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), FeSnO(OH), SnFeO, and Sn-FeO) 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. SnFeO exhibited excellent visible-light absorption and superior photocatalytic activity, while Sn-FeO showed the lowest interfacial resistance and the highest density of Fe/Fe active sites, making it highly effective for PMS activation. Under light-assisted PMS conditions, Sn-FeO achieved a 99 % removal rate of CTC. Radical quenching experiments revealed that SnFeO primarily relied on superoxide radicals (O) and photogenerated holes (h), whereas Sn-FeO involved multiple reactive oxygen species, including sulfate radicals (SO), hydroxyl radicals (OH), O, and singlet oxygen (O). 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.