Aryldiazonium gold salts as efficient oxidants for polymerization of anilines

Investigating transition metal oxidants is a fundamental scientific interest for the synthesis of polymer nanocomposites. In this study, we attempted for the first time to use aryldiazonium cation stabilized with tetrachloroaurate(III) anion [AuCl₄]⁻ in the polymerization of aniline monomer. The reaction was achieved using high mole ratios of oxidant/aniline which resulted in the formation of polyaniline nanocomposites (PANI NCs) of gold-aryl NPs. The facile polymerization can be ascribed to the correlation of the redox potentials of both aniline monomer and diazonium salt (oxidant). Emeraldine-coated gold-aryl NPs were efficiently synthesized at high oxidant/aniline mole ratios of 3:1 and 4:1. UV–visible displayed a broad peak centered at 900 nm assigned to HCl doped emeraldine. However, low oxidant/aniline mole ratios of 1:4 and 1:1 were not successful in aniline polymerization. The thermal gravimetric analysis concluded the stability of PANI NCs with gold percentage residues of 17–20 wt%. High oxidant/aniline mole ratios of 3:1 and 4:1 showed particle sizes in the range of 20–25 nm in transmission electron microscopy images. The emerging oxidant based on diazonium gold salt could be used for the synthesis of other metal and metalloid nanocomposites for energy and environmental applications. This work is critical in establishing our knowledge on diazonium salts stabilized with gold-based anions as friendly oxidants toward aniline and possibly other reducible monomers such as phenol, thiophene, and pyrrole. Graphical abstract: [Figure not available: see fulltext.]