Electrochemical characterization of PVP-functionalized silver nanoparticles, gold nanoparticles and silver-gold nanoalloys

Viktoria Grasmik, University of Duisburg-Essen, Essen, Germany
Matthias Epple, University of Duisburg-Essen, Essen, Germany
En Ning Saw, Ruhr-University Bochum, Bochum, Germany
Kristina Tschulik, Ruhr-University Bochum, Bochum, Germany

Metallic nanoparticles (NP) represent a well-established part of nanoscience today. Especially noble metals like silver, gold and platinum are important. Alloyed nanoparticles open up new possibilities due to their tunable properties, e.g. in catalysis or imaging. Silver and gold represent the most prominent metallic nanoparticles in biomedicine – silver due to its antibacterial effect and gold due to its easy functionalization, e.g. by thiol or phosphane chemistry[1],[2]. A combination of these metals into one nanoparticle enables the combination of these two aspects. Their optical properties vary with their composition and internal nanostructure[3]. Silver and gold represent a classical system for alloys, given their almost identical metallic radii and chemical similarity. Therefore, they constitute a model system for mixed crystals with complete miscibility. In the case of bimetallic AgAu nanoparticles, an important question concerns the actual distribution of the metals inside the nanoparticles, and the resulting effects on their chemical, physical and crystallographic properties.

Silver and gold nanoparticles were prepared using citrate and tannic acid as reducing agents and stabilized with polyvinylpyrrolidone. EDX mapping of AgAu nanoalloys in different compositions showed a gold-rich core and a silver-rich shell[3]. To confirm the results from EDX mapping, the nanoparticles were characterized electrochemically using cyclic voltammetry to get information on the elemental distribution within the particles as well as the shell thickness[4]. For this purpose the AgAuNP were drop cast on a Glassy Carbon Electrode (GCE) and oxidized sequentially in different electrolytes. The size distribution of the NP was obtained by Differential Centrifugal Sedimentation (DCS) and Anodic Particle Coulometry[5].

[1] M. Homberger, U. Simon, Philos. Trans. R. Soc., A, 2010, 368, 1405-1453.
[2] A. Leifert, U. Simon et al., Nanoscale, 2013, 5, 6224-6242.
[3] S. Ristig, M. Epple et al., J. Mater. Chem. B., 2015, 3, 4657-4662.
[4] K. Tschulik, R.G. Compton et al., Adv. Funct. Mater., 2015, 25, 5149-5158.
[5] L.R. Holt, B.J. Plowman, K. Tschulik et al., Angew. Chem. Int. Ed., 2016, 55, 397-400.

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