Accelerating iron redox cycling via acetate modification: a ligand engineering for sustainable fenton-like oxidation

Accelerating the rate-limiting surface Fe(III)/Fe(II) redox cycling is pivotal for efficient iron-mediated Fenton-like decontamination, yet conventional reductants (e.g., toxic hydroxylamine, thiosulfate) suffer from secondary toxicity, self-quenching, and heavy metal leaching. Here, we present an eco-friendly anion surface-modification strategy employing acetate to uniquely enhance Fe₃O₄ surface Fe(II) regeneration via O(p)-Fe(d) orbital hybridization. This hybridization displaces hydration-layer H₂O ligands, forming robust carboxylate-Fe(III) coordination to suppress iron leaching (323.44 mg l^-1 to 5.24 mg l^-1). Specifically, in-situ Raman and X-ray absorption spectroscopy (XAS) confirm this coordination transformation and 0.078 mg l^-1 increase in surface Fe(II). Thanks to acetate appropriate redox potential (0.01 V vs SHE) and coordination-driven solid-phase electron transfer outperform other redox-active oxygen-containing anions, spontaneously satisfying Fe(III) reduction and inhibiting radical quenching. Critically, acetate ligands establish a tripartite synergy with Fe₃O₄ and peroxymonosulfate (PMS, HSO₅^-) through: lowered PMS activation barriers, continuous electron flux from Fe-core to HSO₅^-,and maintained structural integrity. This synergy achieves 16.67-fold faster carbamazepine (CBZ) degradation versus unmodified counterparts. Continuous-flow operation (30 h) and environmental robustness real wastewater assessment validate scalability. This work advances sustainable Fenton-like catalysis via ligand-engineered surfaces, bridging atomic coordination control to industrial water treatment.