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 ¹O₂could 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 H₂I₂O₁₀^4-could serve as the precursors of HO^·. The second-order rate constant for the reaction of H₂I₂O₁₀^4-species with H₂O₂was determined to be ∼1199.5 M^-1s^-1at pH 9.0, which was two orders of magnitude greater than that of H₄IO₆^-(∼2.2 M^-1s^-1at pH 3.0). Taken together, the reaction pathways of H₂O₂with different periodate species were proposed. These fundamental findings could improve our understanding of the periodate-based advanced oxidation processes.