Study On Preparation And Properties Of Aromatic Molecular Modified Carbon Nitride Photocatalyst

Carbon nitride（g-C₃N₄）has the advantages of special electron configuration,good thermal stability,relatively low raw material cost and simple production process.In recent years,g-C₃N₄has been widely used in photocatalytic hydrogen,carbon reduction and decomposition of organic pollutants.However,the photocatalytic performance of unmodified g-C₃N₄is still limited by some factors,such as high recombination rate of photoelectron-hole pairs,small specific surface area and narrow response range in visible light region.In this paper,Carbon nitride samples were synthesized by supramolecular thermal polymerization.First,melamine,cyanogen chloride and aromatic organic compounds were magnetically stirred in anhydrous ethanol to form supramolecular intermediates.Then,a series of modified g-C₃N₄photocatalysts were synthesized by high temperature calcination.The photocatalytic properties of the samples were characterized by photocatalytic hydrogen production and photocatalytic degradation experimental.Benzoic acid,vanillin and p-phenylenediamine were selected as dopants to investigate the effects of organic doping with different functional groups on the structure and properties of g-C₃N₄.The results showed that the organic doping did not change the structure of carbon nitrode,but affected the morphology and optical properties of the catalyst.The specific surface area of the sample containing amino p-phenylenediamine as dopant was 96.333 m²/g.Under visible light irradiation,the hydrogen production within 4 h was 319.97μmol·g^-1higher than that of np-CN sample before doping.g-C₃N₄was modified with trace 4,4’,4"-triamino-trianiline doping,and the influence of the amount of organic doping on the morphology and photocatalytic performance of g-C₃N₄was investigated.The introduction of trianiline structure can provide a large number of electrons for g-C₃N₄group,thus effectively reducing the photoelectron-hole recombination rate and improving the separation efficiency of photogenerated carriers.Among them,the doping amount of 4 mg,namely CN-P_4mg,has the best photocatalytic performance.The photocatalytic degradation rate of 10 mg/L Rh B reached 95.7%in one hour.Under visible light irradiation,the hydrogen production rate reaches 16897.3μmol·g^-1·h^-1within 4 h,which is 1.8 times higher than that of np-CN sample before doping.The free radical capture experiment showed that superoxide radical（·O₂^-）was the main active substance,followed by hole（H⁺）and hydroxyl radical（·OH）.Based on the excellent structure of triphenylamine,diphenylamino-4-benzaldehyde was selected as organic doping modified g-C₃N_4.And modified g-C₃N₄with different doping amount was prepared at the same time.The results show that the doping of diphenylamino-4-benzaldehyde causes the carbon nitride to have ultrathin sheet structure,and CN-D_2mgsample has the highest photocatalytic degradation ability.The photocatalytic degradation rate of Rh B reached 97.8%.After 5 cycles,the photocatalytic degradation rate of g-C₃N₄samples to Rh B can still reach 89.6%.According to the photocatalytic hydrogen production experiment,the hydrogen production rate of CN-D_2mgwithin 4h was 14581.1μmol·g^-1·h^-1,and the hydrogen production rate increased by about 1.6 times than that of np-CN sample before doping.