Study On The Degradation Mechanism Of Perfluorooctanoic Acid By Bismuth Catalyst

Prefluoroocatanoic acid?PFOA?is a typical perfluorinated compound widely used in industrial and domestic products and is toxic.Photocatalytic method can effectively degrade most organic pollutants,study the mechanism of photocatalytic degradation of PFOA,not only can enrich the treatment of refractory organics,but also provide a good new idea for the efficient degradation of perfluorinated compounds.In this paper,low concentration PFOA was selected as the research object.The photocatalytic technology was used as the method to construct a complete and practical photocatalytic reaction device,and the analysis and photocatalytic reaction system of PFOA and product were established.Secondly,fast microwave solvent was used.The oxygen vacancy BiOCl with high structural stability,good dispersibility,less agglomeration,fine crystallites and good crystallinity was prepared by thermal method.Finally,Br/I doped BiOCl with greatly increased visible light response range was synthesized by doping.The main contents of this paper include the following five chapters:The first chapter mainly summarizes and expounds the domestic and foreign research progress and status quo related to this paper,and on this basis,puts forward the necessity and significance of this paper research.The second chapter mainly lists the reagents and instruments needed in the relevant experiments of this paper and the related information of the instruments used in some characterization means,shows the photocatalytic reaction device and describes the photocatalytic reaction steps and the analysis and evaluation methods of PFOA and products.In chapter 3,the effect of surface oxygen vacancy on PFOA photocatalytic defluorination was studied by taking BiOCl as an example.The surface defect BiOCl was synthesized by microwave solvent-thermal method,and compared with BiOCl synthesized by traditional solvent-thermal method and precipitation method,the performance of photocatalytic PFOA defluorination was compared.The results showed that BiOCl prepared by microwave solvent-thermal method showed better photocatalytic performance than BiOCl prepared by precipitation method and traditional solvent method,which was33.8 times and 2.7 times respectively.Its excellent photocatalytic performance is mainly due to its high oxygen vacancy concentration,which can inhibit e^-and photogenic h⁺recombination by forming defect states in the band structure,so more photogenic h⁺can be generated for direct h⁺oxidation defluorination.This work established a conventional and rapid microwave-assisted method for the photocatalytic treatment of perfluorocarboxylic acid compounds by surface oxygen vacancy,which is of great benefit to the study of hole oxidation of PFOA.In the fourth chapter,different ratios of BiOCl_xBr_1-x?X=0.2,0.4,0.6,0.8?and BiOCl_xI_1-x?X=0.2,0.4,0.6,0.8?were prepared by doping.The results of testing and analysis showed that the catalyst BiOCl_0.2I_0.8.8 had the best degradation effect due to doping.The band gap of the catalyst is made smaller,and the absorbance is enhanced,which causes the excitation energy required for the electrons on the valence band to be excited to the conduction band to be correspondingly reduced,and the photocatalytic effect of I doping is better than Br doping.Because the incorporation of I element builds a more complex heterostructure inside the catalyst,the efficiency of separating photogenerated electron-holes is better,and the oxidation activity of photogenerated holes is ensured.Moreover,the incorporation of I element greatly increases the absorption range of visible light of the catalyst,and reduces the band gap to 2.38 eV,which increases the utilization of visible light by the catalyst and increases the efficiency of photocatalysis.This work has developed a new strategy for designing and manufacturing high-efficiency photocatalysts for degrading PFOA under visible light.The purpose of performance regulation by structural regulation and expansion of BiOCl visible light photocatalytic activity is of great significance for the practical application of BiOCl.It provides a feasible method for visible light degradation of PFOA.The fifth chapter is mainly about the summary of this paper and the prospect of practical application.