Understanding the Importance of Periodate Species in the pH-Dependent Degradation of Organic Contaminants in the H2O2/Periodate Process

Although periodate-based advanced oxidation processes have been proven to be efficient in abating organic contaminants, the activation properties of different periodate species remain largely unclear. Herein, by highlighting the role of H4IO6-, we reinvestigated the pH effect on the decontamination performance of the H2O2/periodate process. Results revealed that elevating pH from 2.0 to 10.0 could markedly accelerate the rates of organic contaminant decay but decrease the amounts of organic contaminant removal. This pH-dependent trend of organic contaminant degradation corresponded well with the HO· yield and the variation of periodate species. Specifically, although 1O2 could be detected at pH 9.0, HO· was determined to be the major reactive oxidizing species in the H2O2/periodate process under all the tested pH levels. Furthermore, it was suggested that only H4IO6- and H2I2O104- could serve as the precursors of HO·. The second-order rate constant for the reaction of H2I2O104- species with H2O2 was determined to be ∼1199.5 M-1 s-1 at pH 9.0, which was two orders of magnitude greater than that of H4IO6- (∼2.2 M-1 s-1 at pH 3.0). Taken together, the reaction pathways of H2O2 with different periodate species were proposed. These fundamental findings could improve our understanding of the periodate-based advanced oxidation processes.