Phosphate-modified m-Bi2O4 enhances the absorption and photocatalytic activities of sulfonamide: Mechanism, reactive species, and reactive sites

Abstract

Widespread usage of the sulfonamide class of antibiotics is causing increasing ecotoxicological concern, as they have the capacity to alter ambient ecosystems. Photocatalytic technology is an attractive yet challenging strategy for the degradation of antibiotics. For this work, the phosphate modification of m-Bi2O4 (Bi2O4-P) was prepared via a one-step hydrothermal process involving sodium bismuthate and sodium phosphate, which was employed for the degradation of sulfamethazine (SMZ) under visible light irradiation. The 0.5% Bi2O4-P exhibited excellent photocatalytic performance, which was 1.9 times that of pure m-Bi2O4. The photocatalytic degradation kinetics and mechanism of SMZ was investigated at different pH, whereupon it was revealed that m-Bi2O4-P exhibited improved SMZ adsorption and photocatalytic activities in contrast to pure m-Bi2O4. Compared with other four sulfonamide antibiotics, structures that contained additional methyl on the pyrimidine could be more easily attacked by phosphate modified m-Bi2O4. Reactive species (RS) scavenging experiments revealed that h+ was primarily responsible for the degradation of SMZ. Further studies of RS by ESR technology, and the results of photoelectrochemical properties showed phosphate-modified m-Bi2O4 could make greater use of photogenerated carriers, thereby producing additional RS. Based on the HRAM LC–MS/MS and the Frontier Molecular Orbital Theory, the degradation pathways of SMZ were proposed.