Energy band engineering of graphitic carbon nitride for photocatalytic hydrogen peroxide production

Hydrogen peroxide (H₂O₂) is one of the 100 most important chemicals in the world with high energy density and environmental friendliness. Compared with anthraquinone oxidation, direct synthesis of H₂O₂ with hydrogen (H₂) and oxygen (O₂), and electrochemical methods, photocatalysis has the characteristics of low energy consumption, easy operation and less pollution, and broad application prospects in H₂O₂ generation. Various photocatalysts, such as titanium dioxide (TiO₂), graphitic carbon nitride (g-C₃N₄), metal-organic materials, and nonmetallic materials, have been studied for H₂O₂ production. Among them, g-C₃N₄ materials, which are simple to synthesize and functionalize, have attracted wide attention. The electronic band structure of g-C₃N₄ shows a bandgap of 2.77 eV, a valence band maximum of 1.44 V, and a conduction band minimum of −1.33 V, which theoretically meets the requirements for hydrogen peroxide production. In comparison to semiconductor materials like TiO₂ (3.2 eV), this material has a smaller bandgap, which results in a more efficient response to visible light. However, the photocatalytic activity of g-C₃N₄ and the yield of H₂O₂ were severely inhibited by the electron-hole pair with high recombination rate, low utilization rate of visible light, and poor selectivity of products. Although previous reviews also presented various strategies to improve photocatalytic H₂O₂ production, they did not systematically elaborate the inherent relationship between the control strategies and their energy band structure. From this point of view, this article focuses on energy band engineering and reviews the latest research progress of g-C₃N₄ photocatalytic H₂O₂ production. On this basis, a strategy to improve the H₂O₂ production by g-C₃N₄ photocatalysis is proposed through morphology control, crystallinity and defect, and doping, combined with other materials and other strategies. Finally, the challenges and prospects of industrialization of g-C₃N₄ photocatalytic H₂O₂ production are discussed and envisioned.