Modification Of G-C₃N₄ And Its Application In Photocatalysis And Thermocatalysis

In recent years,the problem of environmental pollution has been affecting the rapid development of human society,so it is particularly urgent to develop new catalysts that can catalyze the degradation of various pollutants.The catalytic technology is an oxidation-reduction reaction under the condition of sunlight irradiation.Its operation has the advantages of environmental protection,simplicity,high efficiency and low cost.Catalysts also play a key role in the process of catalytic degradation of pollutants.In recent years,graphitic carbon nitride?g-C₃N₄?has become a research hotspot in the field of photocatalysis due to its high chemical stability,thermal stability and good photoelectric characteristics.However,due to the shortcomings of g-C₃N₄,such as small specific surface area and easy recombination of photogenic carriers,its catalytic performance is limited.Researchers have made great efforts to develop the highly active g-C₃N₄,which has been proved to be an important means to improve the catalytic activity of catalysts by improving its specific surface area and optimizing the carrier transport capacity.In this paper,g-C₃N₄ was prepared into photocatalyst and photothermal co-catalyst with catalytic properties by special experimental methods.The specific research contents are as follows:1.The g-C₃N₄ photocatalyst with large specific surface area and N defects,characterization analysis and photocatalytic performance test.The g-C₃N₄ with large specific surface area and N defect was prepared by using melamine treated with trace glyoxylic acid as precursor and calcining under special conditions.For example,the TG-DSC spectrum can be used to analyze that the weight loss rate of melamine after the treatment of glyoxylic acid is lower than that of melamine during the calcining process,indicating that the yield of g-C₃N₄ prepared by the treatment of melamine after the treatment of glyoxylic acid has been improved,and the calculated result shows that the yield is about 4 times higher.Analysis of N₂adsorption-desorption and EPR map showed that the sample had large specific surface area and N defects,and its specific surface area(114.95 m²g^-1)was significantly higher than that of g-C₃N₄ prepared by traditional methods(8.36 m²g^-1).In the photocatalytic activity characterization,it can be seen that g-C₃N₄ with large specific surface area and N defects has a higher catalytic activity in the degradation of gaseous organic pollutants,which is about 5.8 times higher than the photocatalytic activity of pure g-C₃N₄.The main reason for the increase of the photocatalytic activity of the sample is the result of the combined action of increasing the specific surface area and producing an appropriate amount of N defects.The increase of the specific surface area of the sample can increase the contact area between the catalyst and the pollutant,which is beneficial to the photocatalytic oxidation-reduction reaction.At the same time,the samples of melamine prepared after the treatment of glyoxylic acid produced N defects that could capture electrons or holes in the process of special treatment,so as to improve the photocatalytic activity.2.High activity Cr₂O₃/g-C₃N₄ composite photothermal co-catalyst and performance test.The Cr₂O₃/g-C₃N₄ composite photothermal co-catalytic materials with high activity were prepared by using chromic nitrate nonahydrate and melamine as precursors.The EDS spectrum analysis showed that the sample was Cr₂O₃/g-C₃N₄composite material.Because of the Cr₂O₃ is a P-type semiconductor material,and g-C₃N₄ is an N-type semiconductor material,the formation of heterojunction at the interface between P-type and N-type semiconductor material can inhibit the recombination of carriers generated by photothermal excitation,thus improving the photothermal catalytic activity.Under the experimental conditions,Xe arc lamp was used to simulate the sunlight to test the activity of the photothermal catalytic samples,and the experimental data of the degradation of gaseous organic pollutants showed that the composite materials were 74 times and 31.9 times higher than the pure g-C₃N₄ and Cr₂O₃,respectively.Therefore,the composite Cr₂O₃/g-C₃N₄ photothermal catalyst prepared in this experiment can degrade gaseous organic pollutants efficiently,which opens up a new way for the preparation of low-cost and highly active photothermal catalyst.