Title: Fe²⁺/HClO Reaction Produces Fe^IVO²⁺: An Enhanced Advanced Oxidation Process

Abstract: The reaction between Fe²⁺ and HClO constitutes a promising advanced oxidation process (AOP) for removing pollutants from wastewater, and ^•OH has been considered the dominant reactive oxidant despite limited evidence for this. Herein, we demonstrate that the Fe²⁺/HClO reaction enables the production of Fe^IVO²⁺ rather than ^•OH in acid medium, a finding that is strongly supported by multiple lines of evidence. Both X-ray absorption near-edge structure spectroscopic tests and Mössbauer spectroscopic tests confirmed the appearance of Fe^IVO²⁺ as the reactive intermediate in the reaction between Fe²⁺ and HClO. The determination of Fe^IVO²⁺ generation was also derived from the methyl phenyl sulfoxide (PMSO)-based probe experiments with respect to the formation of PMSO2 without ^•OH adducts and the density functional theory studies according to the lower energy barrier for producing Fe^IVO²⁺ compared with ^•OH. A dual-anode electrolytic system was established for the in situ generation of Fe²⁺ and HClO that allows the production of Fe^IVO²⁺. The system exhibits an enhanced capacity for oxidizing a model pollutant (e.g., phosphite) from industrial wastewater, making it an attractive and promising AOP for the abatement of aqueous contaminants.