Rationally designed S-scheme heterojunction of BiOCl/g-C3N4 for photodegradation of sulfamerazine: Mechanism insights, degradation pathways and DFT calculation

Antibiotics present in surface water have detrimental effects on both human health and the ecosystem. Additionally, they pose a threat to the effectiveness of biological water treatment processes. In this study, a visible photocatalytic system with BiOCl/g-C3N4 heterojunction was developed to remove sulfonamide antibiotic sulfamethazine (SMZ) in water. The removal rate reached 92.77% under visible light irradiation for 80 min. This photocatalyst remained active after 5 cycles of experiments and maintained a relatively stable removal rate of SMZ of over 80%. The ESR tests indicate that the main active species in this photocatalytic system were h+ and •O2−. The enhanced photocatalytic efficiency was mainly ascribed to the formation of a built-in electric field between BiOCl and g-C3N4 through the carrier transport mechanism of the S-scheme heterojunction. This heterojunction facilitated the photogenerated carrier shift and segregation, and improved the interfacial charge transfer efficiency, as confirmed by photoelectrochemical test and Density functional theory (DFT) calculations. The HPLC-QTOF-MS/MS and DFT analysis revealed possible degradation pathways of SMZ may involve deamination, hydroxylation, SO2 extrusion and bond breaking. This novel BiOCl/g-C3N4 heterojunction has proven to be essential for efficient visible-light photocatalysis.