Study on the applicability and mechanism of Sn-Fe bimetallic oxide catalysts for light-assisted peroxymonosulfate activation in the degradation of chlortetracycline hydrochloride.

Antibiotic pollutants in water pose severe threats to ecosystems and human health, necessitating efficient remediation strategies. Sn-Fe bimetallic oxides, composed of earth-abundant and low-toxicity elements, offer an environmentally friendly catalytic approach for sustainable pollutant degradation. In this study, four Sn-Fe bimetallic oxide catalysts (Fe-SnO(OH)2, FeSnO(OH)5, SnFe2O4, and Sn-Fe3O4) were synthesized via a hydrothermal method by adjusting the amount of NaOH. As the NaOH dosage increased, the crystal phase of the materials gradually transformed from hydroxides to a spinel structure. The catalytic performances of these materials for degrading chlortetracycline hydrochloride (CTC·HCl) were systematically evaluated under photocatalysis, peroxymonosulfate (PMS) activation, and light-assisted PMS activation conditions. SnFe2O4 exhibited excellent visible-light absorption and superior photocatalytic activity, while Sn-Fe3O4 showed the lowest interfacial resistance and the highest density of Fe2+/Fe3+ active sites, making it highly effective for PMS activation. Under light-assisted PMS conditions, Sn-Fe3O4 achieved a 99 % removal rate of CTC. Radical quenching experiments revealed that SnFe2O4 primarily relied on superoxide radicals (O2·-) and photogenerated holes (h+), whereas Sn-Fe3O4 involved multiple reactive oxygen species, including sulfate radicals (SO4·-), hydroxyl radicals (•OH), O2·-, and singlet oxygen (1O2). This study clarifies the relationship between crystal structure, electronic properties, and catalytic mechanisms, providing theoretical support for the development of Sn-Fe-based oxide catalysts in synergistic photocatalytic and PMS activation systems for pollutant degradation.