Study On The Built-in Electric Field Modulation And Enhanced Photocatalytic Performance Of Bismuth Oxybromid

With the rapid development of industry and population growth,environmental problems are becoming increasingly prominent,which seriously restricts the sustainable development of society.In recent years,photocatalytic technology with the advantages of clean and efficient has attracted extensive attention in clean energy and environmental remediation.Recently,photocatalytic technology has been widely used in the degradation of toxic and harmful substances and the treatment of environmental pollution.Bi OBr belongs to a series of Bi OX（X=F、Cl、Br、I）families.It crystallizes into a tetragonal layered structure,which is composed of[Bi₂O₂]sheets,which are double staggered by[Br]atomic sheets,forming a[Bi₂O₂Br₂]layer along the c axis.It has the advantages of high chemical stability,easy preparation and low cost.Although Bi OBr has unique functions,efforts need to be made to improve its efficiency.It is mainly aimed at enhancing the absorption of visible light and inhibiting the recombination of photogenerated charge carriers.In this paper,taking Bi OBr as the matrix material,by compounding with two different ferroelectric materials to adjust its spontaneous polarization characteristics,a semiconductor photocatalytic material with built-in electric field enhancement was constructed,and the action mechanism of built-in electric field in the process of photocatalytic reaction was explored.The main contents of this paper include:（1）A series of tourmaline/BiOBr photocatalysts with different mass percentages were synthesized by one-step solvothermal method.The addition of tourmaline effectively improves the photocatalytic degradation ability of Bi OBr.The composite photocatalytic material 2%T/BOB with 2%tourmaline shows the highest photocatalytic activity and photoelectrochemical properties.It can almost completely degrade Rh B under visible light,and the degradation rate of phenol under all light is 97%,and has the largest photocurrent intensity and the smallest EIS impedance radius.The addition of tourmaline makes the（11 0）crystal plane of Bi OBr have certain dominant growth,and the（1 1 0）crystal plane with high content shows stronger polarization compared with the Bi OBr,which increases the intensity of the built-in electric field.The built-in electric field can drive the separation of photogenerated electrons and holes and inhibit their recombination.According to the band gap and conduction band value of 2%T/BOB photocatalyst,electrons in the conduction band can be captured by adsorbed O₂ molecules to produce·O₂^-free radicals.Holes in VB can directly oxidize pollutants,and pollutants can also react with H₂O to form·OH.In this work,the built in electric field generated by natural ferroelectric mineral tourmaline is used to regulate the built-in electric field of Bi OBr,and the mechanism of improving the performance of photocatalytic degradation of pollutants is explored.（2）A series of BaTiO₃/Bi₄O₅Br₂ composite photocatalytic materials with different molar amounts were prepared by solvothermal method.As a traditional ferroelectric material,Ba Ti O₃ has photorefractive effect and piezoelectric properties,and has simpler crystal structure and stability than tourmaline.It was observed by electron microscope that Bi₄O₅Br₂ nanosheets were evenly distributed on the surface of Ba Ti O₃ crystal.After recombination,the number of active sites was increased and the absorption of visible light by Bi₄O₅Br₂ was expanded.The enhancement of the built-in electric field of the composites effectively separates the photogenerated electron hole pairs and enhances the degradation ability of the photocatalytic materials.In the experiment of photocatalytic degradation of phenol,after capturing·OH,·O₂^-and h⁺,the degradation rates decreased to 43%,24%and36%respectively,indicating that the main active substances are·O₂^-,h⁺and·OH.In this work,the built-in electric field of Bi₄O₅Br₂ is adjusted by the electric field generated by the spontaneous polarization of Ba Ti O₃ to enhance its polarization.The whole composite photocatalytic system has excellent carrier transport performance.