Revisiting the Oxidizing Capacity of the Periodate-H2O2 Mixture: Identification of the Primary Oxidants and Their Formation Mechanisms br

Abstract

This study reexamined the mechanisms for oxidative organic degradation bythe binary mixture of periodate and H2O2(PI/H2O2) that was recently identified as a newadvanced oxidation process. Ourfindings conflicted with the previous claims that (i)hydroxyl radical (center dot OH) and singlet oxygen (1O2) contributed as the primary oxidants, and(ii)center dot OH production resulted from H2O2reduction by superoxide radical anion (O2 center dot-). PI/H2O2exhibited substantial oxidizing capacity at pH < 5, decomposing organicspredominantly by center dot OH. The likelihood of a switch in the major oxidant under varyingpH conditions was revealed. IO4-as the major PI form under acidic conditions underwentone-electron reduction by H2O2to yield radical intermediates, whereas H2I2O104-preferentially occurring at pH > 7 caused1O2generation through two-electron oxidationof H2O2. PI reduction by O2 center dot-was suggested to be a key reaction in center dot OH production, onthe basis of the electron paramagnetic resonance detection of methyl radicals in thedimethyl sulfoxide solutions containing PI and KO2, and the absence of deuterated and18O-labeled hydroxylated intermediatesduring PI activation using D2O and H218O2. Finally, simple oxyanion mixing subsequent to electrochemical PI and H2O2productionachieved organic oxidation, enabling a potential strategy to minimize the use of chemicals.