Modification Of G-C₃N₄ Photocatalysts And Their Photocataiytic Performance

Solar-driven catalysis on semiconductors to produce clean chemical fuels and degrade organic pollutants is widely considered as a promising route to mitigate environmental issues.Among the photocatalysts currently available,graphitic carbon nitride?g-C₃N₄?has been the focus of intensive studies because of its abundance,high thermal stability,and good durability in various chemical environments.However,low efficiency owing to the rapid recombination of photogenerated carriers limits the practical applications of g-C₃N₄.The thesis is devoted to improve the photocatalytic activity of g-C₃N₄.Main research work includes the following aspects:We synthesized the Li-doped g-C₃N₄ through calcination the mixture of melamine and lithium acetate.The samples were characterized by XRD,XPS,ICP and UV-vis techniques.And their photocatalytic activities were investigated via degradation RhB solution under visible light irradiation??>420 nm?.The results showed that Li doping can not only narrow its band gap but also suppress recombination of photogenerated electron-hole pairs.Li doping in g-C₃N₄ does not significantly change the texture and specific surface area of g-C₃N₄.All of the Li-doped g-C₃N₄ showed higher photocatalytic activity than pure g-C₃N₄ under visible light.And higher content Li-doping lead to decreased N-C=N species and increased O-C=O species.During this process,some defect sites acting as photogenerated electron or hole trapping sites would form.This leads to the decreased photocatalytic performance for higher content Li-doped g-C₃N₄.In the photocatalysis process of g-C₃N₄,O 2·-and h+ are the main reactive species.And in the photocatalysis process of Li-doped g-C₃N₄,the main reactive species are O2·-and ·OH.To further improve the visible light photocatalytic activity of Li-doped g-C₃N₄,we conducted Ag photodeposition and a series of characterizations.The obtained Ag/Li?0.15?-CN shows evidently improved light absorption in the visible light region,which can be ascribed to the SPR effect of deposited Ag nanoparticles.And the introduction of Ag leads to Li?0.15?-CN PL quenching,which indicates that recombination of photogenerated electron-hole pairs is efficiently inhibited after Ag photodeposition on Li?0.15?-CN.The photodegradation efficiency of RhB over Ag/Li?0.15?-CN is higher than that of Li?0.15?-CN and Ag/g-C₃N₄.This finding demonstrates that introduction of Li+ and Ag imparts synergistic benefits to improve the photocatalytic activity of g-C₃N₄.