The review on photoactive C_(2-7)N_(1-9) carbon nitrides for the photocatalytic applications

The family of carbon nitrides (CNs), including compounds such as C₂N, C₃N, C₃N_2, C₃N₃, C₃N₄, C₃N₅, C₃N₆, C₃N₇, C₄N, C₄N₃, C₅N, C₅N₂, C₆N₇, C₆N₉H₃, and C₉N₅H₃, has garnered growing attention for their tunable optoelectronic properties and applications in photocatalysis. While g-C₃N₄ remains the most widely studied member, emerging CN phases offer distinct structural motifs, nitrogen configurations, and electronic band structures that may outperform conventional systems. This review provides a comprehensive analysis of photoactive CN materials, with a special emphasis on less-explored C_xN_y compounds. It highlights their synthesis routes, classification based on active sites and solid-state behavior, and structural characteristics such as pore topologies, surface terminations, and nitrogen doping patterns. Furthermore, the diverse roles of CNs in photocatalysis as electron donors, sensitizers, redox mediators, and co-catalyst supports are critically evaluated. By correlating structure-property-performance relationships, this review offers a framework to guide the rational design of advanced CN-based photocatalysts for solar-driven energy conversion.