Abstract
Polyvinylpyrrolidone (PVP) polymer is among one of the widely used surfactants to prepare nano-materials with desired particle shape and particle size. The critical challenge is to remove PVP polymer from the metal surface without loss of the surface arrangement and particle agglomeration. Here, we developed a strategy to remove the surfactant PVP which prefers to form a multi-layer shell and thus blocks the catalytically active surface of the Pt nanocubes (6–7 nm). Since PVP is partially soluble in polar solvents, we studied four different solvent mixtures (volume ratio), (i) methanol/ethanol (3:1), (ii) acetone/water (3:1), (iii) ethanol/chloroform (3:1), and (iv) aqueous 0.1 M acetic acid by using transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV). Only, the washing process with methanol/ethanol and acetone/water generates Pt nanocubes with almost clean particle surface. Based on our FTIR results, a shift of the carbonyl band in IR spectrum was observed for methanol/ethanol-washed Pt nanocubes, indicating the coordination of the carbonyl oxygen of the PVP to platinum. The electrochemical experiments showed that the surface area of the methanol/ethanol-washed Pt nanocubes was increased by a factor of 14 compared to the unwashed, while an improvement of 11 times was achieved by washing in acetone/water. However, the CV profile still signifies the presence of strongly adsorbed PVP on the Pt surface. To remove the chemisorbed PVP, an electrochemical cleaning including 200 potential cycles between 0.06 and 1.00 V vs. RHE at 200 mV s−1 was applied. The potential cycling reveals the potential-controlled ad/desorption behavior of the PVP at the Pt surface. Altogether, we designed a cleaning procedure for surfactant-capped metal nanoparticles and provide insights into the interactions between the PVP and Pt surface.
Acknowledgments
Financial support from the Bundesministerium für Bildung und Forschung (BMBF, FKZ 03SF0539) is gratefully acknowledged. Furthermore, the funding of the JEOL JEM2100F HR-TEM by the DFG (INST 184/106-1 FUGG) is acknowledged. Our appreciation goes to Mr. Volker Stenhoff of DLR – Institute of Network Energy Systems, Oldenburg, Germany, for his assistance with the FTIR measurements.
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Supplementary Material:
The online version of this article offers supplementary material (https://doi.org/10.1515/zpch-2018-1147).
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