Remarkably high catalytic activity of the RuIII(edta)/H2O2 system towards degradation of the azo-dye Orange II

Abstract

The Ru^III(edta)/H₂O₂ system (edta⁴⁻ = ethylenediaminetretaacetate) was found to degrade the azo-dye Orange II at remarkably high efficiency under ambient conditions. Catalytic degradation of the dye was studied by using rapid-scan spectrophotometry as a function of [H₂O₂], [Orange II] and pH. Spectral analyses and kinetic data point towards a catalytic pathway involving the rapid formation of [Ru^III(edta)(OOH)]²⁻ followed by the immediate subsequent degradation of Orange II prior to the conversion of [Ru^III(edta)(OOH)]²⁻ to [Ru^IV(edta)(OH)]⁻ and [Ru^V(edta)(O)]⁻via homolysis and heterolysis of the O–O bond, respectively. The higher oxidation state Ru(IV) and Ru(V) complexes react three orders of magnitude slower with Orange II than the Ru(III)-hydroperoxo complex. In comparison to biological oxygen transfer reactions, the Ru(edta) complexes show the reactivity order Compound 0 ≫ Compounds I and II.