Study On Synthesis,Modification And Photocatalytic Performance Of BiOBr

Solar-powered photocatalytic technology can degrade pollutants in water under mild conditions,and compared with traditional wastewater treatment technology,photocatalytic wastewater treatment technology has the advantages of being economical,green and efficient.However,the separation efficiency of electron-hole pairs is too low to achieve the desired goal in practical applications,so it is a very meaningful topic to modify BiOBr to improve its photocatalytic performance.This thesis focuses on BiOBr photocatalysts,with the aim of preparing highly efficient photocatalysts for application in wastewater treatment,promoting the separation of photogenerated electron-hole pairs and improving photocatalytic efficiency through elemental doping,exposed crystal plane modulation and heterogeneous structure construction.The specific work can be divided into three parts as follows:（1）Under simulated solar irradiation,the degradation ability of Fe,Cu co-doped BiOBr photocatalysts was significantly enhanced compared to BiOBr monomer.The two-dimensional Fe,Cu co-doped BiOBr photocatalysts were successfully prepared by a water bath heating method.The transition metal element doping was able to introduce defects in the BiOBr crystal structure while forming impurity energy levels in the forbidden band,which both lowered the electron leap potential barrier and inhibited the complexation of photogenerated electron-hole pairs.Calculations of the energy band structure of the catalyst reveal that the introduction of Fe,Cu causes some changes in the BiOBr valence and conduction band positions.The effect of different doping amounts on the photocatalytic performance of BiOBr was explored by regulating the introduction of Fe and Cu.The results demonstrate that the 1Fe-1Cu-BiOBr photocatalyst has significantly improved the degradation efficiency of single simulated pollutants（tetracycline hydrochloride and rhodamine B）,while it also shows better photocatalytic degradation performance for a mixture of the two.（2）BiOBr nanosheets with（110）as the main exposed crystalline surface were prepared at room temperature and pressure using Ca CO₃ as a novel guiding agent.The experimental data did not reveal a significant Ca²⁺doping signal,but the introduction of large amounts of Ca CO₃ acted as a modulator of the exposed crystal plane of BiOBr,with the main exposed crystal plane changing from（102）to（110）.The BiOBr nanosheets with exposed（110）crystallographic surface had more Van-der Waals band gaps,and there were a large number of unsaturated bonds and intermediate binding sites on the Van der Waals band gaps,providing more reactive sites for pollutant degradation.The two-dimensional structure of BiOBr results in a higher（110）/（102）ratio,increasing the exposure ratio of the（110）crystal plane.The introduction of Ca CO₃ also increases the specific surface area of the BiOBr nanosheets to a certain extent,increasing the chance of contact between the catalyst and the pollutant and facilitating the photodegradation of the pollutant reaction.BiOBr exhibited the best photocatalytic performance when the molar ratio of Ca to Biwas 5:1.In addition,the introduction of other alkaline earth metal carbonates also played a role in regulating the crystalline surface of BiOBr to a certain extent.（3）BiOBr/PI composite photocatalysts were successfully prepared by growing BiOBr nanosheets on polyimide aerogel（PI）structures by heating in a water bath.Through experimental investigation,the prepared 0.05PI/BiOBr photocatalyst showed the best photocatalytic degradation performance when the PI addition was 0.05 g.PI,as a polymer semiconductor,has a large specific surface area and can better adsorb pollutants in wastewater,thus enabling the BiOBr grown in situ on the PI structure to better contact with the pollutants and improve the BiOBr’s degradation capacity.XPS and Mott Schottky tests revealed that the internal electric field formed by the combination of the two to construct a p-n heterojunction can enable photogenerated electron-hole directional conduction and promote the separation of the two.The spectrum of DRS shows that the introduction of PI broadens the light response range of BiOBr.On the other hand,the hydrophobicity of the treated PI was significantly improved,enabling it to be better used in wastewater treatment applications.