Highly efficient activation of peroxymonosulfate by bismuth oxybromide for sulfamethoxazole degradation under ambient conditions: Synthesis, performance, kinetics and mechanisms

A 3D flower-like bismuth oxybromide (BiOBr) was synthesized by a facile one-pot chemical precipitation method and its potential on sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation was investigated for the first time. The physic-chemical properties of BiOBr were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The key influencing factors in SMX degradation (including catalyst loading, PMS dosage, pH etc.) were discussed. The attack sites and degradation pathway were proposed via the identification of the reactive sites on SMX molecular together with the detection of intermediate degradation products. Furthermore, the toxicity of the intermediate products was evaluated via the ecological activity relationship (ECOSAR) program and the PMS activation mechanism over BiOBr was proposed via the determination of reactive species. Hydroxyl radical and singlet oxygen were identified as the main reactive species in the system and the enhanced catalytic efficiency of BiOBr was attributed to the active metal (Bi³⁺-Bi⁵⁺-Bi³⁺) redox cycles as well as the light effect. The enhancement on SMX degradation from light effect could be observed under visible light irradiation, even at ambient light condition. Finally, the robustness of the BiOBr/PMS system was further examined via multiple organics degradation as well as the performance comparison with other metal oxides. These findings provide an insight for BiOBr as a viable and superior alternative for PMS activation in organics degradation.