Study On Preparation And Its Photocatalytic Properties Of Graphite-like Structured Carbon Nitride

In recent years,the large consumption of non-renewable energy has led to energy shortage and environmental pollution becoming increasingly serious.How to use photocatalyst on a large scale and effectively utilize solar energy is an important solution to alleviate the above-mentioned energy and environmental problems.In this paper,graphite likes structure carbon nitride as the research object,from the preparation method,doping modification and other aspects of the focus on how to improve its photocatalytic performance and expand its application scope.The main research contents and results are as follows:Firstly,With urea as the precursor,M-g-C₃N₄with mesoporous structure and nitrogen defects is obtained by roasting after melting pretreatment.The morphology,microstructure and optical properties are characterized by XRD,FT-IR,XPS,BET and TEM.The results show:The mesoporous structure can significantly improve the specific surface area of g-C₃N₄.At the same time,KHCO₃is introduced into the treatment of the precursor.The small molecule gas generated by pyrolysis makes the catalyst form a large number of mesoporous structures,which can change the specific surface area of g-C₃N₄from21.4m²g^-1to 124.3m²g^-1.According to the characterization of modern analytical instruments,the prepared g-C₃N₄not only has high specific surface area and porous structure,but also has a large number of nitrogen defects,which can not only reduce the band gap of g-C₃N₄,improve its absorption rate to visible light,but also facilitate the separation of photogenic electron hole pairs.The degradation of methyl orange(MO)by catalyst under visible light was investigated,the degradation rate constant of Mo reached0.0086 min^-1,which was 5.05 times that of pure g-C₃N₄.It was found that superoxide free radicals and photogenerated holes were the main active species for the degradation of Mo,which formed the degradation mechanism.At the same time,using the supramolecular polymers of melamine,melamine uric acid and ethylene glycol as precursors,honeycomb like carbon nitride materials with excellent nitrogen fixation ability were prepared by microwave treatmentat 550?.The results show that the electron transition of n-?*was successfully stimulated by the combination of carbon self-doping and microwave treatment.The absorption edge of the catalyst shows a significant“red shift”from 465 nm to nearly 600 nm,which promotes the absorption of visible light.The synergistic effect of carbon self-doping and microwave treatment also improve the surface area and separation efficiency of photogenerated electron hole pairs.The catalyst displays the NH₄⁺concentration of 5.3 mg L^-1g^-1_cat,over11 times higher than that of neat g-C₃N₄,as well as the structural stability.DFT theory was used to calculate the maximum value of valence band and minimum value of conduction band of catalyst,which were composed of carbon 2p orbital and nitrogen 2p orbital.Due to n-?*electron transition,the band gap energy of C_M-GCN decreased.It provides a new way for the preparation of high efficiency photocatalyst.Kapok fiber(KF)modified graphite carbon nitride catalyst(KF-g-C₃N₄)was prepared using dicyandiamide as raw material by one-step pyrolysis method,and the degradation of organic pollutants by catalyst under visible light was investigated.On the one hand,the introduction of KF can generate mesoporous structure,and its multiple scattering effect can improve the absorption and utilization of visible light.On the other hand,KF modification can reduce the gap width of graphite carbon nitride and improve the absorption of optical energy.The photocatalytic degradation of phenol experiment was carried out to investigate the performance of KF-g-C₃N₄.Experimental results show the as-prepared kapok fiber modified graphite carbon nitride displayed the highest phenol degradation rate constant K=0.260 h^-1,which is 4.2 times higher than that neat g-C₃N₄(K=0.060 h^-1),and its degradation rate reached 69%.CeO₂-WO₃/g-C₃N₄composite catalyst was prepared by melting process with ammonium tungstate,cerium nitrate hexahydrate and urea as raw materials.Modern analytical instruments such as XRD,XPS,TEM,(PL)and UV-vis DRS were used for characterization and analysis.The results show that The introduction of CeO₂can improve the dispersion of active component WO₃on g-C₃N₄and inhibit the recombination of photogenerated electron hole pairs.The molar ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺)in CeO₂-WO₃/g-C₃N₄catalyst is 62.75%,which can conducive to the formation of oxygen vacancy and reactive oxygen species.The catalytic oxidation performance of DBT was studied,that the conversion rates of DBT on WO₃/g-C₃N₄and CeO₂-WO₃/g-C₃N₄catalysts are 71.5%and 87.2%,respectively.The experiment is carry out for 8 cycles without significant decrease in catalytic activity of CeO₂-WO₃/g-C₃N₄.