Sulfamethazine degradation in the VUV/PMS/Cu(ii) system: the critical role of VUV and reduction behavior of copper

Abstract

In recent years, vacuum ultraviolet (VUV) radiation has garnered significant attention for its capacity to photodissociate organic compounds and reduce transition metals. However, the exploration of VUV-based Cu(II)/PMS systems has been notably absent. This study explores the efficiency and influencing factors of sulfamethazine (SMZ) degradation utilizing a VUV/Cu(II)/PMS approach. Firstly, the removal efficiencies of different systems were compared. VUV demonstrated significantly superior removal capability to UVC, owing to excellent photolytic capability. Secondly, SMZ degradation in the VUV/Cu(II)/PMS system showed pH independence, minimal anion effects, but high susceptibility to concentrated organic matter. The electron spin resonance (ESR) and quenching experiments indicate that hydroxyl radicals (˙OH) and sulphate radicals (SO₄˙⁻) play a significant role in the degradation mechanism of SMZ, in the presence of Cu(II) reducing the contribution of SO₄˙⁻. Furthermore, quantitative experiments on Cu(I) across different systems demonstrate that VUV exhibits superior reducing power. Finally, degradation products were detected using LC-MS, and four degradation pathways were thereby proposed including Smiles rearrangement, nitration, and breaking of the S–N bond and the C–N bond.