Study On Immobilization Of Bismuth-based Nanocomposites Photocatalysts And Photocatalytic Organics Degradation

Problems such as environmental pollution and energy shortage hinder the sustainable development of human society and have become one of the major issues of global concern.Therefore,the development of environmental pollution efficient technology,is an urgent problem to be solved.Photocatalysis is regarded as an effective technology which can utilize solar energy or convert solar energy into chemical energy to alleviate environmental and energy crisis.However,most semi-conductive powder photocatalysts are difficult to recover.In this study,a novel bismuth-based heterojunction photocatalyst was prepared and the powder photocatalyst was immobilized by an innovative method.On the basis of material characterization and photoelectric performance test,the degradation performance and related mechanism of organic matter were systematically studied.The specific research content and results are mainly divided into two parts:PartⅠ:（1）Firstly,g-C₃N₄ was synthesized by thermal polymerization method,and Bi₂WO₆/BiOI was synthesized by one-step hydrothermal method.Then,g-C₃N₄ and Bi₂WO₆/BiOI were hydrothermal treated to prepare the ternary composite:Bi₂WO₆/BiOI/g-C₃N₄.The results of XRD,FTIR,SEM,TEM,HRTEM,XPS and EDS indicate the successful synthesis of the ternary composite Bi₂WO₆/BiOI/g-C₃N₄.PL,EIS,Mott-Schottky et al.showed that the visible light absorption capacity and charge migration capacity of the photocatalyst were enhanced,and the charge recombination rate was decreased compared with the single component or double group spectroscopic catalysts.（2）When the mass ratio of Bi₂WO₆/BiOI and g-C₃N₄ is 1:1.5,the three-component photocatalyst Bi₂WO₆/BiOI/g-C₃N₄（1:1.5）has the best photoelectric performance,so it shows good degradation ability of organic pollutants.When the dosage of ternary photocatalyst was 1 g L^–1 and the initial p H was 9.0,the degradation efficiency of 20 mg L^–1 tetracycline was 94.5%under visible light degradation for 120 min.The efficiency of degradation of 20 mg L^–1 tetracycline was 89.2%after 5 cycles of degradation experiments with terpolymer photocatalyst,which showed stable catalytic activity and good reuse performance of the photocatalyst.The results of free radical capture experiments showed that visible light irradiation of Bi₂WO₆/BiOI/g-C₃N₄（1:1.5）can produce h⁺,·OH and·O₂^–to degrade organic pollutants,and·O₂^–is the main active substance for degradation of organic matter.（3）In order to avoid the complicated separation process of powder catalyst after photocatalytic degradation of organic matter,Bi₂WO₆/BiOI/g-C₃N₄（1:1.5）was immobilized using the thermal curing property of PTFE emulsion,and boric acid was used as pore-making agent to increase the active reaction site of the immobilized photocatalyst.The main factors affecting the immobilization of photocatalyst include PTFE emulsion,the amount of boric acid and the immobilization pressure.The results show that under the conditions of 0.4 m L g^–1 for tetrafluoroethylene emulsion,0.4 g^–1for boric acid and 7.5 MPa,the immobilized sheet photocatalyst still retains good photocatalytic performance,and has good catalytic stability and mechanical strength.（4）The immobilized Bi₂WO₆/BiOI/g-C₃N₄ photocatalyst showed good tetracycline degradation performance.The degradation of landfill leachate showed that COD and TOC of leachate could be significantly reduced by photocatalytic degradation for 28 h,while photocatalytic degradation for 6 h was sufficient to effectively improve the biodegradability of leachate.PartⅡ:（5）AC/BiVO₄ photocatalyst was prepared by one-step hydrothermal method using glucose as carbon source.The results of XRD,FTIR,SEM,TEM,HRTEM,XPS and EDS analysis proved that AC/BiVO₄ was synthesized successfully.PL,EIS,Mott-Schottky et al.showed that the visible light absorption capacity and charge migration capacity of the composite photocatalyst were enhanced,and the charge recombination rate was decreased,compared with the single component or double group spectroscopic catalyst.（6）When the mass ratio of AC in the composite is 6%,AC/BiVO4 has the best photoelectric performance,so it shows good ability to degrade organic pollutants.When the dosage of AC/BiVO₄ was 1 g L^–1 and the initial p H was 9.0,20 mg L^–1 tetracycline was decomposed in visible light for 120 min,and the degradation efficiency was 86.4%.The degradation efficiency of 20 mg L^–1 tetracycline was 78.7%after 5 cycles of degradation experiments with composite photocatalyst,which showed the photocatalytic activity and good reuse performance of the photocatalyst.The results of free radical capture experiment show that visible light irradiation of 6%AC/BiVO₄ can produce h⁺,·O₂^–,·OH,¹O₂ to degrade organic pollutants,and·O₂^–is the main active substance.（7）Using polytetrafluoroethylene emulsion as binder and sodium chloride as pore-making agent,6%AC/BiVO₄ was immobilized.The immobilized photocatalyst consisted of an intermediate supporting layer and a catalytic layer on the surface.The results showed that the immobilized catalyst had good catalytic stability and mechanical strength,and could effectively degrade tetracycline.AC can improve the photocatalytic performance of BiVO₄ by promoting charge transfer process.