Graphitic carbon nitride and its heterostructures: synthesis, properties, and their applications in photocatalytic H ₂ production and CO ₂ reduction

Graphitic carbon nitride (g-C3N4) has become one of the most significant two-dimensional (2D) materials in material science due to its easy production from the cheapest abundant precursors and its environmentally benign nature. The semi-conductive nature of g-C3N4 has triggered its enormous application in the domain of photocatalysis. In this review, we have thoroughly discussed its potential applications in photocatalytic hydrogen (H2) production through H2O splitting and for CO2 reduction to create value-added compounds. However, low charge separation efficiency and a narrow light absorption range prevent this material from being used for real practical applications in photocatalysis. In that case, various efforts have been made by researchers to develop efficient strategies by modifying g-C3N4 through doping, making heterojunctions with other materials, and fabricating hybrid or composite materials with both metals and nonmetals to overcome its limitations for the enhancement of photocatalytic activity. We summarized and included various advanced synthesis procedures, including their comparative discussion, considering different reaction conditions and a range of precursor materials with varying degrees of condensation. On the other hand, we have focused on their role as support materials for photocatalysts and as components in hybrid, heterostructure, and composite materials used as photocatalysts. Additionally, we focused on their historical development, structural characteristics, surface morphologies, and diverse properties.