Review of Graphitic Carbon Nitride and Its Composite Catalysts for Selective Reduction of CO₂

Influenced by “artificial photosynthesis”, different energy mimetic fuels such as DME, methanol, formic acid, methane, etc. can be prepared by the reduction or hydrogenation of carbon dioxide (CO2), captured from the atmosphere while maintaining different reaction strategies, such as thermal catalysis, electrocatalysis, photocatalysis, and photoelectrocatalysis, and also by means of various enzymatic reactions. Harvesting ubiquitously inherent solar energy and applying the same in photopropagated CO2 reduction toward the generation of value-added energy feedstock using apposite semiconductor photocatalysts have proven to be a sustainable and greener process completing the carbon cycle. Graphitic carbon nitride (g-C3N4) has been recognized as a highly potent photo- as well as electrocatalyst for the CO2 reduction reaction (CRR), primarily due to its high chemical and thermal stability, low toxicity, cost-effectiveness, visible light absorption capacity, and ingeniously tunable synthetic routes as compared to other semiconductor platforms. Nevertheless, a lower specific surface area, lower electrical conductivity, fast recombination of phototriggered excitons, and narrow visible light absorption window hinder the application of this catalytic material for practical photocatalytic utilization. Adapting certain alteration approaches, such as structural modulation, elemental doping, attachment of metal complex motif, functional group modification of g-C3N4 etc., can dramatically reinforce the photocatalytic activity in the direction of efficient CO2 reduction. The present review explores the various perceptions of synthetic routes as well as individual optimization techniques of g-C3N4 promoting CO2 photoreduction adopted by the scientific community from the very outset to the latest findings. Predominantly, this review ruminates on the theoretical and experimental framework of practical photochemical CO2 reduction on g-C3N4-based hybrid platforms while elucidating the respective material optimization techniques employed to boost selectivity and efficiency along with their merits and demerits. The future scope of improvement and a comparative discussion are concluded in the form of an imminent panorama.