Molecular Reforming Of Graphite Carbon Nitride And Its Composite Photocatalysts

With the rapid development of society and economy,semiconductor photocatalyst,as an environmentally friendly photocatalyst,has broad application prospects in solving energy and environmental problems with its unique light stability,chemical resistance,and other properties.Among many semiconductor photocatalysts,the graphitc carbon nitride（g-C₃N₄）has its unique two-dimensional molecular structure,adjust electro-optical properties,non-toxicity,and cost points,which makes g-C₃N₄-based materials become a popular material today.It can be applied to multifunctional nano-platforms,such as photocatalytic water decomposition,degradation of pollutants and reduction of carbon dioxide,and biomarkers and fluorescent probes.However,due to the high recombination probability of photocarriers in g-C₃N₄ materials and the limited visible light absorption range,the activity of a single g-C₃N₄ is very low.Therefore,it is considered as an effective strategy to improve the activity of g-C₃N₄ by reforming the molecular structure,introducing defects,adjusting the C/N atomic ratio,changing the molecular conjugated structure,and then regulating the energy band structure and morphology.It has great theoretical value and practical significance to further understand the mechanism of photocatalytic reactions and solve their application problems in energy and environment.Therefore,this subject is based on the idea of regulating the g-C₃N₄ band structure through in-situ g-C₃N₄ molten salt reforming polymerization,g-C₃N₄molecular structure,stoichiometry ratio regulation,to obtain a good water-soluble defects g-C₃N₄ The bandgap width is adjustable from about 1eV to 2.7eV;the water-soluble graphitic carbon nitride material（WS-GCN）is used as a photosensitive component to modify the nano-TiO₂ to obtain a broad spectrum of photocatalysts.The main work done in this paper is as follows:First,we used high-temperature ionic liquids（NaCl-KCl melt salts-assisted）to polymerize precursors to form g-C₃N₄.Simultaneously with in-situ intercalation,we interfered with the intramolecular conjugated structure and conjugated degree.The molecular structure of g-C₃N₄ was adjusted to obtain WS-GCN with controllable defects,and the effects of different mass ratios of precursors and molten salts on the optical excitation-radiation properties were investigated.The results show that the material has a higher fluorescence quantum yield（22%）,which is 4.95 times higher than that of the directly polymerized g-C₃N₄.Different electron excitation-radiation paths,π*-n andπ*-πare enhanced.The band gap has become significantly narrower,ie,from 2.76 eV（g-C₃N₄）to 0.89-1.62 eV（precursor:molten salt=1:1 to 3:1）,and the corresponding light absorption range has changed from 460 nm to 630 nm 791nm.When the mass ratio of the precursor to the molten salt is 1:1,the light absorption range is the widest.Secondly,in order to expand the light absorption range of TiO₂ photocatalytic materials,WS-GCN shell-coated TiO₂/WS-GCN core-shell structures were synthesized by coupling with WS-GCN.And the effect of photocatalytic properties of different ratio of WS-GCN added was studied.The results show that the photoresponse range of TiO₂/WS-GCN is broadened from 385 nm（TiO₂）to 600 nm（TiO₂/WS-GCN）,while the visible light absorption range of TiO₂/GCN is only less than 460 nm.When the addition amount of WS-GCN is 5%and the wavelength of LED is 550nm,the NO degradation rate of TiO₂/WS-GCN composites is as high as55%,which has the best photocatalytic performance.Finally,in order to further increase the quantum efficiency and further increase the photocatalytic activity,graphene is introduced into TiO₂/WS-GCN Because graphene not only has unique electron transport properties,it can also serve as a carrier for titanium photoelectron.Based on these,a WS-GCN-coated core-shell TiO₂/RGO/WS-GCN ternary composite was prepared by compounding WS-GCN.The effects of different ratios of WS-GCN addition on photocatalytic performance were studied.The results show that the photoresponse range of TiO₂/RGO/WS-GCN is broadened from 385 nm（TiO₂）to 600 nm（TiO₂/RGO/WS-GCN）,while the visible light absorption range of TiO₂/RGO/GCN is only less than 450 nm.When the addition amount of WS-GCN is 5%and the wavelength of LED is 550nm,the NO degradation rate of TiO₂/WS-GCN composites is as high as 60.86%,which has the best photocatalytic performance.