Study On Preparation And Photocatalytic Properties Of G-C₃N₄ Modified By Carbon Doping And Molecular Imprinting

As a new type of visible light semiconductor photocatalytic material,graphite-like phase carbonitride?g-C₃N₄?has been widely concerned due to its advantages of high efficiency,environmental protection,good thermal stability and solar energy conversion capability.However,carbon nitride itself also has defects such as small specific surface area,low quantum efficiency,high recombination rate of photogenerated carriers,and poor selectivity,which seriously restricts the wide application of carbon nitride in the field of catalysis.In view of these shortcomings,the C-doped modification of the hexagonal prism type was prepared by modifying the specific surface area of g-C₃N₄,promoting the generation of electron-hole pairs,inhibiting the compounding and improving the selectivity of g-C₃N₄.The g-C₃N₄ and molecularly imprinted TiO₂/g-C₃N₄ composite catalysts.The main contents are as follows:?1?The results showed that the prepared g-C₃N₄/C composite photocatalyst was a hexagonal column with a loose structure and a layer structure of about 10 nm.The specific surface area is 64.49 m²g^-1,which is 18.4%higher than that of the pure phase g-C₃N₄.Compared with the unmodified pure phase g-C₃N₄,the g-C₃N₄/C layer spacing decreases,the band gap energy decreases,the UV-Vis absorption sideband wavelength red shifts,and the photogenerated electron-hole pair composite probability decreases.The results of photocatalytic experiments showed that the g-C₃N₄/C composite prepared by pyrolysis at500°C for 2h had the best photocatalytic activity.Under visible light irradiation,the degradation rate of RhB was as high as 97.7%after 60 minutes,the kinetic constant was0.1552min^-1,which was 6.4 times that of pure g-C₃N₄.Meanwhile,the g-C₃N₄/C composite photocatalyst had high stability,after repeated use for 4 times,there was no significant decrease in the degradation efficiency of RhB.?2?Molecular imprinting technique was used to prepare molecularly imprinted composite light by using 4-nitrophenol as template molecule,N-tetrabutyl titanate as titanium source and melamine as nitrogen source by thermal polymerization combined with sol-hydrothermal method.Catalyst M-TiO₂/g-C₃N₄.The microstructure and morphology of the composites were characterized by SEM,FT-IR,XRD,BET and UV-Vis absorption spectroscopy.The results showed that when the molar ratio of n-butyl titanate to substrate 4NP is 10:1,M-TiO₂/g-C₃N₄ exhibited a high adsorption capacity for 4NP,and the adsorption capacity is2.0mg/g,which was 2.6 times that of TiO₂/g-C₃N₄?0.76 mg/g?.Selective adsorption experiments showed that the M-TiO₂/g-C₃N₄ photocatalyst had preferential adsorption characteristics for 4NP with a selectivity factor of 2.54.Photocatalytic degradation showed that M-TiO₂/g-C₃N₄ composite photocatalyst had the highest photocatalytic activity when the mass ratio of melamine to titania precursor was 5:1.After 240 minutes degradation under visible light,the removal rate of 4NP was up to 97.67%,which was increased by 17%and55.3%than TiO₂/g-C₃N₄ and pure g-C₃N₄.After 5 cycles of experiments,the M-TiO₂/g-C₃N₄composite photocatalyst could maintain high removal rate of 4NP,therefore the composite photocatalyst has good recyclability.