Preparetion,Characterization And Photocatalytic Activities Of Bismuth Oxyhalide-Based Materials

Photocatalytic technology is use of photo-generated electron-hole pairs to produce redox reactions under the driving of sunlight.Because of its advantages of simple,high efficiency,and environmental protection,it has become one of the important ways to deal with pollutants in water.BiOXs（X=Cl,Br,I）is a typical semiconductor photocatalyst with good catalytic activity.However,the treatment of pollutants with complex molecular structure and higher symmetry such as bisphenol A（BPA）is not optimistic,and there are few reports on the removal of nitrate in the water by BiOCl_nBr_1-n.In this thesis,BiOCl_nBr_1-nphotocatalysis materials were comebined by experimental design and theoretical calculation.The mechanism of excellent catalytic activity of BiOCl_nBr_1-n（0≤n≤1）ultra-thin nano tablets in improving photocatalytic reduction of nitrate and degradation of BPA was revealed.In addition,the carbon layer prepared by simple annealing wich combined with the BiOBr,and the influence of the two-dimensional materials of the BiOBr and the carbon layer on the photocatalytic hydrogen production performance is analyzed based on the surface roughness of the carbon layer.The specific research is as follows:（1）A series of ultra-thin BiOCl_nBr_1-nnanosheets were synthesized by a simple and environmentally friendly hydrothermal method with the same morphology but different Cl and Br ratios.Compared with the pure phases of BiOCl and BiOBr,all dihalogenated BiOCl_nBr_1-nare exhibits stronger light absorption characteristics,charge separation ability,photo-generated carrier migration ability and lower photo-electron-hole pair recombination rate.BiOCl_0.72Br_0.28exhibits the strongest photocatalytic activity.The reduction rate of nitrate is 95%and the degradation rate of bisphenol A reaches 97%.The theoretical calculation results show that the concentration of oxygen vacancies on the catalyst surface is the most important factors to improve the nitrate reduction efficiency and the degradation efficiency of bisphenol A.Cl atoms and Br atoms replace each other in the lattice to generate more oxygen vacancies,as the concentration of oxygen vacancies increases,it is easier to adsorb nitrate while promoting the separation of photo-generated electron-hole pairs.This is the most important factor for the high catalytic activity of BiOCl_0.72Br_0.28.（2）The nitrogen-rich carbon layer（CN layer）was prepared by simple sol-gel method with citric acid as carbon source and urea as nitrogen source.After boron doping,the carbon material was transformed from the CN layer with folded surface to the flat boron doped carbon layer（BNC layer）.BiOBr@CN and BiOBr@BNC were prepared by simple hydrothermal compounding with BiOBr.The flat two-dimensional carbon material means that it can be better compounded with BiOBr.The experimental results confirm that BiOBr@BNC has the strongest light absorption activity with the smallest band gap and the strongest photon carrier transport ability,in the experiment of photocatalytic cracking of water to produce hydrogen,under the same conditions,BiOBr@BNC produced 6.6 times more hydrogen than pure phase BiOBr,and the amount of BiOBr@CN produced hydrogen is 4.4 times that of pure phase BiOBr.