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.

Below, you can either scroll through the complete list of our annually published material, or search for a specific author or term via the free text search to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

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  • 2024 • 290 Electrocatalytic Epoxidation of Cyclooctene on Surface Modified Ni Foam Using Water as Oxygen Source
    Chandra, Shubhadeep and Koul, Adarsh and Zhang, Jian and Seisel, Sabine and Schuhmann, Wolfgang
    Chemistry - A European Journal (2024)
    Electrochemical epoxidation of olefins using water as an oxygen atom source is emerging as an alternative approach for an atom economic and sustainable method towards a highly selective synthesis of epoxides. We report an electrochemical procedure for epoxidation of cyclooctene using water as the sole oxygen atom source over a sodium dodecyl sulfonate (SDS) modified nickel hydroxide Ni(OH)2 catalyst directly grown on Ni foam. The SDS modification facilitates the mass transfer of cyclooctene towards the anode, thus achieving a 2.5-fold higher conversion with more than 90 % selectivity towards the corresponding epoxide compared with pure Ni(OH)2 catalyst. © 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/chem.202303830
  • 2023 • 289 Synthesis and Electrochemical Investigation of Phosphine Substituted Diiron Phosphadithiolate Complexes
    Guseva, Tatiana and Gerschel, Philipp and Siegmund, Daniel and Apfel, Ulf-Peter
    European Journal of Inorganic Chemistry 26 (2023)
    This work reports on ligand exchange reactions between a [FeFe] hydrogenase model containing the higher homologue (PhosDT) and phosphines selected to cover a variety of electronic properties and possible coordination modes. Additionally, the amount of the phosphines and the reaction temperature were varied to study the formation of complexes with multiple phosphines or altered binding modes. Due to steric effects caused by the position of the bridgehead, the phosphines bind preferentially at the more accessible iron centre on the phosphinate averted side. While all ligand exchanges resulted in a ligand-specific main product at room temperature, reflux conditions induced decomposition in case of PhosDT-(κ2-dppe) and PhosDT-(κ2-dppv) and a change in the binding mode for the dppm containing complex. Moreover, we highlight two novel iron complexes obtained as side products of the reactions with dppe and dppv, while in case of dppm an additional model with two bridging phosphine ligands was generated. Finally, the six novel phosphine substituted PhosDT models were electrochemically investigated, revealing a cathodic shift compared to the starting material due to the increased electron density at the iron atoms. Moreover, the models with monodentate ligands exhibit a different CV pattern for the FeIFeI/FeIFe0 process than complexes with bidentate phosphines. © 2023 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ejic.202300470
  • 2022 • 288 A new dual matrix burner for one-dimensional investigation of aerosol flames
    Apazeller, S. and Gonchikzhapov, M. and Nanjaiah, M. and Kasper, T. and Wlokas, I. and Wiggers, H. and Schulz, C.
    Proceedings of the Combustion Institute (2022)
    In spray-flame synthesis of nanoparticles, a precise understanding of the reaction processes is necessary to find optimal process parameters for the formation of the desired products. Coupling the chemistries of flame, solvent, and gas-phase species initially formed from the particle precursor in combination with the complex flow geometry of the spray flame means a special challenge for the modeling of the reaction processes. A new burner has been developed that is capable to observe the reaction of precursor solutions frequently used in spray-flame synthesis. The burner provides an almost flat, laminar, and steady flame with homogeneous addition of a fine aerosol and thus enables detailed investigation and modeling of the coupled reactions independent of spray formation and turbulent mixing. With its two separate supply channel matrices, the burner also enables the use of reactants that would otherwise react with each other already before reaching the flame. These features enable the investigation of a wide range of flame-based synthesis methods for nanoparticles and, due to the flat-flame geometry, kinetics models for these processes can be developed and validated. This work describes the matrix burner development and its gas flow optimization by simulation. Droplet-size distributions generated by ultrasonic nebulization and their interaction with the burner structure are investigated by phase-Doppler anemometry. As an example for nanoparticle-forming flames from solutions, iron-oxide nanoparticle-generating flames using iron(III) nitrate nonahydrate dissolved in 1-butanol were investigated. This effort includes measurements of two-dimensional maps of the flame temperature by a thermocouple and height-dependent concentration profiles of the main species by time-of-flight mass spectrometry. Experimental data are compared with 1D simulations using a reduced reaction mechanism. The results show that the new burner is well suited for the development of reaction models for precursors supplied in the liquid phase usually applied in spray-flame synthesis configurations. © 2022 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.proci.2022.07.166
  • 2022 • 287 Active Buffer Matrix in Nanoparticle-Based Silicon-Rich Silicon Nitride Anodes Enables High Stability and Fast Charging of Lithium-Ion Batteries
    Kilian, S.O. and Wankmiller, B. and Sybrecht, A.M. and Twellmann, J. and Hansen, M.R. and Wiggers, H.
    Advanced Materials Interfaces 9 (2022)
    A very promising way to improve the stability of silicon in lithium-ion battery (LIB) anodes is the use of nanostructured silicon-rich silicon nitride (SiNx), known as a conversion-type anode material. To investigate the conversion mechanism in this material in detail, SiN0.5 nanoparticles are synthesized and examined as LIB anodes using a combination of ex situ X-ray photoelectron spectroscopy and solid-state 7Li MAS NMR measurements. During the initial cycle, the conversion of SiN0.5 nanoparticles results in the formation of lithium silicides and a buffer matrix consisting of different lithium nitridosilicates and lithium nitride. These phases can be reversibly lithiated and contribute to the total reversible capacity of the silicon nitride active material. The structure of the material after conversion is best described by an amorphous solid solution. Further, it is shown that silicon-rich silicon nitrides possess improved rate capability because of the higher ionic conductivity of the buffer matrix compared to pure silicon, and very fine dispersion of silicon clusters throughout the buffer matrix. Thus, unlike most conversion materials, the silicon-rich silicon nitride exhibits an additional intrinsic active functionality of the buffer matrix that goes far beyond the mere reduction of electrolyte contact area and volume expansion. © 2022 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/admi.202201389
  • 2022 • 286 Cooperative Effect in Binuclear Zinc Catalysts in the ROP of Lactide
    Ghosh, S. and Schulte, Y. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Haberhauer, G. and Schulz, S.
    Organometallics 41 2698-2708 (2022)
    Binuclear monomeric L1Zn2R2(R = Me 1 and Et 2; L2Zn2R2, R = Me 3 and Et 4) and dimeric ketodiiminate zinc alkyl complexes [L1(H)ZnR]2(R = Me 5 and Et 6; L1= (Me2NC2H4NC (Me)CH)2CO, L2= (Me2NC3H6NC(Me)CH)2CO) were synthesized and spectroscopically characterized (1H and 13C NMR and IR). Diffusion-ordered NMR spectroscopy and single-crystal X-ray diffraction analysis (1, 2, and 4-6) proved their monomeric (1-4) and dimeric (5 and 6) structures in solution and solid states. Their catalytic activity in the ring-opening polymerization of lactide was studied under various conditions and compared to mononuclear β-ketoimine zinc complexes 7-10. Initiation reactions of the Et-substituted complexes 2, 4, and 6 are faster than for the corresponding Me-substituted complexes 1, 3, and 5, and kinetic studies with catalyst 2 proved the first-order dependency on both the monomer and the catalyst concentration. Quantum chemical calculations revealed that the activation barriers for the addition of CH3-to L-LA via a mononuclear mechanism for the mono- (7) and binuclear (1) Me-substituted and the corresponding MeO-substituted complexes 1-OMe and 7-OMe, which are regarded as model compounds of the "active" catalyst, are similar. However, while the binuclear mechanism for complex 1 is slightly higher in energy than for the mononuclear mechanism, the binuclear pathway for the MeO-substituted complex 1-OMe is favored, clearly proving the beneficial cooperative effect between the two adjacent zinc atoms. © 2022 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.organomet.2c00333
  • 2022 • 285 Early particle formation and evolution in iron-doped flames
    Lalanne, M.R. and Wollny, P. and Nanjaiah, M. and Menser, J. and Schulz, C. and Wiggers, H. and Cheskis, S. and Wlokas, I. and Rahinov, I.
    Combustion and Flame 244 (2022)
    In flame synthesis of nanoparticles, the temperature history experienced by the nascent particle aerosol defines the morphology, composition, and crystallinity of the resulting nanomaterial. Commonly, flame-synthesis processes are modeled with an isothermal approximation assuming that the particle temperature replicates that of the surrounding gas phase, avoiding inclusion of an additional internal coordinate in the population balance model, and thus reducing the computational cost. This simplification neglects the influence of matter- and energy-exchange as well as thermochemistry between the particle and reactive gas phase, impacting the particle temperature. In this work, we investigate the temperature history of the particles in incipient formation stages and their evolution in iron-doped flames, prototypical for many other transition-metal (oxide) synthesis systems. The temperature and relative volume-fraction distributions of early particles forming in H2/O2/Ar flames doped with iron pentacarbonyl were determined for the first time, based on spectrally and spatially resolved flame emission measurements and pyrometric analysis of the continuum emission emanating from the nascent particle aerosol. The nascent particle temperature was found to be several hundred degrees above the gas-phase temperature for all physically reasonable assumptions concerning particle composition and emission efficiency. Early particles volume fraction rises sharply shortly after the decomposition of iron pentacarbonyl and decreases steeply in the flame front, in excellent agreement with previous particle-mass spectrometry/quartz-crystal microbalance measurements. By modeling the evaporation process of isothermal iron particles, we show that vanishing of particles in the flame front cannot be explained by evaporation of particles that are in thermal equilibrium with the gas phase. A single-particle Monte-Carlo simulation based on a simple model comprising Fe-monomer condensation, concurrent with oxidation, reduction, etching, and evaporation occurring at the particle surface, captures both the flame structure with respect to early particle formation and their excess temperature compared to the gas phase. © 2022
    view abstractdoi: 10.1016/j.combustflame.2022.112251
  • 2022 • 284 Enhanced heterogeneous activation of peroxymonosulfate by Ruddlesden-Popper-type La2CoO4+δ nanoparticles for bisphenol A degradation
    Hammad, M. and Alkan, B. and Al-kamal, A.K. and Kim, C. and Ali, M.Y. and Angel, S. and Wiedemann, H.T.A. and Klippert, D. and Schmidt, T.C. and Kay, C.W.M. and Wiggers, H.
    Chemical Engineering Journal 429 (2022)
    The scalable synthesis of stable catalysts for environmental remediation applications remains challenging. Nonetheless, metal leaching is a serious environmental issue hindering the practical application of transition-metal based catalysts including Co-based catalysts. Herein, for the first time, we describe a facile one-step and scalable spray-flame synthesis of high surface area La2CoO4+δ nanoparticles containing excess oxygen interstitials (+δ) and use them as a stable and efficient catalyst for activating peroxymonosulfate (PMS) towards the degradation of bisphenol A. Importantly, the La2CoO4+δ catalyst exhibits higher catalytic degradation of bisphenol A (95% in 20 min) and stability than LaCoO3–x nanoparticles (60%) in the peroxymonosulfate activation system. The high content of Co2+ in the structure showed a strong impact on the catalytic performance of the La2CoO4+δ + PMS system. Despite its high specific surface area, our results showed a very low amount of leached cobalt (less than 0.04 mg/L in 30 min), distinguishing it as a material with high chemical stability. According to the radical quenching experiments and the electron paramagnetic resonance technology, SO4[rad]–, [rad]OH, and 1O2 were generated and SO4[rad]– played a dominant role in bisphenol A degradation. Moreover, the La2CoO4+δ + PMS system maintained conspicuous catalytic performance for the degradation of other organic pollutants including methyl orange, rhodamine B, and methylene blue. Overall, our results showed that we developed a new synthesis method for stable La2CoO4+δ nanoparticles that can be used as a highly active heterogeneous catalyst for PMS-assisted oxidation of organic pollutants. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2021.131447
  • 2022 • 283 Exploring the Si-precursor composition for inline coating and agglomeration of TiO2 via modular spray-flame and plasma reactor
    López-Cámara, C.-F. and Dasgupta, M. and Fortugno, P. and Wiggers, H.
    Proceedings of the Combustion Institute (2022)
    Inline particle coating after the particle formation process to preserve its specific properties is hardly investigated scientifically. Tackling that issue, we have studied the use of three different vaporized organo-siloxanes (tetraethyl orthosilicate TEOS, hexamethyldisiloxane HMDSO, and octamethylcyclotetrasiloxane OMCTS) as precursors for direct inline coating of pristine titanium dioxide (TiO2) nanoparticles made via spray-flame synthesis. The inline silica (SiO2) coating of the formed titanium dioxide nanoparticles is achieved by vaporizing and sending the chosen organo-siloxane precursors into a cylindrical coating nozzle downstream the particle formation zone of the spray-flame. To further explore the effects on morphology and the quality of the resultant TiO2|SiO2 core-shell nanoparticles, a plasma discharge - i.e., dielectric barrier discharge source - is applied after the coating step. The TiO2|SiO2 core-shell nanoparticles are characterized using Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM), X-Ray Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR), Brunauer-Emmett-Teller surface area analysis (BET), elemental analysis, and dynamic light scattering (DLS). Results showed distinct core-shell nanoparticles with shell thicknesses of around 1.5 nm alongside the formation of unattached SiO2 nanoparticles due to homogenous nucleation of SiO2. As the precursor silicon content increased (TEOS < HMDSO < OMCTS), the homogenous nucleation rose to generate materials with high BET surface areas. When employing OMCTS, the high homogeneous nucleation rate led to SiO2 agglomeration, which resulted in large TiO2|SiO2 agglomerates. Morphologically, the phase composition of anatase/rutile of the produced coated nanoparticles did not vary significantly when compared with the reference uncoated TiO2 nanoparticles, indicating that the SiO2 coating is purely a surface phenomenon. Plasma discharge was shown to reduce coated particle agglomeration up to certain extend. Based on these findings, we conclude that the best studied parameters to benefit the synthesis of homogeneously coated TiO2|SiO2 nanoparticles are (i) using TEOS as a coating precursor to minimize SiO2 homogeneous nucleation and (ii) applying a plasma discharge to slightly reduce coated particle agglomeration. © 2022 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.proci.2022.07.137
  • 2022 • 282 Fluorinated β-diketonate complexes M(tfac)2(TMEDA) (M = Fe, Ni, Cu, Zn) as precursors for the MOCVD growth of metal and metal oxide thin films
    Stienen, C. and Grahl, J. and Wölper, C. and Schulz, S. and Bendt, G.
    RSC Advances 12 22974-22983 (2022)
    Partially fluorinated β-diketonate complexes M(tfac)2(TMEDA) (M = Fe 1, Ni 2, Cu 3, Zn 4; tfac = 1,1,1-trifluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) were synthesized and structurally (sc-XRD) and thermochemically (TGA) characterised. A new polymorph of Fe(tfac)2(TMEDA) was found. The structural and physicochemical properties of 1-4 were compared with related M(acac)2(TMEDA) and M(hfac)2(TMEDA) (acac = 2,4-pentanedionate, hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) β-diketonate complexes to evaluate the effect of the degree of fluorination. A positive effect on the thermal behaviour of the metal acetylacetonates was observed, but no discernible trends. Application of complexes 1-4 as precursors in a MOCVD process yielded either metal (Ni, Cu) or metal oxide thin films (Fe3O4, ZnO), which were further oxidized to NiO, CuO and α-Fe2O3 films by calcination in air at 500 °C. © 2022 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d2ra01338j
  • 2022 • 281 In situ measurement of gas-borne silicon nanoparticle volume fraction and temperature by spatially and spectrally line-resolved attenuation and emission imaging
    Liu, G. and Asif, M. and Mohri, K. and Schulz, C. and Dreier, T. and Endres, T. and Menser, J.
    Powder Technology 396 535-541 (2022)
    In this study, the temperature and volume fraction distributions of liquid silicon nanoparticles in the aerosol flow in gas-phase synthesis were retrieved using tomographic reconstruction of emission and extinction spectra in the 230–700 nm range. Measurements were done in an optically accessible microwave-plasma flow reactor fed with a SiH4/H2/Ar gas mixture. Optical emission and extinction spectra in the visible spectral range were captured along a line perpendicular to the flow direction covering the entire cross-section of the Si particle stream. Particle temperature and volume fraction distributions were determined and the preferred location of the silicon particles in a 1-mm thick zone at the circumference of the cylindric flow was revealed. The combined recording of line-resolved emission/extinction spectra is a promising method for spatially-resolved detection of nanoparticles in combustion or gas-phase synthesis. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2021.11.017
  • 2022 • 280 Molecular Emissions from Stretched Excitation Pulse in Nanosecond Phase-Selective Laser-Induced Breakdown Spectroscopy of TiO2 Nanoaerosols
    Xiong, G. and Zhang, Y. and Schulz, C. and Tse, S.D.
    Applied Spectroscopy (2022)
    In phase-selective laser-induced breakdown spectroscopy (PS-LIBS), gas-borne nanoparticles are irradiated with laser pulses (∼2.4 GW/cm2) resulting in breakdown of the nanoparticle phase but not the surrounding gas phase. In this work, the effect of excitation laser-pulse duration and energy on the intensity and duration of TiO2–nanoparticle PS-LIBS emission signal is investigated. Laser pulses from a frequency-doubled neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (532 nm) are stretched from 8 ns (full width at half maximum, FWHM) up to ∼30 ns at fixed pulse energy using combinations of two optical cavities. The intensity of the titanium atomic emissions at around 500 nm wavelength increases by ∼60%, with the stretched pulse and emissions at around 482 nm, attributed to TiO, enhanced over 10 times. While the atomic emissions rise with the stretched laser pulse and decay around 20 ns after the end of the laser pulse, the TiO emissions reach their peak intensity at about 20 ns later and last longer. At low laser energy (i.e., 1 mJ/pulse, or 80 MW/cm2), the TiO emissions dominate, but their increase with laser energy is lower compared to the atomic emissions. The origin of the 482 nm emission is explored by examining several different aerosol setups, including Ti–O, Ti–N, and Ti–O–N from a spark particle generator and Ti–O–N–C–H aerosol from flame synthesis. The 482 nm emissions are attributed to electronically excited TiO, likely resulting from the reaction of excited titanium atoms with surrounding oxidizing (carbonaceous and/or radical) species. The effects of pulse length are attributed to the shift of absorption from the initial interaction with the particle to the prolonged interaction with the plasma through inverse bremsstrahlung. © The Author(s) 2022.
    view abstractdoi: 10.1177/00037028211072583
  • 2022 • 279 Selecting the Reaction Path in On-Surface Synthesis through the Electron Chemical Potential in Graphene
    Kraus, S. and Herman, A. and Huttmann, F. and Krämer, C. and Amsharov, K. and Tsukamoto, S. and Wende, H. and Atodiresei, N. and Michely, T.
    Journal of the American Chemical Society 144 11003-11009 (2022)
    The organometallic on-surface synthesis of the eight-membered sp2 carbon-based ring cyclooctatetraene (C8H8, Cot) with the neighboring rare-earth elements ytterbium and thulium yields fundamentally different products for the two lanthanides, when conducted on graphene (Gr) close to the charge neutrality point. Sandwich-molecular YbCot wires of more than 500 Å length being composed of an alternating sequence of Yb atoms and upright-standing Cot molecules result from the on-surface synthesis with Yb. In contrast, repulsively interacting TmCot dots consisting of a single Cot molecule and a single Tm atom result from the on-surface synthesis with Tm. While the YbCot wires are bound through van der Waals interactions to the substrate, the dots are chemisorbed to Gr via the Tm atoms being more electropositive compared to Yb atoms. When the electron chemical potential in Gr is substantially raised (n-doping) through backside doping from an intercalation layer, the reaction product in the synthesis with Tm can be tuned to TmCot sandwich-molecular wires rather than TmCot dots. By use of density functional theory, it is found that the reduced electronegativity of Gr upon n-doping weakens the binding as well as the charge transfer between the reaction intermediate TmCot dot and Gr. Thus, the assembly of the TmCot dots to long TmCot sandwich-molecular wires becomes energetically favorable. It is thereby demonstrated that the electron chemical potential in Gr can be used as a control parameter in an organometallic on-surface synthesis to tune the outcome of a reaction. © 2022 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/jacs.2c04359
  • 2022 • 278 Surface and Bulk Chemistry of Mechanochemically Synthesized Tohdite Nanoparticles
    De Bellis, J. and Ochoa-Hernández, C. and Farès, C. and Petersen, H. and Ternieden, J. and Weidenthaler, C. and Amrute, A.P. and Schüth, F.
    Journal of the American Chemical Society 144 9421-9433 (2022)
    Aluminum oxides, oxyhydroxides, and hydroxides are important in different fields of application due to their many attractive properties. However, among these materials, tohdite (5Al2O3·H2O) is probably the least known because of the harsh conditions required for its synthesis. Herein, we report a straightforward methodology to synthesize tohdite nanopowders (particle diameter ∼13 nm, specific surface area ∼102 m2g-1) via the mechanochemically induced dehydration of boehmite (γ-AlOOH). High tohdite content (about 80%) is achieved upon mild ball milling (400 rpm for 48 h in a planetary ball mill) without process control agents. The addition of AlF3can promote the crystallization of tohdite by preventing the formation of the most stable α-Al2O3, resulting in the formation of almost phase-pure tohdite. The availability of easily accessible tohdite samples allowed comprehensive characterization by powder X-ray diffraction, total scattering analysis, solid-state NMR (1H and 27Al), N2-sorption, electron microscopy, and simultaneous thermal analysis (TG-DSC). Thermal stability evaluation of the samples combined with structural characterization evidenced a low-temperature transformation sequence: 5Al2O3·H2O → κ-Al2O3→ α-Al2O3. Surface characterization via DRIFTS, ATR-FTIR, D/H exchange experiments, pyridine-FTIR, and NH3-TPD provided further insights into the material properties. © 2022 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/jacs.2c02181
  • 2022 • 277 β-Diketiminate and β-Ketoiminate Metal Catalysts for Ring-Opening Polymerization of Cyclic Esters
    Glöckler, E. and Ghosh, S. and Schulz, S.
    Polymer Reviews (2022)
    This review highlights the ongoing developments on the ring-opening polymerization (ROP) of lactide (LA) and caprolactone (CL) using mononuclear and dinuclear β-diketiminate- and β-ketoiminate-substituted metal complexes. The resulting aliphatic polyesters are of great interest as sustainable replacements to petrochemicals-based polymers with potential applications in tissue engineering, bio-medical, and agricultural sciences. β-Diketiminate and β-ketoiminate metal complexes are very promising ROP catalysts since their steric and electronic properties, and hence their catalytic activity and selectivity can be easily modified. This review compares different classes of β-diketiminate and β-ketoiminate complexes with respect to the controlled synthesis of homopolymers and copolymers of aliphatic polyesters and elaborates on the polymerization kinetics and mechanistic studies. © 2022 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/15583724.2022.2121837
  • 2021 • 276 Characterization and Optimization of AZO Nanoparticles as Coatings for Flexible Substrates toward High IR Reflectivity
    Etemad-Parishanzadeh, O. and Ali, W. and Linders, J. and Straube, T. and Lutz, H. and Aggarwal, V. and Mayer, C. and Textor, T. and Gutmann, J.S. and Mayer-Gall, T.
    ACS Applied Materials and Interfaces 13 61707-61722 (2021)
    Energy consumption by air-conditioning is expansive and leads to the emission of millions of tons of CO2 every year. A promising approach to circumvent this problem is the reflection of solar radiation: Rooms that would not heat up by irradiation will not need to be cooled down. Especially, transparent conductive metal oxides exhibit high infrared (IR) reflectivity and are commonly applied as low-emissivity coatings (low-e coatings). Indium tin oxide (ITO) coatings are the state-of-the-art application, though indium is a rare and expensive resource. This work demonstrates that aluminum-doped zinc oxide (AZO) can be a suitable alternative to ITO for IR-reflection applications. AZO synthesized here exhibits better emissivity to be used as roofing membrane coatings for buildings in comparison to commercially available ITO coatings. AZO particles forming the reflective coating are generated via solvothermal synthesis routes and obtain high conductivity and IR reflectivity without the need of any further post-thermal treatment. Different synthesis parameters were studied, and their effects on both conductive and optical properties of the AZO nanoparticles were evaluated. To this end, a series of characterization methods, especially 27Al-nuclear magnetic resonance spectroscopy (27Al-NMR) analysis, have been conducted for a deeper insight into the particles' structure to understand the differences in conductivity and optical properties. The optimized AZO nanoparticles were coated on flexible transparent textile-based roofing membranes and tested as low-e coatings. The membranes demonstrated higher thermal reflectance compared with commercial ITO materials with an emissivity value lowered by 16%. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acsami.1c22151
  • 2021 • 275 Characterization of tracers for two-color laser-induced fluorescence thermometry of liquid-phase temperature in ethanol, 2–ethylhexanoic-acid/ethanol mixtures, 1-butanol, and o-xylene
    Prenting, M.M. and Shilikhin, M. and Dreier, T. and Schulz, C. and Endres, T.
    Applied Optics 60 C98-C113 (2021)
    The fluorescence spectra of dye solutions change their spectral signature with temperature. This effect is frequently used for temperature imaging in liquids and sprays based on two-color laser-induced fluorescence (2cLIF) measurements by simultaneously detecting the fluorescence intensity in two separate wavelength channels resulting in a temperature-sensitive ratio. In this work, we recorded temperature-dependent absorption and fluorescence spectra of solutions of five laser dyes (coumarin 152, coumarin 153, rhodamine B, pyrromethene 597, and DCM) dissolved in ethanol, a 35/65 vol.% mixture of ethanol/2-ethylhexanoic acid, ethanol/hexamethylsiloxane, o-xylene, and 1-butanol to investigate their potential as temperature tracers in evaporating and burning sprays. The dissolved tracers were excited at either 266, 355, and 532 nm (depending on the tracer) for temperatures between 296 and 393 K (depending on the solvent) and for concentrations ranging between 0.1 and 10 mg/l. Absorption and fluorescence spectra of the tracers were investigated for their temperature dependence, the magnitude of signal re-absorption, the impact of different solvents, and varying two-component solvent compositions. Based on the measured fluorescence spectra, the tracers were analyzed for their 2cLIF temperature sensitivity in the respective solvents. Coumarin 152 showed for single-component solvents the overall best spectroscopic properties for our specific measurement situation related to temperature imaging measurements in spray-flame synthesis of nanoparticles as demonstrated previously in ethanol spray flames [Exp. Fluids 61, 77 (2020)]. © 2021 Optical Society of America
    view abstractdoi: 10.1364/AO.419684
  • 2021 • 274 Directly Measured Electrocaloric Effect in Relaxor Polymer Nanocomposites
    Hambal, Y. and Menze, K.-H. and Shvartsman, V.V. and Lupascu, D.C.
    IEEE International Symposium on Applications of Feeroelectric, ISAF 2021, International Symposium on Integrated Functionalities, ISIF 2021 and Piezoresponse Force Microscopy Workshop, PFM 2021 - Proceedings (2021)
    Composites of electroactive polymers and ferroelectric nanoparticles are promising for energy storage and electrocaloric applications. In this paper we report on synthesis and electrocaloric properties of P(VDF-TrFE-CFE)/ BaZr0.20Ti0.80O3 nanocomposites. BaZr0.20Ti0.80O3 (BZT) nanoparticles were synthesized via the hydrothermal route. The P(VDF-TrFE-CFE)/BZT composite films with varying amount (1.25 vol.% to 5 vol.%) of the nanoparticles were prepared by the solution casting method. The nanocomposite films showed a significant increase in the dielectric permittivity with the amount of nanoparticles. An increase in the polarization as well as in hysteresis losses with the amount of nanoparticles was observed. The direct electrocaloric effect was measured using a custom built quasi-Adiabatic calorimeter. The P(VDF-TrFE-CFE)/BZT nanocomposite film with 5 vol.% BZT showed an electrocaloric temperature change of ~ 1.8 K at room temperature and an electric field of 50 MV/m, which is comparable to literature values. © 2021 IEEE.
    view abstractdoi: 10.1109/ISAF51943.2021.9477327
  • 2021 • 273 Fluorinated β-Ketoiminate Zinc Complexes: Synthesis, Structure and Catalytic Activity in Ring Opening Polymerization of Lactide
    Ghosh, S. and Huse, K. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Zeitschrift fur Anorganische und Allgemeine Chemie 647 1744-1750 (2021)
    Complexes LZnR (L=C6F5NC(CF3)C(H)C(CF3)O; R=Me 1; Et 2) and L2Zn(thf)2 (3) were synthesized and analyzed by NMR (1H, 13C, 19F) and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. Complexes 1 and 2 are dinuclear in the solid state but monomeric in toluene solution according to diffusion-ordered spectroscopy (DOSY-NMR). They showed poor activity in the ring opening polymerization (ROP) of lactide (LA) but moderate activity in the presence of benzyl alcohol (BnOH), yielding polymers with high number average molecular weight (Mn) and moderately controlled molecular weight distribution (PDI). Homonuclear-decoupled 1H NMR analysis of polylactic acid (PLA) obtained from rac-LA showed isotactic enrichment of the polymer microstructure, and kinetic studies of the ROP of L-LA with complex 2 showed a first order dependence of the monomer concentration. Analyses of low molecular weight polymers by 1H NMR and MALDI-ToF mass spectrometry demonstrated the coordination-insertion mechanism (CIM). © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/zaac.202100133
  • 2021 • 272 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 • 271 Influence of the cobalt content in cobalt iron oxides on the electrocatalytic OER activity
    Saddeler, S. and Bendt, G. and Salamon, S. and Haase, F.T. and Landers, J. and Timoshenko, J. and Rettenmaier, C. and Jeon, H.S. and Bergmann, A. and Wende, H. and Roldan Cuenya, B. and Schulz, S.
    Journal of Materials Chemistry A 9 25381-25390 (2021)
    Sub 10 nm cobalt ferrite CoxFe3-xO4 (x ≤ 1.75) nanoparticles and cobalt-rich wüstite (Cox/3Fe(1-x)/3)O nanoparticles (x ≥ 2) were synthesized in a solvothermal approach and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM) as well as energy dispersive X-ray spectroscopy (EDX), IR, Raman, and 57Fe-Mössbauer spectroscopy. Their electrocatalytic activity in the oxygen evolution reaction (OER) was evaluated and the active state formation was tracked by operando X-ray absorption spectroscopy (XAS). Our studies demonstrate that the cobalt-rich wüstite (Cox/3Fe(1-x)/3)O nanoparticles underwent a phase-transformation into the spinels CoxFe3-xO4 (x ≥ 2) under the applied OER conditions. The overpotential η10 at 10 mA cm-2, serving as a benchmark for the OER activity of the cobalt ferrite nanoparticles in alkaline media, was lower than that of magnetite Fe3O4 even with low cobalt concentrations, reaching a minimum of 350 mV for Co2.25Fe0.75O4 with a Tafel slope of 50 mV dec-1. Finally, we identified that the catalytic activity is linked to the nanoparticle size as well as to the degree of Co redox activity and change in coordination during OER. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1ta06568h
  • 2021 • 270 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 • 269 Interface-Dominated Topological Transport in Nanograined Bulk Bi2Te3
    Izadi, S. and Han, J.W. and Salloum, S. and Wolff, U. and Schnatmann, L. and Asaithambi, A. and Matschy, S. and Schlörb, H. and Reith, H. and Perez, N. and Nielsch, K. and Schulz, S. and Mittendorff, M. and Schierning, G.
    Small 17 (2021)
    3D topological insulators (TI) host surface carriers with extremely high mobility. However, their transport properties are typically dominated by bulk carriers that outnumber the surface carriers by orders of magnitude. A strategy is herein presented to overcome the problem of bulk carrier domination by using 3D TI nanoparticles, which are compacted by hot pressing to macroscopic nanograined bulk samples. Bi2Te3 nanoparticles well known for their excellent thermoelectric and 3D TI properties serve as the model system. As key enabler for this approach, a specific synthesis is applied that creates nanoparticles with a low level of impurities and surface contamination. The compacted nanograined bulk contains a high number of interfaces and grain boundaries. Here it is shown that these samples exhibit metallic-like electrical transport properties and a distinct weak antilocalization. A downward trend in the electrical resistivity at temperatures below 5 K is attributed to an increase in the coherence length by applying the Hikami–Larkin–Nagaoka model. THz time-domain spectroscopy reveals a dominance of the surface transport at low frequencies with a mobility of above 103 cm2 V−1 s−1 even at room temperature. These findings clearly demonstrate that nanograined bulk Bi2Te3 features surface carrier properties that are of importance for technical applications. © 2021 The Authors. Small published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/smll.202103281
  • 2021 • 268 Investigation of Structural Changes of Cu(I) and Ag(I) Complexes Utilizing a Flexible, Yet Sterically Demanding Multidentate Phosphine Oxide Ligand
    Kirst, C. and Zoller, F. and Bräuniger, T. and Mayer, P. and Fattakhova-Rohlfing, D. and Karaghiosoff, K.
    Inorganic Chemistry 60 2437-2445 (2021)
    The syntheses of a sterically demanding, multidentate bis(quinaldinyl)phenylphosphine oxide ligand and some Cu(I) and Ag(I) complexes thereof are described. By introducing a methylene group between the quinoline unit and phosphorus, the phosphine oxide ligand gains additional flexibility. This specific ligand design induces not only a versatile coordination chemistry but also a rarely observed and investigated behavior in solution. The flexibility of the birdlike ligand offers the unexpected opportunity of open-wing and closed-wing coordination to the metal. In fact, the determined crystal structures of these complexes show both orientations. Investigations of the ligand in solution show a strong dependency of the chemical shift of the CH2 protons on the solvent used. Variable-temperature, multinuclear NMR spectroscopy was carried out, and an interesting dynamic behavior of the complexes is observed. Due to the introduced flexibility, the quinaldinyl substituents change their arrangements from open-wing to closed-wing upon cooling, while still staying coordinated to the metal. This change in conformation is completely reversible when warming up the sample. Based on 2D NMR spectra measured at -80 °C, an assignment of the signals corresponding to the different arrangements was possible. Additionally, the copper(I) complex shows reversible redox activity in solution. The combination of structural flexibility of a multidentate ligand and the positive redox properties of the resulting complexes comprises key factors for a possible application of such compounds in transition-metal catalysis. Via a reorganization of the ligand, occurring transition states could be stabilized, and selectivity might be enhanced. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.0c03334
  • 2021 • 267 Kinetics of the Thermal Decomposition of Ethylsilane: Shock-Tube and Modeling Study
    Sela, P. and Peukert, S. and Somnitz, H. and Janbazi, H. and Wlokas, I. and Herzler, J. and Fikri, M. and Schulz, C.
    Energy and Fuels (2021)
    The thermal decomposition of ethylsilane (H3SiC2H5, EtSiH3) is investigated behind reflected shock waves and the gas composition is analyzed by gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) in a temperature range of 990-1330 K and pressure range of 1-2.5 bar. The unimolecular decomposition of EtSiH3 is considered to be initiated via a molecular elimination of H2 (H3SiC2H5 → H2 + HSiC2H5) followed by reactions of cyclic silicon-containing species. The main observed stable products were ethylene (C2H4) and silane (SiH4). Measurements are performed with a large excess of a silylene scavenger (C2H2) to suppress bimolecular reactions caused by silylene (SiH2) and to extract unimolecular rate constants. A kinetics mechanism accounting for the gas-phase chemistry of EtSiH3 is developed, which consists of 24 Si-containing species, 31 reactions of Si-containing species, and a set of new thermochemical data. The derived unimolecular rate constant is represented by the Arrhenius expression kuni(T) = 1.96 × 1012 s-1 exp(-205 kJ mol-1/RT). The experimental data is reproduced very well by simulations based on the mechanism of this work and is in very good agreement with literature values. It is shown that EtSiH3 is a promising precursor for the synthesis of SiC nanoparticles. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.energyfuels.0c03425
  • 2021 • 266 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 • 265 Mechanochemical Synthesis of Supported Bimetallic Catalysts
    De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry of Materials 33 2037-2045 (2021)
    In a previous publication, ball milling was introduced as an effective method for the preparation of supported metal catalysts, simply from the coarse powders of the metal and metal oxide support. In this follow-up study, we demonstrate that mixing multiple metal sources can result in supported alloyed nanoparticles, extending the field of application of the method to the synthesis of supported bimetallic catalysts. Ball milling Au and Pd or Au and Cu in a high-energy regime (shaker mill) indeed led to the formation of Au-Pd and Au-Cu nanoparticles, supported on MgO or yttria-stabilized zirconia (YSZ), which were explored as model systems. Powder X-ray diffraction and electron microscopy were the primary means to investigate as-synthesized materials. The catalytic performance in CO oxidation was also investigated to understand better how the synthetic method could affect the features of the final materials as catalysts. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.0c04134
  • 2021 • 264 Metal–Organic-Framework-Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction
    Liang, Z. and Guo, H. and Zhou, G. and Guo, K. and Wang, B. and Lei, H. and Zhang, W. and Zheng, H. and Apfel, U.-P. and Cao, R.
    Angewandte Chemie - International Edition 60 8472-8476 (2021)
    Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)-supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (>70 mV) anodic shift of the half-wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn-air batteries, which exhibited equal performance to that with Pt-based materials. © 2021 Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202016024
  • 2021 • 263 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 • 262 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 • 261 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 • 260 Preparation and characterization of hydrophilic and antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles for polymeric nanocomposites
    Ahsani, M. and Sabouri, R. and Ulbricht, M. and Hazrati, H. and Jafarizad, A. and Yegani, R.
    Journal of Applied Polymer Science (2021)
    Hydrophilic antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles were successfully synthesized in multiple steps. In this regard, silanization of the silica nanoparticles was performed with different concentrations of vinyltrimethoxysilane (VTS) to generate vinyl groups onto the nanoparticles surface. Obtained results showed that by increasing the VTS concentration the amount of vinyl groups on the surface of the silica nanoparticles increased while nanoparticles agglomeration did not occur. Then, poly(vinylpyrrolidone) PVP brushes were grafted onto the silanized silica nanoparticles (SiO2-VTS) via grafting-through polymerization method to obtain PVP-grafted silica nanoparticles (SiO2-PVP). Fourier transform infrared spectroscopy, thermal gravimetric analysis, and dynamic light scattering confirmed the successful generation of the vinyl groups and PVP brushes onto the silica nanoparticles. Finally, Ag-SiO2-PVP nanoparticles were prepared by synthesizing silver nanoparticles onto the SiO2-PVP nanoparticles to render them antibacterial. Energy dispersive X-ray spectroscopy showed that highest grafting of silver nanoparticles onto the SiO2-PVP nanoparticles was obtained for the nanoparticles with highest content of vinyl groups. X-ray photoelectron spectroscopy was used to identify the elements and their chemical structure for the synthesized nanoparticles. Plate colony counting method was applied to assess the antibacterial effects of the Ag-SiO2-PVP nanoparticles which revealed outstanding bactericidal properties of them. © 2021 Wiley Periodicals LLC.
    view abstractdoi: 10.1002/app.50977
  • 2021 • 259 Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis, Modeling, and Application
    Kaur, P. and Mai, L. and Muriqi, A. and Zanders, D. and Ghiyasi, R. and Safdar, M. and Boysen, N. and Winter, M. and Nolan, M. and Karppinen, M. and Devi, A.
    Chemistry - A European Journal 27 4913-4926 (2021)
    Owing to the limited availability of suitable precursors for vapor phase deposition of rare-earth containing thin-film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris-guanidinate and tris-amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C-substituents on the N-C-N backbone (Me, NMe2, NEt2, where Me=methyl, Et=ethyl) and the N-substituents from symmetrical iso-propyl (iPr) to asymmetrical tertiary-butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)3] 1 and [Yb(dpdmg)3] 6 (dpdmg=N,N'-diisopropyl-2-dimethylamido-guanidinate) highlight a monomeric nature in the solid-state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O2) and water (H2O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)3] 1 was used for proof-of-principle ALD depositions of CeO2 thin films using water as co-reactant. The self-limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO2 films formed on Si(100) substrates. This study confirms that moving towards nitrogen-coordinated rare-earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.202003907
  • 2021 • 258 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 • 257 Spray flame synthesis (Sfs) of lithium lanthanum zirconate (llzo) solid electrolyte
    Ali, M.Y. and Orthner, H. and Wiggers, H.
    Materials 14 (2021)
    A spray-flame reaction step followed by a short 1-h sintering step under O2 atmosphere was used to synthesize nanocrystalline cubic Al-doped Li7La3Zr2O12 (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La2Zr2O7 (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I41 /acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14133472
  • 2021 • 256 Thermochemistry of Oxygen-Containing Organosilane Radicals and Uncertainty Estimations of Organosilane Group-Additivity Values
    Janbazi, H. and Schulz, C. and Wlokas, I. and Peukert, S.
    Journal of Physical Chemistry A 125 8699-8711 (2021)
    Si-C-H-O-containing radicals are important intermediates during the combustion and pyrolysis of precursors applied for the gas-phase synthesis of silica nanoparticles. Despite the industrial importance of silica nanoparticles, a comprehensive thermodynamics database of organosilane species is still missing. This work presents thermochemical data of 91 Si-C-H-O radical species. Quantum-chemical calculations and isodesmic reaction schemes are used to determine the standard enthalpy of formation, entropy, and heat capacities covering the 298-2000 K temperature range. In addition, 90 group-additivity values (GAVs) are calculated, which cover all relevant group increments. A combinatorial approach is used to ensure that all possible group increments are considered. The theoretically calculated species are used as a training set to derive 90 GAVs of Si-C-H-O radical species for the first time. In addition, uncertainty contributions of GAVs were estimated. These uncertainty estimates also comprise GAVs that were previously derived to compute thermochemical data of stable Si-C-H species and radicals as well as stable Si-C-H-O compounds. Therefore, uncertainty contributions of GAVs for a whole set of 243 group increments used to predict thermochemical data of Si-organic species are reported. © 2021 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acs.jpca.1c06941
  • 2021 • 255 Thermophysical properties of mixtures of titanium(iv) isopropoxide (ttip) and 2-propanol (ipoh)
    Kohns, M. and Keller, A. and Wlokas, I. and Hasse, H.
    Journal of Chemical and Engineering Data 66 1296-1304 (2021)
    The present work provides thermophysical data on binary mixtures of titanium(IV) isopropoxide (TTIP) and 2-propanol (iPOH), which are important precursor solutions in spray flame synthesis of nanoparticles. The specific density, viscosity, thermal conductivity, and molar isobaric heat capacity were measured at 101.3 kPa and temperatures ranging from 293.15 to 333.15 K. The vapor-liquid equilibrium (VLE) was measured at pressures ranging from 20 to 80 kPa. Furthermore, self-diffusion coefficients of pure iPOH were measured at 101.3 kPa and temperatures ranging from 293.15 to 333.15 K. A qualitative study using 1H NMR spectroscopy provides evidence for a cross-association between TTIP and iPOH in the mixture. Correlations for all studied thermophysical properties are provided. The results establish a rational basis for the design of spray flame synthesis processes. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.jced.0c00941
  • 2020 • 254 Active Ga-catalysts for the ring opening homo- And copolymerization of cyclic esters, and copolymerization of epoxide and anhydrides
    Ghosh, S. and Glöckler, E. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Dalton Transactions 49 13475-13486 (2020)
    A series of gallium complexes L12Ga4Me8(1), L22Ga4Me8(2), and L32Ga4Me8(3) was synthesized by reaction of GaMe3with Schiff base ligands L1-3H2(L1H2= 2,4-di-tert-butyl-6-{[(3-hydroxypropyl)imino]methyl}phenol; L2H2= 2,4-dichloro-6-{[(3-hydroxypropyl)imino]methyl}phenol; L3H2= 4-tert-butyl-2-{[(3-hydroxypropyl)imino]methyl}phenol) and characterized by1H,13C NMR, IR spectroscopy, elemental analysis and single crystal X-ray analysis (1,2), proving their tetranuclear structure in the solid state. Complexes1-3showed good catalytic activity in the ring opening homopolymerization (ROP) and ring opening copolymerization (ROcoP) of lactide (LA) and ε-caprolactone (ε-CL) in the presence of benzyl alcohol (BnOH) in toluene at 100 °C, yielding polymers with the expected average molecular weights (Mn) and narrow molecular weight distributions (MWD), as well as a high isoselectivity for the ROP ofrac-lactide (rac-LA), yielding isotactic-enriched PLAs withPmvalues up to 0.78. Kinetic studies with complex1proved the first order dependence on monomer concentration, while mechanistic studies confirmed the coordination insertion mechanistic (CIM) pathway. Sequential addition of monomers gave well defined diblock copolymers of PCL-b-PLLA and PLLA-b-PCL, proving the living character of the polymerization reactions. The catalysts also showed perfect selectivity for the copolymerization of cyclohexene oxide (CHO) with both succinic anhydride (SA) and maleic anhydride (MA) in the presence of BnOH and produced >99% alternating block copolymers. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0dt02831b
  • 2020 • 253 Additive-free spin coating of tin oxide thin films: Synthesis, characterization and evaluation of tin β-ketoiminates as a new precursor class for solution deposition processes
    Huster, N. and Zanders, D. and Karle, S. and Rogalla, D. and Devi, A.
    Dalton Transactions 49 10755-10764 (2020)
    The fabrication of SnOx in thin film form via chemical solution deposition (CSD) processes is favored over vacuum based techniques as it is cost effective and simpler. The precursor employed plays a central role in defining the process conditions for CSD. Particularly for processing SnO2 layers that are appealing for sensor or electronic applications, there are limited precursors available for CSD. Thus the focus of this work was to develop metalorganic precursors for tin, based on the ketoiminate ligand class. By systematic molecular engineering of the ligand periphery, a series of new homoleptic Sn(ii) β-ketoiminate complexes was synthesized, namely bis[4-(2-methoxyethylimino)-3-pentanonato] tin, [Sn(MEKI)2] (1), bis[4-(2-ethoxyethylimino)-2-pentanonato] tin, [Sn(EEKI)2] (2), bis[4-(3-methoxypropylimino)-2-pentanonato] tin, [Sn(MPKI)2] (3), bis[4-(3-ethoxypropylimino)-2-pentanonato] tin, [Sn(EPKI)2] (4) and bis[4-(3-isopropoxypropylimino)-2-pentanonato] tin, [Sn(iPPKI)2] (5). All these N-side-chain ether functionalized compounds were analyzed by nuclear magnetic resonance (NMR) spectroscopy, electron impact mass spectrometry (EI-MS), elemental analysis (EA) and thermogravimetric analysis (TGA). The solid state molecular structure of [Sn(MPKI)2] (3) was eludicated by means of single crystal X-ray diffraction (SCXRD). Interestingly, this class of compounds features excellent solubility and stability in common organic solvents alongside good reactivity towards H2O and low decomposition temperatures, thus fulfilling the desired requirements for CSD of tin oxides. With compound 3 as a representative example, we have demonstrated the possibility to directly deposit SnOx layers via hydrolysis upon exposure to air followed by heat treatment under oxygen at moderate temperatures and most importantly without the need for any additive that is generally used in CSD. A range of complementary analytical methods were employed, namely X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to analyse the structure, morphology and composition of the SnOx layers. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0dt01463j
  • 2020 • 252 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 • 251 Effect of Spray Parameters in a Spray Flame Reactor During FexOy Nanoparticles Synthesis
    Carvajal, L. and Buitrago-Sierra, R. and Santamaría, A. and Angel, S. and Wiggers, H. and Gallego, J.
    Journal of Thermal Spray Technology 29 368-383 (2020)
    Abstract: Synthesis and characterization of FexOy nanoparticles were carried out in order to study reaction parameters influence in a spray flame reactor. FexOy powders were prepared with three different precursors aiming to understand how the reactor conditions, dispersion gas flow, and precursor solution flow affect morphology, shape, particle size distribution, crystalline phases, and residue content of the obtained materials. Thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy (TEM), x-ray diffraction (XRD), and Raman spectroscopy were employed to characterize the materials. In addition, magnetic behavior of the obtained samples was evaluated. It was found that the evaluated parameters influenced the residue contents obtaining weight changes from 10 to 35%. Particle size distribution centers also showed differences between 17 and 24 nm. By XRD, Raman, and TEM, the presence of hematite (a-Fe2O3), maghemite (γ-Fe2O3), and magnetite (Fe3O4) was evidenced and explained based on the gas and liquid content in the flame. Additionally, the saturation magnetization was measured for selected samples, obtaining values between 26 and 32 emu g−1. These magnetic measurements were correlated with the crystalline phase composition and particle size distributions. Graphic Abstract: [Figure not available: see fulltext.] © 2020, ASM International.
    view abstractdoi: 10.1007/s11666-020-00991-1
  • 2020 • 250 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 • 249 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 • 248 In Situ Generation of Electrolyte inside Pyridine-Based Covalent Triazine Frameworks for Direct Supercapacitor Integration
    Troschke, E. and Leistenschneider, D. and Rensch, T. and Grätz, S. and Maschita, J. and Ehrling, S. and Klemmed, B. and Lotsch, B.V. and Eychmüller, A. and Borchardt, L. and Kaskel, S.
    ChemSusChem 13 3192-3198 (2020)
    The synthesis of porous electrode materials is often linked with the generation of waste that results from extensive purification steps and low mass yield. In contrast to porous carbons, covalent triazine frameworks (CTFs) display modular properties on a molecular basis through appropriate choice of the monomer. Herein, the synthesis of a new pyridine-based CTF material is showcased. The porosity and nitrogen-doping are tuned by a careful choice of the reaction temperature. An in-depth structural characterization by using Ar physisorption, X-ray photoelectron spectroscopy, and Raman spectroscopy was conducted to give a rational explanation of the material properties. Without any purification, the samples were applied as symmetrical supercapacitors and showed a specific capacitance of 141 F g−1. Residual ZnCl2, which acted formerly as the porogen, was used directly as the electrolyte salt. Upon the addition of water, ZnCl2 was dissolved to form the aqueous electrolyte in situ. Thereby, extensive and time-consuming washing steps could be circumvented. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cssc.202000518
  • 2020 • 247 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 • 246 Metal Complexes of Donor-functionalized Fluorinated β-Ketoiminates – Synthesis, Structure, and CVD Application
    Kaiser, K. and Ganesamoorthy, C. and Wölper, C. and Schulz, S.
    Zeitschrift fur Anorganische und Allgemeine Chemie 646 681-691 (2020)
    Six alkali metal complexes of partly-fluorinated, donor-functionalized β-ketoiminate ligands [L1Li (1), L1Na (2), L1K (3), L1Cs (4), L1 = OC(CF3)CHC(CH3)NCH2CH2OCH3; L2Li (5), L2Na (6), L2 = OC(CF3)CHC(CH3)NCH2CH2N(CH3)2] were prepared and structurally characterized. Reactions of L1Li with PtCl2 gave the homoleptic Pt complex L12Pt (7), which was characterized spectroscopically and by single-crystal X-ray diffraction and whose promising application as CVD precursor (chemical vapor deposition) is shown. Polycrystalline, pure Pt films were grown at 500 °C on SiO2@Si(100) substrates at 10–3 mbar and characterized by XRD, SEM, AFM, EDX and XPS. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/zaac.201900239
  • 2020 • 245 Microstructure characteristics of non-monodisperse quantum dots: On the potential of transmission electron microscopy combined with X-ray diffraction
    Neumann, S. and Menter, C. and Mahmoud, A.S. and Segets, D. and Rafaja, D.
    CrystEngComm 22 3644-3655 (2020)
    Although the concept of quantum confinement was introduced more than thirty years ago, a wide application of quantum dots is still limited by the fact that monodisperse quantum dots with controlled optoelectronic properties are typically synthesized on a relatively small scale. Larger scale synthesis techniques are usually not able to produce monodisperse nanoparticles yet. In this contribution, we illustrate the capability of the combination of transmission electron microscopy and X-ray diffraction to reveal detailed and scale-bridging information about the complex microstructure of non-monodisperse quantum dots, which is the first step towards further upscaling of the techniques for production of quantum dots with controlled properties. As a model system, CdSe quantum dots synthesized using an automated robotic hot-injection method at different temperatures were chosen. The combined microstructure analytics revealed the size and shape of the CdSe nanocrystals and the kind, density and arrangement of planar defects. The role of the planar defects in the particle coarsening by oriented attachment and the effect of the planar fault arrangement on the phase constitution, on the crystallographic coherence of the counterparts and on the optoelectronic properties are discussed. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0ce00312c
  • 2020 • 244 On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation
    Anke, S. and Falk, T. and Bendt, G. and Sinev, I. and Hävecker, M. and Antoni, H. and Zegkinoglou, I. and Jeon, H. and Knop-Gericke, A. and Schlögl, R. and Roldan Cuenya, B. and Schulz, S. and Muhler, M.
    Journal of Catalysis 382 57-68 (2020)
    CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min−1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2019.12.007
  • 2020 • 243 Preparation and characterization of polyzwitterionic hydrogel coated polyamide-based mixed matrix membrane for heavy metal ions removal
    Pakizeh, M. and May, P. and Matthias, M. and Ulbricht, M.
    Journal of Applied Polymer Science 137 (2020)
    A novel polyzwitterionic hydrogel coated mixed matrix membrane (MMM) was successfully prepared, characterized and used for Cu2+, Mn2+, and Pb2+ heavy metal ions removal from water. Hydrophilic and porous covalent organic framework (COF) nanoparticles (NP) as filler were synthesized from melamine and terephthalaldehyde, and then incorporated into polyamide (PA) thin film composite (TFC) membrane. The hydrogel coating was applied by using a tailored cross-linkable polymer system in combination with concentration polarization enabled cross-linking. The effects of COF NP loading into PA layer and polyzwitterionic hydrogel coating on the membrane morphology and separation performance were studied using different analyses. The MMM prepared with a COF NP loading of 0.02 wt/wt% in the hexane dispersion used for NP deposition during PA layer formation (leading to 0.42 g/m2) exhibited an increased pure water permeability of around 200% compared with the neat PA TFC membrane while the Mn2+ ion rejection maintained above 98%. Scanning electron microscopy surface images and zeta potential profiles showed that the hydrogel was successfully deposited on the membrane surface. Furthermore, the hydrogel coating could decrease net surface charge of membranes but did not significantly influence the heavy metal ions rejections under nanofiltration conditions. The results of filtration experiment with protein solution indicated that the hydrogel coated membranes exhibited superior antifouling property, as shown by higher flux recovery ratio after washing with water, compared with neat PA TFC membrane and not coated MMM, respectively. © 2020 Wiley Periodicals LLC
    view abstractdoi: 10.1002/app.49595
  • 2020 • 242 Spray-flame synthesis of BaTi1-xZrxO3 nanoparticles for energy storage applications
    Tarasov, A. and Shvartsman, V.V. and Shoja, S. and Lewin, D. and Lupascu, D.C. and Wiggers, H.
    Ceramics International 46 13915-13924 (2020)
    BaTi1-xZrxO3 nanoparticles (x = 0, 0.05, 0.1, 0.15, 0.2) were successfully produced by the spray-flame synthesis method. The as-synthesized powders are characterized by small (~10 nm) particle sizes as shown by TEM images. The as-synthesized powders were pre-heated at 800 °C to remove organic residuals from the surface. Pellets were then pressed and sintered at 1100 °C for 3 h. XRD measurements of the sintered materials show that the crystallite size decreases with increasing Zr concentration, which was additionally confirmed by TEM. Dielectric measurements show that the Curie temperature shifts towards lower temperatures with increasing Zr concentration accompanied by a decrease in the dielectric permittivity values which is attributed to a decreasing crystallite/particle size. In addition, a frequency dispersion of the permittivity values is discovered. This is mostly ascribed to Maxwell-Wagner polarization effects typical for nanograined ceramics. © 2020 Elsevier Ltd and Techna Group S.r.l.
    view abstractdoi: 10.1016/j.ceramint.2020.02.187
  • 2020 • 241 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 • 240 Synthesis of graphene-related carbon nanoparticles from a liquid isopropanol precursor by a one-step atmospheric plasma process
    Bodnar, W. and Schiorlin, M. and Frank, A. and Schulz, T. and Wöhrl, N. and Miron, C. and Scheu, C. and Kolb, J.F. and Kruth, A.
    Applied Surface Science 514 (2020)
    This study presents a cost-efficient single-step-method to synthesize nanographite from isopropanol by bipolar pulsed electric discharges. The influence of pulse width within the nanosecond range, repetition frequency within the kilohertz range and processing time on the product was systematically investigated by Raman spectroscopy, high-resolution transmission electron microscopy and gas chromatography - mass spectrometry. It was found that long pulses in the microsecond range promote the creation of amorphous and oxidic carbon structures. Although, hydrocarbon cracking and subsequent graphitization do occur, these process conditions are not suitable to drive intermediate reduction processes. In contrast, applying short pulses in the nanosecond regime ensures fast reduction processes and formation of graphene-related nanostructures. The number of observed nanographite layers lies in the range of 3–13 with an average interlayer spacing of 3.4(0.3) Å and an average distance between defects of 11.5(6.0) nm meaning that the produced nanographite is in the area of small defect density. Furthermore, no significant influence of process times on the product properties over a period up to 15 min was observed, indicating good process homogeneity. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2020.145926
  • 2020 • 239 Synthesis of plasmonic Fe/Al nanoparticles in ionic liquids
    Schmitz, A. and Meyer, H. and Meischein, M. and Garzón Manjón, A. and Schmolke, L. and Giesen, B. and Schlüsener, C. and Simon, P. and Grin, Y. and Fischer, R.A. and Scheu, C. and Ludwig, Al. and Janiak, C.
    RSC Advances 10 12891-12899 (2020)
    Bottom-up and top-down approaches are described for the challenging synthesis of Fe/Al nanoparticles (NPs) in ionic liquids (ILs) under mild conditions. The crystalline phase and morphology of the metal nanoparticles synthesized in three different ionic liquids were identified by powder X-ray diffractometry (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and fast Fourier transform (FFT) of high-resolution TEM images. Characterization was completed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) for the analysis of the element composition of the whole sample consisting of the NPs and the amorphous background. The bottom-up approaches resulted in crystalline FeAl NPs on an amorphous background. The top-down approach revealed small NPs and could be identified as Fe4Al13 NPs which in the IL [OPy][NTf2] yield two absorption bands in the green-blue to green spectral region at 475 and 520 nm which give rise to a complementary red color, akin to appropriate Au NPs. © 2020 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra01111h
  • 2020 • 238 Thermochemistry of organosilane compounds and organosilyl radicals
    Janbazi, H. and Schulz, C. and Wlokas, I. and Wang, H. and Peukert, S.
    Proceedings of the Combustion Institute (2020)
    Si-C-H-containing radicals and stable species are present in the oxidation of silicon-organic compounds such as methyl and ethyl silanes, which are frequently-used precursors for the synthesis of silicon-based nanoparticles and coatings via combustion processes. Silicon-containing intermediates interact with flame radicals and thus play a major role in flame chemistry and influence flame propagation. Mechanistic understanding of these effects is hampered by very limited thermochemical properties available for relevant organosilane species. This paper presents quantum-chemical calculations and isodesmic reaction schemes for the determination of temperature-dependent heat of formation, entropy, and heat capacity of Si-C-H radicals and molecules, from which group additivity values (GAVs) were obtained from combinatorial considerations. The data for 22 stable Si-C-H species are revised using isodesmic reactions and the related 24 GAVs were refined by considering 19 additional stable Si-C-H species. In addition, quantum chemical calculations are made to calculate the thermochemistry of 61 radicals and used to derive 56 GAVs for Si-C-H containing radicals for the first time. © 2020 The Combustion Institute. Published by Elsevier Inc.
    view abstractdoi: 10.1016/j.proci.2020.06.114
  • 2020 • 237 β-Cyclodextrin-based star polymers for membrane surface functionalization: Covalent grafting via “click” chemistry and enhancement of ultrafiltration properties
    Büning, J. and Frost, I. and Okuyama, H. and Lempke, L. and Ulbricht, M.
    Journal of Membrane Science 596 (2020)
    This work provides the proof-of-concept that surface functionalization of porous membranes with well-defined star-like polymers of varied number of arms and arm length leads to a tunable effective thickness of grafted layers and a specific influence on size-selective sieving through ultrafilter pores. Alkyl-brominated β-cyclodextrine with either 7 or 21 initiator sites per molecule was synthesized and further used for controlled atom transfer radical polymerization of copolymers of 2-dimethylamino(ethyl) methacrylate (DMAEMA) and propargyl methacrylate (PgMA), leading to star polymers with either 7 or 21 arms. Alkyne-containing PgMA segments enable the “click” coupling while DMAEMA segments provide the bulk of the polymer. Star polymers were characterized with respect to chemical structure and molecular weight (M). During ultrafiltration (UF) through cellulose membranes with different molecular weight cut-off, rejection was not simply correlated with star polymer M but was governed by macromolecular architecture, i.e. the smaller colloidal diameter for macromolecules of same M but 21 instead of 7 arms. Azide-functionalized poly(ethylene terephthalate) (PET) track-etched (TE) membranes and cellulose UF membranes were prepared by polymer-analogous surface functionalization so that the alkyne-substituted star polymers could be “click”-grafted. Isoporous PET TE membranes with a nominal pore diameter of 200 nm were used as model system to study the grafting and its effects onto pore size via the reduction of hydraulic permeability. Effective grafted layer thickness in the range of 10–50 nm correlated with macromolecular structure and architecture. For “click”-functionalized cellulose UF membranes, the effective pore size in the barrier layer was influenced by grafted star polymers, and a pronounced additional influence of the architecture and arm length of the grafted star polymer on macromolecular sieving was observed. Of particular interest are results with the more flexible 7-armed star polymers (compared to 21-armed counterparts); their grafting at the UF membrane pores of similar dimension leads to a large increase of test solute rejection at very low reduction of convective water flux, both compared to the unmodified membrane. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2019.117610
  • 2019 • 236 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 • 235 Bimetallic silver-platinum nanoparticles with combined osteo-promotive and antimicrobial activity
    Breisch, M. and Grasmik, V. and Loza, K. and Pappert, K. and Rostek, A. and Ziegler, N. and Ludwig, Al. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
    Nanotechnology 30 (2019)
    Bimetallic alloyed silver-platinum nanoparticles (AgPt NP) with different metal composition from Ag10Pt90 to Ag90Pt10 in steps of 20 mol% were synthesized. The biological effects of AgPt NP, including cellular uptake, cell viability, osteogenic differentiation and osteoclastogenesis as well as the antimicrobial activity towards Staphylococcus aureus and Escherichia coli were analyzed in comparison to pure Ag NP and pure Pt NP. The uptake of NP into human mesenchymal stem cells was confirmed by cross-sectional focused-ion beam preparation and observation by scanning and transmission electron microscopy in combination with energy-dispersive x-ray analysis. Lower cytotoxicity and antimicrobial activity were observed for AgPt NP compared to pure Ag NP. Thus, an enhanced Ag ion release due to a possible sacrificial anode effect was not achieved. Nevertheless, a Ag content of at least 50 mol% was sufficient to induce bactericidal effects against both Staphylococcus aureus and Escherichia coli. In addition, a Pt-related (≥50 mol% Pt) osteo-promotive activity on human mesenchymal stem cells was observed by enhanced cell calcification and alkaline phosphatase activity. In contrast, the osteoclastogenesis of rat primary precursor osteoclasts was inhibited. In summary, these results demonstrate a combinatory osteo-promotive and antimicrobial activity of bimetallic Ag50Pt50 NP. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab172b
  • 2019 • 234 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 • 233 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 • 232 Comparative study of flame-based SiO 2 nanoparticle synthesis from TMS and HMDSO: SiO-LIF concentration measurement and detailed simulation
    Chrystie, R.S.M. and Janbazi, H. and Dreier, T. and Wiggers, H. and Wlokas, I. and Schulz, C.
    Proceedings of the Combustion Institute 37 1221-1229 (2019)
    Depending on the chemical nature of precursor species, the flame-based synthesis of silicon dioxide nanoparticles in lean hydrogen/oxygen flames proceeds via different chemical routes, which affects the generated particle characteristics. Modeling the flame chemistry and particle formation therefore can provide valuable understanding of the underlying gas-phase and particle-formation pathways. In the present study we compare experimentally obtained temperature and semi-quantified SiO-concentration profiles in low-pressure (3 kPa), lean (? < 0.6), inert-gas diluted H 2 /O 2 /Ar burner-stabilized flat flames doped with 200-4000 ppm hexamethyldisiloxane (HMDSO) or tetramethylsilane (TMS) with results from kinetics modeling. Temperature fields in the flames were determined via multi-line laser-induced fluorescence (LIF) imaging using both added NO and native SiO as target species. Gas-phase silicon monoxide (SiO) was detected via LIF by exciting the rovibrational Q(42) transition in the A 1 Π-X 1 Σ + (1,0) vibronic band system at 230.998 nm that provides a weak temperature dependence when analyzing relative SiO mole fractions. Semi-quantitative SiO mole-fraction profiles as a function of height-above-burner (HAB) were obtained for all flames from the measured SiO-LIF intensities corrected for variations of the temperature-dependent ground-state population and the collisional quenching using measured temperatures and effective fluorescence lifetimes, respectively. The experimental data were compared with results of appropriate chemical kinetics mechanisms from the literature with suitable modifications to best reproduce measured SiO mole-fraction profiles. Modeling initial cluster formation is important in this study to unravel the observed 'double-peak'-structure of the SiO concentration profiles assumed to originate from resublimed SiO from early-formed SiO 2 nanoparticles in the rising temperature gradient during initial particle nucleation, and which may be altered by the availability of oxygen in the precursor species. © 2018 The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2018.07.024
  • 2019 • 231 Comparative study of flame-based SiO2 nanoparticle synthesis from TMS and HMDSO: SiO-LIF concentration measurement and detailed simulation
    Chrystie, R.S.M. and Janbazi, H. and Dreier, T. and Wiggers, H. and Wlokas, I. and Schulz, C.
    Proceedings of the Combustion Institute 37 1221-1229 (2019)
    Depending on the chemical nature of precursor species, the flame-based synthesis of silicon dioxide nanoparticles in lean hydrogen/oxygen flames proceeds via different chemical routes, which affects the generated particle characteristics. Modeling the flame chemistry and particle formation therefore can provide valuable understanding of the underlying gas-phase and particle-formation pathways. In the present study we compare experimentally obtained temperature and semi-quantified SiO-concentration profiles in low-pressure (3 kPa), lean (? < 0.6), inert-gas diluted H2/O2/Ar burner-stabilized flat flames doped with 200-4000 ppm hexamethyldisiloxane (HMDSO) or tetramethylsilane (TMS) with results from kinetics modeling. Temperature fields in the flames were determined via multi-line laser-induced fluorescence (LIF) imaging using both added NO and native SiO as target species. Gas-phase silicon monoxide (SiO) was detected via LIF by exciting the rovibrational Q(42) transition in the A1Π-X1Σ+ (1,0) vibronic band system at 230.998 nm that provides a weak temperature dependence when analyzing relative SiO mole fractions. Semi-quantitative SiO mole-fraction profiles as a function of height-above-burner (HAB) were obtained for all flames from the measured SiO-LIF intensities corrected for variations of the temperature-dependent ground-state population and the collisional quenching using measured temperatures and effective fluorescence lifetimes, respectively. The experimental data were compared with results of appropriate chemical kinetics mechanisms from the literature with suitable modifications to best reproduce measured SiO mole-fraction profiles. Modeling initial cluster formation is important in this study to unravel the observed 'double-peak'-structure of the SiO concentration profiles assumed to originate from resublimed SiO from early-formed SiO2 nanoparticles in the rising temperature gradient during initial particle nucleation, and which may be altered by the availability of oxygen in the precursor species. © 2018 The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2018.07.024
  • 2019 • 230 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 • 229 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 • 228 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 • 227 Solution NMR Spectroscopy with Isotope-Labeled Cysteine ( 13 C and 15 N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 767-778 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13 C-labeled and 15 N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1 H- 13 C-heteronuclear single-quantum coherence and 13 C- 13 C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy ( 1 H-, 13 C-, and 1 H- 13 C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au 174 (cysteine) 67 . © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b03840
  • 2019 • 226 Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 767-778 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13C-labeled and 15N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1H-13C-heteronuclear single-quantum coherence and 13C-13C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (1H-, 13C-, and 1H-13C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au174(cysteine)67. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b03840
  • 2019 • 225 Synergistic Effects of Mo2C-NC@CoxFey Core–Shell Nanoparticles in Electrocatalytic Overall Water Splitting Reaction
    Wang, S. and Bendt, G. and Saddeler, S. and Schulz, S.
    Energy Technology 7 (2019)
    Transition metals (TMs) are highly investigated as nonprecious electrocatalysts for hydrogen evolution (HER) and oxygen evolution (OER) reactions. There is a strong demand for highly efficient and inexpensive catalysts for overall water splitting. Herein, the bimetallic CoxFey alloy nanoparticles encapsulated in a N-doped graphene shell containing molybdenum carbide (Mo2C) nanoparticles are synthesized by the pyrolysis of cobalt ferrite (CoxFe3−xO4) nanoparticles coated by melamine-formaldehyde resin cross-linked with molybdic acid. Molybdic acid not only serves as precursor for the formation of highly dispersed Mo2C nanoparticles in the N-doped graphene shell but also enhances the thermal stability of the organic shell, resulting in the formation of smaller CoxFey cores. The formation of Mo2C nanoparticles in the graphene shell is promoted by the CoxFe3−xO4 core. Interestingly, the synergistic presence of Mo2C nanoparticles not only enhances the HER activity of the material but also renders a partial breakage of the graphene shell, which increases the surface concentration of OER-active Co and therefore enhances the OER activity. The as-prepared TM-based materials serve as bifunctional catalysts for the overall water splitting and exhibit improved electrocatalytic performances compared to standard cells based on precious metals, with the potentials of 1.53 and 1.60 V at 10 and 20 mA cm−2 in alkaline media, respectively. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/ente.201801121
  • 2019 • 224 Synthesis and structures of s- and p-block metal complexes containing sterically demanding pentaarylcyclopentadienyl substituents
    Schulte, Y. and Stienen, C. and Wölper, C. and Schulz, S.
    Organometallics 38 2381-2390 (2019)
    The synthesis of alkali metal salts of sterically demanding cyclopentadienyls CpBIGi-PrM (CpBIGi-Pr = Cp(4-i-Pr-Ph)5; M = Li 1, Na 2, K 3, Rb 4, Cs 5), CpBIGn-BuM (CpBIGn-Bu = Cp(4-n-Bu-Ph)5; M = Li 6, Na 7, K 8, Rb 9, Cs 10), and CpBIGt-BuM (CpBIGt-Bu = Cp(4-t-Bu-Ph)5; M = Li 11, Na 12, K 13, Rb 14, Cs 15) and their complete characterization including IR and heteronuclear (1H, 13C, 7Li, 23Na, 87Rb, 133Cs) NMR spectroscopy are reported. In addition, the solid-state structures of 5, 10, 11, and 13 were determined by single-crystal X-ray diffraction, revealing the formation of infinite one-dimensional chain structures in the solid state (5, 10) or solvent-separated ion pairs (11, 13). Salt elimination reactions of CpBIGt-BuK 13 with ECl3 yielded the monosubstituted cyclopentadienyl compounds CpBIGt-BuECl2 (E = P 16, As 17, Sb 18, Bi 19), which were characterized by elemental analysis, IR, and heteronuclear (1H, 13C, 31P) NMR spectroscopy and single-crystal X-ray diffraction (17). © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.9b00203
  • 2018 • 223 An N-Heterocyclic Carbene Based Silver Precursor for Plasma-Enhanced Spatial Atomic Layer Deposition of Silver Thin Films at Atmospheric Pressure
    Boysen, N. and Hasselmann, T. and Karle, S. and Rogalla, D. and Theirich, D. and Winter, M. and Riedl, T. and Devi, A.
    Angewandte Chemie - International Edition 57 16224-16227 (2018)
    A new N-heterocyclic carbene (NHC)-based silver amide compound, 1,3-di-tert-butyl-imidazolin-2-ylidene silver(I) 1,1,1-trimethyl-N-(trimethylsilyl)silanaminide [(NHC)Ag(hmds)] was synthesized and analyzed by single-crystal X-ray diffraction, 1H and 13C NMR spectroscopy, as well as EI mass spectrometry, and subsequently evaluated for its thermal characteristics. This new halogen- and phosphine-free Ag atomic layer deposition (ALD) precursor was tested successfully for silver thin film growth in atmospheric pressure plasma enhanced spatial (APP-ALD). High-purity conductive Ag thin films with a low sheet resistance of 0.9 Ω/sq (resistivity: 10−5 Ωcm) were deposited at 100 °C and characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, optical transmittance, and Rutherford back-scattering techniques. The carbene-based Ag precursor and the new APP-ALD process are significant developments in the field of precursor chemistry as well as metal ALD processing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201808586
  • 2018 • 222 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 • 221 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 • 220 Kinetic study of gold nanoparticles synthesized in the presence of chitosan and citric acid
    Simeonova, S. and Georgiev, P. and Exner, K.S. and Mihaylov, L. and Nihtianova, D. and Koynov, K. and Balashev, K.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 557 106-115 (2018)
    In this work colloidal gold nanoparticles (GNPs) are prepared using a citrate-reduction route, in which citric acid serves as reductive agent for the gold precursor HAuCl4. We demonstrate that a temperature variation on the one hand enables to tune the reaction rate of GNP formation and on the other hand allows modifying the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a multitude of functional amino and hydroxyl groups, facilitates the simultaneous synthesis and surface modification of GNPs in one pot. The resulting GNPs, which are stabilized by a network of chitosan and ß-ketoglutaric acid units, are characterized by UV–vis spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) as well as fluorescence correlation spectroscopy (FCS) and reveal an average diameter of about 10 nm at the end of the synthesis. The kinetics of GNP formation is studied by calculating activation parameters based on UV–vis and AFM data such as the apparent activation energy, entropy and free energy applying the concept of the Finke-Watzky model and harmonic transition state theory. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfa.2018.02.045
  • 2018 • 219 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 < 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 • 218 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 • 217 Synthesis of rare-earth metal and rare-earth metal-fluoride nanoparticles in ionic liquids and propylene carbonate
    Siebels, M. and Mai, L. and Schmolke, L. and Schütte, K. and Barthel, J. and Yue, J. and Thomas, J. and Smarsly, B.M. and Devi, A. and Fischer, R.A. and Janiak, C.
    Beilstein Journal of Nanotechnology 9 1881-1894 (2018)
    Decomposition of rare-earth tris(N, N'-diisopropyl-2-methylamidinato)metal(III) complexes [RE(MeC(N(iPr)2))3] (RE(amd)3; RE = Pr(III), Gd(III), Er(III)) and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium(III) (Eu(dpm)3) induced by microwave heating in the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm][NTf2]) and in propylene carbonate (PC) yield oxide-free rare-earth metal nanoparticles (RE-NPs) in [BMIm][NTf2] and PC for RE = Pr, Gd and Er or rare-earth metal-fluoride nanoparticles (REF3-NPs) in the fluoridedonating IL [BMIm][BF4] for RE = Pr, Eu, Gd and Er. The crystalline phases and the absence of significant oxide impurities in RE-NPs and REF3-NPs were verified by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED) and highresolution X-ray photoelectron spectroscopy (XPS). The size distributions of the nanoparticles were determined by transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to an average diameter of (11 ± 6) to (38 ± 17) nm for the REF3-NPs from [BMIm][BF4]. The RE-NPs from [BMIm][NTf2] or PC showed diameters of (1.5 ± 0.5) to (5 ± 1) nm. The characterization was completed by energy-dispersive X-ray spectroscopy (EDX). © 2018 Siebels et al.
    view abstractdoi: 10.3762/bjnano.9.180
  • 2018 • 216 Tailoring metal oxide nanoparticle dispersions for inkjet printing
    Gebauer, J.S. and Mackert, V. and Ognjanović, S. and Winterer, M.
    Journal of Colloid and Interface Science 526 400-409 (2018)
    There is a growing interest in science and industry for printed electronics. Printed electronics enable the production of large quantities of electronic components at low cost. Even though organic semiconductors are already widely used for printed components, inorganic materials may be advantageous due to their higher durability and superior device performance. Nevertheless, inorganic materials still remain difficult to print making the development of printable and functional inks a necessity. In this work we present the formulation, inkjet printing and processing of newly developed inks based on ethylene glycol as dispersion medium. Different metal oxide nanoparticles (ZnO, TiO2, CuO, SnO2 and In2O3) with high crystallinity and narrow size distribution were produced by chemical vapor synthesis. The particles were stabilized and the colloidal stability was evaluated by a combination of DLVO simulations and dynamic light scattering measurements. Measurements of rheological and interfacial properties, like viscosity and surface tension, are used to determine the printability on the basis of the inverse Ohnesorge number. Inks, developed in this work, have adjustable rheological properties as well as long-term stabilities without particle sedimentation over a period of several months. They are suitable for printing on different substrate materials like silicon and flexible polymeric substrates. © 2018 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2018.05.006
  • 2018 • 215 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 • 214 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 • 213 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 • 212 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 • 211 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 • 210 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 • 209 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 • 208 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 • 207 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 • 206 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 • 205 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 • 204 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 • 203 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 • 202 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 • 201 Localized Synthesis of Conductive Copper-Tetracyanoquinodimethane Nanostructures in Ultrasmall Microchambers for Nanoelectronics
    Xing, Y. and Sun, G. and Speiser, E. and Esser, N. and Dittrich, P.S.
    ACS Applied Materials and Interfaces 9 17271-17278 (2017)
    In this work, the microfluidic-assisted synthesis of copper-tetracyanoquinodimethane (Cu-TCNQ) nanostructures in an ambient environment is reported for the first time. A two-layer microfluidic device comprising parallel actuated microchambers was used for the synthesis and enabled excellent fluid handling for the continuous and multiple chemical reactions in confined ultrasmall chambers. Different precautions were applied to ensure the reduction state of copper (Cu) for the synthesis of Cu-TCNQ charge-transfer compounds. The localized synthesis of Cu and in situ transformation to Cu-TCNQ complexes in solution were achieved by applying different gas pressures in the control layer. Additionally, various diameters of the Cu-TCNQ nano/microstructures were obtained by adjusting the concentration of the precursors and reaction time. After the synthesis, platinum (Pt) microelectrode arrays, which were aligned at the microchambers, could enable the in situ measurements of the electronic properties of the synthesized nanostructures without further manipulation. The as-prepared Cu-TCNQ wire bundles showed good conductivity and a reversible hysteretic switching effect, which proved the possibility in using them to build advanced nanoelectronics. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsami.7b01664
  • 2017 • 200 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 • 199 Microanalysis of single-layer hexagonal boron nitride islands on Ir(111)
    Petrović, M. and Hagemann, U. and Horn-von Hoegen, M. and Meyer zu Heringdorf, F.-J.
    Applied Surface Science 420 504-510 (2017)
    Large hexagonal boron nitride (hBN) single-layer islands of high crystalline quality were grown on Ir(111) via chemical vapor deposition (CVD) and have been studied with low-energy electron microscopy (LEEM). Two types of hBN islands have been observed that structurally differ in their shape and orientation with respect to iridium, where the former greatly depends on the iridium step morphology. Photoemission electron microscopy (PEEM) and IV-LEEM spectroscopy revealed that the two island types also exhibit different work functions and bindings to iridium, which provides an explanation for differences in their shape and growth modes. In addition, various temperatures were used for the CVD synthesis of hBN, and it was found that at temperatures higher than ≈950 °C boron atoms, originating either from decomposed borazine molecules or disintegrated hBN islands, can form additional compact reconstructed regions. The presented results are important for advancement in synthesis of high-quality hBN and other boron-based layered materials, and could therefore expedite their technological implementation. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.05.155
  • 2017 • 198 Micrometer-sized nano-structured silicon/carbon composites for lithium-ion battery anodes synthesized based on a three-step Hansen solubility parameter (HSP) concept
    Sehlleier, Y.H. and Dobrowolny, S. and Xiao, L. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Industrial and Engineering Chemistry 52 305-313 (2017)
    The processing towards Si/C composites, components and synthesis parameters were selected based on the concept of Hansen solubility parameters (HSP). Si/polymer composites were generated through modified bulk polymerization and subsequent pyrolysis transformed the polymer into the desired porous carbon matrix. Coulombic efficiencies (CE) in excess of 76% after the first cycle and 99.95% after solid electrolyte interphase (SEI) formation have been achieved. A notably high specific delithiation capacity of around 1600 mAh/g with an extremely stable cycling performance even after 400 cycles is obtained. This scalable and economical synthesis approach is readily applicable to the commercial production of anode materials. © 2017 The Korean Society of Industrial and Engineering Chemistry
    view abstractdoi: 10.1016/j.jiec.2017.04.001
  • 2017 • 197 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 • 196 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 • 195 Nanophase Segregation of Self-Assembled Monolayers on Gold Nanoparticles
    Meena, S.K. and Goldmann, C. and Nassoko, D. and Seydou, M. and Marchandier, T. and Moldovan, S. and Ersen, O. and Ribot, F. and Chanéac, C. and Sanchez, C. and Portehault, D. and Tielens, F. and Sulpizi, M.
    ACS Nano 11 7371-7381 (2017)
    Nanophase segregation of a bicomponent thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of interchain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by transmission electron microscopy and electron tomography, using silica selective heterogeneous nucleation on acid-rich domains to provide electron contrast, supports simulations and highlights patchy nanoparticles with a trend toward Janus nano-objects depending on the nature of the ligands and the particle size. These results validate our computational platform as an effective tool to predict nanophase separation in organic mixtures on a surface and drive further exploration of advanced nanoparticle functionalization. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.7b03616
  • 2017 • 194 New amidinate complexes of indium(III): Promising CVD precursors for transparent and conductive In2O3 thin films
    Gebhard, M. and Hellwig, M. and Kroll, A. and Rogalla, D. and Winter, M. and Mallick, B. and Ludwig, Ar. and Wiesing, M. and Wieck, A.D. and Grundmeier, G. and Devi, A.
    Dalton Transactions 46 10220-10231 (2017)
    For the first time, synthesis of two new amidinate-ligand comprising heteroleptic indium complexes, namely [InCl(amd)2] (1) and [InMe(amd)2] (2), via salt-metathesis and their detailed characterization is reported. For comparison, the earlier reported homoleptic tris-amidinate [In(amd)3] (3) was also synthesized and analyzed in detail especially with respect to the thermal properties and molecular crystal structure analysis which are reported here for the first time. From nuclear magnetic resonance spectroscopy (NMR) and single-crystal X-ray diffraction (XRD), all three compounds were found to be monomeric with C2 (compound 1 and 2) and C3 symmetry (compound 3). Both halide-free compounds 2 and 3 were evaluated regarding their thermal properties using temperature-dependent 1H-NMR, thermogravimetric analysis (TGA) and iso-TGA, revealing suitable volatility and thermal stability for their application as potential precursors for chemical vapor phase thin film deposition methods. Indeed, metalorganic chemical vapor deposition (MOCVD) experiments over a broad temperature range (400 °C-700 °C) revealed the suitability of these two compounds to fabricate In2O3 thin films in the presence of oxygen on Si, thermally grown SiO2 and fused silica substrates. The as-deposited thin films were characterized in terms of their crystallinity via X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM) and composition through complementary techniques such as Rutherford-backscattering spectrometry (RBS) in combination with nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS). From UV/Vis spectroscopy, the deposited In2O3 thin films on fused silica substrates were found to be highly transparent (T > 95% at 560 nm, compound 3). In addition, Hall measurements revealed high charge carrier densities of 1.8 × 1020 cm-3 (2) and 6.5 × 1019 cm-3 (3) with a Hall-mobility of 48 cm2 V-1 s-1 (2) and 74 cm2 V-1 s-1 (3) for the respective thin films, rendering the obtained thin films applicable as a transparent conducting oxide that could be suitable for optoelectronic applications. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt01280b
  • 2017 • 193 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 • 192 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 • 191 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 • 190 Pulsed laser ablation in liquids: Impact of the bubble dynamics on particle formation
    Reich, S. and Schönfeld, P. and Wagener, P. and Letzel, A. and Ibrahimkutty, S. and Gökce, B. and Barcikowski, S. and Menzel, A. and dos Santos Rolo, T. and Plech, A.
    Journal of Colloid and Interface Science 489 106-113 (2017)
    Pulsed laser ablation in liquids (PLAL) is a multiscale process, involving multiple mutually interacting phenomena. In order to synthesize nanoparticles with well-defined properties it is important to understand the dynamics of the underlying structure evolution. We use visible-light stroboscopic imaging and X-ray radiography to investigate the dynamics occurring during PLAL of silver and gold on a macroscopic scale, whilst X-ray small angle scattering is utilized to deepen the understanding on particle genesis. By comparing our results with earlier reports we can elucidate the role of the cavitation bubble. We find that symmetry breaking at the liquid-solid interface is a critical factor for bubble motion and that the bubble motion acts on the particle distribution as confinement and retraction force to create secondary agglomerates. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2016.08.030
  • 2017 • 189 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 • 188 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 • 187 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 • 186 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 • 185 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 • 184 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 • 183 The Space Confinement Approach Using Hollow Graphitic Spheres to Unveil Activity and Stability of Pt-Co Nanocatalysts for PEMFC
    Pizzutilo, E. and Knossalla, J. and Geiger, S. and Grote, J.-P. and Polymeros, G. and Baldizzone, C. and Mezzavilla, S. and Ledendecker, M. and Mingers, A. and Cherevko, S. and Schüth, F. and Mayrhofer, K.J.J.
    Advanced Energy Materials 7 (2017)
    The performance of polymer electrolyte fuel cells is strongly correlated to the electrocatalytic activity and stability. In particular, the latter is the result of an interplay between different degradation mechanisms. The essential high stability, demanded for real applications, requires the synthesis of advanced electrocatalysts that withstand the harsh operation conditions. In the first part of this study, the synthesis of oxygen reduction electrocatalysts consisting of Pt-Co (i.e., Pt5Co, Pt3Co, and PtCo) alloyed nanoparticles encapsulated in the mesoporous shell of hollow graphitic spheres (HGS) is reported. The mass activities of the activated catalysts depend on the initial alloy composition and an activity increase on the order of two to threefold, compared to pure Pt@HGS, is achieved. The key point of the second part is the investigation of the degradation of PtCo@HGS (showing the highest activity). Thanks to pore confinement, the impact of dissolution/dealloying and carbon corrosion can be studied without the interplay of other degradation mechanisms that would induce a substantial change in the particle size distribution. Therefore, impact of the upper potential limit and the scan rates on the dealloying and electrochemical surface area evolution can be examined in detail. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/aenm.201700835
  • 2017 • 182 Unearthing [3-(Dimethylamino)propyl]aluminium(III) Complexes as Novel Atomic Layer Deposition (ALD) Precursors for Al2O3: Synthesis, Characterization and ALD Process Development
    Mai, L. and Gebhard, M. and de los Arcos, T. and Giner, I. and Mitschker, F. and Winter, M. and Parala, H. and Awakowicz, P. and Grundmeier, G. and Devi, A.
    Chemistry - A European Journal 23 10768-10772 (2017)
    Identification and synthesis of intramolecularly donor-stabilized aluminium(III) complexes, which contain a 3-(dimethylamino)propyl (DMP) ligand, as novel atomic layer deposition (ALD) precursors has enabled the development of new and promising ALD processes for Al2O3 thin films at low temperatures. Key for this promising outcome is the nature of the ligand combination that leads to heteroleptic Al complexes encompassing optimal volatility, thermal stability and reactivity. The first ever example of the application of this family of Al precursors for ALD is reported here. The process shows typical ALD like growth characteristics yielding homogeneous, smooth and high purity Al2O3 thin films that are comparable to Al2O3 layers grown by well-established, but highly pyrophoric, trimethylaluminium (TMA)-based ALD processes. This is a significant development based on the fact that these compounds are non-pyrophoric in nature and therefore should be considered as an alternative to the industrial TMA-based Al2O3 ALD process used in many technological fields of application. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201702939
  • 2017 • 181 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 • 180 (MeZn)2(μ-η2:η2-N6Ph2): A Powerful Starting Reagent for the Synthesis of Metal Hexazene Complexes
    Stienen, C. and Gondzik, S. and Gehlhaar, A. and Haack, R. and Wölper, C. and Jansen, G. and Schulz, S.
    Organometallics 35 1022-1029 (2016)
    [(MeLDippZn)2(μ-η2:η2-PhN6Ph)] (3), which was synthesized by reaction of MeLDipp 2Zn2 with PhN3, reacts with two equivalents of Me2Zn to give [(MeZn)2(μ-η2:η2-PhN6Ph)] (2). The reaction of 2 with pyridine gave [(MeZn)2(μ-η2:η2-PhN6Ph)(Py)2] (4), while reactions with H-acidic ligands (MeLMesH, MeLPhH) occurred with elimination of methane and formation of [(MeLMesZn)2(μ-η2:η2-PhN6Ph)] (1) and [(MeLPhZn)2(μ-η2:η2-PhN6Ph)] (5). The reaction of 1 with two equivalents of MeLi yielded the heterobimetallic hexazene complex [(MeZn)(μ-η2:η2-PhN6Ph)(Li)], which was found to undergo stepwise reaction with Me2AlCl to give [MeZn(μ-η2:η2-PhN6Ph)AlMe2] and finally [(Me2Al)2(μ-η2:η2-PhN6Ph)(thf)2] (6). Compounds 3-6 were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction. Quantum chemical calculations were performed in order to investigate the electronic structure of 4′ and 6′ in more detail and to identify the absorption bands of the hexazene unit. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.6b00116
  • 2016 • 179 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 • 178 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 • 177 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 • 176 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 • 175 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 • 174 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 • 173 Controlled manipulation of the Co-Alq3 interface by rational design of Alq3 derivatives
    Großmann, N. and Magri, A. and Laux, M. and Stadtmüller, B. and Thielen, P. and Schäfer, B. and Fuhr, O. and Ruben, M. and Cinchetti, M. and Aeschlimann, M.
    45 18365-18376 (2016)
    Recently, research has revealed that molecules can be used to steer the local spin properties of ferromagnetic surfaces. One possibility to manipulate ferromagnetic-metal-molecule interfaces in a controlled way is to synthesize specific, non-magnetic molecules to obtain a desired interaction with the ferromagnetic substrate. Here, we have synthesized derivatives of the well-known semiconductor Alq3 (with q = 8-hydroxyquinolinate), in which the 8-hydroxyquinolinate ligands are partially or completely replaced by similar ligands bearing O- or N-donor sets. The goal of this study was to investigate how the presence of (i) different donor atom sets and (ii) aromaticity in different conjugated π-systems influences the spin properties of the metal-molecule interface formed with a Co(100) surface. The spin-dependent metal-molecule-interface properties have been measured by spin-resolved photoemission spectroscopy, backed up by DFT calculations. Overall, our results show that, in the case of the Co-molecule interface, chemical synthesis of organic ligands leads to specific electronic properties of the interface, such as exciton formation or highly spin-polarized interface states. We find that these properties are even additive, i.e. they can be engineered into one single molecular system that incorporates all the relevant ligands. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6dt03183h
  • 2016 • 172 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 • 171 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 • 170 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 • 169 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 • 168 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 • 167 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 • 166 Interlayer expansion using metal-linker units: Crystalline microporous silicate zeolites with metal centers on specific framework sites
    Gies, H. and Feyen, M. and De Baerdemaeker, T. and De Vos, D.E. and Yilmaz, B. and Müller, U. and Meng, X. and Xiao, F.-S. and Zhang, W. and Yokoi, T. and Tatsumi, T. and Bao, X.
    Microporous and Mesoporous Materials 222 235-240 (2016)
    Interlayer expansion using silylating agents to connect layer silicates to 3D framework structures has shown to be a versatile synthesis route to new crystalline, microporous frameworks. We demonstrate here that also Me cations can be introduced on the linker sites applying the same synthesis procedure. An acidic aqueous Fe-chloride solution was used in a hydrothermal reaction to convert the layered hydrous silicate precursor RUB-36 into an interlayer expanded zeolite, containing Fe at the linker sites, Fe-IEZ-RUB-36, Si19.14Fe0.86O38(OH)4. Structure analysis from powder X-ray data using the Rietveld technique confirmed that the porous framework is stable upon calcination and contains Fe on T-sites at the linker position. SEM-EDX analysis is in agreement with the analysis of the electron density maps showing that almost every other linker T-position is occupied by Fe-ions. The material crystallizes in the monoclinic space group Pm with a = 12.200(9) Å, b = 13.981(8) Å, c = 7.369(2) Å, and β = 106.9(1)°. Applying a similar synthesis procedure, the Sn-analog, Sn-IEZ-RUB-36, Si38.6Sn1.4O76(OH)8, has been obtained and structurally characterized. Despite its limited crystallinity, Rietveld analysis of the PXRD data set confirmed the materials framework topology and chemical composition (a = 23.856(14) Å, b = 14.103(7) Å, c = 7.412(7) Å, in SG Pnm21). We conclude, that the synthesis procedure is flexible and, meanwhile, has been extended to other metal cations such as Ti, Zn, Eu and Al leading to microporous materials with potentially active metal cations on well defined sites of the silicate framework. © 2015 Published by Elsevier Inc.
    view abstractdoi: 10.1016/j.micromeso.2015.09.051
  • 2016 • 165 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 • 164 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 • 163 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 • 162 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 • 161 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 • 160 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 • 159 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 • 158 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 • 157 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 • 156 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 • 155 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 • 154 Simultaneous introduction of various palladium active sites into MOF: Via one-pot synthesis: Pd at[Cu3- xPdx(BTC)2]n
    Zhang, W. and Chen, Z. and Al-Naji, M. and Guo, P. and Cwik, S. and Halbherr, O. and Wang, Y. and Muhler, M. and Wilde, N. and Gläser, R. and Fischer, R.A.
    Dalton Transactions 45 14883-14887 (2016)
    Simultaneous incorporation of palladium within Pd-Pd and/or Pd-Cu paddlewheels as framework-nodes and Pd nanoparticle (NP) dispersion into MOF have been achieved for the first time via one-pot synthesis. In particular, the framework substitution of Cu2+ by Pd2+ as well as the pore loading with PdNPs have been confirmed and characterized by XPS. The obtained solids featuring such multiple Pd-sites show enhanced catalytic activity in the aqueous-phase hydrogenation of p-nitrophenol (PNP) with NaBH4 to p-aminophenol (PAP). © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c6dt02893d
  • 2016 • 153 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 • 152 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 • 151 Synthesis and Structure of Bis(diphenylphosphinimino)methanide and Bis(diphenylphosphinimino)methanediide Beryllium Complexes
    Bayram, M. and Naglav, D. and Wölper, C. and Schulz, S.
    Organometallics 35 2378-2383 (2016)
    Reactions of BeEt2 with bis(diphenylphosphinimino)methanes H2C[PPh2NR]2 yielded the first bis(diphenylphosphinimino)methanide and bis(diphenylphosphinimino)methanediide beryllium complexes [CH(PPh2N-2,6-i-Pr2C6H3)2]BeEt (1), [C(PPh2NSiMe3)2](BeEt)2 (2), and [C(PPh2NPh)2](BeEt)2 (3), respectively. 1-3 were characterized by multinuclear NMR and IR spectroscopy as well as single-crystal X-ray diffraction. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.6b00380
  • 2016 • 150 Synthesis and structure of strontium ferrite nanowires and nanotubes of high aspect ratio
    Ebrahimi, F. and Ashrafizadeh, F. and Bakhshi, S.R. and Farle, M.
    Journal of Sol-Gel Science and Technology 77 708-717 (2016)
    Abstract: Strontium hexaferrite nanowires and nanotubes were synthesized in porous anodic aluminum oxide templates. Different solution-based synthesis techniques (spin coating, vacuum suction, and dip coating) were investigated. Strontium ferrite nanopowders were also synthesized by a similar sol–gel process. The morphology, structure, and composition of the embedded hexaferrite nanostructures were examined by field emission scanning electron microscope, X-ray diffraction, and transmission electron microscopy. Strontium ferrite wires with Fe/Sr ratios from 10 to 12 under different annealing temperatures of 500–700 °C were studied. The results showed that dip coating could produce fine and uniform strontium ferrite nanowires. The ratio of Fe/Sr of 11 and a calcination temperature of 650 °C were found to be optimum conditions. The produced material may be of importance for novel microwave-frequency nanoscale devices. Graphical Abstract: [Figure not available: see fulltext.] © 2015, Springer Science+Business Media New York.
    view abstractdoi: 10.1007/s10971-015-3902-2
  • 2016 • 149 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 • 148 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 • 147 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
  • 2015 • 146 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 • 145 A sterically stabilized FeI-FeI semi-rotated conformation of [FeFe] hydrogenase subsite model
    Goy, R. and Bertini, L. and Elleouet, C. and Görls, H. and Zampella, G. and Talarmin, J. and De Gioia, L. and Schollhammer, P. and Apfel, U.-P. and Weigand, W.
    Dalton Transactions 44 1690-1699 (2015)
    The [FeFe] hydrogenase is a highly sophisticated enzyme for the synthesis of hydrogen via a biological route. The rotated state of the H-cluster in the [FeIFeI] form was found to be an indispensable criteria for an effective catalysis. Mimicking the specific rotated geometry of the [FeFe] hydrogenase active site is highly challenging as no protein stabilization is present in model compounds. In order to simulate the sterically demanding environment of the nature's active site, the sterically crowded meso-bis(benzylthio)diphenylsilane (2) was utilized as dithiolate linker in an [2Fe2S] model complex. The reaction of the obtained hexacarbonyl complex 3 with 1,2-bis(dimethylphosphino)ethane (dmpe) results three different products depending on the amount of dmpe used in this reaction: [{Fe2(CO)5{μ-(SCHPh)2SiPh2}}2(μ-dmpe)] (4), [Fe2(CO)5(κ2-dmpe){μ-(SCHPh)2SiPh2}] (5) and [Fe2(CO)5(μ-dmpe){μ-(SCHPh)2SiPh2}] (6). Interestingly, the molecular structure of compound 5 shows a [FeFe] subsite comprising a semi-rotated conformation, which was fully characterized as well as the other isomers 4 and 6 by elemental analysis, IR and NMR spectroscopy, X-ray diffraction analysis (XRD) and DFT calculations. The herein reported model complex is the first example so far reported for [FeIFeI] hydrogenase model complex showing a semi-rotated geometry without the need of stabilization via agostic interactions (Fe⋯H-C). This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c4dt03223c
  • 2015 • 144 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 • 143 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 • 142 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 • 141 Controlling the Spin Texture of Topological Insulators by Rational Design of Organic Molecules
    Jakobs, S. and Narayan, A. and Stadtmüller, B. and Droghetti, A. and Rungger, I. and Hor, Y.S. and Klyatskaya, S. and Jungkenn, D. and Stöckl, J. and Laux, M. and Monti, O.L.A. and Aeschlimann, M. and Cava, R.J. and Ruben, M. an...
    15 6022-6029 (2015)
    We present a rational design approach to customize the spin texture of surface states of a topological insulator. This approach relies on the extreme multifunctionality of organic molecules that are used to functionalize the surface of the prototypical topological insulator (TI) Bi<inf>2</inf>Se<inf>3</inf>. For the rational design we use theoretical calculations to guide the choice and chemical synthesis of appropriate molecules that customize the spin texture of Bi<inf>2</inf>Se<inf>3</inf>. The theoretical predictions are then verified in angular-resolved photoemission experiments. We show that, by tuning the strength of molecule-TI interaction, the surface of the TI can be passivated, the Dirac point can energetically be shifted at will, and Rashba-split quantum-well interface states can be created. These tailored interface properties-passivation, spin-texture tuning, and creation of hybrid interface states-lay a solid foundation for interface-assisted molecular spintronics in spin-textured materials. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.5b02213
  • 2015 • 140 Effect of fluctuations on time-averaged multi-line NO-LIF thermometry measurements of the gas-phase temperature
    Feroughi, O.M. and Kronemayer, H. and Dreier, T. and Schulz, C.
    Applied Physics B: Lasers and Optics 120 429-440 (2015)
    Multi-line NO laser-induced fluorescence (LIF) thermometry enables accurate gas-phase temperature imaging in combustion systems through least-squares fitting of excitation spectra. The required excitation wavelength scan takes several minutes which systematic biases the results in case of temperature fluctuations. In this work, the effect of various types (linear, Gaussian and bimodal) and amplitudes of temperature fluctuations is quantified based on simulated NO-LIF excitation spectra. Temperature fluctuations of less than ±5 % result in a negligible error of less than ±1 % in temperature for all cases. Bimodal temperature distributions have the largest effect on the determined temperature. Symmetric temperature fluctuations around 900 K have a negligible effect. At lower mean temperatures, fluctuations cause a positive bias leading to over-predicted mean temperatures, while at higher temperatures the bias is negative. The results of the theoretical analysis were applied as a guide for interpreting experimental multi-line NO-LIF temperature measurements in a mildly turbulent pilot-plant scale flame reactor dedicated for nanoparticle synthesis. © 2015, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00340-015-6152-7
  • 2015 • 139 Effect of the addition of ethanol to synthesis gas on the production of higher alcohols over Cs and Ru modified Cu/ZnO catalysts
    Walter, K.M. and Schubert, M. and Kleist, W. and Grunwaldt, J.-D.
    Industrial and Engineering Chemistry Research 54 1452-1463 (2015)
    The addition of ethanol to synthesis gas and its influence on the production of higher alcohols (HA) was investigated over Cs- and Ru-Cu/ZnO catalysts at 320 °C and an initial pressure of 5.0 MPa in a batch reactor. A change in the reaction path from aldol-type condensation of C 1 -intermediates to homocoupling of ethanol was found upon increase of the ethanol to CO ratio. Furthermore, the productivity toward HA was enhanced for higher ethanol to CO ratios. The production of HA was maximized with the side products in an acceptable range for n EtOH :n CO = 0.5. Excess of ethanol gave lower production rates and leaching of the metals was observed. Cesium (0.3-1.0 mol %) proved to be a better dopant. Excess of Cs (3 mol %) led to a lower catalyst performance, probably due to a blockage of the active sites and a change in the reducibility of the catalyst. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/ie504066f
  • 2015 • 138 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 • 137 FIMOR: An efficient simulation for ZnO quantum dot ripening applied to the optimization of nanoparticle synthesis
    Haderlein, M. and Segets, D. and Gröschel, M. and Pflug, L. and Leugering, G. and Peukert, W.
    Chemical Engineering Journal 260 706-715 (2015)
    This work presents the application of a Fully Implicit Method for Ostwald Ripening (FIMOR) for simulating the ripening of ZnO quantum dots (QDs). Its stable numerics allow FIMOR to employ the full exponential term of the Gibbs-Thomson equation which significantly outperforms the common Taylor-approximation at typical QD sizes below 10. nm. The implementation is consistent with experimental data for temperatures between 10 and 50. °C and the computational effort is reduced by a factor of 100-1000 compared to previous approaches. This reduced the simulation time on a standard PC from several hours to a few minutes. In the second part, we demonstrate the high potential and accuracy of FIMOR by its application to several challenging studies. First, we compare numeric results obtained for ripening of ZnO QDs exposed to temperature ramps with experimental data. The deviation between simulation and experiment in the mean volume weighted particle size was as small as 5%. Second, a map for the process parameter space spanned by ripening time and temperature is created based on a large number (>50) of FIMOR runs. From this map appropriate process parameters to adjust a desired dispersity are easily deduced. Further data analysis reveals in agreement with literature findings that the particle size distribution converges towards a self-preserving stable shape. Equations describing the time dependent particle size distribution with high accuracy are presented. Finally, we realized the transfer from low volume batch experiments to continuous QD processing. We modeled the continuous ZnO synthesis in a fully automated microreaction plant and found an excellent agreement between the numeric prediction and the experimental results by considering the residence time distribution. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2014.09.040
  • 2015 • 136 High-Quality Solution-Processed Silicon Oxide Gate Dielectric Applied on Indium Oxide Based Thin-Film Transistors
    Jaehnike, F. and Pham, D.V. and Anselmann, R. and Bock, C. and Kunze, U.
    ACS Applied Materials and Interfaces 7 14011-14017 (2015)
    A silicon oxide gate dielectric was synthesized by a facile sol-gel reaction and applied to solution-processed indium oxide based thin-film transistors (TFTs). The SiO<inf>x</inf> sol-gel was spin-coated on highly doped silicon substrates and converted to a dense dielectric film with a smooth surface at a maximum processing temperature of T = 350 °C. The synthesis was systematically improved, so that the solution-processed silicon oxide finally achieved comparable break downfield strength (7 MV/cm) and leakage current densities (<10 nA/cm2 at 1 MV/cm) to thermally grown silicon dioxide (SiO<inf>2</inf>). The good quality of the dielectric layer was successfully proven in bottom-gate, bottom-contact metal oxide TFTs and compared to reference TFTs with thermally grown SiO<inf>2</inf>. Both transistor types have field-effect mobility values as high as 28 cm2/(Vs) with an on/off current ratio of 108, subthreshold swings of 0.30 and 0.37 V/dec, respectively, and a threshold voltage close to zero. The good device performance could be attributed to the smooth dielectric/semiconductor interface and low interface trap density. Thus, the sol-gel-derived SiO<inf>2</inf> is a promising candidate for a high-quality dielectric layer on many substrates and high-performance large-area applications. (Graph Presented). © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b03105
  • 2015 • 135 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 • 134 Influence of carbon content, particle size, and partial manganese substitution on the electrochemical performance of LiFexMn1-xPO4/carbon composites
    Hamid, N.A. and Wennig, S. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Ionics 21 1857-1866 (2015)
    LiFePO<inf>4</inf>/C and LiFe<inf>x</inf>Mn<inf>1-x</inf>PO<inf>4</inf>/C (x = 0.7) nanocomposites were successfully synthesized via scalable spray-flame synthesis followed by solid-state reaction. A solution of iron (III) acetylacetonate and tributyl phosphate in toluene was used to produce amorphous, nanosized FePO<inf>4</inf>⋅H<inf>2</inf>O in a spray-flame reactor which was then milled with Li<inf>2</inf>CO<inf>3</inf> and glucose to produce a LiFePO<inf>4</inf>/C composite material in a solid-state reaction. The influence of calcination temperature and carbon content on the properties of the resulting material was investigated using specific surface area measurements (BET), X-ray diffraction (XRD), electron microscopy, and electrochemical characterization. The impact of manganese addition on the electrochemical behavior was analyzed using cyclic voltammetry (CV) and constant-current (CC) measurements. XRD shows that the combination of gas-phase synthesis and subsequent solid-state reaction yields highly pure LiFePO<inf>4</inf>/C. BET measurement revealed that the particle size of LiFePO<inf>4</inf> in the composite depends on the amount of glucose. A discharge capacity of more than 140 mAh/g at C/20 is achieved for LiFePO<inf>4</inf>/C with a carbon content of 6 wt%. This material supports high charge as well as discharge rates delivering more than 60 mAh/g at 16 C and sustains good cycle stability providing 115 mAh/g at 1 C. The energy density of the olivine increases about 10 % by substituting 30 mol% of iron by manganese while preserving the electrochemical performance of pure LiFePO<inf>4</inf>/C. © 2015, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s11581-015-1366-6
  • 2015 • 133 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 • 132 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 • 131 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 • 130 Mechanism of protection of catalysts supported in redox hydrogel films
    Fourmond, V. and Stapf, S. and Li, H. and Buesen, D. and Birrell, J. and Rüdiger, O. and Lubitz, W. and Schuhmann, W. and Plumeré, N. and Léger, C.
    Journal of the American Chemical Society 137 5494-5505 (2015)
    The use of synthetic inorganic complexes as supported catalysts is a key route in energy production and in industrial synthesis. However, their intrinsic oxygen sensitivity is sometimes an issue. Some of us have recently demonstrated that hydrogenases, the fragile but very efficient biological catalysts of H<inf>2</inf> oxidation, can be protected from O<inf>2</inf> damage upon integration into a film of a specifically designed redox polymer. Catalytic oxidation of H<inf>2</inf> produces electrons which reduce oxygen near the film/solution interface, thus providing a self-activated protection from oxygen [Plumeré et al., Nat Chem. 2014, 6, 822-827]. Here, we rationalize this protection mechanism by examining the time-dependent distribution of species in the hydrogenase/polymer film, using measured or estimated values of all relevant parameters and the numerical and analytical solutions of a realistic reaction-diffusion scheme. Our investigation sets the stage for optimizing the design of hydrogenase-polymer films, and for expanding this strategy to other fragile catalysts. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/jacs.5b01194
  • 2015 • 129 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 • 128 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 • 127 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 • 126 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 • 125 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 • 124 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 • 123 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 • 122 Record figure of merit values of highly stoichiometric Sb2Te3 porous bulk synthesized from tailor-made molecular precursors in ionic liquids
    Heimann, S. and Schulz, S. and Schaumann, J. and Mudring, A. and Stötzel, J. and MacUlewicz, F. and Schierning, G.
    Journal of Materials Chemistry C 3 10375-10380 (2015)
    We report on the synthesis of Sb2Te3 nanoparticles with record-high figure of merit values of up to 1.5. The central thermoelectric parameters, electrical conductivity, thermal conductivity and Seebeck coefficient, were independently optimized. The critical influence of porosity for the fabrication of highly efficient thermoelectric materials is firstly demonstrated, giving a strong guidance for the optimization of other thermoelectric materials. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5tc01248a
  • 2015 • 121 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 • 120 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 • 119 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 • 118 Strategies for permanent immobilization of enzymes on textile carriers
    Kiehl, K. and Straube, T. and Opwis, K. and Gutmann, J.S.
    Engineering in Life Sciences 15 622-626 (2015)
    The economical use of expensive enzymes in chemical synthesis can be improved by the immobilization of the catalyst on a suitable support material. Textile fabrics made of polyester, polyamide, or cotton represent comparatively inexpensive alternative carrier materials in contrast to conventional supports. Textile-inherent advantages like its flexible and lightweight construction allow the use in reactors of arbitrary geometry, a quick separation from the reaction liquor, and the generation of residue-free product. A low preparative and economical expense is needed to prepare fabrics with high enzyme loads (20-70 mg enzyme/g textile carrier), high relative activity (up to 20%) and excellent permanence against enzyme desorption as well. In this study, we present different strategies for the covalent fixation of enzymes on fiber forming polymers such as photochemical grafting, the use of bifunctional anchor molecules, monomeric, and polymeric cross-linking agents or specific enzyme modification for direct immobilization. In addition, we compare the strategies in terms of load, catalytic activity, and reusability. All presented immobilization methods yield products, which exhibit a considerable activity even after twenty recycling steps. In conclusion, we have successfully identified textiles as alternative, new and promising low cost carrier materials for enzymes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/elsc.201400148
  • 2015 • 117 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 • 116 Synthesis and characterization of bimetallic metal-organic framework Cu-Ru-BTC with HKUST-1 structure
    Gotthardt, M.A. and Schoch, R. and Wolf, S. and Bauer, M. and Kleist, W.
    Dalton Transactions 44 2052-2056 (2015)
    The bimetallic metal-organic framework Cu-Ru-BTC with the stoichiometric formula Cu2.75Ru0.25(BTC)2·xH2O, which is isoreticular to HKUST-1, was successfully prepared in a direct synthesis using mild reaction conditions. The partial substitution of Cu2+ by Ru3+ centers in the paddlewheel structure and the absence of other Ru-containing phases was proven using X-ray absorption spectroscopy. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4dt02491e
  • 2015 • 115 Synthesis and X-ray Crystal Structure of Diimidosulfinate Transition Metal Complexes
    Bayram, M. and Bläser, D. and Wölper, C. and Schulz, S.
    Organometallics 34 3421-3427 (2015)
    Bis(trimethylsilyl)sulfurdiimide S(NSiMe3)2 reacts with equimolar amounts of Me2Zn and Cp∗2Zn either with insertion into the metal-carbon bond and formation of the expected S-methyl diimidosulfinate complex [MeZnN(SiMe3)S(Me)NSiMe3]2 1 or the unexpected complex {Me3SiNS[N(SiMe3)SNSiMe3]N(SiMe3)Zn}2 2. Insertion reactions were also observed with Cp∗MMe3 (M = Ti, Zr, Hf), yielding Cp∗(Me)2M[Me3SiNS(Me)NSiMe3] (M = Ti 3, Zr 4, Hf 5), whereas the corresponding Cl-substituted derivatives Cp∗(Cl)2M[(Me3SiNS(Me)NSiMe3] (M = Ti 6, Zr 7, Hf 8) were obtained from salt elimination reactions of Li S-methyl diimidosulfinate (Me3SiN)2S(Me)Li(thf)]2 9 with Cp∗MCl3. Compounds 1-8 were characterized by heteronuclear NMR (1H and 13C) and IR spectroscopy, and the solid state structures of 1-5 and 9 were determined by single crystal X-ray diffraction. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.5b00407
  • 2015 • 114 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 • 113 The effect of the Au loading on the liquid-phase aerobic oxidation of ethanol over Au/TiO2 catalysts prepared by pulsed laser ablation
    Dong, W. and Reichenberger, S. and Chu, S. and Weide, P. and Ruland, H. and Barcikowski, S. and Wagener, P. and Muhler, M.
    Journal of Catalysis 330 497-506 (2015)
    Gold nanoparticles (NPs) synthesized by pulsed laser ablation of a gold target in water were efficiently deposited on TiO<inf>2</inf> (P25) without any post-treatment yielding catalysts with Au loadings up to 10 wt%. Regardless of the loading, the Au NPs had a mean diameter of 8 nm before and after deposition. The ligand-free Au NPs strongly bind to TiO<inf>2</inf> surface oxygen vacancies and maintain a homogeneous distribution with loadings up to 4 wt%, while a further increase in Au content up to 10 wt% results in additional weakly adsorbed Au NPs. The catalytic tests of the Au/TiO<inf>2</inf> samples in the selective oxidation of ethanol in the liquid phase identified an optimal loading of 4 wt% resulting in the highest yield of acetic acid, which is ascribed to the homogeneous Au distribution and the adequate occupation of surface oxygen vacancies by strongly bound Au NPs without significant Au sintering during reaction. © 2015 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2015.07.033
  • 2015 • 112 The Mechanism of CO and CO2 Hydrogenation to Methanol over Cu-Based Catalysts
    Studt, F. and Behrens, M. and Kunkes, E.L. and Thomas, N. and Zander, S. and Tarasov, A. and Schumann, J. and Frei, E. and Varley, J.B. and Abild-Pedersen, F. and Nørskov, J.K. and Schlögl, R.
    ChemCatChem 7 1105-1111 (2015)
    Methanol, an important chemical, fuel additive, and precursor for clean fuels, is produced by hydrogenation of carbon oxides over Cu-based catalysts. Despite the technological maturity of this process, the understanding of this apparently simple reaction is still incomplete with regard to the reaction mechanism and the active sites. Regarding the latter, recent progress has shown that stepped and ZnO<inf>x</inf>-decorated Cu surfaces are crucial for the performance of industrial catalysts. Herein, we integrate this insight with additional experiments into a full microkinetic description of methanol synthesis. In particular, we show how the presence or absence of the Zn promoter dramatically changes not only the activity, but unexpectedly the reaction mechanism itself. The Janus-faced character of Cu with two different sites for methanol synthesis, Zn-promoted and unpromoted, resolves the long-standing controversy regarding the Cu/Zn synergy and adds methanol synthesis to the few major industrial catalytic processes that are described on an atomic level. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cctc.201500123
  • 2015 • 111 The Yin and Yang in the development of catalytic processes: Catalysis research and reaction engineering
    Prieto, G. and Schüth, F.
    Angewandte Chemie - International Edition 54 3222-3239 (2015)
    A synergetic interplay: Catalysis is a key research field within BASF. Successful industrial chemistry is always the result of a combination of catalyst and process development. The interplay of catalyst chemistry and reaction engineering is discussed for processes such as the sulfuric acid production, ammonia synthesis, methanol synthesis, fluid catalytic cracking, and direct epoxidation of propylene. (Figure Presented). © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201409885
  • 2015 • 110 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 • 109 Two step and one step preparation of porous nanocomposite cellulose membranes doped with TiO2
    Wittmar, A. and Vorat, D. and Ulbricht, M.
    RSC Advances 5 88070-88078 (2015)
    Cellulose-TiO2 nanocomposites have been successfully prepared by non-solvent induced phase separation from cellulose acetate solutions in classical organic solvents followed by deacetylation ("regeneration"). The cellulose deacetylation has been performed either sequentially, i.e. after the completion of the phase separation process, or simultaneously, i.e. during the phase separation process. Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as a dispersion in the respective polymer solutions. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Special attention has been given to the complex relation between the conditions of the deacetylation process, the structure of the resulting TiO2 doped cellulose membranes and their corresponding catalytic activities. Two catalytic activity tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the functional characterization of the TiO2 doped nanocomposites. The performed experiments demonstrated the successful photocatalyst immobilization in porous cellulose acetate together with good catalytic activity of this nanocomposite intermediate. By simply varying the conditions of the cellulose deacetylation, nanocomposite cellulose membranes with different structures and properties have been obtained. However after the regeneration of cellulose a partial decrease of the catalytic activity was observed. © 2015 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5ra16337d
  • 2015 • 108 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 • 107 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 • 106 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 • 105 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 • 104 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 • 103 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 • 102 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 • 101 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 • 100 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 • 99 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 • 98 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 • 97 Energetics of the water-gas-shift reaction on the active sites of the industrially used Cu/ZnO/Al2O3 catalyst
    Studt, F. and Behrens, M. and Abild-Pedersen, F.
    Catalysis Letters 144 1973-1977 (2014)
    The energy profile for the water-gas-shift reaction has been calculated on the active sites of the industrially used Cu/ZnO/Al2O3 catalyst using the BEEF-vdW functional. Our theoretical results suggest that both active site motifs, a copper (211) step as well as a zinc decorated step, are equally active for the water-gas-shift reaction. We find that the splitting of water into surface OH∗and H∗constitutes the rate-limiting step and that the reaction proceeds through the carboxyl mechanism. Our findings also suggest that mixed copper-zinc step sites are most likely to exhibit superior activity. © Springer Science+Business Media New York 2014.
    view abstractdoi: 10.1007/s10562-014-1363-9
  • 2014 • 96 Enthalpies of formation of europium alkoxides: What lessons can be drawn from them
    Branco, J.B. and Carretas, J.M. and Epple, M. and Cruz, A. and Pires De Matos, A. and Leal, J.P.
    Journal of Chemical Thermodynamics 75 20-24 (2014)
    The synthesis and characterization of two europium alkoxides, Eu(OCH 3)2 and Eu(OC2H5)2, were described. For the first time the enthalpies of formation of divalent lanthanide alkoxides were determined by using reaction-solution calorimetry. The values obtained are ΔfH0 [Eu(OCH3) 2,cr] = -850.5 ± 5.0 kJ/mol and Δf H0 [Eu(OC2H5)2,cr] = -902.5 ± 5.5 kJ/mol, respectively. Since these compounds have a large use as catalysts or catalysts precursors, the first step of the reaction of them with CO 2 was addressed, which permits to have an idea of the kind of bond involved in those compounds. Moreover, insertion of CO2 in the europium oxygen bond and formation of metal carboxylate complexes, is in both cases presumably bidentate. © 2014 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.jct.2014.04.009
  • 2014 • 95 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 • 94 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 • 93 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 • 92 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 • 91 Indium-tris-guanidinates: A promising class of precursors for water assisted atomic layer deposition of In2O3 thin films
    Gebhard, M. and Hellwig, M. and Parala, H. and Xu, K. and Winter, M. and Devi, A.
    Dalton Transactions 43 937-940 (2014)
    Two closely related mononuclear homoleptic indium-tris-guanidinate complexes have been synthesized and characterized as precursors for atomic layer deposition (ALD) of In2O3. In a water assisted ALD process, high quality In2O3 thin films have been fabricated for the first time using the new class of precursors as revealed by the promising ALD growth characteristics and film properties. © The Royal Society of Chemistry 2014.
    view abstractdoi: 10.1039/c3dt52746h
  • 2014 • 90 Investigation on the effectiveness of chemically synthesized nano cement in controlling the physical and mechanical performances of concrete
    Jo, B.W. and Chakraborty, S. and Kim, K.H.
    Construction and Building Materials 70 1-8 (2014)
    Present investigation deals with the effectiveness of the chemically synthesized nano cement in controlling physical and mechanical performances of concrete. In this investigation, concrete samples were fabricated using variable amounts of aggregates and alkali activator content w.r.t. weight of nano cement. Based on the mechanical properties analyses, it is assessed that chemically synthesized cement is able to produce 43 MPa compressive strength of concrete after 14 days curing instead of 28 days at an optimized amount of aggregates content as well as alkali activator content. Finally, a model has been proposed to explain the overall performances of nano cement based concrete. © 2014 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.conbuildmat.2014.07.090
  • 2014 • 89 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 • 88 Novel β-ketoiminato complexes of zirconium: Synthesis, characterization and evaluation for solution based processing of ZrO2 thin films
    Banerjee, M. and Seidel, R.W. and Winter, M. and Becker, H.-W. and Rogalla, D. and Devi, A.
    Dalton Transactions 43 2384-2396 (2014)
    Treatment of tetrakis(diethylamido)zirconium(iv); [Zr(NEt2) 4] with a series of β-ketoimines ({[RHN]C(CH3)C(H) C(CH3)O} where R is a functionalized side-chain; 4-(2- methoxyethylamino)pent-3-en-2-one, Hmeap; 4-(3-methoxypropylamino)pent-3-en-2- one, Hmpap; 4-(2-(dimethylamino)ethylamino)pent-3-en-2-one, Hdeap; 4-(3-(dimethylamino)propylamino)pent-3-en-2-one, Hdpap) leads to an amine substitution reaction that yielded novel monomeric heteroleptic mixed amido-ketoiminato complexes of the type bis(4-(2-methoxyethylamino)pent-3-en-2- onato)bis(diethylamido)zirconium(iv) (1), bis(4-(3-methoxypropylamino)pent-3-en- 2-onato)bis(diethylamido)zirconium(iv) (2), and bis(4-(3-(dimethylamino) propylamino)pent-3-en-2-onato)bis(diethylamido)zirconium(iv) (3), and eight-coordinated homoleptic complexes tetrakis(4-(2-methoxyethylamino)pent-3- en-2-onato)zirconium(iv) (4) and tetrakis(4-(2-(dimethylamino)ethylamino)pent-3- en-2-onato)zirconium(iv) (5), depending on the ratio of the ligand to zirconium. Adopting a similar strategy with zirconium alkoxide, namely [Zr(O iPr)4·iPrOH], with β-ketoimine Hmeap, leads to the formation of a dimer, bis(μ2-isopropoxo)bis(4- (2-methoxyethylamino)pent-3-en-2-onato)tetrakis(isopropoxo)dizirconium(iv) (6). The newly synthesised complexes were characterized by NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, elemental analysis and thermal analysis. The low decomposition temperature facilitated by the stepwise elimination of the ketominate ligand from the complex and the stability of the complexes obtained in air as well as in solution makes them highly suitable for solution based processing of ZrO2 thin films, which is demonstrated using compound 5 on Si(100) substrates. High quality ZrO2 films were obtained and were investigated for their structure, morphology, composition and optical properties. Low temperature crystallisation of ZrO2 is achieved by a simple chemical deposition process using the new class of Zr precursors and the films exhibit an optical transmittance above 90%. © 2014 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3dt52335g
  • 2014 • 87 Ruthenium complexes as precursors for chemical vapor-deposition (CVD)
    Gaur, R. and Mishra, L. and Siddiqi, M.A. and Atakan, B.
    RSC Advances 4 33785-33805 (2014)
    Ruthenium and its compounds are often used as thin films and can be deposited by chemical vapor deposition. The quality of the films strongly depends on the inorganic precursors, their evaporation behaviour and thermochemistry. This is an area where different aspects of inorganic chemistry and chemical engineering must fit together to provide good thin films. It was noticed that providing firsthand information in one place especially for a learner of this area of research, and collection of reports on different types of ruthenium complexes as CVD precursors would be timely. Thus, in this review a bird's eye view of ruthenium complexes suitable for CVD technology, together with the presentation of different precursors, their synthesis, evaporation, decomposition and film formation is presented. A brief summary of the CVD technique is also presented with future-design, synthesis and usefulness of CVD precursors. This journal is © the Partner Organisations 2014.
    view abstractdoi: 10.1039/c4ra04701j
  • 2014 • 86 Stable performance of Ni catalysts in the dry reforming of methane at high temperatures for the efficient conversion of CO2 into syngas
    Mette, K. and Kühl, S. and Düdder, H. and Kähler, K. and Tarasov, A. and Muhler, M. and Behrens, M.
    ChemCatChem 6 100-104 (2014)
    The catalytic performance of a Ni/MgAlOx catalyst was investigated in the high temperature CO2 reforming of CH4. The catalyst was developed using a Ni, Mg, Al hydrotalcite-like precursor obtained by co-precipitation. Despite the high Ni loading of 55 wt%, the synthesized Ni/MgAlOx catalyst possessed a thermally stable microstructure up to 900 °C with Ni nanoparticles of 9 nm. This stability is attributed to the embedding nature of the oxide matrix, and allows increasing the reaction temperature without losing active Ni surface area. To evaluate the effect of the reaction temperature on the reforming performance and the coking behavior, two different reaction temperatures (800 and 900 °C) were investigated. At both temperatures the prepared catalyst showed high rates of CH4 consumption. The higher temperature promotes the stability of the catalyst performance due to mitigation of the carbon formation. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201300699
  • 2014 • 85 Stable zinc oxide nanoparticle dispersions in ionic liquids
    Wittmar, A. and Gautam, D. and Schilling, C. and Dörfler, U. and Mayer-Zaika, W. and Winterer, M. and Ulbricht, M.
    Journal of Nanoparticle Research 16 (2014)
    The influence of the hydrophilicity and length of the cation alkyl chain in imidazolium-based ionic liquids on the dispersability of ZnO nanoparticles by ultrasound treatment was studied by dynamic light scattering and advanced rheology. ZnO nano-powder synthesized by chemical vapor synthesis was used in parallel with one commercially available material. Before preparation of the dispersion, the nanoparticles characteristics were determined by transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Hydrophilic ionic liquids dispersed all studied nanopowders better and in the series of hydrophilic ionic liquids, an improvement of the dispersion quality with increasing length of the alkyl chain of the cation was observed. Especially, for ionic liquids with short alkyl chain, additional factors like nanoparticle concentration in the dispersion and the period of the ultrasonic treatment had significant influence on the dispersion quality. Additionally, nanopowder characteristics (crystallite shape and size as well as the agglomeration level) influenced the dispersion quality. The results indicate that the studied ionic liquids are promising candidates for absorber media at the end of the gas phase synthesis reactor allowing the direct preparation of non-agglomerated nanoparticle dispersions without supplementary addition of dispersants and stabilizers. © Springer Science+Business Media 2014.
    view abstractdoi: 10.1007/s11051-014-2341-2
  • 2014 • 84 Surface functionalization of microwave plasma-synthesized silica nanoparticles for enhancing the stability of dispersions
    Sehlleier, Y.H. and Abdali, A. and Schnurre, S.M. and Wiggers, H. and Schulz, C.
    Journal of Nanoparticle Research 16 (2014)
    Gas phase-synthesized silica nanoparticles were functionalized with three different silane coupling agents (SCAs) including amine, amine/phosphonate and octyltriethoxy functional groups and the stability of dispersions in polar and non-polar dispersing media such as water, ethanol, methanol, chloroform, benzene, and toluene was studied. Fourier transform infrared spectroscopy showed that all three SCAs are chemically attached to the surface of silica nanoparticles. Amine-functionalized particles using steric dispersion stabilization alone showed limited stability. Thus, an additional SCA with sufficiently long hydrocarbon chains and strong positively charged phosphonate groups was introduced in order to achieve electrosteric stabilization. Steric stabilization was successful with hydrophobic octyltriethoxy-functionalized silica nanoparticles in non-polar solvents. The results from dynamic light scattering measurements showed that in dispersions of amine/phosphonate- and octyltriethoxy-functionalized silica particles are dispersed on a primary particle level. Stable dispersions were successfully prepared from initially agglomerated nanoparticles synthesized in a microwave plasma reactor by designing the surface functionalization. © 2014 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-014-2557-1
  • 2014 • 83 Syntheses and structures of bis-amidinate-alane complexes
    Bayram, M. and Bläser, D. and Wölper, C. and Schulz, S.
    Organometallics 33 2080-2087 (2014)
    Insertion reactions of α,ω-bis-carbodiimides (RNCN) 2X (1-5: R = Et, t-Bu, Ph; X = C3H6, C 4H8) with 2 equiv of AlMe3 yielded the dinuclear tethered bis-amidinate-alane complexes [RNC(Me)NAlMe2] 2X (R = Et, X = C4H8 (6); R = t-Bu, X = C 3H6 (7), C4H8 (8)). Analogous reactions with 4 equiv of AlMe3 resulted in the coordination of two additional AlMe3 molecules, yielding the tetranuclear bis-amidinate complexes [EtN(AlMe3)C(Me)NAlMe2]2X (X = C 3H6 (9), C4H8 (10)) and [t-BuNC(Me)N(AlMe3)AlMe2]2X (X = C 3H6 (11), C4H8 (12)). In addition, equimolar reactions between (RNCN)2X (R = Et, X = C3H 6, C4H8; R = Ph, X = C4H 8) and 2 equiv of AlMe3 at elevated temperatures occurred with intramolecular cyclization and formation of [EtNC(Me)NC3H 6N(AlMe3)CNEt]AlMe2 (13) and [RNC(Me)NC 4H8N(AlMe3)CNR]AlMe2 (R = Et (14), Ph (15)). Hydrolysis of 11 gave the protonated free ligand PhNC(Me)NC 4H8N(H)CNPh (16) in high yield. 6-16 were characterized by elemental analyses, multinuclear NMR (1H, 13C) and IR spectroscopy, and single-crystal X-ray diffraction (7, 10-14, 16). © 2014 American Chemical Society.
    view abstractdoi: 10.1021/om5002217
  • 2014 • 82 Synthesis of α,ω-isocyanate telechelic polymethacrylate soft segments with activated ester side functionalities and their use for polyurethane synthesis
    Eschweiler, N. and Keul, H. and Millaruelo, M. and Weberskirch, R. and Moeller, M.
    Polymer International 63 114-126 (2014)
    Isocyanate homo telechelic poly(methyl methacrylate-co-acryloxy succinimide) and poly(methyl methacrylate-co-acrylamidohexanoic succinimide) were prepared and used as soft segments for polyurethanes. Polymer structures are characterized by SEC, Raman, and 1H NMR spectroscopy. The synthetic route for the preparation of α,ω-isocyanate-telechelic poly(methyl methacrylate-co-acryloxysuccinimide) and α,ω- isocyanate-telechelic poly(methyl methacrylate-co-acrylamidohexanoic succinimide) soft segments is presented. The strategy includes reversible addition fragmentation chain transfer (RAFT) copolymerization and two post polymerization modification steps. The RAFT polymerizations result in copolymers with an activated ester proportion within the polymer chains of 8% N-acryloxysuccinimide and 5% 6-acrylamidohexanoic succinimide. The reactivity ratios of the monomer pairs were determined. In a first post polymerization reaction carboxylic acid homo telechelic polymers were prepared by reacting the ω-dithiobenzoate end-group with an excess of azobis(cyanovaleric acid). In a second modification step the α- and ω-carboxylic acid end-groups were reacted with hexamethylene diisocyanate and 100% isocyanate telechelic copolymers were obtained. Finally segmented polyurethanes were prepared by coupling hexamethylene diisocyanate (HDI) end capped soft segments with hard segments composed of 1,4-butanediol and HDI. © 2013 Society of Chemical Industry.
    view abstractdoi: 10.1002/pi.4535
  • 2014 • 81 The influence of kinetics, mass transfer and catalyst deactivation on the growth rate of multiwalled carbon nanotubes from ethene on a cobalt-based catalyst
    Voelskow, K. and Becker, M.J. and Xia, W. and Muhler, M. and Turek, T.
    Chemical Engineering Journal 244 68-74 (2014)
    CNT growth experiments on a cobalt-based catalyst were conducted in a tubular fixed bed reactor at different temperatures and ethene concentrations. The measured kinetic data were analyzed with an isothermal, dynamic reactor model taking into account pore and film diffusion as well as the size of CNT agglomerates as a function of time. Based on previously published results it was found that the CNT agglomerates are enlarged by an average factor of 6.5 compared to the original diameter of the catalyst particle. Under these conditions, the development of the agglomerate diameter with time can be described with a single parameter which is independent of the reaction conditions. The rate of the CNT growth was determined to be first order in the ethene concentration with an activation energy of 107. kJ/mol. The catalyst deactivation by cumulative encapsulation of active sites was found to be second order with respect to the consumed amount of ethene with a rate constant independent of the temperature. Nevertheless, deactivation takes place faster at higher temperatures and/or ethene concentrations, since the deactivation process is directly coupled to the rate of CNT synthesis. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2014.01.024
  • 2014 • 80 Ultrasmall dispersible crystalline nickel oxide nanoparticles as high-performance catalysts for electrochemical water splitting
    Fominykh, K. and Feckl, J.M. and Sicklinger, J. and Döblinger, M. and Böcklein, S. and Ziegler, J. and Peter, L. and Rathousky, J. and Scheidt, E.-W. and Bein, T. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 24 3123-3129 (2014)
    Ultrasmall, crystalline, and dispersible NiO nanoparticles are prepared for the first time, and it is shown that they are promising candidates as catalysts for electrochemical water oxidation. Using a solvothermal reaction in tert-butanol, very small nickel oxide nanocrystals can be made with sizes tunable from 2.5 to 5 nm and a narrow particle size distribution. The crystals are perfectly dispersible in ethanol even after drying, giving stable transparent colloidal dispersions. The structure of the nanocrystals corresponds to phase-pure stoichiometric nickel(ii) oxide with a partially oxidized surface exhibiting Ni(iii) states. The 3.3 nm nanoparticles demonstrate a remarkably high turn-over frequency of 0.29 s-1 at an overpotential of g = 300 mV for electrochemical water oxidation, outperforming even expensive rare earth iridium oxide catalysts. The unique features of these NiO nanocrystals provide great potential for the preparation of novel composite materials with applications in the field of (photo)electrochemical water splitting. The dispersed colloidal solutions may also find other applications, such as the preparation of uniform hole-conducting layers for organic solar cells. Ultrasmall, crystalline, and dispersible NiO nanoparticles are prepared for the first time using a solvothermal reaction in tert-butanol. These nanocrystals can be prepared with sizes tunable from 2.5 to 5 nm and are highly efficient catalysts for electrochemical oxygen generation. © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201303600
  • 2013 • 79 A thermoelectric generator concept using a p-n junction: Experimental proof of principle
    Becker, A. and Chavez, R. and Petermann, N. and Schierning, G. and Schmechel, R.
    Journal of Electronic Materials 42 2297-2300 (2013)
    Conventional thermoelectric generators (TEGs) use single p- and n-doped legs for thermoelectric energy harvesting. We explore a concept using thermoelectric p-n junctions made from densified silicon nanoparticles. The nanoparticle powder was synthesized in a microwave plasma reactor using silane, diborane and phosphine as precursors. To achieve a bulk sample with a p-n junction, a layer of boron-doped nanoparticle powder was stacked on a layer of phosphorus-doped powder and compacted by current-activated pressure- assisted densification. To use the p-n structure as a TEG, a temperature gradient was applied along the p-n junction. It is expected that this temperature gradient leads to electron-hole pair generation and separation in the junction and diffusion of the charge carriers. A reference method was used to characterize the open-circuit voltage of the p-n junction TEG. © 2013 TMS.
    view abstractdoi: 10.1007/s11664-012-2399-5
  • 2013 • 78 Blocked-micropores, surface functionalized, bio-compatible and silica-coated iron oxide nanocomposites as advanced MRI contrast agent
    Darbandi, M. and Laurent, S. and Busch, M. and Li, Z.-A. and Yuan, Y. and Krüger, M. and Farle, M. and Winterer, M. and Vander Elst, L. and Muller, R.N. and Wende, H.
    Journal of Nanoparticle Research 15 (2013)
    Biocompatible magnetic nanoparticles have been found promising in several biomedical applications for tagging, imaging, sensing and separation in recent years. In this article, a systematic study of the design and development of surface-modification schemes for silica-coated iron oxide nanoparticles (IONP) via a one-pot, in situ method at room temperature is presented. Silica-coated IONP were prepared in a water-in-oil microemulsion, and subsequently the surface was modified via addition of organosilane reagents to the microemulsion system. The structure and the morphology of the as synthesized nanoparticles have been investigated by means of transmission electron microscopy (TEM) and measurement of N2 adsorption-desorption. Electron diffraction and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the IONP structures. Nitrogen adsorption indicates microporous and blocked-microporous structures for the silica-coated and amine functionalized silica-coated IONP, respectively which could prove less cytotoxicity of the functionalized final product. Besides, the colloidal stability of the final product and the presence of the modified functional groups on top of surface layer have been proven by zeta-potential measurements. Owing to the benefit from the inner IONP core and the hydrophilic silica shell, the as-synthesized nanocomposites were exploited as an MRI contrast enhancement agent. Relaxometric results prove that the surface functionalized IONP have also signal enhancement properties. These surface functionalized nanocomposites are not only potential candidates for highly efficient contrast agents for MRI, but could also be used as ultrasensitive biological-magnetic labels, because they are in nanoscale size, having magnetic properties, blocked-microporous and are well dispersible in biological environment. © 2013 Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-013-1664-8
  • 2013 • 77 Buoyancy induced limits for nanoparticle synthesis experiments in horizontal premixed low-pressure flat-flame reactors
    Weise, C. and Faccinetto, A. and Kluge, S. and Kasper, T. and Wiggers, H. and Schulz, C. and Wlokas, I. and Kempf, A.
    Combustion Theory and Modelling 17 504-521 (2013)
    Premixed low-pressure flat-flame reactors can be used to investigate the synthesis of nanoparticles. The present work examines the flow field inside such a reactor during the formation of carbon (soot) and iron oxide (from Fe(CO)5) nanoparticles, and how it affects the measurements of nanoparticle size distribution. The symmetry of the flow and the impact of buoyancy were analysed by three-dimensional simulations and the nanoparticle size distribution was obtained by particle mass spectrometry (PMS) via molecular beam sampling at different distances from the burner. The PMS measurements showed a striking, sudden increase in particle size at a critical distance from the burner, which could be explained by the flow field predicted in the simulations. The simulation results illustrate different fluid mechanical phenomena which have caused this sudden rise in the measured particle growth. Up to the critical distance, buoyancy does not affect the flow, and an (almost) linear growth is observed in the PMS experiments. Downstream of this critical distance, buoyancy deflects the hot gas stream and leads to an asymmetric flow field with strong recirculation. These recirculation zones increase the particle residence time, inducing very large particle sizes as measured by PMS. This deviation from the assumed symmetric, one-dimensional flow field prevents the correct interpretation of the PMS results. To overcome this problem, modifications to the reactor were investigated; their suitability to reduce the flow asymmetry was analysed. Furthermore, 'safe' operating conditions were identified for which accurate measurements are feasible in premixed low-pressure flat-flame reactors that are transferrable to other experiments in this type of reactor. The present work supports experimentalists to find the best setup and operating conditions for their purpose. © 2013 Copyright Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/13647830.2013.781224
  • 2013 • 76 Correlation of electronic and magnetic properties of thin polymer layers with cobalt nanoparticles
    Kharchenko, A. and Lukashevich, M. and Popok, V. and Khaibullin, R. and Valeev, V. and Bazarov, V. and Petracic, O. and Wieck, A. and Odzhaev, V.
    Particle and Particle Systems Characterization 30 180-184 (2013)
    Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co+ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non-monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin-dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 1017 cm-2) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs. Nanoparticles of cobalt are synthesized in shallow layers of polyimide using low-energy implantation of cobalt ions. Nucleation of individual particles and their percolation are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites. By tuning the implantation regimes magnetoresistance and transitions between the superparamagnetic and ferromagnenic behavior can be controlled. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppsc.201200042
  • 2013 • 75 Designing magnetic field responsive nanofiltration membranes
    Yang, Q. and Himstedt, H.H. and Ulbricht, M. and Qian, X. and Ranil Wickramasinghe, S.
    Journal of Membrane Science 430 70-78 (2013)
    Base, thin film composite polyamide, nanofiltration membranes have been modified using surface initiated atom transfer radical polymerization to graft poly(2-hydroxyethyl methacrylate) (polyHEMA) chains from the surface of the membrane. A modified Gabriel synthesis procedure was used to attach superparamagnetic (Fe3O4) nanoparticles to the chain ends. Chain density and chain length were independently varied by adjusting the initiator density and polymerization time. Membranes were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The performance of modified membranes was investigated by determining deionized water fluxes as well as permeate fluxes and salt rejection for aqueous feed streams containing 500ppm CaCl2 and 2000ppm MgSO4. All experiments were conducted in dead end mode. Modified membranes display a reduced permeate flux and increased salt rejection compared to unmodified membranes in the absence of a magnetic field. Since both grafted chain density and chain length are expected to affect membrane performance differently, the decrease in permeate flux and increase in salt rejection is not directly proportional to the increase in grafted polymer weight. Modified membranes display both increased permeate fluxes and increased salt rejection in the presence of an oscillating magnetic field compared to their performance in the absence of an oscillating magnetic field. Magnetically responsive membranes could represent a new class of fouling resistant membranes. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2012.11.068
  • 2013 • 74 Direct gas-phase synthesis of single-phase β-FeSi2 nanoparticles
    Bywalez, R. and Orthner, H. and Mehmedovic, E. and Imlau, R. and Kovacs, A. and Luysberg, M. and Wiggers, H.
    Journal of Nanoparticle Research 15 (2013)
    For the first time, phase-pure β-FeSi2 nanoparticles were successfully produced by gas-phase synthesis. We present a method to fabricate larger quantities of semiconducting β-FeSi2 nanoparticles, with crystallite sizes between 10 and 30 nm, for solar and thermoelectric applications utilizing a hot-wall reactor. A general outline for the production of those particles by thermal decomposition of silane and iron pentacarbonyl is provided based on kinetic data. The synthesized particles are investigated by X-ray diffraction and transmission electron microscopy, providing evidence that the as-prepared materials are indeed β-FeSi2, while revealing morphological characteristics inherent to the nanoparticles created. © 2013 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-013-1878-9
  • 2013 • 73 Effect of carrier gas composition on transferred arc metal nanoparticle synthesis
    Stein, M. and Kiesler, D. and Kruis, F.E.
    Journal of Nanoparticle Research 15 (2013)
    Metal nanoparticles are used in a great number of applications; an effective and economical production scaling-up is hence desirable. A simple and cost-effective transferred arc process is developed, which produces pure metal (Zn, Cu, and Ag) nanoparticles with high production rates, while allowing fast optimization based on energy efficiency. Different carrier gas compositions, as well as the electrode arrangements and the power input are investigated to improve the production and its efficiency and to understand the arc production behavior. The production rates are determined by a novel process monitoring method, which combines an online microbalance method with a scanning mobility particle sizer for fast production rate and size distribution measurement. Particle characterization is performed via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction measurements. It is found that the carrier gas composition has the largest impact on the particle production rate and can increase it with orders of magnitude. This appears to be not only a result of the increased heat flux and melt temperature but also of the formation of tiny nitrogen (hydrogen) bubbles in the molten feedstock, which impacts feedstock evaporation significantly in bi-atomic gases. A production rate of sub 200 nm particles from 20 up to 2,500 mg/h has been realized for the different metals. In this production range, specific power consumptions as low as 0.08 kWh/g have been reached. © 2013 Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-012-1400-9
  • 2013 • 72 Fundamental studies on the electrocatalytic properties of metal macrocyclics and other complexes for the electroreduction of O2
    Masa, J. and Ozoemena, K.I. and Schuhmann, W. and Zagal, J.H.
    Lecture Notes in Energy 9 157-212 (2013)
    The high prospects of exploiting the oxygen reduction reaction (ORR) for lucrative technologies, for example, in the fuel cells industry, chlor-alkali electrolysis, and metal-air batteries, to name but a few, have prompted enormous research interest in the search for cost-effective and abundant catalysts for the electrocatalytic reduction of oxygen. This chapter describes and discusses the electrocatalysis of oxygen reduction by metallomacrocyclic complexes and the prospect of their potential to be used in fuel cells. Since the main interest of most researchers in this field is to design catalysts which can achieve facile reduction of O2 at a high thermodynamic efficiency, this chapter aims to bring to light the research frontiers uncovering important milestones towards the synthesis and design of promising metallomacrocyclic catalysts which can accomplish the four-electron reduction of O2 at low overpotential and to draw attention to the fundamental requirements for synthesis of improved catalysts. Particular attention has been paid to discussion of the common properties which cut across these complexes and how they may be aptly manipulated for tailored catalyst synthesis. Therefore, besides discussion of the progress attained with regard to synthesis and design of catalysts with high selectivity towards the four-electron reduction of O2, a major part of this chapter highlights quantitative structure-activity relationships (QSAR) which govern the activity and stability of these complexes, which when well understood, refined, and carefully implemented should lead to rational design of better catalysts. A brief discussion about nonmacrocyclic copper (I) complexes, particularly Cu(I) phenanthrolines, and those with a laccase-like structure which exhibit promising activity for ORR has been included in a separate section at the end. © Springer-Verlag London 2013.
    view abstractdoi: 10.1007/978-1-4471-4911-8_7
  • 2013 • 71 Impact of rapid thermal annealing on thermoelectric properties of bulk nanostructured zinc oxide
    Engenhorst, M. and Gautam, D. and Schilling, C. and Winterer, M. and Schierning, G. and Schmechel, R.
    Materials Research Society Symposium Proceedings 1543 99-104 (2013)
    In search for non-toxic thermoelectric materials that are stable in air at elevated temperatures, zinc oxide has been shown to be one of only few efficient n-type oxidic materials. Our bottom-up approach starts with very small (< 10 nm) Al-doped ZnO nanoparticles prepared from organometallic precursors by chemical vapor synthesis using nominal doping concentrations of 2 at% and 8 at%. In order to obtain bulk nanostructured solids, the powders were compacted in a current-activated pressure-assisted densification process. Rapid thermal annealing was studied systematically as a means of further dopant activation. The thermoelectric properties are evaluated with regard to charge carrier concentration and mobility. A Jonker-type analysis reveals the potential of our approach to achieve high power factors. In the present study, power factors larger than 4× 10-4 Wm-1K-2 were measured at temperatures higher than 600 °C. © 2013 Materials Research Society.
    view abstractdoi: 10.1557/opl.2013.932
  • 2013 • 70 Influence of the cation alkyl chain length of imidazolium-based room temperature ionic liquids on the dispersibility of TiO2 nanopowders
    Wittmar, A. and Gajda, M. and Gautam, D. and Dörfler, U. and Winterer, M. and Ulbricht, M.
    Journal of Nanoparticle Research 15 (2013)
    The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO2 nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO2 nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation. © 2013 Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-013-1463-2
  • 2013 • 69 N-doped carbon synthesized from N-containing polymers as metal-free catalysts for the oxygen reduction under alkaline conditions
    Zhao, A. and Masa, J. and Muhler, M. and Schuhmann, W. and Xia, W.
    Electrochimica Acta 98 139-145 (2013)
    Nitrogen-doped carbon materials were synthesized and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR) under alkaline conditions. The synthesis was achieved by thermal treatment of nitrogen-containing polymers diluted in different carbon materials. Polypyrrole, polyaniline and polyacrylonitrile were used as N precursors. Carbon black and two types of commercial carbon nanotubes were used as carbon matrices. The obtained N contents were in the range of 1-1.8 wt.%. Different N species including pyridinic, pyrrolic and quaternary N were quantitatively determined by X-ray photoelectron spectroscopy. The ORR activities were evaluated in 0.1 M KOH. Rotating disc electrode studies revealed the presence of multiple active centers in all the samples. The sample obtained using polypyrrole and small diameter nanotubes (ca. 15 nm) had the highest onset potential at -0.07 V vs. Ag/AgCl/3 M KCl, which also showed a significantly higher electrochemical stability than the sample from carbon black and polypyrrole. The ORR activity was not correlated to the total nitrogen amount, but to the amount of pyridinic and quaternary N species. For the onset potential and the (Npyridinic + Nquaternary)/Ntotal ratio a quasi-linear relation was found, which points to the substantial role of pyridinic- and quaternary-N species in ORR catalysis. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2013.03.043
  • 2013 • 68 Nano-gold diggers: Au-Assisted SiO2-decomposition and desorption in supported nanocatalysts
    Ono, L.K. and Behafarid, F. and Cuenya, B.R.
    ACS Nano 7 10327-10334 (2013)
    An investigation of the thermal stability of size-selected Au nanoparticles (NPs) synthesized via inverse micelle encapsulation and deposited on SiO 2(4 nm)/Si(100) is presented. The size and mobility of individual Au NPs after annealing at elevated temperatures in ultrahigh vacuum (UHV) was monitored via atomic force microscopy (AFM). An enhanced thermal stability against coarsening and lack of NP mobility was observed up to 1343 K. In addition, a drastic decrease in the average NP height was detected with increasing annealing temperature, which was not accompanied by the sublimation of Au atoms/clusters in UHV. The apparent decrease in the Au NP height observed is assigned to their ability to dig vertical channels in the underlying SiO 2 support. More specifically, a progressive reduction in the thickness of the SiO2 support underneath and in the immediate vicinity of the NPs was evidenced, leading to NPs partially sinking into the SiO2 substrate. The complete removal of silicon oxide in small patches was observed to take place around the Au NPs after annealing at 1343 K in UHV. These results reveal a Au-assisted oxygen desorption from the support via reverse oxygen spillover to the NPs. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/nn404744b
  • 2013 • 67 Optical investigation of carbon nanotube agglomerate growth on single catalyst particles
    Voelskow, K. and Nickelsen, L. and Becker, M.J. and Xia, W. and Muhler, M. and Kunz, U. and Weber, A.P. and Turek, T.
    Chemical Engineering Journal 234 74-79 (2013)
    A setup for optically monitoring the agglomerate growth of multiwalled carbon nanotubes (MWCNTs) by catalytic chemical vapor deposition on single Co-Mn-Al-Mg oxide catalyst particles with ethene as carbon precursor has been developed. Ethene concentrations and temperatures were varied between 5. -75. Vol.% and 550-770. °C, respectively. It could be shown that the agglomerate growth is rapid and the final diameter is reached after a few ten seconds to about 3. min depending on the reaction conditions. The average enlargement factor of the agglomerates over all experiments was found to be 6.5. ±. 1.2 compared to the original diameter of the catalyst particle. The growth rate is enhanced by both, reaction temperature and ethene concentration. Hence it is concluded that the agglomerate growth rate is associated with the reaction rate of MWCNT synthesis. Short time experiments and analysis of the resulting agglomerates have confirmed an earlier proposed growth mechanism. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.cej.2013.08.068
  • 2013 • 66 Particle size effect in methane activation over supported palladium nanoparticles
    Ota, A. and Kunkes, E.L. and Kröhnert, J. and Schmal, M. and Behrens, M.
    Applied Catalysis A: General 452 203-213 (2013)
    A synthesis method for producing MgAl oxide supported uniform palladium nanoparticles with varying diameters has been developed. The method consists of reductive-thermal decomposition of a PdMgAl hydrotalcite-like compound, formed via co-precipitation of metal nitrate salts and sodium carbonate. The hydrotalcite-like precursors were characterized by XRD, TG-MS and SEM, and were found to contain a well-defined crystalline structure and a uniform distribution of all constituent elements. The resulting catalysts were characterized by XRD, TEM, Chemisorption of CO and in situ IR measurements of CO, and were found to consist of partially oxide-embedded Pd nanoparticles with diameters ranging from d = 1.7 to 3.3 nm and correspond dispersions of 67-14%. Furthermore, the particle size was found to be inversely related to Pd loading. The palladium catalysts were studied for methane activation via chemisorption at 200 and 400°C followed by a temperature programmed surface hydrogenation. The most disperse catalyst (d = 1.7 nm) possessed an intrinsic methane adsorption capacity, which was an order of magnitude larger than that of other catalysts in the series, indicating a strong structure sensitivity in this reaction. Additionally, the methane adsorption capacity of the hydrotalcite-derived Pd catalysts was nearly two orders of magnitude higher than that of catalysts derived through other synthesis pathways such as colloidal deposition or sonochemical reduction. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.apcata.2012.11.021
  • 2013 • 65 Polyoxometalate-stabilized, water dispersible Fe2Pt magnetic nanoparticles
    Seemann, K.M. and Bauer, A. and Kindervater, J. and Meyer, M. and Besson, C. and Luysberg, M. and Durkin, P. and Pyckhout-Hintzen, W. and Budisa, N. and Georgii, R. and Schneider, C.M. and Kögerler, P.
    Nanoscale 5 2511-2519 (2013)
    Magnetic Fe2Pt core-shell nanoparticles with 2 nm cores were synthesized with a monolayer coating of silicotungstate Keggin clusters. The core-shell composition is substantiated by structural analysis performed using high-resolution scanning transmission electron microscopy (HR-STEM) and small angle X-ray scattering (SAXS) in a liquid suspension. The molecular metal oxide cluster shell introduces an enhanced dispersibility of the magnetic Fe-Pt core-shell nanoparticles in aqueous media and thereby opens up new routes to nanoparticle bio-functionalization, for example, using pre-functionalized polyoxometalates. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3nr33374d
  • 2013 • 64 Rheological studies on PNIPAAm hydrogel synthesis via in situ polymerization and on resulting viscoelastic properties
    Adrus, N. and Ulbricht, M.
    Reactive and Functional Polymers 73 141-148 (2013)
    Bulk poly(N-isopropylacrylamide) hydrogels were prepared via free radical polymerization. Two different initiation methods were studied: redox- and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion (>95%) and adjustable swelling were only obtained by selecting best suited initiation conditions. For redox polymerization, this was achieved by tuning the ratio of accelerator N,N,N′,N′-tetramethylethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoiniated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels, in particular for the integration of smart soft matrices within membrane pores or other microsystems via a rapid reaction. Rheology was also used to investigate the hydrogel after ex situ preparation, revealing "perfect" soft-rubbery behavior. A good correlation between the mesh sizes determined from swelling and rheology was also found. In conclusion, rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character. © 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.reactfunctpolym.2012.08.015
  • 2013 • 63 Silver-doped calcium phosphate nanoparticles: Synthesis, characterization, and toxic effects toward mammalian and prokaryotic cells
    Peetsch, A. and Greulich, C. and Braun, D. and Stroetges, C. and Rehage, H. and Siebers, B. and Köller, M. and Epple, M.
    Colloids and Surfaces B: Biointerfaces 102 724-729 (2013)
    Spherical silver-doped calcium phosphate nanoparticles were synthesized in a co-precipitation route from calcium nitrate/silver nitrate and ammonium phosphate in a continuous process and colloidally stabilized by carboxymethyl cellulose. Nanoparticles with 0.39wt% silver content and a diameter of about 50-60nm were obtained. The toxic effects toward mammalian and prokaryotic cells were determined by viability tests and determination of the minimal inhibitory and minimal bactericidal concentrations (MIC and MBC). Three mammalian cells lines, i.e. human mesenchymal stem cells (hMSC) and blood peripheral mononuclear cells (PBMC, monocytes and T-lymphocytes), and two prokaryotic strains, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used. Silver-doped calcium phosphate nanoparticles and silver acetate showed similar effect toward mammalian and prokaryotic cells with toxic silver concentrations in the range of 1-3μgmL-1. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2012.09.040
  • 2013 • 62 Structural mimicking of inorganic catalyst supports with polydivinylbenzene to improve performance in the selective aerobic oxidation of ethanol and glycerol in water
    Richter, F.H. and Meng, Y. and Klasen, T. and Sahraoui, L. and Schüth, F.
    Journal of Catalysis 308 341-351 (2013)
    Many forms of polymers have been prepared and studied as polymeric catalyst support for metal nanoparticles and solid acid catalysts. The nanocasted mesoporous polydivinylbenzene (PDVB)-supported platinum catalysts presented here are distinguished by their customized mesoporosity and bulk morphology that are comparable to typical carbon-and alumina-supported powdered catalysts. Platinum nanoparticles are deposited on PDVB at loadings between 1 wt% and 9 wt% and a mean size between 2.7 nm and 6.2 nm, dependent on the synthesis method. Bifunctional catalysts containing platinum and acidic functionality are prepared by gas-phase sulfonation of the Pt/PDVB catalysts. The PDVB-supported catalysts are active for the oxidation of ethanol with molecular oxygen in water with up to 94% yield of acetic acid. In the analogous oxidation of glycerol, up to 60% yield of glyceric acid is reached with the bifunctional catalyst, and the polymer-supported catalysts feature lower formation of unidentified side products than Pt/C and Pt/Al2O3. Altogether, we find the polymers to be more active than the alumina and more selective than the carbon supports and thus overall have optimized performance. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2013.08.014
  • 2013 • 61 Synthesis and characterization of surface functional polymer nanoparticles by a bottom-up approach from tailor-made amphiphilic block copolymers
    Engelhardt, N. and Ernst, A. and Kampmann, A.-L. and Weberskirch, R.
    Macromolecular Chemistry and Physics 214 2783-2791 (2013)
    Core-crosslinked nanoparticles presenting secondary amine functional groups in the hydrophilic shell are synthesized by a bottom-up approach. The route utilizes polymerization of 2-oxazolines to prepare tailor-made block copolymers with a primary or secondary amine end group in the hydrophilic block and alkynyl moieties in the hydrophobic part of the polymer. Upon solubilization in the aqueous media, these block copolymers form micelles that are photocrosslinked by a radical polymerization process to afford two types of core-crosslinked nanoparticles, either with secondary amines, NP1, or primary amines, NP2, on the surface. The dimensions and stability of the core-crosslinked nanoparticles are characterized by dynamic light scattering and fluorescence spectroscopy. The availability and reactivity of the amine groups in the hydrophilic shell are demonstrated by reaction with different aromatic model compounds resulting in a degree of surface functionalization of 4-47% for NP1 nanoparticles with secondary amino groups and a 20-95% degree of surface functionalization for NP2 with primary amine groups, as determined by UV-vis spectroscopy. Core-crosslinked nanoparticles with surface functional groups are interesting materials for medical applications. Micelle formation of amphiphilic block copolymers with two orthogonal chemical groups is used to prepare core-crosslinked nanoparticles by UV-irradiation of the alkynyl moieties in the hydrophobic block. Further surface functionalization is achieved via primary or secondary amine end groups in the hydrophilic shell. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/macp.201300573
  • 2013 • 60 Synthesis of α,ω-isocyanate-telechelic poly(methyl methacrylate-co-allyl methacrylate) soft segments
    Greving, N. and Keul, H. and Millaruelo, M. and Weberskirch, R. and Moeller, M.
    European Polymer Journal 49 235-246 (2013)
    Isocyanate homo telechelic poly(methyl methacrylate-co-allyl methacrylate)s were prepared and used as soft segments for thermoplastic polyurethanes. Copolymerization of allyl methacrylate and methyl methacrylate by RAFT leads to selective conversion of the methacrylate C,C double bonds, leaving the allyl groups in the polymer side chain intact. A hetero telechelic MMA/AMA copolymer (Het-PMMA/AMA, molar ratio of MMA/AMA = 10/1) with a carboxylic acid and a dithiobenzoate terminus was obtained using 4,4-azobis(4-cyano pentanoic acid) as initiator and 4-cyano pentanoic acid dithiobenzoate as chain transfer agent. In a second reaction step the dithiobenzoate terminus is converted to carboxylic acid groups by a radical exchange reaction. The carboxylic acid homo telechelic statistical copolymer (Ca-Hot-PMMA/AMA) is converted quantitatively by reaction with hexamethylene diisocyanate in order to form isocyanate homo telechelic copolymer (Is-Hot-PMMA/AMA). Last the obtained soft segments were used for polyurethane synthesis. The well-defined polymer structures are characterized by SEC, Raman, and 1H NMR spectroscopy.© 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.eurpolymj.2012.09.018
  • 2013 • 59 The origin of thermochromic behavior in distibines: Still an open question
    Schulz, S. and Heimann, S. and Kuczkowski, A. and Bläser, D. and Wölper, C.
    Organometallics 32 3391-3394 (2013)
    A detailed structural investigation of Sb2Et4 using an in situ crystallization technique clearly shows that thermochromic behavior of distibines cannot be solely attributed to the formation of intermolecular Sb···Sb interactions in the solid state. Both the yellow and the red phase of Sb2Et4 showed almost identical bond lengths and angles including rather short intermolecular Sb·· ·Sb bond distances. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/om4003413
  • 2013 • 58 The structural and electronic promoting effect of nitrogen-doped carbon nanotubes on supported Pd nanoparticles for selective olefin hydrogenation
    Chen, P. and Chew, L.M. and Kostka, A. and Muhler, M. and Xia, W.
    Catalysis Science and Technology 3 1964-1971 (2013)
    A high-performance Pd catalyst for selective olefin hydrogenation was synthesized by supporting Pd nanoparticles on nitrogen-doped carbon nanotubes (NCNTs). X-ray diffraction, hydrogen chemisorption, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize Pd supported on NCNTs and nitrogen-free oxygen-functionalized CNTs (OCNTs). The Pd nanoparticles were stabilized on NCNTs with narrower size distribution compared with OCNTs. The XPS analysis revealed that the nitrogen functional groups favor the reduction of Pd on CNTs suggesting an electronic promoter effect. The Pd/NCNT catalyst showed extraordinary catalytic performance in terms of activity, selectivity and stability in the selective hydrogenation of cyclooctadiene, which is related to the structural and electronic promoting effect of the NCNT support. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3cy00097d
  • 2013 • 57 The transition from spark to arc discharge and its implications with respect to nanoparticle production
    Hontañón, E. and Palomares, J.M. and Stein, M. and Guo, X. and Engeln, R. and Nirschl, H. and Kruis, F.E.
    Journal of Nanoparticle Research 15 (2013)
    The synthesis of nanoparticles by means of electrical discharges between two electrodes in an inert gas at atmospheric pressure, as driven by a constant current ranging from a few milliamps to tens of amps, is investigated in this work. An extensive series of experiments are conducted with copper as a consumable electrode and pure nitrogen as the inert gas. Three different DC power supplies are used to drive electrical discharges for the entire operating current range. Then, three electrical discharge regimes (spark, glow, and arc) with distinct voltage-current characteristics and plasma emission spectra are recognized. For the first time, nanoparticles are synthesized by evaporation of an electrode by atmospheric pressure inert gas DC glow discharge of a few millimeters in size. The discharge regimes are characterized in terms of the mass output rate and the particle size distribution of the copper aerosols by means of online (tapered element oscillating microbalance, TEOM; and scanning mobility particle sizer, SPMS) and offline (gravimetric analysis; small and wide angle X-ray scattering, SWAXS; and transmission electron microscopy, TEM) techniques. The electrical power delivered to the electrode gap and the gas flow rate are two major parameters determining the aerosol mass output rate and the aerosol particle size distribution. The mass output rate of copper aerosols raises from 2 mg h-1 to 2 g h-1 when increasing the electrical power from 9 to 900 W. The particle mean size (SMPS dg) varies between 20 and 100 nm depending upon the electrical power and the gas flow rate, whereas the particle size dispersion (SMPS σg) ranges from 1.4 to 1.7 and is only weakly dependent on the gas flow rate. © 2013 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-013-1957-y
  • 2013 • 56 Towards the understanding of sintering phenomena at the nanoscale: Geometric and environmental effects
    Behafarid, F. and Roldan Cuenya, B.
    Topics in Catalysis 56 1542-1559 (2013)
    One of the technologically most important requirements for the application of supported metal nanoparticles (NPs) to the field of heterogeneous catalysis is the achievement of thermally and chemically stable systems under reaction conditions. For this purpose, a thorough understanding of the different pathways underlying coarsening phenomena is needed. In particular, in depth knowledge must be achieved on the role of the NP synthesis method, geometrical features of the NPs (size and shape), initial NP dispersion on the support (interparticle distance), support pre-treatment (affecting its morphology and chemical state), and reaction environment (gaseous or liquid medium, pressure, temperature). This study provides examples of the stability and sintering behavior of nanoscale systems monitored ex situ, in situ, and under operando conditions via transmission electron microscopy, atomic force microscopy, scanning tunneling microscopy, and X-ray absorption fine-structure spectroscopy. Experimental data corresponding to physical-vapor-deposited and micelle-synthesized metal (Pt, Au) NPs supported on TiO<inf>2</inf>, SiO<inf>2</inf> and Al<inf>2</inf>O <inf>3</inf> will be used to illustrate Ostwald-ripening and diffusion coalescence processes. In addition, the role of the annealing environment (H<inf>2</inf>, O<inf>2</inf>, water vapor) on the stability of NPs will be discussed. © 2013 Springer Science+Business Media New York.
    view abstractdoi: 10.1007/s11244-013-0149-4
  • 2012 • 55 A new synthesis route for Os-complex modified redox polymers for potential biofuel cell applications
    Pöller, S. and Beyl, Y. and Vivekananthan, J. and Guschin, D.A. and Schuhmann, W.
    Bioelectrochemistry 87 178-184 (2012)
    A new synthesis route for Os-complex modified redox polymers was developed. Instead of ligand exchange reactions for coordinative binding of suitable precursor Os-complexes at the polymer, Os-complexes already exhibiting the final ligand shell containing a suitable functional group were bound to the polymer via an epoxide opening reaction. By separation of the polymer synthesis from the ligand exchange reaction at the Os-complex, the modification of the same polymer backbone with different Os-complexes or the binding of the same Os-complex to a number of different polymer backbones becomes feasible. In addition, the Os-complex can be purified and characterized prior to its binding to the polymer. In order to further understand and optimize suitable enzyme/redox polymer systems concerning their potential application in biosensors or biofuel cells, a series of redox polymers was synthesized and used as immobilization matrix for Trametes hirsuta laccase. The properties of the obtained biofuel cell cathodes were compared with similar biocatalytic interfaces derived from redox polymers obtained via ligand exchange reaction of the parent Os-complex with a ligand integrated into the polymer backbone during the polymer synthesis. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.bioelechem.2011.11.015
  • 2012 • 54 Characterization of oxidation and reduction of Pt-Ru and Pt-Rh-Ru alloys by atom probe tomography and comparison with Pt-Rh
    Li, T. and Bagot, P.A.J. and Marquis, E.A. and Tsang, S.C.E. and Smith, G.D.W.
    Journal of Physical Chemistry C 116 17633-17640 (2012)
    Pt-based alloys containing Rh and Ru are effective catalysts in a range of applications, including pollution control and low-temperature fuel cells. As the Pt group metals are generally rare and expensive, minimizing the loading of them while also increasing the efficiency of catalyst materials is a continual challenge in heterogeneous catalysis. A smart method to "nanoengineer" the surface of the nanocatalyst particles would greatly aid this goal. In our study, the oxidation of a Pt-8.9 at. % Ru alloy between 773 and 973 K and the oxidation and oxidation/reduction behavior of a Pt-23.9 at. % Rh-9.7 at. % Ru alloy at 873 K for various exposure times were studied using atom probe tomography. The surface of the Pt-Ru alloy is enriched with Ru after oxidation at 773 K, whereas it is depleted in Ru at 873 K, and at 973 K. The surface oxide layer vanishes at higher temperatures, leaving behind a Pt-rich surface. In the case of the Pt-Rh-Ru alloy, oxidation initiates from the grain boundaries, forming an oxide with a stoichiometry of MO 2. As the oxidation time increases, this oxide evolves into a twophase nanostructure, involving a Rh-rich oxide phase (Rh, Ru) 2O 3 and a Ru-rich oxide phase (Ru, Rh)O 2. When this two-phase oxide is reduced in hydrogen at low temperatures, separate Rh-rich and Ru-rich nanoscale regions remain. This process could, therefore, be useful for synthesizing complex island structures on Pt-Rh-Ru nanoparticle catalysts. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jp304359m
  • 2012 • 53 Chemical vapor functionalization: A continuous production process for functionalized ZnO nanoparticles
    Ali, M. and Donakowski, M.D. and Mayer, C. and Winterer, M.
    Journal of Nanoparticle Research 14 (2012)
    The continuous functionalization of nanoparticles in the gas-phase directly after their generation, chemical vapor functionalization, is studied with ZnO and 1-hexanol as a model system using two reactors in series. In the first reactor ZnO nanoparticles are synthesized in the gas-phase from diethylzinc and oxygen at 1,073 K with grain sizes of 13 nm as determined by Rietveld refinement of X-ray diffractograms. The second reactor, connected at the exit of the first reactor and kept at lower temperatures (573, 673, and 773 K), is used as a functionalization chamber. At the connection point of the two reactors, the vapor of 1-hexanol is injected to react with the surface of ZnO nanoparticles in the gas phase. The process has been analyzed by quadrupole mass spectrometry to obtain information about optimal conditions for functionalization. Dynamic light scattering data show that the functionalized particles have substantially improved colloidal dispersibility with hydrodynamic diameters of 60 nm. Diffuse reflectance fourier transform infrared spectra and 1H nuclear magnetic resonance spectra are consistent with 1-hexanol adsorbed at the particle surface acting as a functionalizing agent. The agglomerate size is substantially reduced owing to chemical vapor functionalization. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-011-0689-0
  • 2012 • 52 Coarsening phenomena of metal nanoparticles and the influence of the support pre-treatment: Pt/TiO 2(110)
    Behafarid, F. and Roldan Cuenya, B.
    Surface Science 606 908-918 (2012)
    One of the technologically most important requirements for the application of oxide-supported metal nanoparticles (NPs) in the fields of molecular electronics, plasmonics, and catalysis is the achievement of thermally stable systems. For this purpose, a thorough understanding of the different pathways underlying thermally-driven coarsening phenomena, and the effect of the nanoparticle synthesis method, support morphology, and degree of support reduction on NP sintering is needed. In this study, the sintering of supported metal NPs has been monitored via scanning tunneling microscopy combined with simulations following the Ostwald ripening and diffusion-coalescence models. Modifications were introduced to the diffusion-coalescence model to incorporate the correct temperature dependence and energetics. Such methods were applied to describe coarsening phenomena of physical-vapor deposited (PVD) and micellar Pt NPs supported on TiO 2(110). The TiO 2(110) substrates were exposed to different pre-treatments, leading to reduced, oxidized and polymer-modified TiO 2 surfaces. Such pre-treatments were found to affect the coarsening behavior of the NPs. No coarsening was observed for the micellar Pt NPs, maintaining their as-prepared size of ~ 3 nm after annealing in UHV at 1060 °C. Regardless of the initial substrate pre-treatment, the average size of the PVD-grown NPs was found to increase after identical thermal cycles, namely, from 0.5 ± 0.2 nm to 1.0 ± 0.3 nm for pristine TiO 2, and from 0.8 ± 0.3 nm to 1.3 ± 0.6 nm for polymer-coated TiO 2 after identical thermal treatments. Although no direct real-time in situ microscopic evidence is available to determine the dominant coarsening mechanism of the PVD NPs unequivocally, our simulations following the diffusion-coalescence coarsening route were in significantly better agreement with the experimental data as compared to those based on the Ostwald-ripening model. The enhanced thermal stability of the micellar NPs as compared to the PVD clusters might be related to their initial larger NP size, narrower size distribution, and larger interparticle distances. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.susc.2012.01.022
  • 2012 • 51 Cobalt ferrite/barium titanate core/shell nanoparticles
    Etier, M. and Gao, Y. and Shvartsman, V.V. and Elsukova, A. and Landers, J. and Wende, H. and Lupascu, D.C.
    Ferroelectrics 438 115-122 (2012)
    Cobalt ferrite/barium titanate nanoparticles with a core/shell structure were synthesized by combining co-precipitation and organosol methods. The average particle size was about 110 nm with an average shell thickness of about 40 nm. Dielectric and magnetic properties of the particles were studied using impedance and Mössbauer spectroscopy, respectively. The particles are promising for fabrication of multiferroic ceramics with the core-shell structure. Copyright © Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00150193.2012.743773
  • 2012 • 50 Emission measurement and safety assessment for the production process of silicon nanoparticles in a pilot-scale facility
    Wang, J. and Asbach, C. and Fissan, H. and Hülser, T. and Kaminski, H. and Kuhlbusch, T.A.J. and Pui, D.Y.H.
    Journal of Nanoparticle Research 14 (2012)
    Emission into the workplace was measured for the production process of silicon nanoparticles in a pilot-scale facility at the Institute of Energy and Environmental Technology e.V. (IUTA). The silicon nanoparticles were produced in a hot-wall reactor and consisted of primary particles around 60 nm in diameter. We employed real-time aerosol instruments to measure particle number and lungdeposited surface area concentrations and size distribution; airborne particles were also collected for offline electron microscopic analysis. Emission of silicon nanoparticles was not detected during the processes of synthesis, collection, and bagging. This was attributed to the completely closed production system and other safety measures against particle release which will be discussed briefly. Emission of silicon nanoparticles significantly above the detection limit was only observed during the cleaning process when the production system was open and manually cleaned. The majority of the detected particles was in the size range of 100-400 nm and were silicon nanoparticle agglomerates first deposited in the tubing then resuspended during the cleaning process. Appropriate personal protection equipment is recommended for safety protection of the workers during cleaning. © 2012 Springer Science+Business Media B.V.
    view abstractdoi: 10.1007/s11051-012-0759-y
  • 2012 • 49 Ga-Pd/Ga 2O 3 Catalysts: The Role of Gallia Polymorphs, Intermetallic Compounds, and Pretreatment Conditions on Selectivity and Stability in Different Reactions
    Li, L. and Zhang, B. and Kunkes, E. and Föttinger, K. and Armbrüster, M. and Su, D.S. and Wei, W. and Schlögl, R. and Behrens, M.
    ChemCatChem 4 1764-1775 (2012)
    A series of gallia-supported Pd-Ga catalysts that consist of metallic nanoparticles on three porous polymorphs of Ga 2O 3 (α-, β-, and γ-Ga 2O 3) were synthesized by a controlled co-precipitation of Pd and Ga. The effects of formation of Ga-Pd intermetallic compounds (IMCs) were studied in four catalytic reactions: methanol steam reforming, hydrogenation of acetylene, and methanol synthesis by CO and CO 2 hydrogenation reactions. The IMC Pd 2Ga forms upon reduction of α- and β-Ga 2O 3-supported materials in hydrogen at temperatures of 250 and 310°C, respectively. At higher temperatures, Ga-enrichment of the intermetallic particles is observed, leading to formation of Pd 5Ga 3 before the support itself is reduced at temperatures above 565°C. In the case of Ga-Pd/γ-Ga 2O 3, no information about the metal particles could be obtained owing to their very small size and high dispersion; however, the catalytic results suggest that the IMC Pd 2Ga also forms in this sample. Pd 2Ga/gallia samples show a stable selectivity towards ethylene in acetylene hydrogenation (≈75%), which is higher than for a monometallic Pd reference catalyst. An even higher selectivity of 80% was observed for Pd 5Ga 3 supported on α-Ga 2O 3. In methanol steam reforming, the Ga-Pd/Gallia catalysts showed, in contrast to Pd/Al 2O 3, selectivity towards CO 2 of up to 40%. However, higher selectivities, which have been reported for Pd 2Ga in literature, could not be reproduced in this study, which might be a result of particle size effects. The initially higher selectivity of the Pd 5Ga 3-containing samples was not stable, suggesting superior catalytic properties for this IMC, but that re-oxidation of Ga species and formation of Pd 2Ga occurs under reaction conditions. In methanol synthesis, CO hydrogenation did not occur, but a considerable methanol yield from a CO 2/H 2 feed was observed for Pd 2Ga/α-Ga 2O 3. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201200268
  • 2012 • 48 Lanthanide(III) complexes of bis-semicarbazone and bis-imine-substituted phenanthroline ligands: Solid-state structures, photophysical properties, and anion sensing
    Nadella, S. and Selvakumar, P.M. and Suresh, E. and Subramanian, P.S. and Albrecht, M. and Giese, M. and Fröhlich, R.
    Chemistry - A European Journal 18 16784-16792 (2012)
    Phenanthroline-based hexadentate ligands L1 and L2 bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as LaIII, EuIII, TbIII, LuIII, and YIII metal ions, were synthesized, and the crystal structures of [ML1Cl3] (M=LaIII, EuIII, Tb III, LuIII, or YIII) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big LnIII ion exhibits a coordination number (CN) of 10, whereas the corresponding EuIII, TbIII, LuIII, and YIII centers with smaller ionic radii show CN=9. Complexes of L2, namely [ML2Cl3] (M=EuIII, TbIII, LuIII, or YIII) ions could also be prepared. Only the complex of EuIII showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5′-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5′-diphosphate (ADP) and adenosine-5′-monophosphate (AMP) was found. 31P NMR spectroscopic studies revealed the formation of a [EuL2(ATP)] coordination species. Illuminating the ion: Hexadentate bis-semicarbazone-based achiral and bis-imine chiral ligands of phenathroline together with their respective lanthanide complexes were synthesized. The crystal structures obtained for bis- semicarbazone-based LnIII complexes reveal coordination numbers of 9 and 10. Among the bis-imine chiral complexes, a luminescent EuIII complex was investigated for sensing various anions, and selectivity towards adenosine-5′-triphosphate (ATP) was achieved in an aqueous medium (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201201705
  • 2012 • 47 Magnetization enhancement and cation valences in nonstoichiometric (Mn,Fe) 3-δO 4 nanoparticles
    Antic, B. and Kremenovic, A. and Jovic, N. and Pavlovic, M.B. and Jovalekic, C. and Nikolic, A.S. and Goya, G.F. and Weidenthaler, C.
    Journal of Applied Physics 111 (2012)
    We present a study of the structural and magnetic properties of (Mn,Fe) 3-δO 4 nanoparticles synthesized by soft mechanochemistry using Mn(OH) 2 × 2 H 2O and Fe(OH) 3 powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe) 3-δO 4 type are found to have a core/shell structure with different Mn/Fe ratios in the core and at the surface. XPS analysis points to valences of 2, 3, and 4 for Mn and 3 for Fe at the particle surface. Combined results of XRPD, Mössbauer spectroscopy, and EDX analysis suggest that there is a deviation from stoichiometry in the nanoparticle core compared to the shell, accompanied by creation of cation polyvalence and vacancies. The value of saturation magnetization, M S, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.3700228
  • 2012 • 46 Nanoscale size effect on surface spin canting in iron oxide nanoparticles synthesized by the microemulsion method
    Darbandi, M. and Stromberg, F. and Landers, J. and Reckers, N. and Sanyal, B. and Keune, W. and Wende, H.
    Journal of Physics D: Applied Physics 45 (2012)
    Uniformly sized and crystalline iron oxide nanoparticles (IONPs) with spinel structure and mean diameters of about 3, 6 and 9nm were synthesized in high yield using the microemulsion route at room temperature. The nanoparticles (NPs) were stabilized in situ by organic surfactant molecules which acted both as a stabilizer of the microemulsion system and as a capping layer of the NP surface. NP size control was attained by careful adjustment of the preparation conditions. The structure, morphology and NP size distribution were investigated by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. A particular effort was devoted in this work to study the effect of size and capping of these NPs on their magnetic structure by in-field Mössbauer spectroscopy at 4.2K. The mean canting angle (relative to the applied field direction) of the Fe spins was observed to increase with decreasing NP size due to the enhanced surface-to-volume ratio. Comparing bare and capped NPs of the same diameter, we verified that the spin canting was not affected by the organic capping. This implied almost identical magnetic orientations of bare and capped NPs. Simultaneously, the capping material was capable of preventing agglomeration effects which can occur in case of direct particle contact. Using a core/shell model, we showed that spin canting originated from the surface shell of the NPs. Furthermore, the Mössbauer spectral parameters provided evidence for the existence of a high fraction of Fe 3O 4 (magnetite) in the IONP. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/45/19/195001
  • 2012 • 45 Silver, gold, and alloyed silver-gold nanoparticles: Characterization and comparative cell-biologic action
    Mahl, D. and Diendorf, J. and Ristig, S. and Greulich, C. and Li, Z.A. and Farle, M. and Köller, M. and Epple, M.
    Journal of Nanoparticle Research 14 (2012)
    Silver, gold, and silver-gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy waterbased synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly(N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15-25 nm), gold (5-6 nm), and silver-gold (50:50; 10-12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver-gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver-gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver-gold nanoparticles in the concentration range of 5-20 μg mL -1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-012-1153-5
  • 2012 • 44 Size-controlled synthesis and microstructure investigation of Co 3O 4 nanoparticles for low-temperature CO oxidation
    Dangwal Pandey, A. and Jia, C. and Schmidt, W. and Leoni, M. and Schwickardi, M. and Schüth, F. and Weidenthaler, C.
    Journal of Physical Chemistry C 116 19405-19412 (2012)
    Noble-metal-free functional oxides are active catalysts for CO oxidation at low temperatures. Spinel-type cobalt oxide (Co 3O 4) nanoparticles can be easily synthesized by impregnation of activated carbon with concentrated cobalt nitrate and successive carbon burn off. Mean size and particle size distribution can be tuned by adding small amounts of silica to the carbon precursor, as witnessed by whole powder pattern modeling of the X-ray powder diffraction data. The catalytic tests performed after silica removal show a significant influence of the mean domain size and of size distribution on the CO oxidation activity of the individual Co 3O 4 specimens, whereas defects play a less important role in the present case. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jp306166g
  • 2012 • 43 Surface Diels-Alder reactions as an effective method to synthesize functional carbon materials
    Kaper, H. and Grandjean, A. and Weidenthaler, C. and Schüth, F. and Goettmann, F.
    Chemistry - A European Journal 18 4099-4106 (2012)
    The post-synthesis chemical modification of various porous carbon materials with unsaturated organic compounds is reported. By this method, amine, alcohol, carboxylate, and sulfonic acid functional groups can be easily incorporated into the materials. Different carbonaceous materials with surface areas ranging from 240 to 1500 m 2 g -1 and pore sizes between 3.0 and 7.0 nm have been studied. The resulting materials were analyzed by elemental analysis, nitrogen sorption, FTIR spectroscopy, zeta-potential measurements, thermogravimetric analysis, photoelectron spectroscopy, and small-angle X-ray scattering. These analyses indicated that the degree of functionalization is dependent on the nature of the dienophile (reactivity, steric hindrance) and the porosity of the carbon material. As possible applications, the functionalized carbonaceous materials were studied as catalysts in the Knoevenagel reaction and as adsorbents for Pb 2+ from aqueous solution. Making grafting on carbon as easy as grafting on silica? A new and easy approach, based on surface Diels-Alder reactions, allows the introduction of organic functionalities into the framework of mesoporous carbon (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201102718
  • 2012 • 42 Surfactant-induced nonhydrolytic synthesis of phase-pure ZrO2 nanoparticles from metal-organic and oxocluster precursors
    Sliem, M.A. and Schmidt, D.A. and Bétard, A. and Kalidindi, S.B. and Gross, S. and Havenith, M. and Devi, A. and Fischer, R.A.
    Chemistry of Materials 24 4274-4282 (2012)
    Nonhydrolytic/non-sol-gel pyrolytic synthesis technique, as a convenient method, was applied to synthesize zirconium oxide nanoparticles (ZrO2 NPs). Pyrolysis of either the mononuclear keto ester/alkoxide complex zirconium bis(isopropoxide)bis(tert-butylacetoacetate) [Zr(OiPr) 2(tbaoac)2] (I) or the oligonuclear oxocluster compound [Zr6(OH)4O4(OMc)12] (II, Mc = methacrylate) generated ZrO2 NPs at moderate conditions of 300-400 °C. Trioctylamine, stearic acid, and/or oleic acid, which act as both solvents and stabilizing agents, were used. Under the adopted process conditions, the stabilizing agent oleic acid plays a vital role in determining the phase of as-synthesized colloidal ZrO2 nanoparticles, which yield the high-temperature tetragonal phase at moderate conditions of 335 °C. Those as-synthesized samples that contained both monoclinic and tetragonal ZrO2 phases (depending on the choice of the surfactant) were transformed into pure tetragonal phase at 1000 °C. An unambiguous phase determination of ZrO2 nanoparticles was carried out by the combination of powder X-ray diffraction (XRD) and Raman spectroscopy. Furthermore, the samples were analyzed by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared (FT-IR) spectroscopy to elucidate the structure, chemical composition, and morphology of the obtained nanoparticles. Also, the phase transformations of the as-synthesized ZrO2 nanoparticles upon annealing were followed via Raman spectroscopy. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cm301128a
  • 2012 • 41 Synthesis and mechanical properties of organic-inorganic hybrid materials from lignin and polysiloxanes
    Lippach, A.K.W. and Krämer, R. and Hansen, M.R. and Roos, S. and Stöwe, K. and Stommel, M. and Wenz, G. and Maier, W.F.
    ChemSusChem 5 1778-1786 (2012)
    The preparation of silica-containing organic-inorganic hybrid materials composed of kraft lignin, alkoxysilanes, and organic linkers was investigated. 3-Glycidyloxypropyltrimethoxysilane, 3-(triethoxysilyl)propylisocyanate (IPTES), and bis(trimethoxysilyl)hexane were selected as the most promising linkers. The best materials obtained showed improved mechanical and thermal properties compared with lignin itself. The reaction of the hydroxyl groups with IPTES and the sol-gel reaction between the organic linker molecules were studied by attenuated total reflectance FTIR and solid-state 29Si magic-angle spinning NMR spectroscopy. The homogeneous composition was demonstrated by electron microscopy and energy-dispersive X-ray spectroscopy mapping. The mechanical properties were investigated by microindentation and dynamic mechanical thermal analysis. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.201200095
  • 2012 • 40 Synthesis of hybrid microgels by coupling of laser ablation and polymerization in aqueous medium
    Nachev, P. and Van 'T Zand, D.D. and Coger, V. and Wagener, P. and Reimers, K. and Vogt, P.M. and Barcikowski, S. and Pich, A.
    Journal of Laser Applications 24 (2012)
    Loading microgels with bioactive nanoparticles (NPs) often requires multiple synthesis and purification steps, and organic solvents or precursors that are difficult to remove from the gel. Hence, a fast and aqueous synthesis procedure would facilitate the synthesis of inorganic-organic hybrid microgels. Two microgel compounds were hybridized with laser-generated zinc oxide (ZnO) NPs prepared in a single-step procedure. ZnO NPs were formed by laser ablation in liquid, while the polymer microgels were synthesized in-situ inside the ablation chamber. Further, the authors report the preparation of two different microgel systems. The first one was produced without the use of chemical initiator forming hydrogels with ZnO NPs and diffuse morpholgy. Typical microgel colloids were also synthesized via a conventional chemical method in a preheated reaction chamber. The existence of microgel colloids partially loaded with ZnO NPs was confirmed in a transmission electron microscopy investigation. Fourier transform infrared spectroscopic measurements and dynamic light scattering verify the formation of polymer colloids. These initial results indicate the application potential of laser ablation in microgel precursor solution for the fabrication of polymeric carriers for inorganic nanoparticles. Preliminary biological tests using zinc chloride demonstrated negative dose effects on primary cell culture with zinc concentrations above 200 μM but no noticeable influence at 100 μM. © 2012 Laser Institute of America.
    view abstractdoi: 10.2351/1.4730803
  • 2012 • 39 Tailored star-shaped statistical teroligomers via ATRP for lithographic applications
    Wieberger, F. and Forman, D.C. and Neuber, C. and Gröschel, A.H. and Böhm, M. and Müller, A.H.E. and Schmidt, H.-W. and Ober, C.K.
    Journal of Materials Chemistry 22 73-79 (2012)
    A series of five star-shaped teroligomers consisting of a saccharose core, and arms, composed of α-gamma butyrolactone methacrylate (GBLMA), methyl adamantyl methacrylate (MAMA) and hydroxyl adamantyl methacrylate (HAMA) with defined arm length and number of arms were prepared via the core-first atom transfer radical polymerization (ATRP) route. The saccharose core was modified with ATRP initiating sites and non-reactive sites, enabling the synthesis of star polymers with a smaller arm number but identical core. Star teroligomers were synthesized with narrow molecular weight distributions with low polydispersity indices (PDIs < 1.1) showing negligible side reactions only at higher conversions of Xp &gt; 50%. The absence of side reaction and the precise achievement of the target molecular weight indicated excellent control over the reaction. A selected star-shaped teroligomer was investigated for the first time as a photoresist material. The delicate conditions of the lithographic process were optimized by a combinatorial approach. The obtained low line edge and line width roughness of the observed pattern demonstrate the potential of the star architecture for this application.
    view abstractdoi: 10.1039/c1jm11922b
  • 2011 • 38 A facile synthesis of mesoporous crystalline tin oxide films involving a base-triggered formation of sol-gel building blocks
    Fried, D.I. and Ivanova, A. and Müller, V. and Rathousky, J. and Smarsly, B.M. and Fattakhova-Rohlfing, D.
    Nanoscale 3 1234-1239 (2011)
    We have developed a new facile procedure for manufacturing crystalline thin films of SnO2 with a uniform mesoporous architecture and full crystallinity of the walls. The procedure is based on the evaporation-induced self-assembly (EISA) of prehydrolyzed tin oxide precursor directed by a commercially available Pluronic polymer. The formation of the tin oxide precursor, which can be self-assembled into a mesoporous structure, is achieved by an addition of ammonium hydroxide to a tin tetrachloride solution. The relative concentration of ammonium hydroxide as well as the duration and temperature of the hydrolysis reaction influence significantly the properties of hydrolyzed tin oxide species and the mesostructure assembled from them. The films coated from these precursor solutions and calcined at 300 °C to 400 °C exhibit a well-developed worm-like porosity with a wall to wall distance of ca. 18 nm, a surface area of up to 50 cm2 cm-2 (corresponding to 55 ± 5 m2 g-1), and high crystallinity. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0nr00872a
  • 2011 • 37 Design and synthesis of Raman reporter molecules for tissue imaging by immuno-SERS microscopy
    Schutz, M. and Muller, C.I. and Salehi, M. and Lambert, C. and Schlücker, S.
    Journal of Biophotonics 4 453-463 (2011)
    The design and synthesis of Raman reporter molecules comprising olefin or alkyne moieties with strong and characteristic vibrational Raman bands is presented. Chemisorption onto the surface of colloidal Au/Ag shells yields a self-assembled monolayer. Hydrophilic stabilization of such SERS labels can be achieved by short terminal ethylene glycol units attached to the Raman reporter. Encapsulation by silica with subsequent functionalization of the glass surface allows the conjugation to biomolecules such as antibodies. We demonstrate the use of SERS-labeled antibodies for tissue imaging of the tumor suppressor p63 in prostate biopsies. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/jbio.201000116
  • 2011 • 36 Facile synthesis of triblock co- and terpolymers of styrene, 2-vinylpyridine, and methyl methacrylate by a new methodology combining living anionic diblock copolymers with a specially designed linking reaction
    Hirao, A. and Matsuo, Y. and Oie, T. and Goseki, R. and Ishizone, T. and Sugiyama, K. and Gröschel, A.H. and Müller, A.H.E.
    Macromolecules 44 6345-6355 (2011)
    Triblock co- and terpolymers with orders of blocks synthetically difficult to be obtained by means of sequential living anionic polymerization were successfully synthesized by developing a new methodology combining living anionic block copolymers with a specially designed linking reaction. The synthesized polymers involve ACB and BAC triblock terpolymers and ABA′, ACA′, and BCB′ triblock copolymers, where A, B, and C are polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate) segments, respectively. The A′, A as well as B, B′ are identical in polymer structure but different in molecular weight. All of them are new type triblock ter- and copolymers with well-defined structures, i.e., predictable molecular weights, compositions, and narrow molecular weight distributions. Transmission electron microscopic studies were performed on bulk morphologies of ACB and BAC triblock terpolymers to exemplarily investigate the influence of changing block sequence and thus changing interfaces. Although both terpolymers showed the tendency to form a lamella-lamella morphology, ACB revealed unusually strongly curved lamellae and BAC even undulated lamellae. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ma201352z
  • 2011 • 35 Highly active metal-free nitrogen-containing carbon catalysts for oxygen reduction synthesized by thermal treatment of polypyridine-carbon black mixtures
    Xia, W. and Masa, J. and Bron, M. and Schuhmann, W. and Muhler, M.
    Electrochemistry Communications 13 593-596 (2011)
    A straight-forward method for the synthesis of metal-free catalysts for oxygen reduction by thermal treatment of a mixture of poly(3,5-pyridine) with carbon black in helium is reported. The catalyst was characterized by X-ray diffraction and photoelectron spectroscopy, cyclic voltammetry and rotating disk electrode measurements. The new catalyst exhibited remarkable activity similar to Pt-based catalysts in alkaline media. © 2011 Elsevier B.V. All Rights Reserved.
    view abstractdoi: 10.1016/j.elecom.2011.03.018
  • 2011 • 34 Nanocrystalline calcium-deficient hydroxyapatite prepared by a microwave-assisted solvent-free reaction
    Zyman, Z. and Goncharenko, A. and Rokhmistrov, D. and Epple, M.
    Materialwissenschaft und Werkstofftechnik 42 154-157 (2011)
    A microwave-assisted solvent-free synthesis of hydroxyapatite from calcium nitrate and sodium phosphate is reported. The product was characterized with respect to the presence of foreign ions and its thermal behavior. An apatite phase was formed in the mixture after irradiation with 2.45 GHz microwaves for 4 min at 350 or 700 W. Structurally, the product was a nanocrystalline calcium-deficient hydroxyapatite (CDHA) with a Ca/P ratio around 1.5, containing some H2O, HPO4 2- and CO3 2-. After heating to 900°C for 1 h, β-tricalcium phosphate (β-TCP) was formed, demonstrating that this microwave-assisted solvent-free synthesis is well suited to prepare a precursor to bioceramics. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201100749
  • 2011 • 33 Organic proton-conducting molecules as solid-state separator materials for fuel cell applications
    Jiménez-García, L. and Kaltbeitzel, A. and Enkelmann, V. and Gutmann, J.S. and Klapper, M. and Müllen, K.
    Advanced Functional Materials 21 2216-2224 (2011)
    Organic proton-conducting molecules are presented as alternative materials to state-of-the-art polymers used as electrolytes in proton-exchanging membrane (PEM) fuel cells. Instead of influencing proton conductivity via the mobility offered by polymeric materials, the goal is to create organic molecules that control the proton-transport mechanism through supramolecular order. Therefore, a series of phosphonic acid-containing molecules possessing a carbon-rich hydrophobic core and a hydrophilic periphery was synthesized and characterized. Proton conductivity measurements as well as water uptake and crystallinity studies (powder and single-crystal X-ray analysis) were performed under various conditions. These experiments reveal that proton mobility is closely connected to crystallinity and strongly dependent on the supramolecular ordering of the compound. This study provides insights into the proton-conducting properties of this novel class of materials and the mechanisms responsible for proton transport. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201002357
  • 2011 • 32 Polythiophene-assisted vapor phase synthesis of carbon nanotube-supported rhodium sulfide as oxygen reduction catalyst for HCl electrolysis
    Jin, C. and Nagaiah, T.C. and Xia, W. and Bron, M. and Schuhmann, W. and Muhler, M.
    ChemSusChem 4 927-930 (2011)
    Rhodium Drive: Carbon nanotube-supported rhodium sulfide electrocatalysts are prepared by sequential chemical vapor deposition of iron, controlled vapor phase polymerization of thiophene, and finally impregnation of the rhodium precursor and pyrolysis. The electrocatalysts are applied in the oxygen reduction reaction under HCl electrolysis conditions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.201000315
  • 2011 • 31 Stimuli-responsive track-etched membranes via surface-initiated controlled radical polymerization: Influence of grafting density and pore size
    Tomicki, F. and Krix, D. and Nienhaus, H. and Ulbricht, M.
    Journal of Membrane Science 377 124-133 (2011)
    The surface-functionalization of poly(ethylene terephthalate) track-etched membranes of different nominal pore sizes (400, 1000 and 3000. nm) with stimuli-responsive poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) via surface-initiated (SI) atom transfer radical polymerization (ATRP) was performed. Variations of grafting density and grafted chain length were achieved by variation of synthesis conditions. It could be clearly demonstrated that mixtures of reaction solutions containing different ratios of acyl bromides, only one bearing the initiator group necessary for the SI ATRP, led to different initiator group densities on the resulting track-etched membrane surface which had been verified by X-ray photoelectron spectroscopy. Moreover the mass increase as function of reaction time strongly correlated with the amount of initiator bound to the membrane surface indicating that the ATRP reaction was not limited by monomer diffusion into the pores. Scanning electron microscopy images and permporometry measurements indicated an even functionalization on the entire membrane surface which was the basis for further investigations. The stimuli-responsive properties of PDMAEMA grafted track-etched membranes were studied by permeability measurements with citrate and glycine buffers as function of pH (2 and 10) and temperature (25 and 60 °C). By that the barrier properties of the membranes could be effectively changed in two steps. The results agree with the expectation that a change in grafting density and chain length has an effect on the stimuli-responsive properties of the membrane. Results for membranes having similar degrees of grafting clearly showed that the reversible swelling of grafted polymeric layers was more pronounced for lower grafting density. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2011.04.028
  • 2011 • 30 Structurally designed synthesis of mechanically stable poly(benzoxazine-co- resol)-based porous carbon monoliths and their application as high-performance CO2 capture sorbents
    Hao, G.-P. and Li, W.-C. and Qian, D. and Wang, G.-H. and Zhang, W.-P. and Zhang, T. and Wang, A.-Q. and Schüth, F. and Bongard, H.-J. and Lu, A.-H.
    Journal of the American Chemical Society 133 11378-11388 (2011)
    Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO2 capture and separation capacities, high selectivity, and facile regeneration at room temperature. At 1 bar, the equilibrium capacities of the monoliths are in the range of 3.3 - 4.9 mmol g- 1 at 0 °C and of 2.6 - 3.3 mmol g - 1 at 25 °C, while the dynamic capacities are in the range of 2.7 - 4.1 wt % at 25 °C using 14% (v/v) CO2 in N2. The carbon monoliths exhibit high selectivity for the capture of CO2 over N2 from a CO2/N2 mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO2 release in an argon stream at 25 °C, indicating a good regeneration capacity. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja203857g
  • 2011 • 29 Synthesis and ink-jet printing of highly luminescing silicon nanoparticles for printable electronics
    Gupta, A. and Khalil, A.S.G. and Offer, M. and Geller, M. P. and Winterer, M. and Lorke, A. and Wiggers, H.
    Journal of Nanoscience and Nanotechnology 11 5028-5033 (2011)
    The formation of stable colloidal dispersions of silicon nanoparticles (Si-NPs) is essential for the manufacturing of silicon based electronic and optoelectronic devices using cost-effective printing technologies. However, the development of Si-NPs based printable electronics has so far been hampered by the lack of long-term stability, low production rate and poor optical properties of Si- NPs ink. In this paper, we synthesized Si-NPs in a gas phase microwave plasma reactor with very high production rate, which were later treated to form a stable colloidal dispersion. These particles can be readily dispersed in a variety of organic solvents and the dispersion is stable for months. The particles show excellent optical properties (quantum yields of about 15%) and long-term photoluminescence (PL) stability. The stable ink containing functionalized Si-NPs was successfully used to print structures on glass substrates by ink-jet printing. The homogeneity and uniformity of large-area printed film was investigated using photoluminescence (PL) mapping. Copyright © 2011 American Scientific Publishers.
    view abstractdoi: 10.1166/jnn.2011.4184
  • 2011 • 28 Synthesis and magnetic properties of cobalt ferrite nanoparticles
    Etier, M.F. and Shvartsman, V.V. and Stromberg, F. and Landers, J. and Wende, H. and Lupascu, D.C.
    Materials Research Society Symposium Proceedings 1398 12-19 (2011)
    Nanopowders of cobalt iron oxide (CoFe2O4) were successfully fabricated by the co-precipitation method followed by a technique to prevent particle agglomeration. Particle sizes were in the range of 24 to 44 nm. The size of cobalt iron oxide particles decreases with increasing the concentration of the precipitation agent. The crystal structure was confirmed by X-ray diffraction (XRD), the chemical composition by energy dispersive spectroscopy (EDS), and phase changes by thermogravimetric differential thermal analysis (TGA-TDA). The particle morphology was analyzed by scanning electron microscopy (SEM). Magnetic properties were investigated by SQUID magnetometry and Mössbauer spectroscopy. Being nearly monodisperse and non-agglomerated the prepared cobalt iron oxide powders are the base for synthesizing magnetoelectric composites embedded in a ferroelectric BaTiO3 matrix. © 2012 Materials Research Society.
    view abstractdoi: 10.1557/opl.2012.699
  • 2011 • 27 Synthesis of bifunctional Au/Pt/Au core/shell nanoraspberries for in situ SERS monitoring of platinum-catalyzed reactions
    Xie, W. and Herrmann, C. and Kömpe, K. and Haase, M. and Schlücker, S.
    Journal of the American Chemical Society 133 19302-19305 (2011)
    The synthesis of bifunctional Au/Pt/Au nanoraspberries for use in quantitative in situ monitoring of platinum-catalyzed reactions by surface-enhanced Raman scattering (SERS) is presented. Highly convolved SERS spectra of reaction mixtures can be decomposed into the contributions of distinct molecular species by multivariate data analysis. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja208298q
  • 2011 • 26 Synthesis of fluorescent core-shell hydroxyapatite nanoparticles
    Neumeier, M. and Hails, L.A. and Davis, S.A. and Mann, S. and Epple, M.
    Journal of Materials Chemistry 21 1250-1254 (2011)
    Lanthanide-doped fluorescent hydroxyapatite/silica core-shell nanorods, 50-100 nm in length and 30 nm in width, were prepared by precipitation of calcium phosphate in the presence of Eu3+ and Y3+ ions at 60 °C, followed by hydrothermally enhanced crystallization, stabilization with poly(ethyleneimine), and reaction with tetraethyl orthosilicate. The fluorescence intensity of the Eu3+-doped hydroxyapatite nanorods was enhanced threefold by co-doping with Y3+ and doubled after hydrothermal treatment. Significantly, fluorescence quenching by water was reduced in the presence of the thin silica nanoshell to give a further doubling of the fluorescence intensity compared with lanthanide-doped hydroxyapatite nanoparticles prepared in the absence of tetraethyl orthosilicate. Our results suggest that a combination of lanthanide doping, controlled crystallization and core-shell fabrication is a promising route to the preparation of biocompatible calcium phosphate nanoparticles with enhanced fluorescence for potential use in biomedical applications. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0jm02264k
  • 2011 • 25 Synthesis, structural properties, and catalytic behavior of Cu-BTC and mixed-linker Cu-BTC-PyDC in the oxidation of benzene derivatives
    Marx, S. and Kleist, W. and Baiker, A.
    Journal of Catalysis 281 76-87 (2011)
    Mixed-linker metal-organic frameworks based on the Cu-BTC structure have been synthesized in which the benzene-1,3,5-tricarboxylate (BTC) linkers have been partially replaced by pyridine-3,5-dicarboxylate (PyDC). X-ray-based techniques (powder XRD and XAS), thermal analysis, and infrared spectroscopy proved that a desired amount of PyDC (up to 50%) can be incorporated without changing significantly the crystal structure. The pyridine unit can be seen as a defect site in the local coordination environment of the dimeric copper units, which is significantly altering their electronic structure and the catalytic properties. Both Cu-BTC and the mixed Cu-BTC-PyDCs catalyze the demanding direct hydroxylation of toluene both in acetonitrile and in neat substrate. Different selectivity toward the desired ortho- and para-cresol and other oxidation products (benzaldehyde, benzyl alcohol, methylbenzoquinone) was observed for Cu-BTC and the Cu-BTC-PyDCs, respectively. Leaching tests and comparison with homogeneously dissolved Cu catalysts indicate mainly a heterogeneous reaction pathway. © 2011 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2011.04.004
  • 2010 • 24 A Physicist's Perspective on "Views on Macroscopic Kinetics of Plasma Polymerisation"
    von Keudell, A. and Benedikt, J.
    Plasma Processes and Polymers 7 376--379 (2010)
    doi: 10.1002/ppap.201000011
  • 2010 • 23 Carbon nanotube-supported sulfided Rh catalysts for the oxygen reduction reaction
    Jin, C. and Xia, W. and Guo, J. and Nagaiah, T.C. and Bron, M. and Schuhmann, W. and Muhler, M.
    Studies in Surface Science and Catalysis 175 161-168 (2010)
    Carbon nanotube (CNT) supported sulfided Rh catalysts were prepared applying three different routes: deposition-precipitation (DP), grafting of colloidal Rh nanoparticles, and polythiophene-assisted synthesis. The catalysts (1.4-1.8 wt%) prepared by DP were synthesized on CNTs from RhCl3 using hydrogen peroxide and subsequent exposure to on-line generated H 2S followed by heat treatment. The Rh particles were found to be highly dispersed on the CNT surface. Alternatively, RhSx/Rh nanoparticles with four different loadings (4.3-21.9 wt%) grafted on carbon nanotubes were prepared through a functionalization of CNTs with short chain thiols and subsequent binding of colloidal Rh nanoparticles onto the thiolated CNTs. All steps of the synthesis were monitored by XPS. Finally, polythiophene/CNT composites were prepared and employed in the preparation of Rh17S15/Rh nanoparticles supported on CNTs. The CNTs with the highest polythiophene loading yielded the highest amount of Rh 17S15 after Rh deposition and thermal treatment. The activity and stability of the prepared catalysts were studied towards the oxygen reduction reaction. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/S0167-2991(10)75020-5
  • 2010 • 22 Carbon nanotubes modified with electrodeposited metal porphyrins and phenanthrolines for electrocatalytic applications
    Schilling, T. and Okunola, A. and Masa, J. and Schuhmann, W. and Bron, M.
    Electrochimica Acta 55 7597-7602 (2010)
    Composites consisting of multi-walled carbon nanotubes (MWCNTs) and iron-nitrogen containing compounds as catalysts for the electroreduction of oxygen in acidic media were directly prepared on a glassy carbon (GC) electrode in a bottom-up synthesis. In a first step, MWCNTs were drop-coated in form of an ink onto the electrode. Afterwards the nanotubes were modified with catalytically active films of iron porphyrin (FeTMPP-Cl) or iron phenanthroline (Fe(phen)3) through a pulsed potential deposition technique. Finally the prepared electrodes were heat-treated in an inert gas atmosphere. By employing cyclic voltammetry and rotating disc electrode measurements it is shown that the activity for the oxygen reduction reaction (ORR) at such composites increases progressively with every applied synthesis step showing the possibility for direct synthesis of a catalyst on an electrode. The activities of FeTMPP-Cl/MWCNT and Fe(phen)3/MWCNT composites prepared by this technique are higher than that of similar electrocatalysts prepared by wet impregnation and heat treatment. The presented approach opens possibilities for systematic tuning of electrode structures, for example by stepwise build-up of gas diffusion electrodes. © 2009 Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2009.11.092
  • 2010 • 21 Efficient phase separation and product recovery in organic-aqueous bioprocessing using supercritical carbon dioxide
    Brandenbusch, C. and Bühler, B. and Hoffmann, P. and Sadowski, G. and Schmid, A.
    Biotechnology and Bioengineering 107 642-651 (2010)
    Biphasic hydrocarbon functionalizations catalyzed by recombinant microorganisms have been shown to be one of the most promising approaches for replacing common chemical synthesis routes on an industrial scale. However, the formation of stable emulsions complicates downstream processing, especially phase separation. This fact has turned out to be a major hurdle for industrial implementation. To overcome this limitation, we used supercritical carbon dioxide (scCO2) for both phase separation and product purification. The stable emulsion, originating from a stereospecific epoxidation of styrene to (S)-styrene oxide, a reaction catalyzed by recombinant Escherichia coli, could be destabilized efficiently and irreversibly, enabling complete phase separation within minutes. By further use of scCO2 as extraction agent, the product (S)-styrene oxide could be obtained with a purity of 81% (w/w) in one single extraction step. By combining phase separation and product purification using scCO2, the number of necessary workup steps can be reduced to one. This efficient and easy to use technique is generally applicable for the workup of biphasic biocatalytic hydrocarbon functionalizations and enables a cost effective downstream processing even on a large scale. Biotechnol. Bioeng. 2010;107:642-651. © 2010 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/bit.22846
  • 2010 • 20 Fabrication and RF performance of InAs Nanowire FET
    Prost, W. and Tegude, F.J.
    Device Research Conference - Conference Digest, DRC 279-282 (2010)
    Nanowires can excellently be controlled during synthesis with respect to physical and chemical characteristics, including composition, size, electronic and optical properties. They may be used both as devices and interconnects, and thus can open doors for downscaled integration concepts not seen before. The non-lithographic bottom up synthesis approach on the nanoscale may be extremely cost-effective, especially when making use of the large material diversity stemming from decoupling of device from substrate material without loss of structural quality, e.g. growing metallic, Ge or III-V nanowires on Si substrates. Going down to very small dimensions one may make use of quantum confinement effects like reduced phonon scattering and related high carrier mobility, tunable electrical and optical properties, or implementing heterostructures for quantum dot and single electron devices. © 2010 IEEE.
    view abstractdoi: 10.1109/DRC.2010.5551958
  • 2010 • 19 Gas-phase synthesis of gradient catalyst libraries consisting of nanoparticles supported on high surface area porous substrates
    Xia, W. and Mei, B. and Muhler, M.
    Nanoscience and Nanotechnology Letters 2 1-6 (2010)
    Despite the advances in high throughput experimentation in recent years the synthesis of realistic catalyst libraries especially gradient catalyst libraries remains as a challenge in material science. Recently, we have developed a method for the synthesis of gradient catalyst libraries consisting of nanoparticles supported on high surface area porous substrates. Chemical vapor deposition (CVD) was employed as a gas-phase method for the synthesis. The method made use of the lateral concentration profile of the precursor-loaded carrier gas stream during CVD, resulting in concentration profile of the deposits on porous substrates. In this report, high surface area materials of both powders (e.g., silica) and bulk composites (e.g., hierarchical carbon structures) were successfully employed as substrates for the deposition of single metal or bimetallic catalyst libraries. The synthesis was achieved by controlling the flow behavior of the effluent precursor stream. The resulting effusion cone led to a radial deposition gradient on the substrate. Different from thin film-type model catalyst libraries, the obtained catalysts can be tested under realistic reaction conditions. Methanol oxidation was studied as a test reaction using scanning mass spectrometry. Copyright © 2010 American Scientific Publishers.
    view abstractdoi: 10.1166/nnl.2010.1046
  • 2010 • 18 Laser ablation-based one-step generation and bio-functionalization of gold nanoparticles conjugated with aptamers
    Walter, J.G. and Petersen, S. and Stahl, F. and Scheper, T. and Barcikowski, S.
    Journal of Nanobiotechnology 8 (2010)
    Background: Bio-conjugated nanoparticles are important analytical tools with emerging biological and medical applications. In this context, in situ conjugation of nanoparticles with biomolecules via laser ablation in an aqueous media is a highly promising one-step method for the production of functional nanoparticles resulting in highly efficient conjugation. Increased yields are required, particularly considering the conjugation of cost-intensive biomolecules like RNA aptamers.Results: Using a DNA aptamer directed against streptavidin, in situ conjugation results in nanoparticles with diameters of approximately 9 nm exhibiting a high aptamer surface density (98 aptamers per nanoparticle) and a maximal conjugation efficiency of 40.3%. We have demonstrated the functionality of the aptamer-conjugated nanoparticles using three independent analytical methods, including an agglomeration-based colorimetric assay, and solid-phase assays proving high aptamer activity. To demonstrate the general applicability of the in situ conjugation of gold nanoparticles with aptamers, we have transferred the method to an RNA aptamer directed against prostate-specific membrane antigen (PSMA). Successful detection of PSMA in human prostate cancer tissue was achieved utilizing tissue microarrays.Conclusions: In comparison to the conventional generation of bio-conjugated gold nanoparticles using chemical synthesis and subsequent bio-functionalization, the laser-ablation-based in situ conjugation is a rapid, one-step production method. Due to high conjugation efficiency and productivity, in situ conjugation can be easily used for high throughput generation of gold nanoparticles conjugated with valuable biomolecules like aptamers. © 2010 Walter et al; licensee BioMed Central Ltd.
    view abstractdoi: 10.1186/1477-3155-8-21
  • 2010 • 17 Magnetic coupling mechanisms in particle/thin film composite systems
    Confalonieri, G.A.B. and Szary, P. and Mishra, D. and Benitez, M.J. and Feyen, M. and Lu, A.H. and Agudo, L. and Eggeler, G. and Petracic, O. and Zabel, H.
    Beilstein Journal of Nanotechnology 1 101-107 (2010)
    Magnetic Γ-Fe 2O 3 nanoparticles with a mean diameter of 20 nm and size distribution of 7% were chemically synthesized and spin-coated on top of a Si-substrate. As a result, the particles self-assembled into a mono layer with hexagonal close-packed order. Subsequently, the nanoparticle array was coated with a Co layer of 20 nm thickness. The magnetic properties of this composite nanopar-ticle/thin film system were investigated by magnetometry and related to high-resolution transmission electron microscopy studies. Herein three systems were compared: i.e. a reference sample with only the particle monolayer, a composite system where the particle array was ion-milled prior to the deposition of a thin Co film on top, and a similar composite system but without ion-milling. The nanoparticle array showed a collective super-spin behavior due to dipolar interparticle coupling. In the composite system, we observed a decoupling into two nanoparticle subsystems. In the ion-milled system, the nanoparticle layer served as a magnetic flux guide as observed by magnetic force microscopy. Moreover, an exchange bias effect was found, which is likely to be due to oxygen exchange between the iron oxide and the Co layer, and thus forming of an antiferromagnetic CoO layer at the Γ-Fe 2O 3/Co interface. © 2010 Confalonieri et al.
    view abstractdoi: 10.3762/bjnano.1.12
  • 2010 • 16 Novel synthetic pathway for new Zn-Zn-bonded compounds from dizincocene
    Gondzik, S. and Bläser, D. and Wölper, C. and Schulz, S.
    Chemistry - A European Journal 16 13599-13602 (2010)
    Making it new! A novel synthetic pathway for the synthesis of Zn-Zn-bonded complexes (see graphic) under mild reaction conditions is presented. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201002482
  • 2010 • 15 Optimum between purification and colloidal stability of ZnO nanoparticles
    Marczak, R. and Segets, D. and Voigt, M. and Peukert, W.
    Advanced Powder Technology 21 41-49 (2010)
    Crystalline ZnO quantum dots have been synthesized by hydrolysis of zinc acetate dihydrate with lithium hydroxide in ethanolic solution. By varying different parameters of the synthesis process, the size of the ZnO particles can be controlled. Detailed investigation of the ripening of the nanoparticles evidenced that despite of the well-known influence of ageing temperature and time, the presence of the reaction byproduct lithium acetate strongly affects the ripening behaviour. In particular, the particle size can be almost completely arrested by the removal of this byproduct via reversible flocculation of the ZnO nanoparticles using heptane as an antisolvent. A closer analysis of the repeated washing process shows an initial improvement of the colloidal stability of the ZnO nanoparticles during the first purification cycle as it mainly removes the lithium acetate from the suspension and not the stabilizing acetate groups directly bound to the particle surface. With further washing the remaining acetate ligands are unable to maintain the stabilization against agglomeration of the ZnO nanoparticles. Thus, there exists an optimum between purification progress and colloidal stability. These findings are also confirmed by calculations according to the DLVO theory, which show that there exists nearly no primary minimum of small ZnO nanoparticles below 5 nm in the presence of stabilizing acetate ions whereas the decrease in acetate ions bound to the particle surface leads to a more and more pronounced primary minimum. The present work is of particular significance for the preparation of purified colloidal ZnO nanoparticles for studies of their electrical and optical properties with respect to their wide range of potential applications. © 2009 The Society of Powder Technology Japan.
    view abstractdoi: 10.1016/j.apt.2009.10.005
  • 2010 • 14 Regioselectively controlled synthesis of colloidal mushroom nanostructures and their hollow derivatives
    Feyen, M. and Weidenthaler, C. and Schüth, F. and Lu, A.-H.
    Journal of the American Chemical Society 132 6791-6799 (2010)
    In this study, a facile and controllable synthetic route for the fabrication of mushroom nanostructures (Fe xO y@PSD-SiO 2) and their hollow derivatives has been established. The synthesis consists of partial coating of Fe xO y (Fe 3O 4 or Fe 2O 3) with polymer spheres, followed by attaching silica hemispheres. The surface-accessible Fe xO y nanoparticles on the Janus-type Fe xO y@PSD nanospheres are key for directing the growth of the silica hemisphere on the Fe xO y@PSD seeds. The size and the porosity of the silica hemispheres are tunable by adjusting the amount of TEOS used and addition of a proper surfactant in a Stöber-type process. After the iron oxide cores were leached out with concentrated HCl, mushroom nanostructures with hollow interiors were obtained, where the morphology of the hollow interior faithfully replicates the shape of the iron oxide core previously filling this void. This synthetic strategy provides a controllable method for the large-scale preparation of asymmetric colloidal nanostructures which could serve as building blocks for the assembly of new types of nanostructures. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja101270r
  • 2010 • 13 Salen-ligands based on a planar-chiral hydroxyferrocene moiety: Synthesis, coordination chemistry and use in asymmetric silylcyanation
    Niemeyer, J. and Cloppenburg, J. and Fröhlich, R. and Kehr, G. and Erker, G.
    Journal of Organometallic Chemistry 695 1801-1812 (2010)
    Condensation of the O-protected hydroxyferrocene carbaldehyde (Sp)-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(Sp,Sp)-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,Sp,Sp)-3b and (R,R,Sp,Sp)-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (Rp)-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route. The (Sp)-series of these newly developed N2O2-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45-62% enantiomeric excess. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jorganchem.2010.04.008
  • 2010 • 12 Scaleup of lipase-catalyzed polyester synthesis
    Korupp, C. and Weberskirch, R. and Müller, J.J. and Liese, A. and Hilterhaus, L.
    Organic Process Research and Development 14 1118-1124 (2010)
    One of the critical steps for the commercialization of new enzyme-based products is the successful scaleup of the catalyzed reaction. In the study presented here, we achieved a scaleup for the enzymatic production of glycerol adipate on a 500 g scale in a heated, solvent-free system. The influence of various reaction conditions (i.e., temperature, pressure, enzyme concentration, reactants ratio, stirrer type, stirring rate, and reaction time) on the substrate conversion and molecular weight of the product was investigated. Conversions were higher than 0.9, and molecular weights were in the desired range of 2000-3000 Da. Space time yields of 370 g d-1 L-1 could be achieved. Maximal polymer yield was achieved at 60 °C, < 20 mbar, 3 wt % Novozym 435, glycerol:adipic acid ratio 1.1:1, < 48 h while stirring at 100 rpm. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/op1000868
  • 2010 • 11 Spatially and size selective synthesis of Fe-based nanoparticles on ordered mesoporous supports as highly active and stable catalysts for ammonia decomposition
    Lu, A.-H. and Nitz, J.-J. and Comotti, M. and Weidenthaler, C. and Schlichte, K. and Lehmann, C.W. and Terasaki, O. and Schüth, F.
    Journal of the American Chemical Society 132 14152-14162 (2010)
    Uniform and highly dispersed γ-Fe 2O 3 nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe 2O 3 nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe 2O 3/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60 000 cm 3 g cat -1 h -1. At a space velocity of 7500 cm 3 g cat -1 h -1, complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe 2O 3 nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe 2O 3 and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe 2O 3/CMK-5 catalyst is much more active than the benchmark NiO/Al 2O 3 catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe 2O 3 nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja105308e
  • 2010 • 10 Stable aqueous dispersions of ZnO nanoparticles for ink-jet printed gas sensors
    Khalil, A.S.G. and Hartner, S. and Ali, M. and Gupta, A. and Wiggers, H. and Winterer, M.
    INEC 2010 - 2010 3rd International Nanoelectronics Conference, Proceedings 440-441 (2010)
    For the preparation of printable devices based on ZnO nanoparticles (ZnO NP), stable colloidal dispersions of these materials are highly desirable. ZnO NP have been synthesized by Chemical Vapor Synthesis. The particles have a spherical shape with a narrow size distribution. Stable aqueous dispersions of the ZnO NP have been successfully prepared after the addition of a polymeric stabilizer. The prepared dispersions are stable for at least 2 months without observable sedimentation. These stable dispersions are used to prepare ZnO NP films on different substrates by ink-jet printing. The viscosity and the surface tension of the dispersion as well as the printing parameters have been optimized for forming layers with high quality. Dense and low porosity layers of ZnO NP with a thickness between 100-250 nm have been prepared on different substrates. First measurements on ink-jet printed ZnO films are done on self fabricated inter digital capacitors (IDCs) at room temperature. The ZnO films show resistivity at room temperature of 7.76 kΩ.cm. For sensing measurements in hydrogen atmosphere, the sheet resistance decreases rapidly until it reaching metallic behavior. This behavior is reversible. ©2010 IEEE.
    view abstractdoi: 10.1109/INEC.2010.5424503
  • 2010 • 9 Synthesis and brittle-to-ductile transition of the ω-Al0.7Cu0.2Fe0.1 tetragonal phase
    Laplanche, G. and Joulain, A. and Bonneville, J. and Gauthier-Brunet, V. and Dubois, S.
    Materials Science and Engineering A 527 4515-4518 (2010)
    Synthesis of ω-Al-Cu-Fe single phase material is reported. Microhardness tests performed over the temperature range 293-898K indicate a brittle-to-ductile transition between 673K and 823K. Fracture toughness was determined from indentation cracks at 293K. Both the hardness and fracture toughness are comparable to that of the icosahedral Al0.635Cu0.240Fe0.125 material. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2010.02.049
  • 2010 • 8 Synthesis and characterization of ZnO nanowires for nanosensor applications
    Lupan, O. and Emelchenko, G.A. and Ursaki, V.V. and Chai, G. and Redkin, A.N. and Gruzintsev, A.N. and Tiginyanu, I.M. and Chow, L. and Ono, L.K. and Roldan Cuenya, B. and Heinrich, H. and Yakimov, E.E.
    Materials Research Bulletin 45 1026-1032 (2010)
    In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H2 of a gas nanosensor based on an individual ZnO nanowire is also reported. © 2010 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.materresbull.2010.03.027
  • 2010 • 7 Synthesis and structural characterization of new zinc amidinate complexes
    Schmidt, S. and Schulz, S. and Bläser, D. and Boese, R. and Bolte, M.
    Organometallics 29 6097-6103 (2010)
    The synthesis and reactivity of heteroleptic zinc complexes of the type LZnX (X = Me, I) containing amidinate ligands L of varying steric bulk were investigated. Complexes of the type LZnMe, which were obtained from the homoleptic complexes L2Zn upon reaction with ZnMe2, react with iodine with subsequent formation of LZnI. Single-crystal X-ray structures of the amidinate zinc complexes [{MeC(Ni-Pr)2}ZnMe]2, 1, [{MeC(Ni-Pr)2}ZnI]2LiI(OEt)2, 3, [t-BuC(NDipp)2]ZnMe, 5, [t-BuC(NDipp)2]ZnMe(t-BuPy), 6, [{t-BuC(NDipp)2}Zn(μ-I)]2, 7, and [t-BuC{N(H)Dipp} 2][Al{OC(CF3)3}4], 8, are reported. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/om1008549
  • 2010 • 6 Synthesis and structure analysis of RUB-50, an LEV-type aluminosilicate zeolite
    Yamamoto, K. and Ikeda, T. and Onodera, M. and Muramatsu, A. and Mizukami, F. and Wang, Y. and Gies, H.
    Microporous and Mesoporous Materials 128 150-157 (2010)
    An LEV-type aluminosilicate zeolite RUB-50 was synthesized in the presence of diethyldimethylammonium (DEDMA) cation as a structure-directing agent (SDA), and its crystal structure was analyzed in detail by the Rietveld refinement and the maximum entropy method (MEM). RUB-50 was crystallized from an Al-containing mother gel with relatively low water content. As-made RUB-50 contained a large amount of organic SDAs in the cavity, and therefore calcined RUB-50 exhibited a large micropore volume. Through the MEM analysis of the as-made RUB-50, the actual conformation of the SDA molecule occluded in the cavity emerged. In accordance with the structural analysis, quaternary ammonium cations possibly having molecular conformations similar to that of DEDMA successfully direct the crystallization of LEV-type zeolites. © 2009 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2009.08.016
  • 2010 • 5 Synthesis and x-ray crystal structures of tetranuclear zincamidinate complexes
    Gutschank, B. and Schulz, S. and Westphal, U. and Bläser, D. and Boese, R.
    Organometallics 29 2093-2097 (2010)
    Polynuclear amidinate zinc halide complexes of the general type{C[C(Ni-Pr)2ZnX]4} [X = Cl, 2; Br, 3; I, 4] were prepared in high yields via methyl/halide exchange reaction of {C[C(Ni-Pr) 2ZnMe]4} (1a) with AlX3. 2-4 were characterized by elemental analysis, multinuclear NMR, and IR spectroscopy and single-crystal X-ray diffraction. Computational calculations of halide-substituted complexes {C[C(Ni-Pr)2ZnX]4} [X = F-I] were performed to clarify the influence of the halide atom on the structural parameters of the complexes and to elucidate their electronic structure and bonding situation. The capability of these halide-substituted complexes to serve as suitable starting reagents for further salt elimination reactions was proven by reaction of 2 with LiR (R = Me, n-Bu) and EtMgBr, which yielded the corresponding Zn-alkyl species {C[C(Ni-Pr)2ZnR]4} [R = Me, 1a; n-Bu, 5; Et, 6]. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/om100065w
  • 2010 • 4 Synthesis of structurally stable colloidal composites as magnetically recyclable acid catalysts
    Feyen, M. and Weidenthaler, C. and Schüth, F. and Lu, A.-H.
    Chemistry of Materials 22 2955-2961 (2010)
    In this study, we provide a simple and reproducible method for the preparation of highly active and recyclable colloidal acid catalysts. First, 16-heptadecenoic acid-functionalized magnetite nanoparticles were encapsulated in monodisperse cross-linked polymer spheres. This was achieved by emulsion copolymerization technique in an aqueous phase of styrene and divinylbenzene (DVB). Different ratios of styrene and DVB were used to tune the structural stability and surface morphology of the composites. With increase in DVB content, the surfaces of the colloidal composites become increasingly rougher. The obtained colloids were functionalized with sulfonic acid groups to obtain magnetically recyclable catalysts with H+ contents in the range of 2.2-2.5 mmol g-1 and surface areas of 45-120 m2 g -1. For the condensation reaction of benzaldehyde and ethylene glycol, magnetic acid catalyst prepared only from DVB precursor was found to be active and with high selectivity and long-term stability. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/cm100277k
  • 2010 • 3 Synthesis, characterization and structure analysis of UZM-22, a MEI-type zeolite framework structure
    Wang, G. and Marler, B. and Gies, H. and Fyfe, C.A. and Sidhu, P. and Yilmaz, B. and Müller, U.
    Microporous and Mesoporous Materials 132 43-53 (2010)
    ZSM-18 related zeolite UZM-22, framework type MEI, was synthesized with choline as structure directing agent (SDA). Sr2+ and Li+ are additional essential components in the synthesis. Rietveld structure analysis of the as synthesized sample confirmed the proposed crystal structure in space group P63/m with a = 13.1544(7) and c = 15.7409(3) and composition (Sr1.17Li0.05)[Si27.92Al6.08 O68]*3.69SDA*23.85H2O. Calcination showed that the material is stable up to at least 600 °C. Solid state NMR experiments revealed that the framework de-aluminated upon calcination and that Li is part of the as-made material as cation. N2 adsorption experiments confirmed the low framework density with a high surface area of 592 m2/g. The 12R pore has a diameter of 6.9 Å. Ammonium TPD revealed a high number of acid sites. © 2009 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2009.08.021
  • 2010 • 2 Synthesis, structure, and reactivity of a tetranuclear amidinato zinc hydride complex
    Gutschank, B. and Schulz, S. and Bläser, D. and Boese, R. and Wölper, C.
    Organometallics 29 6133-6136 (2010)
    The tetranuclear amidinato zinc hydride complex (C[C(Ni-Pr) 2ZnH]4) (3) was synthesized by reaction of the Cl-substituted complex (C[C(Ni-Pr)2ZnCl]4) with CaH 2. 3 was found to react with phenylacetylene and acetylene at ambient temperature with elimination of H2 and subsequent formation of C[C(Ni-Pr)2ZnC≡CPh]4 (4) and (C[C(Ni-Pr) 2ZnC≡CH]4 (5), respectively. 3-5 have been characterized by multinuclear NMR (1H, 13C) and IR spectroscopy, elemental analyses, and single-crystal X-ray diffraction. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/om100966d
  • 2010 • 1 The synthesis of highly loaded Cu/Al2O3 and Cu/Zno/Al2O3 catalysts by the two-step CVD of Cu IIdiethylamino-2-propoxide in a fluidized-bed reactor
    Becker, M. and D'Alnoncourt, R.N. and Kähler, K. and Sekulic, J. and Fischer, R.A. and Muhler, M.
    Chemical Vapor Deposition 16 85-92 (2010)
    Highly loaded copper catalysts supported on alumina are synthesized applying the cyclic two-step CVD of the precursor copper(II)diethylamino-2- propoxide in a fluidized-bed reactor. Copper/zinc oxide/alumina composites are synthesized by either the CVD of the precursor bis[bis (trimethylsilyl) amido]zinc on Cu/Al2O3, or the CVD of the Cu precursor on Zn-pretreated alumina, impregnating with diethyl zinc in addition. The composites are extensively characterized by atomic absorption spectroscopy (AAS), elemental analysis (EA), mass spectrometry (MS), N2 physisorption, N2O reactive frontal chromatography (RFC), and X-ray diffraction (XRD). The Cu and ZnO nanoparticles originating from the efficient two-step procedure, consisting of adsorption and subsequent decomposition of the adsorbed species in two separated steps, are highly dispersed, X-ray amorphous, and, in the case of the Cu-containing catalysts, have high specific Cu surface areas. The catalytic activities are determined both in methanol synthesis, to judge the contact between the deposited Cu and ZnO nanoparticles, and in the steam reforming of methanol (SRM) to probe the stability of the Cu particles. The turn-over frequencies (TOF) in methanol synthesis of these Cu/ZnO/Al 2O3 catalysts are higher than that of a commercial ternary catalyst. The varied sequence of the CVD of Cu and ZnO on alumina leads to catalysts with similar activities in the case of similar specific Cu areas. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.200906808