Photocatalytic degradation of organic dyes on Li-doped graphitic carbon nitrides

Lithium-doped graphitic carbon nitrides (g-C3N4) with varied lithium contents (i.e., Li-r-CN) were synthesized using LiCl and melamine as precursors and then served as catalysts for photocatalytic degradation of dyes in aqueous solution. The samples were characterized by X-ray diffraction patterns, infrared spectroscopy, N-2 physisorption isotherms, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectrum, Photoluminescence, and photocurrent measurements. Results indicated that the Li doping slightly increases the surface area and pore size, lowers the band gap, and improves the electron-hole separation efficiency, and in particular, results in the formation of polytriazineimide, which can cooperate with g-C3N4 and yield synergistic contribution to the reaction. Catalytic tests showed that the Li doping enhances the activity of g-C3N4 for photocatalytic degradation of rhodamine B (RhB), with the optimal efficiency obtained at molar ratio of LiCl to melamine equals to 0.5, i.e., Li-0.5-CN, which exhibited 93.4% RhB conversion within 30 min. Moreover, Li-0.5-CN is also highly active for the removal of other organic dyes, such as methyl orange and methylene blue, potentiating its promising applications for the removal of dyes in complex environment.