Abstract: Constructing the hetrostructure is a feasible strategy to enhance the performances of photocatalysts. However, there are still some fundamental details and mechanisms for the specific design of photocatalysts with heterostructure, which need further confirming and explain. In this work, g-C₃N₄-based heterostructures are constructed with TiO₂ in different ways, and their intrinsic factors to improve the photocatalytic activity are systematically studied by density functional theory (DFT). When g-C₃N₄ combines horizontally with TiO₂ to form a heterostructure, the interaction between them is dominated by van der Waals interaction. Although the recombination of photo-generated electron-hole pair cannot be inhibited significantly, this van der Waals interaction can regulate the electronic structures of the two components, which is conducive to the participation of photo-generated electrons and holes in the photocatalytic reaction. When the g-C₃N₄ combines vertically with TiO₂ to form a heterostructure, their interface states show obvious covalent features, which is very beneficial for the photo-generated electrons' and holes' transport along the opposite directions on both sides of the interface. Furthermore, the built-in electric field of g-C₃N₄/TiO₂ heterostructure is directed from TiO₂ layer to g-C₃N₄ layer under equilibrium, so the photo-generated electron-hole pairs can be spatially separated from each other. These calculated results show that no matter how g-C₃N₄ and TiO₂ are combined together, the g-C₃N₄/TiO₂ heterostructure can enhance the photocatalytic performance through corresponding ways.

Key words: photocatalysis, g-C₃N₄, TiO₂, heterostructures, interfacial states