Tuning photocatalytic performance via oxygen vacancies and in situ ZnS formation on ZnO for hydrogen evolution

The quest for renewable energy solutions drives research into photocatalytic materials for hydrogen evolution, with zinc oxide (ZnO) emerging as a promising candidate. This study systematically examines the structural, optical, and photocatalytic properties of ZnO and oxygen-deficient ZnO x , synthesized via the hydrothermal method. Powder X-ray diffraction (P-XRD) reveals a crystal phase transition from the Zn(OH) 2 to ZnO 2 precursor, evolving into wurtzite ZnO and ZnO x . UV–Vis DR spectroscopy indicates enhanced visible light absorption and narrowed band gaps in ZnO x , suggesting improved photocatalytic water splitting capabilities. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirm the presence of oxygen vacancies and Zn +2 ions in the lattice. Transmission electron microscopy (TEM) shows well-faceted crystals with size increases at higher annealing temperatures. Oxygen-deficient ZnO annealed at 400 °C (ZnO x -400) exhibits superior photocatalytic hydrogen production efficiency (5780 μmol g −1 cat ), emphasizing the critical role of oxygen vacancies in enhancing activity. Under alkaline sulfide environments, in situ ZnS formation on ZnO surfaces creates stable ZnS/ZnO composite structures, enhancing photocatalyst durability and recyclability. This study underscores the importance of oxygen vacancies, ZnS formation, and structural tuning in optimizing ZnO for visible-light-driven hydrogen evolution, advancing renewable energy solutions.