Boundary unsaturated Iron coordination engineering on S-scheme heterojunctions steering selective H₂O₂ homolysis for...

Redirecting photocatalytic H₂O₂ activation from inefficient heterolytic cleavage toward the homolytic generation of hydroxyl radicals (•OH) is paramount for maximizing oxidant utilization in photo-Fenton-like water purification. Herein, we propose a selective H₂O₂ homolytic activation strategy enabled by a SrFe₁₂O₁₉/C₃N₄ (SCN-50) S-scheme heterojunction synthesized via urea-assisted thermal polymerization. The engineered coordinatively unsaturated Fe sites, characterized by an upshifted d-band center, effectively diminish the thermodynamic barrier for *OH intermediate formation, thereby steering H₂O₂ dissociation toward the homolytic •OH pathway. Consequently, the integrated SCN-50 architecture delivers an exceptional •OH generation selectivity of 86.3%. Driven by the S-scheme internal electric field, the synergistic preservation of strongly oxidizing holes (h⁺) at the oxidative terminus establishes a highly efficient relay degradation network for ofloxacin (OFX). Mechanistically, initial mild oxidation initiates preliminary side-chain dismantling, whereas the abundant •OH and preserved h⁺ cooperatively drive subsequent ring-opening and deep degradation. SCN-50 exhibits a rapid OFX degradation rate of 0.10 min^-1, surpassing pristine C₃N₄ and SrFe₁₂O₁₉ by 2.5 and 16.7 times, respectively, alongside robust stability across four batch cycles and a 100-min continuous-flow operation. This work provides profound insights into tailoring H₂O₂ homolysis and engineering S-scheme-driven multi-species relay degradation for environmental remediation.