Construction Of Bismuth-based Semiconductor Composite Material And Study On The Performance And Mechanism Of Photocatalytic Degradation Of Antibiotic

The widespread use of antibiotics in the pharmaceutical industry and clinics,and the abuse of antibiotics in the breeding and animal husbandry industries have caused serious damage to the water environment and threatened the balance of the ecological environment.It was urgent to solve the problem that efficiently remove antibiotic pollutants in the water environment and purify water resources.Photocatalytic technology,as a new type of advanced oxidation technology,has the advantages of high efficiency,stability,environmentally friendly and convenient operation.Among,bismuth-based semiconductor photocatalyst has stable physical and chemical properties.More importantly,the special electronic structure made it responsive in the visible light range.Thus,bismuth-based seminconductor photocatalyst have attracted much attention.However,the photocatalytic performance of bulk bismuth-based seminconductor photocatalyst was still subject to some limitations,such as the rapid recombination of electron-hole pairs,low visible-light utilization and poor dispersion.Therefore,improving the performance of bismuth-based semiconductor photocatalysts has always been the focus of researches.It was well known that methods such as morphology control,construction of heterojunctions,and surface modification can enhance the light energy utilization rate and electron transfer efficiency of semiconductors,thereby helping to improve photocatalytic activity.Therefore,in this study,a series of bismuth-based semiconductor composite materials were prepared by the strategies of constructing heterojunctions,surface modification,and growth control,respectively,and analyzed the light energy utilization and electron transfer capabilities of the prepared composite materials.The results proved that the different bismuth-based semiconductor composite materials constructed have good photocatalytic activity;the capture experiments proved the active species involved in the reaction in the catalytic process,and combined with the energy band position to clarify the process of the photocatalytic degradation reaction and the mechanism.This work provided theoretical guidance for improving the photocatalytic performance of bismuth-based semiconductor materials.The content of this thesis mainly includes the following three aspects:1.Construction of Bi₁₂Ti O₂₀-based Heterojunction Semiconductor CompositeMaterial and Its Photocatalytic Degradation Antibiotic Performance andMechanism(1)To inhibit the recombination of the photo-generated electron-hole pairs of the Bi₁₂Ti O₂₀ semiconductor photocatalyst,a type-II Bi VO₄/Bi₁₂Ti O₂₀ heterojunction composite material was prepared by the ultrasonic-assisted in-situ growth method.The microstructure and physicochemical properties of Bi VO₄/Bi₁₂Ti O₂₀ heterojunction composite materials were explored through various testing methods.The results of PL,photocurrent and EIS showed that the Bi VO₄/Bi₁₂Ti O₂₀ heterojunction composite material has better separation efficiency of electron-hole pairs.The results of antibiotic degradation experiments showed that the optimal degradation rates of Bi VO₄/Bi₁₂Ti O₂₀heterojunction composites were 1.9 and 2.6 times higher than the pure Bi₁₂Ti O₂₀ and Bi VO₄,respectively.Through the capture experiments and the energy band position,the main active species during the degradation process were systematically analyzed.The photocatalytic mechanism of the type-II Bi VO₄/Bi₁₂Ti O₂₀ heterojunction composite material was proposed.(2)To improve the charge separation efficiency and retain the strong redox ability,a direct Z-type Ti O₂/Bi₁₂Ti O₂₀ heterojunction composite photocatalyst was synthesized by loading Ti O₂ QDs on the surface of Bi₁₂Ti O₂₀.The Ti O₂/Bi₁₂Ti O₂₀ heterojunction composite material showed excellent photocatalytic degradation antibiotic activity under visible light irradiation,and the optimal degradation rate for gatifloxacin was 3.0 times higher than that of pure Bi₁₂Ti O₂₀.The photoelectrochemical analysis results demonstrated that the heterojunction structure greatly improved the separation and transfer efficiency of photoexcited charge carriers between Ti O₂ QDs and Bi₁₂Ti O₂₀.In addition,the main active species in the photocatalytic degradation process were determined through capture experiments,and the charge transfer pathway and photocatalytic mechanism of the Z-type Ti O₂/Bi_12Ti O₂₀ heterojunction were proposed.2.Construction of Surface Modified Bi₄Ti₃O₁₂-based Semiconductor CompositeMaterial and Its Photocatalytic Degradation Antibiotic Performance andMechanism(1)A novel 2D/2D Ni(OH)₂/Bi₄Ti₃O₁₂ composite material was constructed by using non-precious metals Ni(OH)₂ nanosheets with excellent electronic conductivity to modify Bi₄Ti₃O₁₂ nanosheets.The 2D/2D Ni(OH)₂/Bi₄Ti₃O₁₂ composite materials was analyzed with various analytical methods,which demonstrated the materials were combined in a face-to-face manner.Through UV-vis DRS,PL,photocurrent and EIS analysis,it was shown that the light absorption range of Ni(OH)₂/Bi₄Ti₃O₁₂ composite material was widened and the carrier separation efficiency was increased.Under the visible light degradation experiments of antibiotics,the optimal degradation rates of Ni(OH)₂/Bi₄Ti₃O₁₂ composites were 11.1 and 7.2 times that of Ni(OH)₂ and Bi₄Ti₃O₁₂,respectively.The effect of different environmental media on the photocatalytic degradation performance was explored,which showed that the Ni(OH)₂/Bi₄Ti₃O₁₂composite material has good photocatalytic degradation performance under different environmental conditions.Through the capture experiments,the mechanism of photocatalytic degradation was deeply analyzed.(2)Carbon dots(CDs)were prepared from cheap and easily available biomass materials and used to modify Bi₄Ti₃O₁₂ nanosheets.The 0D/2D CDs/Bi₄Ti₃O₁₂ composite material was obtained by a simple physical mixing method.The abundant functional groups on the surface of the CDs enhanced the bonding between the materials,thus the CDs can be better loaded on the Bi₄Ti₃O₁₂ nanosheets.Through a series of characterizations,the material's microscopic morphology,size,crystal structure,and photoelectrochemical performance were systematically analyzed.The results proved that the visible light absorption range of the 0D/2D CDs/Bi₄Ti₃O₁₂ composite material was expanded,and the separation efficiency of electron-hole pairs was improved.Photocatalytic degradation of antibiotics experiments showed that the optimal degradation rate of 0D/2D CDs/Bi₄Ti₃O₁₂ composite material was 6.2 times that of the pure Bi₄Ti₃O₁₂.The capture experiments confirmed the main active species involved in the reaction during the photocatalytic process,and clarified the mechanism of the 0D/2D CDs/Bi₄Ti₃O₁₂ composite photocatalyst.3.Construction of Lignin-induced Bismuth-based Semiconductor CompositeMaterial and Its Photocatalytic Degradation Antibiotic Performance andMechanism(1)The adjustment of the morphology and structure was an effective way to improve the photocatalytic performance of bismuth-based semiconductors.In this experiment,the3D macromolecular structure of lignin was used as the active agent and carbon source,a porous structure Bi VO₄-LC nanocomposite material was synthesized by a simple one-step hydrothermal method.The addition of lignin effectively controled the self-growth process of Bi VO₄.At the same time,the lignin was carbonized to form a carbon material to modify Bi VO₄ and leaved holes.Through a series of analysis and testing methods,the crystal structure,microscopic morphology,and elemental state of the obtained samples were explored.UV-vis DRS and electrochemical test results proved that Bi VO₄-LC nanocomposite has a wider visible light absorption range and improvement of the separation efficiency of electron-hole pairs.In the experiment of photocatalytic degradation of antibiotics,the optimal degradation rate of Bi VO₄-LC nanocomposite was4.0 times that of pure Bi VO₄.In addition,the photocatalytic degradation process of Bi VO₄-LC nanocomposites was proposed through capture experiments.(2)To enhance the performance of biomass carbon and improve the dispersion of bismuth-based semiconductor photocatalysts,a vanadium-doped lignin carbon/bismuth oxide(V-LC/Bi₂O₃)composite material was synthesized by a one-step calcination method.The crystal structure and surface characteristics of the samples were characterized by XRD,Raman,and FT-IR,which confirmed the formation of Bi₂O₃semiconductor and the doping of vanadium.The morphological characteristics of the samples were analyzed by SEM and TEM,which confirmed that the Bi₂O₃ nanoparticles were successfully dispersed on the V-LC carrier.The photoelectrochemical test confirmed that the light energy absorption range and electron migration capacity of the V-LC/Bi₂O₃composite material have been improved.The optimal degradation rate of the V-LC/Bi₂O₃composite was 3.5 times higher than that of the pure sample.Through the capture experiments,the main active species participating in the reaction during the degradation process were determined,and the mechanism of the photocatalytic degradation of the V-LC/Bi₂O₃ composite material was propossed.