Vacancy-Rich S-Scheme Core–Shell-Like ZnO@ZnS for Visible-Light Photocatalytic Degradation of Oxytetracycline and Hydrogen Production in Seawater

Reducing seawater antibiotic pollution while producing hydrogen is a major challenge crucial for environmental protection and easing energy shortages. In this work, an S-scheme heterojunction ZnO@ZnS with a large number of vacancies [including zinc, sulfur, and oxygen vacancies (V Zn, V S, V O )] was prepared in situ using metal–ligand coordination polymers as templates. The characterization results demonstrated that ZnS, synthesized using a metal–ligand template agent, progressively develops into a core–shell heterojunction semiconductor wherein it serves as the core with ZnO functioning as the shell, depending on varying calcination temperatures. The experimental data indicate that 550 °C–ZnO@ZnS (which exhibits a higher concentration of V Zn and V O ) achieves a degradation rate of 60.2% over 5 cycles of OTC degradation under high-salinity conditions. Furthermore, 500 °C–ZnO@ZnS (which exhibits a higher concentration of V Zn and V S ) demonstrates a hydrogen production capacity from seawater that is 15.98 times greater than that of ZnS and 25.80 times greater than that of ZnO. PL, EPR and UPS data show that the excellent redox performance of ZnO@ZnS lies in the organic coupling of numerous vacancies which are generated during the preparation process with the built-in electric field at the heterojunction. This interaction enhances the recombination and transportation of charge carriers, thereby increasing the photocatalytic efficiency of both electrons and holes.