Preparation And Catalytic Performance Of Carbon Nitride Photocatalyst

As a carbon nitride material,g-C₃N₅ has a relatively narrow band gap range,stable chemical properties and high light utilization rate,so it has been widely concerned.However,the narrow band gap leads to high carrier recombination efficiency,which limits the catalytic performance.In order to improve the photocatalytic activity of g-C₃N₅,a series of carbon nitride composite photocatalysts were prepared by constructing heterojunction,element doping,noble metal loading,etc.,and the photocatalytic performance of hydrogen evolution and pollutant treatment and its catalytic process were studied.Specific research contents are as follows:1.Sulfur-doped g-C₃N₄（10%-s-g-C₃N₄）and fluorine-doped g-C₃N₅（5%F-g-C₃N₅）heterojunction（10%S-g-C₃N₄/5%F-g-C₃N₅）were prepared by one-step calcination method using thiourea,trimino-1,2,4-triazole and ammonium fluoride as raw materials.Then,three heterostructures（3%Au/10%S-g-C₃N₄/5%F-g-C₃N₅）were obtained by loading Au with light.XRD,SEM,XPS and other characterization methods were used to analyze the phase structure,morphology,elemental valence and other properties of the samples.The photocatalytic hydrogen production of Au/10%S-N₄/0.5%F-N₅ was studied.The results showed that the hydrogen production of Au/S-N₄ and Au/N₅ were 481.87μmol·g^-1and 850.17μmol·g^-1 under 3h illumination.The hydrogen production capacity of Au/10%S-N₄/0.5%F-N₅ is 2055.87μmol·g^-1,and the hydrogen production performance has been significantly improved.Au/10%S-N₄/0.5%F-N₅ cycle test showed that the activity of catalyst did not change significantly after 3 h illumination,indicating strong stability.Through element doping,the position of the conductance band of N₅ is moved down,the heterojunction is constructed and the load of Au is constructed,which cooperatively promotes the photocatalytic hydrogen evolution reaction.2.N-deficient g-C₃N₅（NVs-g-C₃N₅）and N-doped NVs-g-C₃N₅（0.1%N/NVs-g-C₃N₅）were synthesized by one-step calcination using triamino-1,2,4-triazole and citric acid monohydrate as raw materials.Then,Au/0.1%N/NVs-g-C₃N₅ is obtained by light loading Au.The phase structure,elemental valence state and morphology of the samples were analyzed by XRD,XPS,SEM and TEM.The photocatalytic hydrogen production performance of Au/0.1%N/NVs-g-C₃N₅ was investigated.The results showed that the hydrogen production rate of Au/NVs-g-C₃N₅ was 208.60μmol·g^-1·h^-1,and that of Au/0.1%N/NVs-g-C₃N₅ was 589.62μmol·g^-1·h^-1.The sample Au/0.1%N/NVs-g-C₃N₅doped with N element is 2.83 times of Au/NVs-g-C₃N₅.The increased activity may be due to the formation of new C-N bonds and the loading of Au,which synergistically promote the photocatalytic hydrogen evolution reaction.3.A layer of S-doped perylene imide（S-PDI）was obtained using thioacetamide as the amino group of S-PDI.N-deficient g-C₃N₅（NVs）with porous network structure was obtained by calcination in Ar atmosphere.NVs modified S-PDI（NVs/S-PDI）was synthesized by electrostatic self-assembly.The phase structure,chemical bond,morphology and elemental valence state of the samples were analyzed by XRD,FT-IR,TEM and XPS.At 30%NVs/S-PDI,the reduction rate of Cr（Ⅵ）reaches 77.96%,the degradation rate of phenol is 92.99%,and the yield of H₂O₂ is 30.68μmol·L^-1 after 2 hours.In the mixed solution of Cr（Ⅵ）and phenol,reduction and degradation have increased to varying degrees compared with that of single solution,the main reason is that the photoautofenton system is formed in the reaction,and the REDOX reaction is promoted.