Preparation And Photocatalytic Properties Of C/g-C₃N₄ Composite

In recent years,the new polymer semiconductor-graphite carbon nitride（g-C₃N₄）has received extensive attention in the field of semiconductor photocatalysis due to its good visible-light response and low band gap,which have been applied in photocatalytic degradation of organic pollutants,photolysis of hydrogen,photocatalytic CO₂ reduction,and photocatalytic organic synthesis reactions.However,the problems of low specific surface area,easy recombination of photogenerated electrons and holes have seriously affected the photocatalytic performance of g-C₃N₄ and its large-scale application in photocatalysis.In this paper,a partial formaldehyde-methylolated dicyanodiamide（PFMD）was used as a novel precursor and prepare a carbon/graphite carbon nitride composites（C/g-C₃N₄）by in-situ-one-step method;The soft-template and hard-template method was used to further improve the specific surface area and the photocatalytic activity of C/g-C₃N₄composites.Finally,the Xe lamp was used as the simulated light source,methylene blue（MB）as the target pollutant,and the photocatalytic properties and photocatalytic mechanism of the composites were investigated.The specific research contents are as follows:1.Dicyanodiamide（DCDA）and formaldehyde（F）as the main raw materials,PFMD was synthesized first,and PFMD was used as precursor to synthesize carbon/graphite carbon nitride composite（C/CN-x）with controlled carbon content by in-situ-step synthesis.The effects of the molar ratio of formaldehyde to dicyanodiamide on the carbon content,specific surface area and photocatalytic properties of the composites were investigated.The composites were characterized to infrared spectra（FT-IR）,X-ray diffraction（XRD）,thermogravimetric（TG）analysis,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,elemental analysis,surface area（BET）analysis,photoluminescence（PL）emission spectra,and UV-vis diffuse reflectance spectroscopy（UV-vis DRS）.The results show that the carbon content and the specific surface area of the composites increase with the increase of the molar ratio of formaldehyde to dicyanodiamide.The introduction of carbon can significantly improve the photocatalytic performance of the composites.When the molar ratio of formaldehyde to dicyanodiamide is 0.125,the specific surface area and photocatalytic rate constant of the composites are 21.6 m²?g^-1 and0.00599 min^-1,respectively,which is 2.85 and 1.54 higher than that of pure g-C₃N₄.The mechanism of photocatalytic degradation of MB shows that hydroxyl radicals（·OH）is the main active substance that affects photocatalysis.2.Carbon/graphite carbon nitride composites（C/CN-P）was prepared by using PFMD as precursor and nonionic surfactant（P123）as soft-template.The composites were investigated the effects of the mass ratio of soft-template and precursor on the carbon content,specific surface area and photocatalytic properties of the composites.The results show that the carbon content of the composites increases with the increase of the mass ratio of soft-template to precursor.When the mass ratio of soft-template to precursor reaches 0.8,the carbon content and specific surface area of the composites are 49.30.%and 27.7 m²?g^-1.The photocatalytic experiment results show that C/CN-P exhibits good photocatalytic performance,and its photocatalytic degradation rate of MB is 1.92 times higher than that of pure g-C₃N₄.3.Carbon/graphite carbon nitride composites（C/CN-T）was prepared by hard-template method using PFMD as precursor and tetraethyl orthosilicate（TEOS）as silicon source.The effects of the mass ratio of TEOS and precursor on the carbon content,specific surface area and photocatalytic properties of the composites were investigated.The composites were characterized to FT-IR,XRD,TG,SEM,TEM,BET,XPS,PL,UV-vis DRS,etc.The results show that the specific surface area and pore volume of the composites reach the maximum when the mass ratio of the precursor to TEOS is 4,which is 174.1 m²?g^-1 and 0.710 cm³?g^-1,which are respectively 15.8 and 8.6 times of pure g-C₃N₄.The photocatalytic experiment results show that the increase of specific surface area of C/CN-T can significantly improve the photocatalytic performance of the composites,and its photocatalytic rate constant is 9.73 times that of pure g-C₃N₄.The mechanism study on photocatalytic degradation of MB shows that·OH is the main active substance affecting photocatalysis.