Preparation and Characterisation of Atomic Metals in Polyaniline
Experimental Condensed Matter Physics
Solid State and Surface Chemistry, Material Synthesis
Final Report Abstract
This work focussed on the development and investigation of the properties of supposedly atomic gold in polyaniline (PANI). Tetrachloroaurate anions were precisely attached to the protonated imine sites of PANI at electrochemical holding potentials that prevents reduction, followed by a controlled reduction using cyclic voltammetry in a flow cell system to synthesize the PANI/gold (PANI/Au) composite. Unfortunately, in contrast to previous studies reporting on the fabrication of atomic-scale gold clusters using this method, this research demonstrates that the electrochemical reduction instead leads to a nucleation and growth of gold nanoparticles. Both SEM and TEM was used to conduct a comprehensive structural analysis of the size dispersion of gold nanoparticles in PANI/Au composite. Rutherford backscattering spectroscopy revealed that the tetrachloroaurate anions were homogeneously dispersed in the PANI during and shortly after the exposure step. However, the subsequent reduction step caused aggregation and surface segregation of the gold atoms. The distribution of gold nanoparticles became polydispersed after multiple deposition cycles due to the growth of previously formed nanoparticles and the formation of new ones. Additional investigations using transmission electron microscopy and elemental mapping revealed the existence of tiny clusters of gold chloride when the applied holding potential was removed without CV reduction. Moreover, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy were used to confirm that these clusters are likely to be composed of gold-chloride and are not stable. Instead they undergo a gradual partial reduction from Au(III) to intermediate Au(I) and ultimately to Au(0). An investigation was conducted on the electrochemical oxidation behavior of PANI/Au composites in alkaline media. The presence of platinum was essential to initiate the electrooxidation process, in contrast to the inactive glassy carbon substrate. An oscillation pattern of peak current density which describes the catalytic activity was formerly attributed to the presence of atomic metals. However, we could demonstrate that the oscillatory behaviour can also be explained by the complex interactions of Pt substrate, the PANI thickness and the amount and position of Au NPs.
Publications
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Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline. Nanomaterials, 13(14), 2089.
Zhao, Bin; Becker, Hans-Werner & Gutsch, Sebastian
