Ligand-mediated electron transfer in pH-tolerant Mn(II)/Fe(VI) bimetallic system: High-valent iron-oxo generation for efficient antibiotic removal.

Ferrate-based advanced oxidation processes (Fe(VI)-AOPs) show promise for antibiotic abatement in water, but their practical application is typically limited by pH sensitivity, unstable active species, and insufficient electron transfer in real water matrices. To address these issues, we developed a novel ethylenediaminetetraacetic acid (EDTA)-bridged Mn(II)/Fe(VI) bimetallic synergistic system. Such a unique system could achieve 96.26% degradation of target antibiotics within 2 min via a non-radical direct electron transfer pathway, with stable performance across a wide pH range (5.0-9.0) relevant to natural and engineered water systems. Comprehensive characterization confirmed that EDTA functioned as a ligand to stabilize Mn(II) by complexation, suppressed the disproportionation of Mn(III) intermediates, key processes that enhanced pollutant removal. Moreover, the EDTA-Mn complex acted as an electron mediator, facilitating the conversion of Fe(VI) to highly reactive high-valent iron-oxo species (Fe(IV)=O and Fe(V)=O) and establishing a synergistic reaction pathway of ligand regulation-metal cycling-electron transfer-high-valent iron generation. Notably, computational toxicology combined with multi-level biological assays (microbial inhibition, phytotoxicity, and animal developmental toxicity) demonstrated that the system could effectively degrade antibiotics and also substantially reduce their acute and chronic ecotoxicity, addressing a critical gap in conventional AOPs that often overlook post-degradation ecological risks. This study systematically clarified the molecular mechanisms, catalytic oxidation performance, and environmental safety of the ligand-bridged bimetallic system, providing a robust basis for developing green, stable, and scalable water treatment technologies suitable for real-world antibiotic remediation.