrode kinetics of the Fe(CN)3-/4- 6 couple. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201402014
  • 2014 • 293 Ostwald-Freundlich diffusion-limited dissolution kinetics of nanoparticles
    Ely, D.R. and Edwin García, R. and Thommes, M.
    Powder Technology 257 120-123 (2014)
    For many years, nanoparticles have garnered increasing interest in pharmaceutical investigations. It is well known that the solubility of nanoparticles increases with decreasing size due to the Gibbs-Thomson effect. However, there are currently no analytical models to describe the kinetics of nanoparticle dissolution. The purpose of this article is to provide a Thermodynamics-based description of the kinetics of nanoparticle dissolution. In particular, the Ostwald-Freundlich relation is used to correct dissolution times for small particles, which have higher solubilities than larger particles. The developed model is an extension of the Hixson-Crowell cube root law in which the total normalized dissolution time is corrected by a "solubility size factor" that approaches unity for increasing initial particle size. This model enables rapid estimation of the total dissolution time of spherical nanoparticles in a gently agitated, zero solute concentration reservoir. The total dissolution time predicted differs from Hixson-Crowell by nearly 10% for initial particle sizes fifty times larger than the characteristic particle size, and increases to more than a factor of six at the characteristic particle size. This work provides a physics-based description of the nanoparticle dissolution kinetics and details the reaches and limitations of the developed model. The theoretical framework provided herein is valid for a wide range of dissolution processes and size scales affording it a high level of practicality. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2014.01.095
  • 2014 • 292 Oxidation of bioethanol using zeolite-encapsulated gold nanoparticles
    Mielby, J. and Abildstrøm, J.O. and Wang, F. and Kasama, T. and Weidenthaler, C. and Kegnæs, S.
    Angewandte Chemie - International Edition 53 12513-12516 (2014)
    With the ongoing developments in biomass conversion, the oxidation of bioethanol to acetaldehyde may become a favorable and green alternative to the preparation from ethylene. Here, a simple and effective method to encapsulate gold nanoparticles in zeolite silicalite-1 is reported and their high activity and selectivity for the catalytic gas-phase oxidation of ethanol are demonstrated. The zeolites are modified by a recrystallization process, which creates intraparticle voids and mesopores that facilitate the formation of small and disperse nanoparticles upon simple impregnation. The individual zeolite crystals comprise a broad range of mesopores and contain up to several hundred gold nanoparticles with a diameter of 2-3 nm that are distributed inside the zeolites rather than on the outer surface. The encapsulated nanoparticles have good stability and result in 50%conversion of ethanol with 98% selectivity toward acetaldehyde at 200°C, which (under the given reaction conditions) corresponds to 606 mol acetaldehyde/mol Au hour-1. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA Weinheim.
    view abstractdoi: 10.1002/anie.201406354
  • 2014 • 291 Oxygen-deficient titania as alternative support for Pt catalysts for the oxygen reduction reaction
    Zhao, A. and Masa, J. and Xia, W.
    Journal of Energy Chemistry 23 701-707 (2014)
    Insufficient electrochemical stability is a major challenge for carbon materials in oxygen reduction reaction (ORR) due to carbon corrosion and insufficient metal-support interactions. In this work, titania is explored as an alternative support for Pt catalysts. Oxygen deficient titania samples including TiO<inf>2-x</inf> and TiO<inf>2-x</inf>N<inf>y</inf> were obtained by thermal treatment of anatase TiO<inf>2</inf> under flowing H<inf>2</inf> and NH<inf>3</inf>, respectively. Pt nanoparticles were deposited on the titania by a modified ethylene glycol method. The samples were characterized by N<inf>2</inf>-physisorption, X-ray diffraction and X-ray photoelectron spectroscopy. The ORR activity and long-term stability of supported Pt catalysts were evaluated using linear sweep voltammetry and chronoamperometry in 0.1 mol/L HClO<inf>4</inf>. Pt/TiO<inf>2-x</inf> and Pt/TiO<inf>2-x</inf>N<inf>y</inf> showed higher ORR activities than Pt/TiO<inf>2</inf> as indicated by higher onset potentials. Oxygen deficiency in TiO<inf>2-x</inf> and TiO<inf>2-x</inf>N<inf>y</inf> contributed to the high ORR activity due to enhanced charge transfer, as disclosed by electrochemical impedance spectroscopy studies. Electrochemical stability studies revealed that Pt/TiO<inf>2-x</inf> exhibited a higher stability with a lower current decay rate than commercial Pt/C, which can be attributed to the stable oxide support and strong interaction between Pt nanoparticles and the oxygen-deficient TiO<inf>2-x</inf> support. © 2014 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/S2095-4956(14)60202-3
  • 2014 • 290 Particle size effects in the catalytic electroreduction of CO2 on Cu nanoparticles
    Reske, R. and Mistry, H. and Behafarid, F. and Roldan Cuenya, B. and Strasser, P.
    Journal of the American Chemical Society 136 6978-6986 (2014)
    A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (∼2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/ja500328k
  • 2014 • 289 Plasmonic and photonic scattering and near fields of nanoparticles
    Schmid, M. and Andrae, P. and Manley, P.
    Nanoscale Research Letters 9 1-11 (2014)
    We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell's equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results. © 2014 Schmid et al.
    view abstractdoi: 10.1186/1556-276X-9-50
  • 2014 • 288 Polydisperse NiTi nanoparticles investigated by X-ray standing waves and electron microscopy - A comparative study
    Brücher, M. and Chakif, M. and Gurevich, E.L. and Hergenröder, R.
    Spectrochimica Acta - Part B Atomic Spectroscopy 98 60-64 (2014)
    A polydisperse mixture of nickel-titanium nanoparticles generated by femtosecond-laser ablation was investigated by the application of different analytical methods in order to characterize the distribution of particle sizes. Images obtained with scanning and transmission electron microscopy and intensity curves of fluorescence excited by X-ray standing waves (XSW) were evaluated and the resulting distributions were plotted in several histograms. Based on the differences found in the results, the possibilities, limitations and appropriate criteria of application of the respective technique are discussed. The principles of the XSW technique and the evaluation procedure are explained in more detail. The respective analytical methods were compared in terms of spatial resolution, information content, the risk of artifacts, the statistics of the evaluation and the availability of experimental facilities. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.sab.2014.05.004
  • 2014 • 287 Pressure-dependent effect of hydrogen adsorption on structural and electronic properties of Pt/γ-Al2O3 nanoparticles
    Mistry, H. and Behafarid, F. and Bare, S.R. and Roldan Cuenya, B.
    ChemCatChem 6 348-352 (2014)
    Understanding the interaction of hydrogen with subnanometer platinum nanoparticles (NPs) under industrially relevant conditions is of great importance to heterogeneous catalysis. In this work, we investigate the pressure-dependent changes in hydrogen coverage on size- and shape-selected Pt/γ-Al2O3 NPs by in situ X-ray absorption near-edge structure (XANES) analysis. Difference XANES calculations revealed an increase in the H/Pt ratio from 1.9 to 2.5 upon increasing the hydrogen pressure from 1 to 21 bar at room temperature (1 bar=100 kPa). In addition, extended X-ray absorption fine structure measurements of the local geometrical structure showed changes in Pt - Pt bond length and coordination number, revealing a morphological transformation in the NPs from a 2 D to a 3 D shape under increasing H2 pressure at room temperature. Such shape evolution leads to a decrease in the NP-support contact area and is thus expected to affect the NP stability against coarsening. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201300783
  • 2014 • 286 Proinflammatory and cytotoxic response to nanoparticles in precision-cut lung slices
    Hirn, S. and Haberl, N. and Loza, K. and Epple, M. and Kreyling, W.G. and Rothen-Rutishauser, B. and Rehberg, M. and Krombach, F.
    Beilstein Journal of Nanotechnology 5 2440-2449 (2014)
    Precision-cut lung slices (PCLS) are an established ex vivo alternative to in vivo experiments in pharmacotoxicology. The aim of this study was to evaluate the potential of PCLS as a tool in nanotoxicology studies. Silver (Ag-NPs) and zinc oxide (ZnO-NPs) nanoparticles as well as quartz particles were used because these materials have been previously shown in several in vitro and in vivo studies to induce a dose-dependent cytotoxic and inflammatory response. PCLS were exposed to three concentrations of 70 nm monodisperse polyvinylpyrrolidone (PVP)-coated Ag-NPs under submerged culture conditions in vitro. ZnO-NPs (NM110) served as 'soluble' and quartz particles (Min-U-Sil) as 'non-soluble' control particles. After 4 and 24 h, the cell viability and the release of proinflammatory cytokines was measured. In addition, multiphoton microscopy was employed to assess the localization of Ag-NPs in PCLS after 24 h of incubation. Exposure of PCLS to ZnO-NPs for 4 and 24 h resulted in a strong decrease in cell viability, while quartz particles had no cytotoxic effect. Moreover, only a slight cytotoxic response was detected by LDH release after incubation of PCLS with 20 or 30 μg/mL of Ag-NPs. Interestingly, none of the particles tested induced a proinflammatory response in PCLS. Finally, multiphoton microscopy revealed that the Ag-NP were predominantly localized at the cut surface and only to a much lower extent in the deeper layers of the PCLS. In summary, only 'soluble' ZnO-NPs elicited a strong cytotoxic response. Therefore, we suggest that the cytotoxic response in PCLS was caused by released Zn2+ ions rather than by the ZnO-NPs themselves. Moreover, Ag-NPs were predominantly localized at the cut surface of PCLS but not in deeper regions, indicating that the majority of the particles did not have the chance to interact with all cells present in the tissue slice. In conclusion, our findings suggest that PCLS may have some limitations when used for nanotoxicology studies. To strengthen this conclusion, however, other NP types and concentrations need to be tested in further studies. © 2014 Hirn et al.
    view abstractdoi: 10.3762/bjnano.5.253
  • 2014 • 285 Prophylactic and therapeutic vaccination with a nanoparticle-based peptide vaccine induces efficient protective immunity during acute and chronic retroviral infection
    Knuschke, T. and Bayer, W. and Rotan, O. and Sokolova, V. and Wadwa, M. and Kirschning, C.J. and Hansen, W. and Dittmer, U. and Epple, M. and Buer, J. and Westendorf, A.M.
    Nanomedicine: Nanotechnology, Biology, and Medicine 10 1787-1798 (2014)
    Retroviral infections e.g. HIV still represent a unique burden in the field of vaccine research. A common challenge in vaccine design is to find formulations that create appropriate immune responses to protect against and/or control the given pathogen. Nanoparticles have been considered to be ideal vaccination vehicles that mimic invading pathogens. In this study, we present biodegradable calcium phosphate (CaP) nanoparticles, functionalized with CpG and retroviral T cell epitopes of Friend virus (FV) as excellent vaccine delivery system. CaP nanoparticles strongly increased antigen delivery to antigen-presenting cells to elicit a highly efficient T cell-mediated immune response against retroviral FV infection. Moreover, single-shot immunization of chronically FV-infected mice with functionalized CaP nanoparticles efficiently reactivated effector T cells which led to a significant decrease in viral loads. Thus, our findings clearly indicate that a nanoparticle-based peptide immunization is a promising approach to improve antiretroviral vaccination. From the Clinical Editor: In this study, biodegradable calcium phosphate nanoparticles were used as a vaccine delivery system after functionalization with CpG and Friend virus-derived T-cell epitopes. This vaccination strategy resulted in increased T-cell mediated immune response even in chronically infected mice, providing a promising approach to the development of clinically useful antiretroviral vaccination strategies. © 2014 Elsevier Inc.
    view abstractdoi: 10.1016/j.nano.2014.06.014
  • 2014 • 284 PVP-coated, negatively charged silver nanoparticles: A multi-center study of their physicochemical characteristics, cell culture and in vivo experiments
    Ahlberg, S. and Antonopulos, A. and Diendorf, J. and Dringen, R. and Epple, M. and Flöck, R. and Goedecke, W. and Graf, C. and Haberl, N. and Helmlinger, J. and Herzog, F. and Heuer, F. and Hirn, S. and Johannes, C. and Kittler, ...
    Beilstein Journal of Nanotechnology 5 1944-1965 (2014)
    PVP-capped silver nanoparticles with a diameter of the metallic core of 70 nm, a hydrodynamic diameter of 120 nm and a zeta potential of -20 mV were prepared and investigated with regard to their biological activity. This review summarizes the physicochemical properties (dissolution, protein adsorption, dispersability) of these nanoparticles and the cellular consequences of the exposure of a broad range of biological test systems to this defined type of silver nanoparticles. Silver nanoparticles dissolve in water in the presence of oxygen. In addition, in biological media (i.e., in the presence of proteins) the surface of silver nanoparticles is rapidly coated by a protein corona that influences their physicochemical and biological properties including cellular uptake. Silver nanoparticles are taken up by cell-type specific endocytosis pathways as demonstrated for hMSC, primary T-cells, primary monocytes, and astrocytes. A visualization of particles inside cells is possible by X-ray microscopy, fluorescence microscopy, and combined FIB/SEM analysis. By staining organelles, their localization inside the cell can be additionally determined. While primary brain astrocytes are shown to be fairly tolerant toward silver nanoparticles, silver nanoparticles induce the formation of DNA double-strand-breaks (DSB) and lead to chromosomal aberrations and sister-chromatid exchanges in Chinese hamster fibroblast cell lines (CHO9, K1, V79B). An exposure of rats to silver nanoparticles in vivo induced a moderate pulmonary toxicity, however, only at rather high concentrations. The same was found in precision-cut lung slices of rats in which silver nanoparticles remained mainly at the tissue surface. In a human 3D triple-cell culture model consisting of three cell types (alveolar epithelial cells, macrophages, and dendritic cells), adverse effects were also only found at high silver concentrations. The silver ions that are released from silver nanoparticles may be harmful to skin with disrupted barrier (e.g., wounds) and induce oxidative stress in skin cells (HaCaT). In conclusion, the data obtained on the effects of this well-defined type of silver nanoparticles on various biological systems clearly demonstrate that cell-type specific properties as well as experimental conditions determine the biocompatibility of and the cellular responses to an exposure with silver nanoparticles. © 2014 Ahlberg et al.
    view abstractdoi: 10.3762/bjnano.5.205
  • 2014 • 283 Shape-dependent catalytic oxidation of 2-butanol over Pt nanoparticles supported on γ-Al2O3
    Mistry, H. and Behafarid, F. and Zhou, E. and Ono, L.K. and Zhang, L. and Roldan Cuenya, B.
    ACS Catalysis 4 109-115 (2014)
    This study illustrates the effect of nanoparticle (NP) shape on the reactivity of size-selected Pt/γ-Al2O3 nanocatalysts for 2-butanol oxidation. Nanoparticles similar in size [transmission electron microscopy (TEM) diameter of ∼1 nm] but with different shapes were prepared via encapsulation in inverse micelles. The NP shape was resolved by combining information extracted from extended X-ray absorption fine structure spectroscopy (EXAFS) data, TEM, and modeling. A correlation was observed between the average first nearest neighbor coordination number of atoms at the NP surface and their catalytic activity. In particular, the NPs with the largest number of weakly coordinated surface atoms (i.e., edges and corners) were found to be the least active for the total oxidation of 2-butanol. This result highlights that not only size but also shape control must be achieved to tailor the catalytic properties of nanoscale materials. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/cs400888n
  • 2014 • 282 Simultaneous electrochemical and 3D optical imaging of silver nanoparticle oxidation
    Batchelor-Mcauley, C. and Martinez-Marrades, A. and Tschulik, K. and Patel, A.N. and Combellas, C. and Kanoufi, F. and Tessier, G. and Compton, R.G.
    Chemical Physics Letters 597 20-25 (2014)
    The oxidation of AgNPs at a thin-film gold electrode is simultaneously investigated via digital holography and electrochemistry. The use of holography allows, for the first time, the 3D visualization of the electrochemical interfacial region at a relatively high acquisition rate. It is demonstrated how the coupling of these two techniques provides complementary chemical information. The ensemble response of the oxidation of surface-adsorbed silver nanoparticles to AgCl is monitored electrochemically, whereas this process is difficult to observe optically. Conversely, the subsequent chemical dissolution of individual AgCl nanocrystals can be tracked optically due to the associated decrease in the scattered light intensity. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.