Preparation Of Bi-based Multiple Oxides And Study On Its Photocatalytic Degradation Performance

The rapid development of economy and society drives the upgrading of industrial technology,and the large-scale discharge of industrial waste water and domestic sewage seriously threatens the survival of mankind.Photocatalytic technology has gradually attracted people’s attention due to its advantages of green and safety,low price and easy availability of materials.Due to the valence structure of bismuth,most of the research on bismuth-based materials has focused on Bi³⁺ compounds such as Bi₂O₃,BiOCl and（BiO）₂OHCl.However,when bismuth-based materials are used alone as photocatalysts,their application in the field of photocatalysis is also limited due to their weak electron（e^-）-hole（h⁺）separation,poor response to visible light,and slow carrier transport.In this paper,the bismuth-based multi-element oxides Bi₂O₃,BiOCl and（BiO）₂OHCl are used as the research objects,and a series of modification methods such as the construction of semiconductor heterojunctions,carbon quantum dot modification,and biological template morphology control were used to explore the modified composite materials.The main research contents and results of the photocatalytic degradation activity and the degradation reaction mechanism of organic pollutants in wastewater are as follows:（1）The（BiO）₂OHCl/La（OH）₃ binary composite material（BOL-x,x=1,2,3,4）was successfully synthesized by a simple hydrothermal method.By changing the concentration of La³⁺ in the solution to adjust the loading of（BiO）₂OHCl and La（OH）₃ and optimize the reaction conditions,（BiO）₂OHCl/La（OH）₃ binary heterojunction can be further obtained.According to the photocatalytic activity test,the BOL composite material has strong photocatalytic activity against high concentrations of tetracycline hydrochloride（TC）and o-nitrophenol（o-NP）.Among them,BOL-2 has a strong photocatalytic activity against 30 % within 100 min and 120 min.The degradation rates of 30 mg/L TC and 30 mg/L o-NP were approximately 93.1 % and 91.3 %,respectively,while the degradation efficiency of（BiO）₂OHCl was only 32.9 % and 52 %.This means that the heterojunction formed between composite materials can effectively separate photogenerated electron-hole pairs.（2）Using carbonized eggshell membranes（CEMs）as biological templates,a series of carbon quantum dots（CQDs）modified BiOCl/CMEs composite materials（BiC-x,x=1,2,3,4）were synthesized.The obtained composite material,especially BiC-0.05,showed excellent removal efficiency for several organic pollutants,namely TC,rhodamine B（RhB）and o-NP.React for 30 minutes in a dark environment to allow the absorption and desorption of organic pollutants and catalytic materials to reach equilibrium,and then photocatalytic degradation is carried out under visible light（λ> 420 nm,300 W xenon lamp）for 5 minutes and 30 minutes to remove them,respectively 100% and 98% of RhB and TC.BiC-0.05 composite material can also be used for the treatment of actual industrial wastewater.Compared with using BiOCl to degrade 43.1 % of chemical oxygen demand（COD）,BiC-0.05 composite material can reduce COD by 73.1 %.According to the analysis of capture experiment and ESR technology,superoxide radical（·O2^-）is the main active free radical in the catalytic degradation.Among them,the synergistic effect of oxygen vacancies（OVs）,CEMs and CQD also makes the charge transfer faster,thereby realizing the improvement of catalytic performance.（3）Bi₂O₃/SiO₂/ZrO₂ ternary composite materials（BSZ-x,x=1,2,3,4,5）were prepared by solvothermal-calcination method.Various methods are used to characterize the structural characteristics and physical and chemical properties of composite materials.The target pollutants were TC,levofloxacin（LVF）and oxytetracycline hydrochloride（OTC）for evaluating the photocatalytic activity of the prepared samples.Among them,the degradation efficiency of BSZ-2composite material to the target products（TC,LVF,OTC）under visible light irradiation is 90.1 %,90.0 %,92 %,respectively,which is 45 times,13 times and 4 times higher than that of Bi₂O₃.The improvement of the photocatalytic activity of the composite material is mainly due to the addition of mesoporous SiO2 nanospheres,which intersperse in the nanosheets to prevent the mutual accumulation of Bi₂O₃.The specific surface area of the prepared BSZ-2 composite sample is 13.3times larger than that of pure Bi₂O₃,which helps to increase the active sites.In addition,the p-n heterojunction formed between the p-type semiconductor Bi₂O₃ and the n-type semiconductor ZrO₂ can greatly promote the separation of photogenerated e^--h⁺,which is conducive to the increase in the catalytic activity of the composite material.