Controllable Synthesis And Photocatalytic Activity Of BiOBr Matrix Composites

The new 2D nanomaterials,with their unique structure and electronic performance,are widely used in photocatalytic hydrogen evolution,photocatalytic carbon dioxide reduction,photocatalytic nitrogen fixation,photocatalytic organic synthesis and photocatalytic removal of contaminants.The new 2D nanomaterials have shown the huge potential in the field of photocatalysis.The 2D nanomaterial BiOX?X=Cl,Br,I?has a special layered structure in which the[Bi₂O₂]⁺layer and the halogen layer are staggered which can promote the separation of photogenerated electrons and holes,so that the performance is improved in the photocatalytic reaction process.Due to its excellent photocatalytic performance,BiOX has attracted the much attention of researchers,However,because of its low quantum efficiency,low light absorption efficiency,low adsorption capacity,and high recombination of photogenerated electron-holes,the photocatalytic activity of BiOX is still limited.In this paper,BiOBr is used as the research object,and the composite photocatalytic material can be synthesized by simple hydrothermal reaction and ion exchange at room temperature controllably.So that the performance of BiOBr in the photocatalytic system is improved.The research content of this paper specifically includes the following parts:?1?Synthesizing TiO₂/BiOBr by growing BiOBr on a TiO₂ nanorod array for photoelectrochemical decomposition research of water properties.Firstly,synthesizing TiO₂ nanorod array on FTO by hydrothermal reaction.Then,the TiO₂ nanorod array was placed in the BiOBr reaction solution to synthesize the BiOBr/TiO₂ composite photocatalytic material by hydrothermal reaction,The morphology and properties of the composites could be controlled by adjusting the reaction temperature and concentration.TiO₂/BiOBr is used as the photoanode in the experiment of photoelectrochemical decomposition of water to test the performance.The experimental results shown that the photocurrent of the BiOBr/TiO₂-2 composite photocatalyst obtained at a synthesis temperature of 160?and a reaction time of 30 min reached 1.17 mA/cm²?1.23 V vs RHE?at 1.23 V vs RHE,which was 1.3 times that of TiO₂nanorods?0.9 mA/cm²?.From the results of light absorption and electrochemical tests,it could be seen that BiOBr/TiO₂ heterostructure had advantages for improving the light-capturing ability of the photoanode,increasing the carrier density,enhancing the charge transport capability and the charge separation efficiency.Thus,the performance of BiOBr/TiO₂ heterostructure in photoelectrochemistry was improved.?2?Composite photocatalytic material Bi₂S₃/BiOBr was formed by Synthesizing Bi₂S₃ particles on a2D BiOBr layer structure for the study on photocatalytic nitrogen fixation performance.Firstly,the BiOBr layered structure was synthesized by one-step hydrothermal method.Then,using BiOBr as carrier and thioacetamide?TAA?as sulfur source,Bi₂S₃/BiOBr composite could be obtained stirring at room temperature for anion exchange.The size and loading of barium sulfide?Bi₂S₃?particles could be controlled by adjusting the reaction temperature,reaction solution concentration and other experimental conditions.Bi₂S₃/BiOBr was used for photocatalytic nitrogen reduction performance test,it could be seen from the results that photocatalyst Bi₂S₃/BiOBr-2 was obtained at a synthesis temperature of 160?,a reaction time of 30 min and an ion exchange time of 2 hours.Under a 300 W xenon lamp,after 60 min photocatalytic reaction,the yield of NH₃ could reach 878?mol/g,which was 5.6 times that of pure BiOBr nanosheets?158?mol/g?.From the results of light absorption and photocatalytic nitrogen reduction tests,it can be seen that Bi₂S₃/BiOBr is more conducive to the transfer of electrons,and could promote the separation of photogenerated electrons and holes,so that its photocatalytic performance is improved.It may be because of the substitution of S atoms provided by TAA for the O atoms on the surface of BiOBr,and ion exchange occurs,which forms an"electron-deficient state"on the surface of bromine oxime.?3?Obtaining ZIF-8/BiOBr composite by Growing ZIF-8 on the surface of two-dimensional BiOBr layered structure for photocatalytic nitrogen fixation.First,the BiOBr is synthesized by hydrothermal method.Then the ZIF-8/BiOBr composite can be obtained by using BiOBr as a carrier and stirred in a precursor solution of ZIF-8 for 24 hours.The morphology and properties of composite materials could be controlled by adjusting the experimental conditions such as reaction temperature and solution concentration.ZIF-8/BiOBr composite was used to do nitrogen reduction performance and photocatalytic performance test,it could be seen from the results that after 60 min of 300 W xenon illumination,the photocatalyst?ZIF-8/BiOBr-2?yielded NH₃ at 445?mol/g,which was 2.8 times that of pure BiOBr nanosheets?158?mol/g?.For the ZIF-8/BiOBr composite photocatalyst,with the change of the amount of BiOBr carrier and the decrease of the concentration of ZIF-8 precursor solution,the thickness of the sample became thinner,the specific surface area and active sites increased,so that the photocatalytic nitrogen fixation performance could be improved.