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

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.