Tailoring g-C₃N₄ properties through P and K co-doping: advancing photocatalytic CO₂ reduction to CH₄

The development of high-performance photocatalysts for CO₂ reduction to CH₄ has garnered significant attention. Graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst; however, its performance is hindered by poor charge separation and low reaction kinetics. Tailoring its adsorption capacity, crystallinity, and electronic properties can effectively address these limitations. In this study, we synthesized a g-C₃N₄ photocatalyst with optimized adsorption capacity, crystallinity, and electronic density through simultaneous P and K doping for efficient CO₂ photoreduction. The P_a-K-CN photocatalyst exhibited enhanced charge separation, light harvesting, CO₂ adsorption, crystallinity, and electronic density, thereby promoting CH₄ production. The P_0.05-K-CN sample achieved a maximal CH₄ yield of 19.34 μmol/g/h with 92.8 % selectivity, nearly 22 times higher than that of pure CN. Characterization and theoretical results revealed that P-substituted C atoms in heptazine rings boosted CO₂ adsorption, enhanced charge separation, and contributed to cyano group formation, whereas K doping between CN layers increased crystallinity, charge transfer, electronic density and further promoting cyano group formation. In-situ DRIFTS and DFT calculations elucidated the reaction pathways and identified *CHO as the key intermediate and the rate-determining step in CH₄ formation. This paper presents an innovative technique for developing g-C₃N₄ photocatalysts with superior adsorption capacity, crystallinity, and localized electron density for efficient CO₂ reduction to value-added products.