Study On Preparation Of Graphitic Carbon Nitride（g-C₃N₄）-Based Semiconductor Materials And Its Performance For Photocatalytic Hydrogen Production

With the global society and economy developed rapidly,making the supply of traditional fossil fuels become shorttly,people has to find ways to develop a large amount of traditional fossil fuels for using.However,limited traditional fossil energy has been exploited and used in large quantities by human that caused environmental pollution and energy scarcity,which discouraged sustainable development of society seriously.Utilizing a green,clean and renewable energy to exchange traditional fossil energy has gradually become a beautiful method to solve those problems.Hydrogen energy（H₂）as an efficient and clean secondary energy carrier is a necessary choice for human sustainable development.Currently,photocatalytic water splitting hydrogen generation technology driven by solar energy was emergancing which brought expectation to human to solve energy crisis and environmental pollution problems.Graphitic carbon nitride（g-C₃N₄）,due to the well photoelectric properties,non-toxic and harmless,and its main composition being rich in C and N elements,makes it stand out among many emerging semiconductor photocatalytic materials,and is extensive attention.Unfortunately,g-C₃N₄has a low separation rate of photogenerated electron-hole pairs and small specific surface area,that only exhibits poor photocatalytic efficiency.For broaden practical application range of g-C₃N₄in field of photocatalysic,this paper takes different experimental methods to improve photocatalytic activity of g-C₃N₄,and made some physicochemical characterization techniques to systematically analyzed microscopic morphology,crystal structure,chemical components,specific surface area and optical properties of prepared samples.The main content of this paper is disscused as the following three aspects:（1）Using melamine as precursor,through a one-step rapid polymerization method to successfully synthesis high crystalline g-C₃N₄with lattice spacing was 0.33nm.Under visible light irradiation（λ>420 nm）,photocatalytic hydrogen production activity of highly crystalline g-C₃N₄was discussed.Through various characterization information results,found that compared with bulk g-C₃N₄,synthesized highly crystalline g-C₃N₄has fewer structural defects,larger specific surface area,faster photogenerated carrier separation efficiency and less photocharge lifetime.So shows improved photocatalytic hydrogen production performance.the hydrogen production rates of highly crystalline g-C₃N₄are 339.4 and 1031.3μmol g^-1h^-1under visible light and full-spectrum irradiation respectively.which are approximately 2.06 and1.49 times than g-C₃N₄under the same conditions.In addition,it is found through cycling experiments that the synthesized high-crystalline g-C₃N₄also exhibits excellent photostability.（2）The melamine group formed by nitric acid-induced hydrothermal method was used as the precursor,and the unique curly architectured g-C₃N₄with a thickness of 10 nm was successfully synthesized by high-temperature calcination method.Under visible light irradiation（λ>400 nm）,the photocatalytic hydrogen production performance of curly architectured g-C₃N₄was studied.Compared with g-C₃N₄,curly architectured g-C₃N₄has faster photogenerated electron-hole separation rate,larger specific surface area,and stronger H⁺thermodynamic driving force,exhibits 1949μmol g^-1h^-1hydrogen production rate that is 4 times than g-C₃N₄under the same conditions.Finally,through a 20-hour cycle experiment,it was found that the sample has excellent photostability.（3）Using sulfuric acid and melamine to hydrothermally form the precursor,and then successfully synthesize the ultrathin g-C₃N₄nanosheets with a thickness of only3 nm through high-temperature calcination of precursor method.Under visible light irradiation（λ>400 nm）,the photocatalytic hydrogen production activity of ultrathin g-C₃N₄nanosheets was discussed.Through various characterization information results,it is found that the ultrathin g-C₃N₄nanosheets have faster photo-generated electron-hole separation rate,larger specific surface area,and longer photocharge lifetime,The visible light-driven photocatalytic hydrogen production rate was 2590μmol g^-1h^-1that 9.9 times than g-C₃N₄.In addition,through light cycle experiments,it was found that ultra-thin g-C₃N₄nanosheets have excellent photostability.