In situ DTSA ligand engineering of CoWO4: a robust peroxymonosulfate activator for benzophenone-3 and tetracycline degradation

Abstract

Pharmaceuticals and personal care products (PPCPs) are pervasive aquatic micropollutants that raise growing concerns due to their phytotoxic, carcinogenic and endocrine-disrupting effects. Herein, we report an in situ ligand-modulated cobalt tungstate, DTSA/CoWO₄, prepared by incorporating 2,2′-dithiosalicylic acid (DTSA) into CoWO₄ to regulate its interfacial coordination environment and redox behavior toward peroxymonosulfate (PMS) activation. Comprehensive characterization (SEM, XRD, XPS and FT-IR) confirms the successful construction of DTSA-modified CoWO₄. Relative to pristine CoWO₄, DTSA/CoWO₄ exhibits markedly enhanced catalytic activity for the oxidative removal of representative PPCPs, achieving >90% degradation of benzophenone-3 (BP-3) within 30 min (k = 0.12 min⁻¹) and 99% degradation of tetracycline (TC) within 20 min (k = 0.214 min⁻¹), corresponding to 3.29-fold and 2.19-fold rate enhancements. Mechanistic studies, combining quenching experiments and electron paramagnetic resonance (EPR) analysis, identified superoxide anion (O₂˙⁻) and singlet oxygen (¹O₂) as the dominant reactive species, whereas the involvement of sulfate radicals (SO₄˙⁻) and hydroxyl radicals (˙OH), although suggested by quenching results, could not be directly confirmed under the current aqueous EPR conditions. LC-MS/MS analysis showed that BP-3 could be effectively converted into smaller products, and ECOSAR-based toxicity prediction indicated that the overall toxicity of the converted products was reduced after treatment. Notably, DTSA/CoWO₄ retains its activity over four repeated cycles, and quantitative analysis via ICP-MS reveals that the leaching of cobalt and tungsten is negligible. These results indicate that ligand engineering of CoWO₄ is an effective strategy for obtaining promising persulfate activators for the degradation of personal care products and pharmaceuticals.