Understanding the Importance of Periodate Species in the pH-Dependent Degradation of Organic Contaminants in the H 2 O 2 /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 H 4 IO 6 - , we reinvestigated the pH effect on the decontamination performance of the H 2 O 2 /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 1 O 2 could be detected at pH 9.0, HO · was determined to be the major reactive oxidizing species in the H 2 O 2 /periodate process under all the tested pH levels. Furthermore, it was suggested that only H 4 IO 6 - and H 2 I 2 O 10 4- could serve as the precursors of HO · . The second-order rate constant for the reaction of H 2 I 2 O 10 4- species with H 2 O 2 was determined to be ∼1199.5 M -1 s -1 at pH 9.0, which was two orders of magnitude greater than that of H 4 IO 6 - (∼2.2 M -1 s -1 at pH 3.0). Taken together, the reaction pathways of H 2 O 2 with different periodate species were proposed. These fundamental findings could improve our understanding of the periodate-based advanced oxidation processes.