Synthesis Of Bismuth Oxybromide-base Photocatalyst And Application On The Photocatalytic Degradation Of Chlortetracycline

As a promising photocatalyst,bismuth oxyhalide BiOX?X=Cl,Br,I?has attracted more and more attention due to its special layered structure and excellent performance in photocatalytic field.BiOBr photocatalyst has a narrower band gap than BiOCl,and has better stability than BiOI.However,BiOBr itself has poor migration ability of photo-excited electron and hole pairs,high recombination rate,and its photocatalytic activity needs to be improved.Therefore,we selected BiOBr as the main object of the study.By combining with other materials,the separation of photogenerated electron-hole pairs can be improved to enhance the photocatalytic performance.The theoretical calculation and simulation method is used to study the doping of BiOBr structure.The improved photocatalytic activity was stressed by analyzing the Ta and Nb dopingmodels.The main work of this thesis can be divided into the following points:1.Flower-like BiOBr self-assembled by nanosheets was synthesized by solvothermal method,and hydrothermal reflux method was used to make CdS nanoparticles uniformly formed on the surface of BiOBr.A series of composite catalysts were synthesized by adjusting the atomic ratio of Cd to Bi in the raw materials.The degradation of chlortetracycline as a target pollutant under visible light showed that the photocatalytic effect of CdS/BiOBr composite catalyst was significantly improved compared with pure phase photocatalyst.When Cd:Bi is 1:1,the photocatalytic effect is the best,and the removal rate of chlortetracycline at a concentration of 20 ppm in 40 minutes reaches 86.8%.The mechanism of degradation of chlortetracycline by the composite catalyst was further explored by the capture experiment.It was found that h⁺,·OH and·O₂^-played a role in the degradation process.The improvement of the photocatalytic effect of the composite catalyst is due to the formation of a heterojunction between CdS and BiOBr,which promotes the separation and transfer of photogenerated electron-hole pairs.2.Carbon quantum dots?CQDs?were synthesized by hydrothermal method and combined with nano-platelet BiOBr using a simple room temperature precipitation method.A series of composites CQDs/BiOBr were synthesized by adjusting the amount of CQDs.The synthesized photocatalyst was used to degrade the target pollutants rhodamine B,chlortetracycline and tetracycline under visible light.The results showed that the photocatalytic effect of BiOBr was improved by the addition of CQDs.The photocatalyst with a CQDs content of 4.7 wt%showed the best removal effect on the target contaminants.It has been further confirmed by capture experiments that h⁺plays a major role in the degradation process,while·O₂^-synergistically oxidizes contaminants.It is indicated by theory and experiment that the addition of CQDs with the merits of the induced migration and storage of electrons could promote the separation and transfer of photogenerated electron-hole pairs of BiOBr,and thus the photocatalytic performance is improved.3.Density functional theory was used to estimate the energy band structure and band gap by doping of Nb and Ta atoms into BiOBr cells,respectively.Through the analysis of the system band structure,density of states,doping energy and other results,the results are obtained:the doping of Ta could cause a large change in structure,and the structural change caused by the substitution doping of Nb is the weakest.Obviously,by doping Nb and Ta atoms into BiOBr cells,the band gap moves down,and the band gap is reduced to some extent due to the appearance of impurity levels.It is found that all four doping processes are energy release,indicating that the system becomes more stable after doping,in which the substitution doping of Ta has the highest energy,and the doping structure is most stable.