A novel WO3/ZnIn2S4/CoWO4 heterojunction for enhancement of photocatalytic degradation sparfloxacin: Dual S-scheme multi-charge transfer mode and Mechanistic pathway

The novel dual S-scheme WO3/ZnIn2S4/CoWO4 heterojunction was formed by loading WO3 and CoWO4 onto ZnIn2S4 (ZIS) using a simple two-step hydrothermal method. Sparfloxacin (SPX) degradation rate constant of WO3/ZnIn2S4/CoWO4 heterojunction reached 0.0312 min−1, which was nearly 26-, 8.4–34.7-, and 1.6- fold greater than those of WO3, ZIS, CoWO4, and WO3/ZIS, respectively. The multi-charge transfer and separation mechanism of dual S-scheme heterojunction photocatalysts is deeply explored by experiments and density functional theory: the carriers moved in reverse contributed to an interfacial heterotropic built-in electric field, which accelerated the photogenerated carriers' separation and interfacial transfer ability and lifetime. Further, no recombined electrons and holes with higher reducing and oxidizing properties produced more •O2−, h+ and •OH, which could attack the active atoms of SPX with a high Fukui index. By combining with liquid chromatography mass spectrometry-ion trap-time of flight, plausible SPX degradation intermediates, pathways and mechanisms were presented. SPX was degraded into humic acid-like intermediates, and its environmental risk was significantly reduced. This paper offers insight into developing a novel ZIS-based dual S-scheme heterojunction strategy for solving environmental issues.