Surface‐Bound Superoxide Radical‐Mediated Photo‐Fenton Mineralization of Ciprofloxacin on Fe‐Sillenite Nanosheets

ABSTRACT Refractory antibiotics frequently generate highly toxic and persistent intermediates during advanced oxidation processes, which severely limit their safe and complete removal. Recent studies show that the fluoroquinolone antibiotic ciprofloxacin (CIP) commonly accumulates quinone‐imine intermediates in Fenton systems, leading to reduced mineralization efficiency and increased toxicity risks. In this work, iron‐based sillenite (Bi ₁₂ FeO ₂₀ ) nanosheets are developed to construct an efficient photo‐Fenton system, achieving rapid degradation (94.3% in 8 min) and deep mineralization (TOC 93.8% in 2 h). Comprehensive intermediate‐state identification and theoretical calculations reveal that Bi ₁₂ FeO ₂₀ stabilizes surface‐bound superoxide radicals (·O ₂ ⁻ ) with significantly enhanced reducing capability, whose HOMO energy levels are markedly higher than those of free·O ₂ ⁻ . These surface‐bound radicals efficiently inject electrons into the LUMO of quinone‐imine intermediates, triggering aromatic ring‐opening reduction followed by progressive oxidation, ultimately enabling complete structural destruction and toxicity elimination. Compared with conventional pathways dominated by free ROS, this study establishes a surface‐bound radical‐driven “interfacial directed reduction–oxidation coupled mineralization mechanism.” This work highlights the structural advantages of sillenite for interfacial radical regulation and the removal of refractory intermediates, offering a new materials strategy for designing Fenton catalysts and achieving safe antibiotic treatment in aquatic environments.