Anion vacancy engineered Cu/ZnIn₂S₄-V_S/TiO₂-V_O S-scheme heterojunction for enhancing photocatalytic overall water splitting

Heterojunction materials for photocatalytic overall water splitting (POWS) become popular in recent times. However, even in the superior S-scheme heterojunction, the two semiconductor materials still do not have an efficient activity to separate and migrate photogenerated carriers. To further improve the charge separation and enhance the activity of POWS, a novel S-scheme heterojunction photocatalyst, Cu/ZnIn₂S₄-V_S/TiO₂-V_O, was synthesized using solvothermal and calcination methods. The photocatalyst consists of Cu/ZnIn₂S₄ with sulfur vacancies (Cu/ZIS-V_S) and TiO₂ with oxygen vacancies (TiO₂-V_O). The resultant photocatalyst exhibited optimal hydrogen and oxygen evolution rates of 1245.3 μmol/g/h and 621.4 μmol/g/h, respectively. The apparent quantum efficiency reached 5.8 % at 365 nm. The corresponding characterization and theoretical calculations demonstrated the S-scheme heterojunction between Cu/ZIS-V_S and TiO₂-V_O was successfully synthesized and resulted in a notable enhancement in the effective separation of carriers. Sulfur and oxygen vacancies in ZIS and TiO₂, respectively, led to a reduction in their band gaps, which is beneficial for electron migration. Moreover, copper doping augmented the light absorption capabilities. Sulfur vacancies caused charge delocalization which facilitated the transfer of electrons and consequently enhanced the photocatalytic activity. This research provided an innovative perspective on the exploration and development of S-scheme heterojunctions aimed at POWS.