Study On The Modification Of GC₃N₄ With Heterogeneous Elements And Its Photocatalytic Performance

In recent years,the use of solar energy for photocatalytic reaction is considered to be one of the ideal ways to solve energy crisis and environmental pollution.Therefore,the development of new and efficient photocatalyst has become one of the research topics of great concern to many researchers.Recently,graphite phase carbon nitride（g-C₃N₄,CN）has become one of the photocatalytic hotspot materials due to its high thermal stability,narrow band gap,low cost,easy preparation and good chemical stability.However,g-C₃N₄ also has some disadvantages,such as small specific surface area,faster recombination of photogenerated electron-hole pairs,and the like,which limits the photocatalytic activity of g-C₃N₄.Therefore,we want to prepare a new g-C₃N₄composite with different heterogeneous modifications by a simple method,and further improve the photocatalytic activity by using the composite structure.Aiming at some problems of g-C₃N₄ material,the non-metal boron modified g-C₃N₄tube（BCN）was successfully prepared by modifying the heterogeneous element of g-C₃N₄ material with inorganic acid.The optimum ratio of feed was determined by experiment,namely melamine/boric acid=1:1.Under this condition,a tubular BCN material having a tube length of about 100μm and a diameter of 4μm was obtained.A series of characterizations shows that the BCN material has a larger specific surface area than the bulk CN,providing more active sites for the photocatalytic reaction;and it can better inhibit the recombination of electron-hole pairs,thereby improving photocatalytic activity.The performance of the BCN material was evaluated by degrading the dye and the nitrobenzene solution,and the BCN-3 sample had the highest degradation efficiency.Under simulated sunlight,the non-metallic modified g-C₃N₄ material degrades the nitrobenzene solution by about 70%.Due to the interaction between metal cations and negatively charged nitrogen,g-C₃N₄ materials can easily capture metal cations,and metal-modified semiconductor photocatalysts can effectively improve light absorption,reduce band gap,and accelerate carrier migration.These are all necessary conditions for improving photocatalytic activity.Therefore,the functional modification of the heterogeneous element of the g-C₃N₄ material is carried out using different metal（Co,Cu,Zn）complexes（M-CN）.The morphology and structure of the novel g-C₃N₄ matrix composites were characterized by XRD,FT-IR,UV-vis,PL,XPS,SEM and BET.The photocatalytic properties of the composites were systematically studied.The experimental results show that the Cu-CN sample has the highest photocatalytic activity under simulated sunlight,and the degradation rate of nitrobenzene solution reaches 85%.In addition,the TTC-dehydrogenase activity test proved that the catalyst was not harmful to activated sludge.The reason for the analysis is that g-C₃N₄ samples can provide nutrients as a source of C and an N source for microbial growth.On this basis,the photocatalytic activated sludge process was improved,and the steps of separating the catalyst in the original process were removed,and the illumination was realized.Docking of catalytic and activated sludge degradation:taking the actual wastewater of dairy products as an example,and using Cu-CN as a catalyst and photocatalytic activated sludge process,the TOC test was used to detect the treatment effect.The experimental results show that the wastewater treated by Cu-CN sample has the lowest TOC value and the mineralization rate is 32%.The results indicate that the catalyst can be used in a photocatalytic activated sludge process,which fundamentally solves the problem of catalyst separation.It was found that the metal modified g-C₃N₄ material showed better performance through the above experiments,but the preparation process of experiment is complicated and costly.Therefore,this part selects better and cheaper raw materials,and further simplifies the preparation process to prepare metal Cu modified g-C₃N₄ material（CuCN）.It was found that the metal Cu was successfully modified to the surface of g-C₃N₄ material,which has a tubular structure,and has a larger specific surface area,higher separation efficiency of electron-hole pairs.It provides more possibilities for increasing photocatalytic activity.The photocatalytic performance of the catalyst was determined by degrading the nitrobenzene solution,and the CuCN-2 sample had the highest degradation rate（97%）.Similarly,the advanced oxidation and activated sludge process were combined and applied to the milk wastewater treatment.The TOC test showed that the CuCN-2 sample had the highest mineralization rate（35%）.