Preparation And Photocatalytic Performance Of BiOBr-based Composite Photocatalysts

With the development of industrial technology,the discharge of industrial wastewater into the environment without effective treatment seriously affects the balance of the ecosystem.Therefore,a scientific and technological means effectively treating wastewater pollutants is urgently needed.Semiconductor photocatalysis technology,as a green,simple and efficient oxidation technology,has attracted much attention.Bi OBr is considered as one of the most promising photocatalysts due to its unique layered structure,non-toxicity and chemical stability.However,pure Bi OBr exhibits unsatisfactory photocatalytic performance due to its weak visible light absorption capacity and faster photoelectron recombination rate.Therefore,in order to ameliorate the above situations,we modified and optimized Bi OBr by constructing heterojunction,morphology regulation and other methods.BiO_1-XBr/Bi OCl,BiO_1-XBr/g-C₃N₄,and BiO_1-XBr/Fe₂O₃composites semiconductor were successfully prepared by hydrothermal method.Various characterization equipments were performed to study photoelectric performance.These results showed that the Bi OBr-based composites had excellent visible light absorption capacity and electron separation rate,and were superior to the pristine Bi OBr in degradation of organic pollutants and antibiotics.（1）Oxygen vacancies（OVs）-rich 3D/2D BiO_1-XBr/Bi OCl composites were prepared via a facile hydrothermal process,and the chemical composition,crystal structure,microstructure,oxygen vacancy concentration and photoelectric properties of the samples were characterized.In this work,the photocatalytic performance of samples was evaluated by TC photodegradation.The result showed that the BiO_1-XBr/Bi OCl composites with optimal mass ratio could degrade 83%of tetracycline in 25 minutes,which was 2.3 and 1.9 times of that of BiO_1-XBr and oxygen vacancy-poor composite,respectively.In addition,BiO_1-XBr/Bi OCl composites showed excellent stability.The enhanced photocatalytic performance attributed to the synergistic effect of 3D/2D heterostructure and oxygen vacancies.2D Bi OCl nanosheets deposited on 3D BiO_1-XBr surface to form 3D/2D structural heterojunction,which can produce abundant active sites,more contact surfaces,and shorten the bulk-plane distribution to improve the charge transfer ability.The introduction of rich oxygen vacancies can form defect energy levels under BiO_1-XBr conduction band,so transfer electrons on conduction band will transfer to defect energy level,thus promoting the electron-hole pair separation rate and shortening the band gap.Furthermore,the mechanism of BiO_1-XBr/Bi OCl degradation of tetracycline was revealed by active species capture experiments.（2）In order to explore the effect of different charge transport mechanisms on photocatalytic performance,oxygen vacancies（OVs）-assisting 2D/2D Z-scheme BiO_1-XBr/g-C₃N₄photocatalysts were synthesized successfully via a simple hydrothermal treatment.We detected the photocatalytic performance of the samples by degradation Rh B,in which BiO_1-XBr/g-C₃N₄composites with optimal mass ratio showed the best Rh B degradation ability,and the removal rate was almost 100%for 25 minutes,which was 5.02 and 3.31 times that of the simple BiO_1-XBr,g-C₃N₄,and the degradation ability did not change significantly after five cycles.The improved photodegradation activity over BiO_1-XBr/g-C₃N₄ was mainly attributed to the synergistic effect of 2D/2D heterostructure and oxygen vacancies.2D/2D structure can provide a large number of active sites and promote charge separation.While oxygen vacancies act as electron mediator in Z-scheme heterojunctions,it not only promotes the separation of photogenerated electron holes,but also improves the visible-light absorption ability of photocatalyst.（3）Oxygen vacancy-rich 3D/2D Z-scheme BiO_1-XBr/Fe₂O₃composites was prepared via a facile hydrothermal process.Through visible light tetracycline degradation experiments,the BiO_1-XBr/Fe₂O₃showed excellent photocatalytic activity and degraded 85%in 25 min,which was 1.71 and 2.8 times of BiO_1-XBr and Fe₂O₃,respectively.The increased activity was attributed to the synergistic effect of 3D/2D Z-scheme heterojunction and oxygen vacancies.The 3D/2D structure provides a large number of active sites,produces more contact surfaces,and can shorten the volume-plane distribution to increase the charge transfer ability.Oxygen vacancies in Z-scheme heterojunction can not only improve the visible light absorption ability of the catalyst,but also act as an electron mediator to promote the separation rate of electron-hole pair.BiO_1-XBr/Fe₂O₃also showed excellent chemical stability and reusability.After repeated degradation,the photocatalytic capability and crystal structure did not change significantly.Furthermore,a possible photocatalytic mechanism for BiO_1-XBr/Fe₂O₃degradation of tetracycline was proposed by free radical trapping experiments.