Gold-polyaniline nanocomposites have been synthesized by a well-established redox procedure involving the simultaneous polymerization of aniline and reduction of a gold salt, initially mixed on a molecular scale. The essential physical chemistry surrounding the catalytic action of the nanogold particles in the composite for the oxidation of 4-nitrophenol is revealed. Substituted anilines have also been used to form the composites. Atoms substituted on the benzene ring on PANI are likely to form H-bonds with AuCl4– ions adsorbed on Au NPs. This then strengthens the interaction between Au NPs with PANICl relative to the situation found with PANIMe which cannot form H-bonds via the methyl group. Metal-support interactions have been shown to affect the catalytic activity of a number of polymer-based catalysts. Functional groups that interact strongly with Au NPs such as the mercapto group lowered the activity of the catalyst despite the small Au NPs present. The high catalytic activity of Au-PANIMe is therefore due to the weak interactions between PANIMe and Au NPs induced by the steric hindrance due to the methyl group and its inability to form H-bonds. Nitrophenol reduction kinetics obeyed the Langmuir–Hinshelwood mechanism. The order of the catalytic activity for the reduction of 4-NP was Au-PANICl > Au-PANI > Au-PANIMe. The activity of the catalyst was determined by the nature of the interaction of Au NPs with the polymer.

Keywords: Au-PANI; Catalysis; Synthesis; Polyaniline; 4-Nitrophenol; Gold

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