Alkali metal-doped g-C3N4: a multifunctional photocatalytic platform for solar-induced energy conversion and environmental restoration

Abstract

Alkali metal doping has emerged as a powerful strategy to unlock the full photocatalytic potential of graphitic carbon nitride (g-C₃N₄) by modulating the structural and electronic parameters. Notably, incorporating alkali metal ions into the crystal lattice of g-C₃N₄ serves as an effective strategy to modulate its crystalline structure, enhance photon-harvesting capabilities, improve surface area, and optimize photocatalytic performance, all while retaining environmental compatibility. This review summarizes recent developments in alkali metal doping of g-C₃N₄, focusing on design strategies, structural modifications, and the resulting alterations in electronic and physicochemical properties. DFT calculations, theoretical modelling, and various characterization techniques were systematically reviewed for structural elucidation and optical modification after alkali metal ion doping in g-C₃N₄. We also provide concrete case studies by reviewing the structure–activity relationships of various alkali metal-doped g-C₃N₄-based photocatalysts having potential applications in artificial photosynthesis, ranging from solar fuel production, biomass conversion, organic transformation, and pollutant degradation to other miscellaneous applications, mainly supported by the in-depth photocatalytic mechanism. Finally, we conclude by highlighting the research gap and future perspectives. We believe this review is intended to serve as a comprehensive reference for both academic researchers and industrial practitioners engaged in the rational design of alkali-doped g-C₃N₄-based photocatalytic systems.