High-crystalline g-C3N4 photocatalysts: Synthesis, structure modulation, and H2-evolution application

Graphitic carbon nitride (g-C3N4) has received extensive attention in the photocatalytic field because of its low cost, nontoxicity, suitable bandgap structure, and high physicochemical stability among diverse photocatalysts. However, traditional g-C3N4 materials prepared by the high-temperature calcination of various organic precursors generally exhibit poor crystallinity and possess numerous internal and surface defects, leading to the rapid recombination of photo-excited charges. Constructing a highly crystalline g-C3N4 photocatalyst, as opposed to the traditional poorly crystalline g-C3N4, effectively reduces internal and surface defects, facilitating efficient separation and rapid transfer of photoexcited charges. As a result, the photocatalytic performance is significantly enhanced. In this review, recent progress in highly crystalline g-C3N4 photocatalysts is summarized. The microstructural characteristics of highly crystalline g-C3N4 photocatalysts are discussed in detail. Synthetic methods for highly crystalline g-C3N4, such as the salt-assisted (multicomponent salt and single-component salt), template, two-step calcination method, microwave-assisted method, and others, are meticulously presented. Additionally, various modification strategies for highly crystalline g-C3N4, encompassing bandgap engineering, heterojunction construction, and co-catalyst modification, are presented. Subsequently, a detailed description of the photocatalytic H2-evolution applications of highly crystalline g-C3N4 materials is given. Lastly, the paper concludes with a discussion on the outlook for highly crystalline g-C3N4 photocatalysts, aiming to offer novel insights into the design of highly efficient crystalline g-C3N4 photocatalysts.