Substrate versus oxidant activation in RuIII(edta) catalyzed dye degradation

Abstract

The [Ru^III(edta)(H₂O)]⁻ (edta⁴⁻ = ethylenediaminetetraacetate) catalyzed oxidative degradation of methylene blue (MB) in the presence of H₂O₂ has been achieved. Complete degradation of 0.05 mM MB was noticed within 300 s in the presence of 5.0 μM of Ru(edta) catalyst under ambient conditions. Catalytic degradation of the dye was investigated by using rapid-scan spectrophotometry as a function of [Ru(edta)], [H₂O₂], [MB] and pH at 25 °C. Spectral analyses and kinetic data point towards a catalytic pathway that involves the rapid coordination of MB to the Ru^III(edta) complex to yield [Ru^III(edta)(MB)]⁻ species that react directly with hydrogen peroxide. The catalytic-active intermediate [Ru^III(edta)(OOH)]²⁻ was also found to be operative at high H₂O₂ concentration over the Ru(edta) catalyst in effecting MB degradation under the specified conditions.