Preparation And Photo Catalytic Properties Of Bismuth Oxybromide-based Composite Materials

New demands for improving environment and developing new energy was put forward due to the crisis caused by environmental pollution and energy depletion with rapid development of global economy.Nanometer photocatalysis technology has become a potential hot research field with characteristic of simple operation,normal temperature oxidation removal of pollutants and no secondary pollution,and the core of which is photo catalyst.Focused by people especially,Bismuth oxybromide(BiOBr)is an indirect semiconductor material with a layered structure that can replace wide-band gap TiO2.The built-in electric field formed between the layers can facilitate the separation of electrons and holes.The focus of current research is on how to regulate the morphology and expose the active crystal surface,and further improve its photocatalytic activity through doping or compounding,so as to meet the requirements of actual water environment treatment.In this thesis,BiOBr is taken as the research object,based on a comprehensive review of BiOBr-based photocatalytic materials,a series of modification studies are conducted to explore the morphology-controlled synthesis of binary and ternary composite materials of BiOBr.The optimum preparation conditions were determined by characterization analysis of the prepared samples.The photocatalytic performances of the synthesized materials were evaluated with norfloxacin(NOR)as the target degradation product,which provided support for the practical application of bismuth visible catalytic materials in the degradation of antibiotics.The main research contents and conclusions are as follows:1.BiOBr with different morphologies were prepared by hydrothermal and solvent thermal methods,respectively.The crystal phase,microstructure and light absorption performance of the samples were characterized by XRD,SEM,EDS and UV-vis DRS,and the formation mechanisms of BiOBr prepared under different solvent conditions were proposed.The photocatalytic degradation rate of NOR over BiOBr nanosheet with a absorption edge at 423 nm was 34.7%.Two binary composites of SnO2/BiOBr and Bi/BiOBr were obtained using BiOBr nanosheet as the precursor,respectively.The characterization results show that SnO2 nanoparticles anchored on the surface of BiOBr,indicating the formation of SnO2/BiOBr p-n heterojunction,and Bi nanowires are interwoven and attached on the BiOBr nanosheet in Bi/BiOBr composite.Compared to the pure BiOBr,the photocatalytic performance of two binary composites were enhanced.In addition,the photocatalytic degradation rate of NOR over Bi/BiOBr with the optical absorption edge at 502 nm,97.2%,was higher than that of SnO2/BiOBr2.Deeply,the two ternary composites,Bi2WO6/Bi/BiOBr and CdS/Bi/BiOBr,were successfully prepared using Bi/BiOBr binary composite as the precursor,respectively.The results show that the surface of Bi2WO6/Bi/BiOBr with a spherical structure was the honeycomb network structure,and the CdS nanoparticles loaded on the surface of CdS/Bi/BiOBr with a block structure using Bi nanowires as the director.The formation mechanism and photocatalytic performance of the two composites with p-n heterojunction were proposed and evaluated.The photocatalytic degradation rate of NOR over CdS/Bi/BiOBr with the optical absorption edge at 620 nm,97.4%,was higher than that of Bi/BiOBr and Bi2WO6/Bi/BiOBr.3.Based on the active species trap test and the UV-vis DRD,the degradation mechanism of binary and ternary composites were proposed.The results show that the active species were changed with the constituents of as-prepared sample i.e.The main active species of SnO2/BiOBr and Bi/BiOBr were superoxide radicals(·O2-)and holes(h+);the main active species of Bi2WO6/Bi/BiOBr were hydroxyl radicals(·OH)and h+;the main active species of CdS/Bi/BiOBr were ·O2-,·OH and h+.