Surface hydroxyl engineering governs interfacial chlorite activation for selective antibiotic oxidation

Chlorite (NaClO 2 ) is a promising yet underexplored oxidant precursor for selective water decontamination. However, current activation strategies mainly focus on bulk composition and metal redox properties, while the decisive role of the surface chemical environment, particularly surface hydroxyl groups, remains poorly understood. Herein, by simply tuning the Co/Fe atomic ratio during hydrothermal synthesis, we developed a hydroxyl-enriched Fe Co spinel oxide catalyst and established a surface-mediated NaClO 2 activation system for efficient sulfamethoxazole (SMX) degradation. The hydroxyl-enriched catalyst achieved approximately 80.0% SMX removal within 30 min, whereas its hydroxyl-poor counterpart showed negligible reactivity. Spectroscopic, electrochemical, and theoretical analyses reveal that increased Co content enhances the electron density of Co sites, preferentially stabilizing Co-OH coordination and generating hydroxylated interfacial sites. These sites anchor NaClO 2 and promote Cl O bond polarization, thereby driving the formation of Co(IV) = O as the dominant oxidizing species, with an estimated 81.6% contribution to SMX degradation based on the phenyl methyl sulfoxide (PMSO) probe transformation experiment, along with ClO 2 and minor 1 O 2 production. Toxicity assessment and plant germination tests further demonstrate that the treated solution exhibits reduced environmental risk. This study identifies surface hydroxyl enrichment as a critical interfacial factor governing NaClO 2 activation and provides a mechanistic basis for designing selective oxidation systems for antibiotic abatement.