Study On Catalytic Degradation Of Organic Dyes In Printing And Dyeing Wastewater By Modified G-C₃N₄ Under Visible Light

Although the rapid development of science and technology has brought endless convenience to people's lives,it has also seriously polluted the global water environment.Therefore,it is extremely urgent to deal with water pollution and save the living environment.In recent years,a green semiconductor photocatalytic technology has been developed,which plays an important role in degrading water and pollutants in the atmosphere and decomposing water to produce hydrogen.However,conventional photocatalytic materials?TiO₂?have incapable of utilizing visible light,wide band gap and.low degradation efficiency.Graphite phase carbonitride?g-C₃N₄?is a promising photocatalytic material widely used by researchers because of its non-metallic nature,its ability to utilize visible light,its stability,its low cost and its high photocatalytic performance.Photodegradation of organic pollutants.g-C₃N₄ has a conjugated large?bond structure and is easily modified or complexed with other compounds,which is also an advantage.In this paper,the research background and current status of g-C₃N₄ were discussed.On the basis of the preparation of bulk g-C₃N₄ by different precursors,the modification was carried out by doping other semiconductor materials.The structure and properties of the prepared materials were studied by means of XRD,DRS,SEM,TEM,PL and FT-IR.Organic dyes with different properties were selected as target pollutants to detect the photocatalytic activity of each material,and the effects of different experimental conditions on the photocatalytic effect were investigated.Finally,the possible photodegradation mechanism was speculated,and g-C₃N₄ was applied to printing and dyeing wastewater in the future.The main research contents and results of this paper were as follows:?1?The bulk g-C₃N₄ was prepared by calcination using melamine and urea as precursors,respectively,for catalytic degradation of rhodamine B under visible light.The results showed that the photodegradation rate and the adsorption amount of rhodamine B by g-C₃N₄ prepared by urea as precursor were higher than that prepared by using melamine as precursor.Moreover,in the photocatalytic experiment,the catalyst was consumed less,and the Rhodamine B solution which degrades different initial concentrations and initial pH can be adapted.The experiment also found that it had a certain photocatalytic degradation effect on methyl orange and acid red 1,indicating that photocatalysis of g-C₃N₄ was universal.Finally,g-C₃N₄ prepared with urea as the precursor was selected for subsequent modification experiments.?2?The g-C₃N₄ was modified by BiOI and BiPO₄ for photocatalytic degradation of methyl orange and reactive blue 19 under visible light,respectively.The experimental results showed that the doping of these two lanthanide compounds increased the photocatalytic activity of the monomer g-C₃N₄.According to the characterization analysis,the photocatalytic activity was improved because the doping modification reduced the band gap value of g-C₃N₄,improved the utilization of visible light,and reduced the recombination rate of photogenerated electron-hole pairs,prolonged their life expectancy.According to the trap experiment,the active factors which play a major role in the photocatalytic process of the two binary catalysts were superoxide radicals,and their photocatalytic degradation mechanism may followed the Z-type heterojunction scheme.?3?The two binary materials were modified by AgBr to increase the efficiency of photocatalytic degradation of methyl orange and reactive blue 19,respectively.It was found through characterization that the incorporation of AgBr further enhanced the utilization of visible light by the binary catalyst and enhanced the absorption intensity of visible light,which was more conducive to the formation of active factors inside the material.Therefore,the photocatalytic efficiency of the two three-way catalysts doped with AgBr was much higher than that of the binary catalyst.At the same time,the semiconductor doping modification did not change the characteristics of the organic dye solution which was small in consumption of raw materials and suitable for different initial concentrations and different initial pH.In the trap experiment,the active factors in the process of photocatalytic degradation of methyl orange by AgBr/BiOI/g-C₃N₄ were holes and superoxide radicals.And the degradation mechanism might follow the double Z heterojunction scheme and Ag/AgBr system with strong electron capture effect.The active factor that playd a major role in the photocatalytic degradation of reactive blue 19 by AgBr/BiPO₄/g-C₃N₄was superoxide radicals.The degradation mechanism may be due to the conduction band and valence band potential difference of g-C₃N₄,BiPO₄ and AgBr.Led to the accumulation of photogenerated electrons in the conduction bands of BiPO₄ and AgBr,and the photogenerated holes accumulated on the valence band of g-C₃N₄,effectively reducing the recombination rate of photogenerated electron-hole pairs,plus the strong electron capture of Ag/AgBr system.The effect of the ternary material on the photocatalytic efficiency of Reactive Blue 19 was greatly enhanced.