Synthesis And Modification Of G-C₃N₄ And Its Performance In Visible Light Catalytic Degradation Of Dye Waste Water

Graphite phase carbon nitride（g-C₃N₄）,as a new type of semiconductor material,has good visible light absorption capacity,stable physical and chemical properties,simple synthesis steps,low manufacturing cost,and good photocatalytic activity.Therefore,the research on the use of g-C₃N₄ visible light catalytic degradation of organic pollutants has become a hot issue in many academic fields.However,the g-C₃N₄material has the problems of narrow absorption range of sunlight and easy recombination of photogenerated carriers,which severely limits the activity of its photocatalyst.Therefore,it has become particularly important to modify the g-C₃N₄photocatalyst material to improve its photocatalytic performance.In this paper,g-C₃N₄and Zn（Ⅱ）/g-C₃N₄,Ag/g-C₃N₄ composite photocatalyst materials were successfully prepared by thermal polymerization method and in-situ precipitation method using melamine solid powder as precursor.FTIR,XRD,UV-Vis,XPS,SEM,TEM characterization were carried out.Rhodamine B and Reactive Red X-3B simulated wastewater were used as representatives of triphenylmethane dye and azo dye wastewater,respectively.The process of catalyzing the degradation of target pollutants by different photocatalytic materials was studied.The effect of different initial p H values on the visible light catalytic effect was explored,and its photocatalytic mechanism was initially revealed.The main results are as follows:（1）After 180 minutes of visible light irradiation,the degradation rate of rhodamine B by g-C₃N₄ can reach more than 98%.The p H value has a significant effect on the degradation of Rhodamine B by g-C₃N₄ photocatalysis.The reaction rate is the fastest under acidic conditions with a p H of 3,and the slowest under alkaline conditions with a p H of 11.The active materials that play a major role in the reaction are superoxide radicals（·O₂-）and holes（h⁺）.（2）From the characterization results of SEM,it can be seen that the introduction of Zn（Ⅱ）changes the surface morphology of g-C₃N₄.Compared with pure g-C₃N₄,Zn（Ⅱ）/g-C₃N₄ composite has a wider absorption spectrum,and the absorption intensity in the visible light region has been significantly improved.The 5%Zn（Ⅱ）/g-C₃N₄composite material showed the best photocatalytic degradation activity,and its first-order reaction kinetic constant was 0.054 min^-1,which was 2.7 times that of g-C₃N₄material.The p H value has a significant effect on the performance of the photocatalytic degradation of reactive red X-3B by Zn（Ⅱ）/g-C₃N₄ material.The reaction rate is the fastest under acidic conditions with a p H of 5,and the slowest under alkaline conditions with a p H of 9.The active species that play a major role in the photocatalytic degradation of reactive red X-3B are holes（h⁺）and superoxide radicals（·O₂-）.Cyclic experiments prove that Zn（Ⅱ）/g-C₃N₄ composite has good stability.（3）From the characterization results of SEM,it can be seen that the load of Ag changes the surface morphology of g-C₃N₄.Compared with pure g-C₃N₄,Ag/g-C₃N₄composite has a wider absorption spectrum.In the ultraviolet region,the absorption intensity of the Ag/g-C₃N₄ composite material for ultraviolet light is significantly higher than that of pure g-C₃N₄,and it gradually increases with the increase of Ag loading.The 5%Ag/g-C₃N₄ composite material showed the best photocatalytic degradation activity.The first-order reaction kinetic constant is 0.071 min^-1,which is3.6 times that of g-C₃N₄ material and 1.3 times that of 5%Zn（Ⅱ）/g-C₃N₄ composite material.The p H value has a significant effect on the performance of Ag/g-C₃N₄material for photocatalytic degradation of reactive red X-3B.The reaction rate is the fastest under acidic conditions with a p H of 5,and the slowest under alkaline conditions with a p H of 9.The active species that play a major role in the photocatalytic degradation of reactive red X-3B are hydroxyl radicals（·OH）,holes（h⁺）,and superoxide radicals(·O_2-).Cyclic experiments show that Ag/g-C₃N₄ composites have good stability.