Preparation Of Novel Carbon Nitride Photocatalytic Material And Its Photocatalytic Performance

In the situation of the increasingly serious energy crisis,people pay more and more attention to low cost to obtain a higher energy method.The photocatalytic technology is a simple,green,low cost of energy storage and conversion technology.Although the research on photocatalytic technology has made great progress,the industrial application of photocatalytic technology is still limited.This has led to develop highly stable,efficient,low-cost and environmentally friendly photocatalysts.At present,TiO2 is the only photocatalyst that has been commercial utilized,but it can only absorb ultraviolet light.And the utilization rate of solar energy is very low.Therefore,it is necessary to develop new photocatalysts to play a role in the visible region so as to make better use of solar energy.Scientists have developed some new visible light responsive photocatalytic materials,such as silver based catalysts and bismuth based catalysts,and some novel photocatalytic materials.Scientists have found that by combining,doping,modification and other ways to broaden the range of semiconductor light absorption and enhance photocatalytic activity.In this thesis,the photocatalytic properties of a series of carbon nitride composites and their structure-activity relationship were studied by using the method of semiconductor composite.In this paper,g-C₃N₄ is used as substrate,and other materials are compounded on this basis,such as Ag-Ag₂ O,GO/MoS₂ and GO/Ag₃PO₄ to be Ag-Ag₂O/g-C₃N₄,GO/Ag₃PO₄/g-C₃N₄ 和 GO/MoS₂/g-C₃N₄.Through a series of characterization,the degradation of methyl orange and RhB were studied in the experiment.Then the free radical trapping experiment was carried out to explore the reaction mechanism.The main contents are as follows:（1）g-C₃N₄ was prepared by calcination method.On this basis,Ag-Ag₂O/g-C₃N₄ composites were successfully prepared by chemical precipitation method.Ag-Ag₂O/g-C₃N₄ was prepared by changing the quality of silver nitrate and sodium carbonate by fixed the quality of g-C₃N₄.Then they were characterized by the XRD,SEM,HR-TEM,FT-IR,XPS,DRS and so on.XRD showed that Ag-Ag₂O/g-C₃N₄ containedAg,Ag₂ O and g-C₃N₄.SEM and HR-TEM revealed a heterojunction between Ag-Ag₂ O and g-C₃N₄.DRS showed that the absorption property of Ag-Ag₂O/g-C₃N₄ was better than that of g-C₃N₄ in the visible region.Photocatalytic degradation experiments showed that,after visible light irradiation for 3.5 h,the degradation of MO by 50 wt% Ag-Ag₂O/g-C₃N₄ was up to 89.5%,which was about 7.5 times of g-C₃N₄.Based on the energy band theory,the degradation mechanism of Ag-Ag₂O/g-C₃N₄ composite photocatalyst for MO was put forward.It was found that the hole played a major role in the trapping experiments.The results showed that when the Ag-Ag₂ O nanoparticles were loaded on the surface of g-C₃N₄ with a synergistic effectiton.Conducive to the migration of photogenerated carriers,thereby enhancing photocatalytic activity.（2）GO/Ag₃PO₄/g-C₃N₄ photocatalysts were successfully synthesized by chemical precipitation method with GO,Ag₃PO₄ and g-C₃N₄.Then they were characterized by the XRD,FT-IR,Raman,SEM,XPS,DRS and so on.XRD,FT-IR and Raman showed that GO/Ag₃PO₄/g-C₃N₄ contained GO,Ag₃PO₄ and g-C₃N₄.SEM showed that GO had a cleavage effect on Ag₃PO₄ and enabled Ag₃PO₄ to form regular patterns of smaller particles.DRS revealed that the introduction of GO/Ag₃PO₄ broadened the absorption of g-C₃N₄ in the visible region.Photocatalytic degradation experiments showed that,under visible light irradiation for 50 minutes,the degradation rate of RhB reached 94.8%,which was increased by 79.1%,88.8%and 30.4%,respectively compared with Ag₃PO₄,g-C₃N₄,and 1wt% GO/Ag₃PO₄.It could be seen that the composite photocatalyst had a significant improvement.The active species of GO/Ag₃PO₄/g-C₃N₄ in the degradation process were studied by free radical trapping experiment.It was found that the hole and superoxide radical played a major role,and the mechanism was explained.（3）GO/MoS₂/g-C₃N₄ photocatalyst was prepared by hydrothermal method with GO,MoS₂ and g-C₃N₄.Then it was characterized by XRD,FT-IR,Raman,SEM,XPS,DRS and other instruments.XRD,FT-IR and Raman showed that GO/MoS₂/g-C₃N₄ contained GO,MoS₂ and g-C₃N₄.SEM,TEM,and HR-TEM displayed the GO/MoS₂ tightly attach to the surface of the g-C₃N₄.Photocatalytic degradation experimentsshowed that,after visible light irradiation for 5 hours,the degradation effect of GO/MoS₂/g-C₃N₄ on RhB was up to 96.7%,which was increased by 20.5%,85% and30.5% respectively compared with g-C₃N₄,MoS₂ and 5%wt% GO/MoS₂.PT,EIS and PL tests show that GO/MoS₂/g-C₃N₄ has stronger separation ability of photogenerated electrons and holes than g-C₃N₄.The cyclic experiments proved that the catalyst has good stability.The active species of the system were investigated by trapping experiments and ESR,and the reaction mechanism was elucidated.