First-principles investigation of the two-dimensional van der Waals g-C3N4/g-ZnO heterojunction: Enhancing the photocatalytic hydrogen evolution activity

The 2D heterostructure composed of two-dimensional (2D) catalysts combined by van der Waals force constraints can significantly improve the photocatalytic performance, which provides a new idea for the renewable energy and the pollutant degradation. In this research, a catalyst for photocatalysis was developed by combining g-ZnO and g-C3N4, and their electronic and optical characteristics were analyzed by using a density-functional theory (DFT). g-C3N4/g-ZnO (CNZNO), a 2D layered semiconducting material with an indirect bandgap (Eg=2.2884 eV) and a typical Z-type heterojunction structure. This structure can effectively prevent the recombination of photogenerated carriers at the interface, which improves their lifetime, and the energy band edges of the catalyst are aligned appropriately to facilitate hydrogen production via water splitting. In the heterojunction of CNZNO, the charge dissipation region (hole aggregation region) occurs near the surface of g-C3N4, the charge accumulation region occurs near the surface of g-ZnO, and the charge transfers from g-C3N4 to g-ZnO. The uneven charge distribution caused by charge transfer, which generates an electric field at the heterojunction interface. The CNZNO heterojunction has very stable solar-to-hydrogen (STH) efficiency and can be adapted to different environments. This result contributes to the development of efficient and stable photocatalysts.