Visible-light driven In₂O₃/ferrate system for efficient micropollutant removal: formation of reactive iron species induced by the capture of photogenerated electrons

A Vis–LED-driven In₂O₃/ferrate (Fe(VI)) system was developed to rapidly degrade micropollutants. Vis–LED/In₂O₃/Fe(VI) achieved 92.2% removal of sulfamethoxazole (SMX) within 10 min, outperforming other oxidizers (Mn(VII), etc.) and photocatalysts (g–C₃N₄, etc.) by 41.0–91.9% and 15.0–32.7%, respectively. Mechanistic analysis revealed that Fe(VI) exhibited the strongest affinity for In₂O₃ (adsorption energy: −3.82 eV), and In₂O₃ served both as a photocatalyst and an electron transfer platform in Vis–LED/In₂O₃/Fe(VI). Under Vis–LED irradiation, Fe(VI) adsorbed on the In₂O₃ surface could efficiently capture photogenerated electrons (e_CB⁻), thereby accelerating charge separation (photocurrent: ∼2.36 μA/cm²) and enhancing pollutant degradation. Additionally, Fe(VI) preferentially captures e_CB⁻ over O₂, thereby inhibiting the generation of non-selective ^•OH, while driving the generation of ‌Fe(IV)/Fe(V)‌. The relative contribution results confirmed that SMX degradation was mainly mediated by Fe(IV)/Fe(V) (> 97% contribution), with Fe(IV) (52.3%) dominating due to its ‌38.4% lower formation energy‌ versus Fe(V). The system showed high tolerance to matrix interferences (Cl⁻, HCO₃⁻, etc.) and outperformed the Fe(VI) alone system by 50.7–84.4% in real water (WWTPs effluent, tap water, etc.). Under sunlight irradiation, the In₂O₃/Fe(VI) system achieved degradation efficiencies exceeding 91% for typical micropollutants such as SMX and diclofenac (DCF). Overall, Vis–LED/In₂O₃/Fe(VI) enables energy-efficient, and selective pollutant degradation, offering a sustainable alternative to traditional radical-based processes.