The Preparation Of Graphitic Carbon Nitride-Based Compounds For Visible Light Photocatalytic H₂ Evolution

Photocatalytic hydrogen evolution from water splitting has been thought as one of the most promising strategies to solve the problems of environmental pollution and the increasing need for energy.However,it’s a great challenge to effectively convert solar energy to storable hydrogen energy.As one of the semiconductors,graphitic carbon nitrde(g-C3N4)has caught more and more researchers’ eyes due to its properties of easy preparation,visible light response,chemical stability,non-toxic and adjustable band structure.However,the activities of pristine g-C3N4 that is prepared by directly thermal polymerizztion are dramatically limited by the low specific surface area,low visible light utilization rate,high photogenerated electron-hole pair recombination rate and few active sites.Therefore,how to improve the visible light catalytic activity of graphitic carbon nitride has become the focus of researchers.In this paper,considering the above disadvantages,we skillfully designed the graphitic carbon nitride based photocatlysts with enhanced photocatalytic performance,and the main work is listed below:1.In the second part,we recommended a general surface grafting strategy followed by the in-situ carbonization treatment to obtain carbon modified graphitic carbon nitride (CMCN)using the p-phenylene diisocyanate(PPDI)as the modifier agent.After the PPDI is grafted on the surface of graphitic carbon nitride,the CMCN composite is obtained by in-situ carbonization.The CMCN composite presents enhanced visible light catalytis performance with the hydrogen evolution rate up to 5.549 mmol g-1 h-1,which is 13.3 times higher than that of pristine graphitic carbon nitride(MCN).Besides,we have demonstrated the universality of this method by changing the precursor of graphitic carbon nitride,and the CUCN(using urea as the precursor)with much promoted photocatalytic activity was successfully developed via the surface grafting and followed in-situ carbonization method.More importantly,the catalyst realizes the substitution of benzyl alcohol as sacrificial agent to produce benzaldehyde,an organic intermediate with high demand,which further reveals practicability of CMCN.The rates of H2 and benzaldehyde are up to 0.288、0.230 mmol g-1 h-1,respectively,which are more than 5 times higher than that of pure graphitic carbon nitride.2.In the third oart,taking the band gap structures into consideration,the commercial P25 and graphitic carbon nitride were chosen to devise the composite photocatalysts(P25/CNsp)with unique core-shell structure of TiO2/graphitic carbon nitride heterojunction core and graphitic carbon nitride shell.Experiments show that the unique core-shell structure P25/CNsp with an interior rich heterojunction interface can not only prompt the separation efficiency of charge carriers and the visible light absorption ability,but also provide a larger specific surface area and decrease the overpotential for hydrogen evolution.The optimized composite presents higher photocatalytic hydrogen evolution performance under visible light irradiation(X,>420 nm)with the H2 evolution rate of 6.899 mmol h-1 g-1,which is 6.5 times higher than that of CNsp.More importantly,the unique core-shell structure P25/CNsp composites were proved to be a dual functional photocatalyst by coupling with the oxidation of benzyl alcohol into benzaldehyde.