Study On Preparation And Photocatalytic Performance Of Modified Graphite Carbon Nitride

g-C₃N₄is a visible light catalyst widely researched at present.However,the photocatalytic activity of g-C₃N₄is severely limited due to its shortcomings such as small specific surface area,low visible light utilization rate and easy recombination of photogenerated carriers.In this study,from the aspects of morphology control,structural defects,and construction of heterojunctions,two kinds of g-C₃N₄with high catalytic activity and stability were designed and synthesized.Various methods were used to characterize the catalyst samples.The photocatalytic activity of them was evaluated by photocatalytic degradation of organic pollutants such as tetracycline or rhodamine B,and hydrogen production from water decomposition under visible light irradiation.Besides,the photocatalytic mechanism was discussed.The main research contents and results of this study are as follows:A simple one-step thermal polymerization method was used to calcine the thiosemicarbazide at 600°C to prepare g-C₃N₄?TCN-600?with both carbon vacancies and two-dimensional nanosheet structure.The specific surface area of TCN-600 is as high as144.5 m²/g,which is 35 times that of bulk g-C₃N₄?4.14 m²/g?,and the carbon vacancy makes TCN-600 have a narrower band gap and a more negative conduction band potential than bulk g-C₃N₄.The results of PL spectrum,time-resolved fluorescence decay spectrum and photoelectric corresponding characteristics show that the synergy of carbon vacancies and two-dimensional nanosheet structure effectively promotes the migration of photogenerated charges and inhibits electron-hole recombination.TCN-600 has excellent photocatalytic performance,its photocatalytic hydrogen production rate is1.86 mmol·g^-1h^-1,which is 11.6 times that of bulk g-C₃N₄.The photocatalytic degradation efficiency of TC is83.3%,and the degradation rate constant is 0.0178min^-1,which is 5.6 times that of bulk g-C₃N₄.The ternary heterojunction composite photocatalytic material g-C₃N₄/InVO₄/CQDs was prepared by one-pot hydrothermal method.g-C₃N₄/InVO₄/CQDs are strongly absorbed in the entire ultraviolet-visible region.The formation of heterojunctions and the conduction of CQDs to electrons synergistically promote the migration of photogenerated charges,inhibit the recombination of electrons and holes,and make g-C₃N₄/InVO₄/CQDs have high photocatalytic activity.Within 90 minutes of visible light irradiation,its photocatalytic efficiency for Rh B was 99.6%,and the degradation rate constant k was 6.64,43.9,and 3.3times that of g-C₃N₄,InVO_4,and the binary composite g-C3N₄/InVO₄,respectively.Through the results of active species capture experiments and theoretical analysis,it was determined that the ternary heterojunction g-C₃N₄/InVO₄/CQDs is a Z Scheme heterojunction.The charge transfer mechanism is:both g-C₃N₄and InVO₄are excited by visible light to generate photogenerated electrons and holes,and the photogenerated electrons in the conduction band of InVO₄are quickly transferred to the surface of CQDs and combined with h⁺in the VB of g-C₃N₄,and the electrons in the conduction band of g-C₃N₄and the holes in the valence band of InVO₄can be quickly accumulated.The electrons in the conduction band of g-C₃N₄capture O₂to generate·O₂^-.The h⁺in the InVO₄valence band oxidize the OH^-in the solution to·OH,and the generated·OH and·O₂^-degrade Rh B into small molecule products or H₂O and CO₂.In addition,h⁺in the InVO₄valence band can also directly participate in the degradation of RhB.