Reduction of hexavalent chromium at a polypyrrole-coated aluminium electrode: Synergistic interactions

Abstract

Adherent polypyrrole films were electropolymerized from a tosylic acid solution onto an aluminium substrate and used for the reduction of Cr(VI). The reduction of Cr(VI) to the trivalent state was found to proceed by pseudo-first-order kinetics with an activation energy barrier of 15.13 kJ mol⁻¹. This catalyst could be regenerated by reducing the composite at a sufficiently negative potential, in the absence of Cr(VI). However, it was found that the catalyst functioned also through a self-sustained regeneration mechanism. In this mechanism, Cr(VI) was reduced by PPy⁰ to generate PPy⁺, but the PPy⁺ was subsequently reduced to PPy⁰ by oxidation of the aluminium substrate, thus regeneration of the catalytic PPy⁰ surface giving rise to a synergistic action between the polypyrrole and the aluminium substrate.