Generation of dynamic oxygen vacancies in graphene quantum dots/NaNbO3 heterojunction for boosting photocatalytic hydrogen evolution.

The design and theoretical study of green, low-cost heterojunction photocatalysts with strong interfacial interactions are crucial for achieving efficient and stable photocatalytic hydrogen evolution (PHE). This study proposes a simple method to synthesizing graphene quantum dots (GQDs)/NaNbO3 heterojunction with dynamic oxygen vacancies. GQDs promote the formation of oxygen vacancies and increase the surface-active sites of NaNbO3, significantly enhancing light absorption efficiency. This results in superior separation of photogenerated charge carriers in the GQDs/NaNbO3 composite and improves PHE activity and stability. Under the reaction conditions of methanol as a sacrificial agent, the 0.5%GQDs/NaNbO3 catalyst exhibited the highest hydrogen production rate of 775.9 μmol·g-1·h-1. Notably, in cyclic stability tests, the catalyst demonstrated higher catalytic activity in subsequent cycles compared to the initial cycle. The activity of the second round was 1.5 times that of the first round, and the hydrogen evolution rate was 1204.9 μmol·g-1·h-1. This improvement is likely attributed to the fast electron transport channel between NaNbO3 and GQDs, which facilitated the transfer of photo-generated electrons from NaNbO3 to GQDs, thereby promoting the generation of dynamic oxygen vacancies and improving the PHE performance. Electron Spin Resonance (ESR) and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed the crucial role of dynamic oxygen vacancies in enhancing catalytic activity. Furthermore, Density Functional Theory (DFT) calculations and experimental results elucidated the charge transfer mechanism and PHE process. This study provides valuable insights for the design of efficient and durable photocatalysts.