Study On Modification Of Graphite Phase Carbon Nitride-based Photocatalyst And Its Photocatalytic Performance

Graphite phase carbon nitride（g-C₃N₄）is an organic semiconductor photocatalyst.It has the advantages of excellent physical and chemical stability,low cost of raw materials,simple preparation process,etc.Bedsides,its energy level position is suitable for a variety of photocatalytic reactions.However,the photocatalytic performance of pure g-C₃N₄ made by recent methods is still unsatisfactory.Therefore,we adopted methods such as morphology control,construction of heterojunctions with metal oxide semiconductors and construction of ternary composite materials to improve its performance of photocatalytic degradation of rhodamine B and photocatalytic reduction of CO₂.the mechanism of its photocatalytic performance was also studied.The specific research content of this paper is as follows:（1）First,we prepared the bulk g-C₃N₄ by using urea as precursor and heated the bulk g-C₃N₄ in different gas atmospheres（NH₃,H₂,N₂）.The results of X-ray Diffraction Spectrometer（XRD）,X-ray Photoelectron Spectrometer（XPS）and Transmission Electron Microscopy（TEM）illustrated that the thickness of the bulk g-C₃N₄have been reduced without destroying its basic crystal structure.The test showed that it had the highest specific surface area,which is103.09 m²/g.The photocatalytic performance test result showed that the g-C₃N₄ nanosheets heated in NH₃ atmosphere had the best performance of photocatalytic degradation of rhodamine B,and its yield of CO from the photocatalytic reduction of CO₂ was 2.5 times that of the unmodified g-C₃N₄,but the limited visible light absorption ability and high carrier recombination rate limit its photocatalytic efficiency.The method used in this part can provide some reference for other two-dimensional material morphology control.（2）Then,Cu O/g-C₃N₄ composites with different mass ratios of Cu O were prepared through chemical solution method by using copper acetate solution as the precursor.TEM photos showed the Cu O particles which have a loose structure grew in situ on the surface of g-C₃N₄,and the chemical composition and phase structure were characterized by XRD,XPS,Fourier Transform Infrared Spectrometer（FT-IR）.UV-visible diffuse reflectance spectroscopy（UV-vis）and Photoluminescence spectroscopy（PL）test indicated that the visible light absorption ability and carrier separation efficiency of Cu O/g-C₃N₄ were significantly enhanced.photocatalytic performance tests suggested that the performance of the Cu O/g-C₃N₄ composite with a Cu O mass fraction of 24%to degrade rhodamine B is significantly improved compared with the unmodified g-C₃N₄ and its yield of CO from the photocatalytic reduction of CO₂ was nearly 9 times that of g-C₃N₄ nanosheets heated in NH₃ atmosphere and was nearly 20 times that of the unmodified g-C₃N₄.（3）Finally,the ternary composite photocatalysts Ti O₂/Cu O/g-C₃N₄（A）and Ti O₂/Cu O/g-C₃N₄（B）was prepared by the one-step method and the stepwise method.Characterizations such as XRD,XPS,TEM and FT-IR proved that g-C₃N₄,Cu O,and Ti O₂ exist in the prepared materials.Photocatalytic activity of the ternary composite materials was improved because the synergy between the three materials in the ternary composite materials effectively inhibits the recombination of photo-generated carriers and the reduction performance of photo-generated electrons is greatly enhanced.The yield of Ti O₂/Cu O/g-C₃N₄（B）to reduct CO₂to CO was nearly twice that of Cu O/g-C₃N₄ and was nearly 43 times that of the unmodified g-C₃N₄.Studies on the ternary composite system which designed in this chapter can provide a certain foundation for its research and application in the field of photocatalysis.