Study On The Promotion Effect Of Different G-C₃N₄ Modification Methods On Its Photocatalytic Performance

Photocatalytic technology has the advantages of complete degradation,green and pollution-free,which is helpful to solve the environmental pollution problems caused by industrial development.Graphite carbon nitride（g-C₃N₄）has attracted more and more interests in recent years because of its good stability,small band gap and visible light response.However,the practical application and promotion of g-C₃N₄ are severely restricted by its small specific surface area and serious photo-generated carrier recombination.In view of the above problems,this paper proposed three different methods to modify bulk g-C₃N₄,which effectively improved the photocatalytic degradation performance of g-C₃N₄.（1）Using melamine as precursor,ammonium chloride and ammonium sulfate as auxiliary agents,the modified g-C₃N₄ was prepared by one-step calcination by adjusting the molar ratio of ammonium chloride to melamine,ammonium sulfate to melamine.Compared with the bulk g-C₃N₄,the band gap of the modified g-C₃N₄ prepared by ammonium chloride and ammonium sulfate increased by 0.22eV and 0.21eV,respectively,which effectively enhanced the reoxidization ability of the photogenerated electron holes.With the increase of the molar ratio of the auxiliary agent to melamine,the photocatalytic degradation performance of the modified g-C₃N₄ was firstly improved and then decreased.When the molar ratios of ammonium chloride to melamine and ammonium sulfate to melamine were8/10 and 4/10,the degradation rate constants of the prepared modified g-C₃N₄ to Rhodamine B were 3.6 times and 4.8 times of the original,respectively,showing the best performance.（2）The hydrothermal method was used to modify the bulk g-C₃N₄ with dilute sulfuric acid of different concentrations,and acid modification of g-C₃N₄ was used for photocatalytic degradation of methyl blue and rhodamine B.It was concluded that sulfuric acid modification could optimize the morphology of g-C₃N₄,broaden the band gap,and improve the adsorption and degradation performance of g-C₃N₄.Within a certain range,the higher the concentration of sulfuric acid,the more the adsorption performance improved.The adsorption performance of g-C₃N₄ modified with 4mol/L sulfuric acid was 5.2 times higher than the original,and the kinetic constant of rhodamine B degradation was increased to 2.8 times of the original.（3）The hydrothermal modification of g-C₃N₄ with different mass fractions of hydrogen peroxide was carried out by hydrothermal method.SEM,XRD and UV-Vis DRS tests showed that the surface roughness of g-C₃N₄ was increased,the interlayer distance was shortened,and the band gap width was increased by up to 0.25eV compared with the original,which effectively enhanced the reoxidation and reduction ability of photogenerated electron holes.The experimental results of photocatalytic degradation of methyl blue showed that when the mass fraction of hydrogen peroxide was 10%,the degradation efficiency of the modified g-C₃N₄ improved by 29.1%compared with that before modification.