Mechanistic details of the catalytic degradation of methylene blue by hydrogen peroxide in basic solution. The unexpected innocence of percarbonate

Abstract

Recently it was shown that the MnIII(TPPS) – hydrogen peroxide system in alkaline media exhibits a vigorous catalase activity. Intermediate (TPPS)MnVO formed in a catalytic cycle in the system is an efficient degrading agent for a model dye, Orange II, in carbonate buffers. The high efficacy of the catalyst under these conditions is attributed to the generation of strongly oxidising percarbonate ions, a commonly known effect. The detailed study on the MnIII(TPPS) catalysed rapid degradation of methylene blue by hydrogen peroxide, performed using stopped-flow electronic spectroscopy as a function of the catalyst, hydrogen peroxide, pH and carbonate concentrations reported herein, has surprisingly evidenced a minor role of percarbonate in the overall catalytic cycle.