Energy Band Engineering Of Graphitic Carbon Nitride Based Materials For Visble-light Photocatalytic H₂-generation Performance

With the huge consumption of fossil energy fulfilling various demanding of industry and life,the reserves are decreasing sharply.Therefore,the development of renewable energy as substitutions of fossil energy is imperative.Photocatalytic hydrogen production technology can effectively produce clean and pollution-free hydrogen by using solar energy,which is an ideal means to solve the energy crisis and pollution.Carbon nitride is a low-cost metal-free catalyst with suitable band gap width and stable physicochemical properties.However,the unmodified carbon nitride has small specific surface area,high carrier recombination rate and poor utilization of visible light,which greatly restricts its further development and utilization.Visible light accounts for nearly 50%of sunlight.Therefore,the utilization of visible light is particularly important for catalysts.Aiming at overcoming the disadvantages of carbon nitride(CN)materials such as poor visible light absorption ability and high carrier recombination rate,modified CN materials has been synthesized through molecular doping and molecular adsorption,which results in tuning its energy band structure,enhancing its visible light absorption ability,and improving its photocatalytic hydrogen production performance under visible light.The main research contents are as follows:(1)The benzene ring structure can be incorporated into the framework of carbon nitride by using copolymers of 1,3,5-benzenetricarboxylic acid and melamine as precursor.FT-IR,NMR and XPS spectra were used to prove the success of the benzene ring incorporation.The UV-vis and PL spectra indicated that the benzene ring incorporating into CN can improve visible light absorption ability,inhibit the carrier recombination,and tune the energy band structure.The effects of different incorporation amounts of benzene group were explored.When the wt%ratio of 1,3,5-benzenetricarboxylic acid and melamine is 0.020,the materials obtained the best photocatalytic hydrogen production performance,which was about seven times than that of unmodified carbon nitride under visible light.(2)Based on the foundation of the doping theory,the donor tetrathiafultene was used to tune the property and performance of the carbon nitride materials by physical adsorption.The XPS spectra proved the successful adsorption of tetrathionofultene.The UV-vis and PL spectra indicated that physical adsorpted tetrathiafultene onto the surface of the CN can tune its energy band structure,improve the carrier separation and transport,and enhance the performance of photocatalytic hydrogen production.When the wt%ratio of tetrathiafulvalene and CN is 0.133,the tetrathiafultene modified CN exhibited the best visible light photocatalytic hydrogen production performance,which is twice as large as that of unmodified carbon nitride.