Investigations On The Modification Of BiOBr And Its Photocatalytic Degradation Of Antibiotics

Antibiotics,as effective pharmaceuticals in treating bacterial infections,have been extensively used in many fields due to numerous advantages,such as little side effect,good antibacterial effect and wide applications.However,because of high chemical stability,antibiotics cannot be effectively metabolized by organisms.As a result,most antibiotics are released into the environment in the form of non-metabolism,which poses a potential threat to the ecological environment.Recently,antibiotic residues have been detected in water,soil and plants due to its unreasonable use.To eliminate the adverse effects of antibiotics on the environment,researchers have developed many effective techniques,such as physical adsorption,biological degradation,Fenton oxidation,and so on.Unfortunately,these methods still have some disadvantages,such as high cost and secondary pollution,which limit their further development in practical applications.Photocatalytic degradation possesses some merits including high degradation efficiency and easy to process.Therefore,it has been widely employed for degradating antibiotic pharmaceuticals.Bismuth halide oxide（BiOX,X=Cl,Br,I）is commonly used Bi-based photocatalysts in visible light region.Bismuth halide oxide possesses layered structure which is benefit for doping and modification,thus helping to improve their performances in photocatalytic degradation.Therefore,many attentions have been paid for developing novel nanomaterials based on BiOX.However,the photogenerated carriers recombined quickly in pure BiOX.Hence,it is obliged to further modification to retard photogenerated electron-hole pairs recombination and enhance the photogradation activities.In this dissertation,BiOBr/β-Bi₂O₃ and rGO/Bi₄O₅Br₂ nanocomposites were successfully fabricated.The photocatalytic properties of these nanocomposites were evaluated by degradating different antibiotics with simulated solar light as the excitation source.The main contents of the dissertation are as follows:（1）A facile solvothermal process was adapted to controllably synthesize BiOBr/β-Bi₂O₃ composites via a one-step strategy.Bi（NO₃）₃·5H₂O and1,3-bis（3-bromopropyl）imidazole bromide（DIBPIBr）ionic liquid were used as precursors,respectively.By changing the molar ratio of precursors,β-Bi₂O₃ could be grown in situ on the surface of BiOBr.The successful synthesis of BiOBr/β-Bi₂O₃heterojunction was confirmed by XRD,XPS,HR-TEM for composition analysis.Furthermore,the photocatalytic properties of BiOBr/β-Bi₂O₃ composites synthesized with different precursor ratios were evaluated by using norfloxacin（NOR）solution as pollutant model.The results showed that the BiOBr/β-Bi₂O₃ composites prepared at the precursor ratio of 3:1 had the best photocatalytic activity,which was attributed to thatβ-Bi₂O₃ formed on the surface could significantly affect the crystal structure and optical absorption properties of the composites.The mechanism of photocatalysis was further proposed based on the results of capture experiment and ESR data.This work provided a simple and effective method for in-situ growth of Bi₂O₃ on Bi-based materials to form double Bi-based heterojunction for the degradation of antibiotics wastewater.（2）Graphene oxide（GO）was synthesized by Hummers method with some modifications.Then,rGO/Bi₄O₅Br₂ catalysts with different amount of graphene loading were prepared by hydrothermal method.Raman spectra confirmed that GO was reduced to rGO.The as-prepared rGO/Bi₄O₅Br₂ were used to degrade ciprofloxacin（CIP）,NOR and tetracycline（TC）under simulated solar irradiation.The results indicate that rGO/Bi₄O₅Br₂ nanocomposites possess high photocatalytic activities.Among them,1.0 wt%rGO/Bi₄O₅Br₂ shows the best catalytic performance.The removal efficiency of CIP,NOR and TC at 60 min is 97.6%,80.7%and 98.7%,which is much higher than that of pure Bi₄O₅Br₂.The enhanced effect on photocatalytic performance mainly comes from graphene,possessing high conductivity,can accelerate the transfer of photogenerated carriers in Bi₄O₅Br₂ and suppress its recombination.According to the data of capture experiment and ESR,the free radicals including h⁺,·OH and·O₂^-play the main roles in photocatalytic degradation.Based on this,the photocatalytic mechanism of rGO/Bi₄O₅Br₂composites was proposed.