Highly efficient activation of chlorite by Lewis acid sites-enriched pyrite for sulfonamides degradation

Herein, FeS₂ was synthesized via a hydrothermal method and employed to activate ClO₂^- for the degradation of sulfonamide antibiotics (SAs). The FeS₂/ClO₂^- system reaches degradation efficiencies of 96.8% for SM2, 97.5% for SMX, and 95.8% for STZ within 30 min. X-ray photoelectron spectroscopy (XPS) and pyridine-infrared spectroscopy (Py-IR) demonstrate that Fe(III) species, formed from the inevitable oxidation of the FeS₂ surface, function as Lewis acid sites. These sites enable a dual activation mechanism for ClO₂^-, including direct reduction to ClO₂ and Fe(IV), as well as catalytic decomposition yielding O₂ and Cl^-. Simultaneously, surface-bound Fe(II) efficiently activates O₂ to generate the superoxide anion (•O₂^-). Reactive species analysis and quenching experiments confirm that singlet oxygen (¹O₂), generated through the synergistic activation of ClO₂ and •O₂^- within the acidic micro-environment on the FeS₂ surface, acts as the dominant oxidative species accountable for SM2 degradation. By-products analysis verifies the sequential breakdown of SM2 into low-molecular-weight fragments through desulfonation, cleavage of the CN bond, oxidation of amino groups, and heterocyclic reconstruction, with partial mineralization to CO₂ and H₂O. This study pioneers a novel strategy for utilizing iron-based materials to efficiently activate ClO₂^- and degrade SAs via non-radical pathways, thus making a significant leap in advanced oxidation technology.