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

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.