Review on synthesis and modification of g-C₃N₄ for photocatalytic H₂ production

Photocatalysis is a zero-carbon route for energy generation by scavenging photon energy from sunlight to convert renewable feedstock into hydrogen gas. Photocatalytic reaction relies on semiconductor performances to absorb photons and generates photoinduced electron and hole pairs. This review analyses recent studies on synthesis methods and modification strategies of g-C₃N₄ to improve hydrogen production, emphasizing the effect of surface area, crystallinity, band gap energy, and electron-hole pairs separation and transfer. The effect of precursor and synthesis temperature of g-C₃N₄ synthesized using the pyrolysis method is discussed in developing polymeric g-C₃N₄ structures, encompassing the type of solvent, temperature, and the use of catalysts. Structural modification of g-C₃N₄ via heat treatment, exfoliation, protonation, and ionic solvent methods aim to improve the crystallinity and surface area while optimizing the structural defect is also reviewed. Modification of electronic properties is divided into metal impregnation - generated Schottky junction and surface plasmon resonance effect, metal and non-metal doping, and heterojunction formation to improve the absorption in the visible light region, separation and transfer of electron-hole pairs. The mechanism of heterojunction is also discussed to provide details on the transfer and separation process of photogenerated charge carriers.