Preparation Of Graphitic Carbon Nitride Based Composites And Photocatalytic Performance For Hydrogen Evolution

Since the beginning of the new century,due to the rapid growth of the global population and economy,human energy demand has soared.However,the excessive development and use of fossil energy such as coal,oil and natural gas have triggered global climate change and energy crisis.In order to cope with the increasingly prominent shortage of energy and environmental degradation,the development of renewable clean energy has become a hot research topic.The use of semiconductors as photocatalysts to convert water into hydrogen production under the driving of solar energy is one of the effective strategies to solve the energy crisis and environmental pollution.Due to its unique energy band structure and excellent chemical stability,graphitic carbon nitride?g-C₃N₄?,as a potential visible light photocatalyst has been widely applied in photocatalytic hydrogen production,organic pollution degradation and reduction of CO₂.However,the practical application of bulk g-C₃N₄ has been limited due to its low specific surface area,narrow visible light absorption range and high photoelectron-hole recombination rate.Therefore,increasing the specific surface area of g-C₃N₄,broaden its light absorption range and improve its separation efficiency of photogenerated electrons and holes is particularly important to enhance the photocatalytic performance of g-C₃N₄.Given this,the utilization rate of g-C₃N₄ for light energy and the separation rate of photogenerated electron-hole pairs were enhanced via structure regulation,surface modification and construction heterojunction,thus improving the photocatalytic hydrogen evolution of g-C₃N₄.The specific contents are as follows:?1?g-C₃N₄/TiATA photocatalytic hydrogen production:Firstly,we synthesized the g-C₃N₄ nanosheets by thermal condensation.Then the amino-titanium MOFs?TiATA?were prepared by solvent-thermal method and deposited onto g-C₃N₄ nanosheets to form MOFs modified g-C₃N₄ composite,g-C₃N₄/TiATA.The characterization results show that the photocatalytic water splitting performance of g-C₃N₄/TiATA composite is significantly higher than that of pure g-C₃N₄ under 300W Xenon lamp.When the mass ratio of g-C₃N₄ to TiATA is 5,the hydrogen production rate can reach 265.8?mol h^-1,which is about 3.4 times as much as g-C₃N₄/Pt.?2?BCN/AZIS photocatalytic hydrogen production:Based on the functional modification of triazine ring structure unit of g-C₃N₄ nanosheets,we prepared the g-C₃N₄ nanosheets by thermal condensation method,and modified the nanosheet with benzoic acid to obtain carboxyl functionalized carbon nitride?BCN?.In addition,the flower-like ZnIn₂S₄ was prepared by solvothermal method and modified with?3-aminopropyl?triethoxysilane?APTES?by hydrolysis condensation to obtain amino functionalized ZnIn₂S₄?AZIS?.Finally,the BCN/AZIS composite catalyst was obtained by coupling BCN with AZIS through electrostatic interaction and dehydration reaction between carboxyl group and amino group.A series of characterization results show that the photocatalytic water splitting performance of BCN/AZIS composite is significantly higher than that of pure g-C₃N₄ under 300W xenon lamp.When the mass ratio of AZIS to BCN is 2,the hydrogen production rate can reach 485.4?mol h^-1.?3?g-C₃N₄@CoNiS_x photocatalytic hydrogen production:Firstly,we prepared the g-C₃N₄ nanosheets by thermal condensation method,and then the amorphous bimetallic sulfide co-catalyst CoNiS_x was anchored onto the surface of g-C₃N₄nanosheets by photoinduced deposition method to obtain g-C₃N₄@CoNiS_x composite.During the photoinduction process,Ni²⁺,Co²⁺and S^2-in the solution were combined to form CoNiS_x cocatalysts and deposited in situ the electron transfer sites of g-C₃N₄.The method is simple and mild,and can inhibit the agglomeration of CoNiS_x nanoparticles.A series of representational results show:the photocatalytic water splitting performance of g-C₃N₄@CoNiS_x composite is significantly higher than that of pure g-C₃N₄ under 300W xenon lamp.At 20 min of photoinduction,the hydrogen production rate can reach 286.1?mol h^-1.