A comprehensive performance evaluation of heterogeneous Bi₂Fe₄O₉/peroxymonosulfate system for sulfamethoxazole...

In this study, a Bi₂Fe₄O₉ catalyst with nanoplate morphology was fabricated using a facile hydrothermal method. It was used as a catalyst to activate peroxymonosulfate (PMS) for aqueous sulfamethoxazole (SMX) removal. A comprehensive performance evaluation of the Bi₂Fe₄O₉/PMS system was conducted by investigating the effects of pH, PMS dosage, catalyst loading, SMX concentration, temperature, and halides (Cl^- and Br^-) on the degradation of SMX. The Bi₂Fe₄O₉/PMS system demonstrated a remarkable catalytic activity with >95% SMX removal within 30 min (conditions: pH 3.8, [Bi₂Fe₄O₉] = 0.1 g L^-1, [SMX]:[PMS] mol ratio =1:20). It was found that both Cl^- and Br^- can lead to the formation of PMS-induced reactive halide species (i.e. HClO, HBrO, and Br₂) which can also react with SMX forming halogenated SMX byproducts. Based on the detected degradation byproducts, the major SMX degradation pathway in the Bi₂Fe₄O₉/PMS system is proposed. The SMX degradation by Bi₂Fe₄O₉/PMS system in the wastewater secondary effluent (SE) was also investigated. The results showed that SMX degradation rate in the SE was relatively slower than in the deionized water due to (i) reactive radical scavenging by water matrix species found in SE (e.g.: dissolved organic matters (DOCs), etc.), and (ii) partial deactivation of the catalyst by DOCs. Nevertheless, the selectivity of the SO₄^•- towards SMX degradation was evidenced from the rapid SMX degradation despite the high background DOCs in the SE. At least four times the dosage of PMS is required for SMX degradation in the SE to achieve a similar SMX removal efficiency to that of the deionized water matrix.