• WO 3 /C 3 N 5 composite shows superior visible-light photocatalytic H 2 evolution without precious-metal cocatalysts. • Composite annealing shrinks C 3 N 5 via bridging-N loss and defect formation • Band bending at the WO 3 /C 3 N 5 interface was evaluated using XPS/UPS/IPES/DFT. • Extensive photocatalytic tests and DFT jointly confirm an ideal S-scheme charge-transfer pathway. Composite photocatalysts have many advantages, such as visible light response, charge separation efficiency, and the lack of precious metal use, and are attracting attention as high-performance photocatalytic materials that that can solve many of the problems associated with single photocatalysts. On the other hand, there remain many unknowns regarding charge transfer, the understanding of which is key to improving the performance of composite photocatalysts. In particular, elucidating the details of the charge transfer process at the photocatalyst interface is an urgent and important issue that must be understood to improve the performance of future composite photocatalysts. In this study, we have focused on composite formation of tungsten trioxide (WO 3 ) and nitrogen-rich carbon nitride (C 3 N 5 ), and have investigated the band bending occurring at the interface during complexation and the charge transfer before and after light irradiation over the composite photocatalysts using various experimental techniques and simulations. The results support the presence of the ideal S-scheme mechanism and the overall photocatalytic performance of WO 3 /C 3 N 5 was superior to that of the other individual photocatalysts. In addition, C 3 N 5 particle size was found to decrease during annealing treatment when complexed with WO 3 , which is surmised to be due to the loss of bridging nitrogen.
Ito et al. (Sun,) studied this question.