pH dependent periodate activation by photosensitized DOM via triplet state and superoxide radical

Dissolved organic matter (DOM) is ubiquitous in real waters and can photosensitize oxidant activation. However, the mechanisms of DOM-photosensitized periodate (PI) activation remain unclear. This study systematically investigated the pH-dependent kinetics and mechanisms of this process. PI decay exhibited a pronounced positive pH dependence: Raising pH from 5.0 to 10.0 increased the decay rate constant by 2.9-fold, from 14.51(± 0.46) × 10^-2 min^-1 to 57.03(± 0.06) × 10^-2 min^-1, in DOM solutions, whereas an opposite trend was observed without DOM. Triplet DOM (³DOM*) and superoxide radical (O₂^•⁻) were identified to play critical and cooperative roles in PI activation. Upon laser flash photolysis, the second-order rate constants of triplet model photosensitizers quenched by PI ( [Formula: see text] ) at pH 7.0 were determined in the range of 3.64(± 0.04) × 10⁸-3.01(± 0.08) × 10⁹ M^-1 s^-1, with the [Formula: see text] for H₄IO₆^- being 27-fold higher than that for H₃IO₆^2-. The 27% decrease in the [Formula: see text] determined in 50% D₂O further indicated that ³DOM* tends to activate PI through a proton-coupled electron transfer pathway, while O₂^•⁻ mainly reacts with PI through the electron transfer reaction. Hydroxyl radical (HO^•) was unequivocally identified as the dominant reactive species generated from PI activation, which substantially enhanced carbamazepine degradation by 38.5-143% in the presence of DOM isolates (1.0-7.0 mg_Cl^-1). The enhancement in CBZ degradation correlated strongly with the accelerated PI decay across pH 6.0-10.0 (r² > 0.99). Importantly, this process remained effective in realistic water matrices, and in the tested DOM solutions, PI was completely converted to non-toxic iodate without generating iodinated disinfection byproducts. This work elucidates the pH dependent mechanism of PI activation by DOM photosensitization, and demonstrates the feasibility of a catalyst-free, solar-driven advanced oxidation process that leverages naturally occurring water constituents for sustainable emerging contaminant removal in realistic water matrices.