Design and application of active sites in g-C3N4-based photocatalysts

With the development in photocatalysis field, photocatalysts have received increasing attention due to their important role in environmental pollution and energy crisis. As a nonmetallic photocatalyst, graphitic carbon nitride (g-C3N4) has been widely recognized because of its excellent optical properties, low cost, and environment friendliness. In the g-C3N4 intrinsic frameworks, carbon atom tends to be the reducing active site, while nitrogen atom tends to be the oxidizing active site and reducing active site according to the difference of electronegativity. However, the quantity and quality of these active sites are affected by many factors, including CN covalent bonds, surface properties, etc. Active sites play an important role in photocatalysis; however, this role is not detailed in most reports. In this review, we proposed the following possible mechanisms of active sites in improving the photocatalytic activity of traditional g-C3N4 based on its intrinsic: morphology regulation, carrier migration, surface active treatment, and substrate adsorption. The following factors affecting the active sites of g-C3N4, including basal engineering and hybrid engineering, were also investigated. The roles of these active sites in improving the photocatalytic activity of g-C3N4-based photocatalytic materials, including morphology regulation, surface treatment, heteroatom doping, and interfacial interaction, were also expounded. Current challenges and future development of g-C3N4-based photocatalysts that are rich in active surface sites were also discussed. This review provides an in-depth understanding of g-C3N4-based photocatalysts.