Iron species activating chlorite: Neglected selective oxidation for water treatment

Chlorite (ClO₂ ^-) is the by-product of the water treatment process carried out using chlorine dioxide (ClO₂) as an effective disinfectant and oxidant; however, the reactivation of ClO₂ ^- has commonly been overlooked. Herein, it was unprecedentedly found that ClO₂ ^- could be activated by iron species (Fe_b: Fe⁰, Fe^II, or Fe^III), which contributed to the synchronous removal of ClO₂ ^- and selective oxidative treatment of organic contaminants. However, the above-mentioned activation process presented intensive H⁺-dependent reactivity. The introduction of Fe_b significantly shortened the autocatalysis process via the accumulation of Cl^- or ClO^- during the protonation of ClO₂ ^- driven by ultrasonic field. Furthermore, it was found that the interdependent high-valent-Fe-oxo and ClO₂, after identification, were the dominant active species for accelerating the oxidation process. Accordingly, the unified mechanisms based on coordination catalysis ([Fe (H₂O) (ClO ) ] ⁺-P) were putative, and this process was thus used to account for the pollutant removal by the Fe_b-activated protonated ClO₂ ^-. This study pioneers the activation of ClO₂ ^- for water treatment and provides a novel strategy for "waste treating waste". Derivatively, this activation process further provides the preparation methods for sulfones and ClO₂, including the oriented oxidation of sulfoxides to sulfones and the production of ClO₂ for on-site use.