Semiconductor polymeric graphitic carbon nitride photocatalysts: The "holy grail" for the photocatalytic hydrogen evolution reaction under visible light

Semiconductor polymeric graphitic carbon nitride (g-C₃N₄) photocatalysts have attracted dramatically growing attention in the field of the visible-light-induced hydrogen evolution reaction (HER) because of their facile synthesis, easy functionalization, attractive electronic band structure, high physicochemical stability and photocatalytic activity. This review article presents a panorama of the latest advancements in the rational design and development of g-C₃N₄ and g-C₃N₄-based composite photocatalysts for HER application. Concretely, the review starts with the development history, synthetic strategy, electronic structure and physicochemical characteristics of g-C₃N₄ materials, followed by the rational design and engineering of various nanostructured g-C₃N₄ (e.g. thinner, highly crystalline, doped, and porous g-C₃N₄) photocatalysts for HER application. Then a series of highly efficient g-C₃N₄ (e.g., metal/g-C₃N₄, semiconductor/g-C₃N₄, metal organic framework/g-C₃N₄, carbon/g-C₃N₄, conducting polymer/g-C₃N₄, sensitizer/g-C₃N₄) composite photocatalysts are exemplified. Lastly, this review provides a comprehensive summary and outlook on the major challenges, opportunities, and inspiring perspectives for future research in this hot area on the basis of pioneering works. It is believed that the emerging g-C₃N₄-based photocatalysts will act as the "holy grail" for highly efficient photocatalytic HER under visible-light irradiation.