Study On Modification And Performance Of The Photocatalysts Based On Bi₂O₃ And BiOBr Oxygen Defects Constructed

In the field of wastewater treatment,the research and application of semiconductor photocatalysts have attracted extensive attention.Researchers have devoted themselves to developing various kinds of photocatalysts with high efficiency and stability for the use of pollutant degradation utilizing solar energy.However,the existing catalysts failed to make good use of visible wavelengths,and most researchers have not given enough attention to the toxicity of catalysts and the cost of raw materials.Therefore,this paper took Bi₂O₃ and Bi OBr as basic photocatalysts to prepare a novel type of visible light photocatalyst with high stability,low toxicity,strong visible light absorption,low raw material cost and easy obtainment by introducing defect engineering,rare earth elements,plasma methods and half metal semiconductor Bi.Tetracycline hydrochloride was selected as the representative antibiotic pollutant to study the photocatalytic performance and degradation mechanism of the modified material.Meanwhile,the disturbance and stimulation of the environment caused by the photocatalysts were evaluated through metabonomics analysis,so as to systematically construct the preparation and toxicity evaluation system of the novel photocatalysts.The main results were as follows:（1）Bi₂O₃-Bi₂O_3-x visible light catalysts doped with rare earth metals（La,Ce and Er）were successfully prepared by double-zone temperature-controlled vacuum melting method and impregnation method.This paper not only explored the morphology,crystal structure,optical properties and other microscopic characteristics of the photocatalyst,but also studied the photocatalytic degradation paths and mechanism of tetracycline hydrochloride（TC-HCl）by modified photocatalysts.The results showed that the degradation rate of TC-HCl by Ce/Bi₂O₃-Bi₂O_3-x was 90.15%,and h⁺and·OH were the main active substances in visible irradiation.It was also found that La³⁺,Ce³⁺and Er³⁺could act as electron receptors to temporarily capture photogenerated electrons and reduce electron-hole recombination.In addition,two possible degradation pathways of TC-HCl were obtained by analyzing the intermediates.The modified materials were proved to be highly reusable after 4 degradation cycles.（2）The Ag/Ag Br-Bi₂O₃-Bi₂O_3-x heterojunction composited photocatalysts were successfully prepared by the simple method of in-situ growth of Ag/Ag Br nanoparticles on Bi₂O₃-Bi₂O_3-x.Both of the effective integration of plasma photocatalyst（Ag/Ag Br）with oxygen deficient metal oxide(Bi₂O₃-Bi₂O_3-x)and the mechanism of pollutants degradation by composited materials were investigated in this paper.The results showed that the degradation rate of 10%Ag/Ag Br-Bi₂O₃-Bi₂O_3-x was about 2.5 and 4.5 times that of pure Bi₂O₃-Bi₂O_3-xand Ag/Ag Br crystals,respectively.It was confirmed that the Ag/Ag Br-Bi₂O₃-Bi₂O_3-x had stronger photocatalytic activity.This enhancement was mainly based on the surface plasma effect of metal nanoparticles（NPs）,which changed the photoelectron transfer path of composited heterojunction materials so as to promote the separation of photoelectron hole pairs.Additionally,the electron transfer and band structure changes of heterojunction were verified by experiments and characterization,and the mechanism of improving photocatalytic performance and photostability of Z-scheme heterojunction photocatalysts was further explored.（3）X-OVs-Bi/Bi OBr photocatalysts based on high（001）plane was successfully synthesized by a simple one-step hydrothermal method.The synergism effect of OVs（oxygen vacancy）introduction and over-Bi doping on the performance of the synthesized photocatalysts and the mechanism of TC-HCl degradation by the modified photocatalyst was investigated.It was showed that the photocatalytic efficiency of 3-OVs-Bi/Bi OBr microspheres for TC-HCl was up to 95%.The optimal degradation conditions were obtained as follows:at room temperature,the initial pollutant concentration was 15 mg/L,the photocatalyst dosage was 200 mg,the mole ratio of Bi to Bi OBr was 3.2,and the degradation reaction time was 120 min.It was found that 3-OVs-Bi/Bi OBr had a narrower band gap,which could shorten the distance of electron transition from valence band to conduction band to accelerate the electron transition and enhancing the light-trapping performance.The introduced OVs captured photogenerated electrons,which could effectively inhibit the photocharge recombination and prolong the photoactive life of 3-OVs-Bi/Bi OBr.The degradation rate of 3-OVs-Bi/Bi OBr was only reduced by 20%after 4 cycles of degradation experiments.The crystal structure of 3-OVs-Bi/Bi OBr was basically unchanged,indicating that the properties of 3-OVs-Bi/Bi OBr was stable.Furthermore,the synergistic effect of heterojunction and surface oxygen vacancy on the photocatalytic performance of bismuth oxide halide was revealed.（4）The effects of different Bi-based photocatalysts stress on metabolic network and phylogenetic level of E.coli were analyzed,and by analyzing the expression patterns of differential metabolites,metabolite pathway enrichment and metabolic network changes via KEGG library,the safety evaluation results of 3 kinds of photocatalysts were obtained.It was showed that the toxicity of Ce/Bi₂O₃-Bi₂O_3-x to E.coli was low,mainly affecting purine and energy metabolism,and after being exposed to 3-OVs-Bi/Bi OBr,purine metabolism and amino acid biosynthesis were affected to some extent,but the DNA synthesis and metabolic activities were not significantly interfered.Compared with Ce/Bi₂O₃-Bi₂O_3-x and 3-OVs-Bi/Bi OBr,the effect of 10%Ag/Ag Br-Bi₂O₃-Bi₂O_3-x on E.coli was slightly greater,the metabolic disturbance of which was mainly involved in energy metabolism,amino acid synthesis,and aminoyl-transfer RNA biosynthesis.In this paper,the preparation and toxicity evaluation system of modified photocatalytic materials doped with rare earth elements（La,Ce,Er）,plasma and Bi semi-metallic semiconductor were based on the oxygen defect Bi₂O₃ and Bi OBr constructed.The performance of modified photocatalysts and the mechanism of degradation of antibiotic pollution were explored.It provided theoretical and technical support for the development,application and environmental safety evaluation of novel high efficiency bismuth photocatalysts.