Revisiting the Oxidizing Capacity of the Periodate-H 2 O 2 Mixture: Identification of the Primary Oxidants and Their Formation Mechanisms.

This study reexamined the mechanisms for oxidative organic degradation by the binary mixture of periodate and H 2 O 2 (PI/H 2 O 2 ) that was recently identified as a new advanced oxidation process. Our findings conflicted with the previous claims that (i) hydroxyl radical ( • OH) and singlet oxygen ( 1 O 2 ) contributed as the primary oxidants, and (ii) • OH production resulted from H 2 O 2 reduction by superoxide radical anion (O 2 •- ). PI/H 2 O 2 exhibited substantial oxidizing capacity at pH < 5, decomposing organics predominantly by • OH. The likelihood of a switch in the major oxidant under varying pH conditions was revealed. IO 4 - as the major PI form under acidic conditions underwent one-electron reduction by H 2 O 2 to yield radical intermediates, whereas H 2 I 2 O 10 4- preferentially occurring at pH > 7 caused 1 O 2 generation through two-electron oxidation of H 2 O 2 . PI reduction by O 2 •- was suggested to be a key reaction in • OH production, on the basis of the electron paramagnetic resonance detection of methyl radicals in the dimethyl sulfoxide solutions containing PI and KO 2 , and the absence of deuterated and 18 O-labeled hydroxylated intermediates during PI activation using D 2 O and H 2 18 O 2 . Finally, simple oxyanion mixing subsequent to electrochemical PI and H 2 O 2 production achieved organic oxidation, enabling a potential strategy to minimize the use of chemicals.