Enhanced optical absorption and photocatalytic H₂ production activity of g-C₃N₄/TiO₂ heterostructure by interfacial coupling : A DFT+U study

The electronic and optical properties of g-C₃N₄/TiO₂ heterostructure are investigated using spin-polarized DFT+U calculations. The equilibrium spacing (1.94 Å) and binding energy (24 meV/Ų) show that g-C₃N₄/TiO₂ is a van der Waals heterostructure. And the calculated band gap of g-C₃N₄/TiO₂ is significantly reduced compared with TiO₂. Therefore, the visible light response of g-C₃N₄/TiO₂ heterostructure is remarkably improved. Besides, the predicted type II band alignment would ensure that the electrons can migrate from g-C₃N₄ monolayer to anatase TiO₂ (101) surface, which leads oxidation and redox reactions can occur on g-C₃N₄ and TiO₂, respectively. Finally, a built-in electric field within the interface region will be set. Above processes can benefit the separation of photoexcited carriers and enhance the hydrogen-evolution activity. In addition, compared with TiO₂, g-C₃N₄/TiO₂ with higher conduction band minimum energy can effectively produce higher-energy electrons to reduce hydrogen ions. Moreover, the influence of composite distance and the number of g-C₃N₄ layers are also investigated systematically. The results indicate that the optical absorption is enhanced over the whole spectrum with the increase of the number of g-C₃N₄ layers. Similar visible light enhancing is also found when the composite distance is decreased.