Built-in Electric Field Modulation Of Bismuth Oxybromide And Its Enhanced Photocatalytic Performance

With the rapid development of human society,environmental problems have become increasingly prominent,which seriously restricts the sustainable development of human civilization.As an advanced oxidation technology,semiconductor photocatalysis has potential application value in environmental remediation.Among the developed impressive photocatalysts,BiOBr is a typical visible light response semiconductor with a band gap of about 2.6eV,which is composed of[Bi2O2]2+ layers interleaved with double Br layers along the c-axis direction,and it is characterized by stability,easy preparation and low cost.However,BiOBr has some problems,such as fast recombination rate of photogenerated electrons and holes,poor carrier migration and so on,which greatly limit its photocatalytic activity and can not meet the requirements of commercial applications.Precently,the internal electric field has been revealed to be an efficient strategy to promote photogenerated carrier separation from the bulk and/or surface of semiconductors in the opposite direction of the Coulomb field,which thus greatly boosts the solar energy conversion efficiency.In this paper,semiconductor photocatalytic materials with internal electric field were prepared and constructed by using BiOBr as matrix material,using the spontaneous polarization characteristics of materials and the construction of heterojunctions.The mechanism of internal electric field in the photocatalytic reaction process was explored by characterizing the structure and related photocatalytic properties of the materials.The main contents include:In the first section,a series of BiOBr1-xIx/BiOBr hierarchical microsphere photocatalyst were designed and controllably synthesized by a conventional solvothermal process.The visible light photocatalytic activity was evaluated by the degradation of phenol.The resultant materials showed a significantly improved photocatalytic degradation efficiency towards phenol removal in water upon visible light illumination,and the optimal BiOBr1-xIx/BiOBr(x=0.25)exhibited over 92%degradation efficiency of phenol within 150 min,which was 24.5 and 3.1 times greater than that of pure BiOBr and pure BiOI,respectively.Also,this excellent photoactivity could expand to other colorless organic contaminants.The internal electric field was formed under the function of the polarization,which promoted the separation of photocarriers and enhances the photocatalytic activity.Therefore,the photocatalytic properties were enhanced.In the second section,a two-step solvothermal route has been used to uniformly deposit ZnFe2O4 nanoparticles on BiOBr nanosheets and the Z-scheme heterojunction was constructed due to the appropriate staggered band structure.The optimal ZnFe2O4/BiOBr composites with 3%ZnFe2O4 showed the highest photocatalytic degradation.The degradation efficiency of phenol under visible light irradiation 120 min was 99.02%,and the photodegradation rate of which was almost 3.11 times of pure BiOBr.And the photocurrent of the 3%ZnFe2O4/BiOBr was 58.29 μA·cm-2,which was 35 times higher than that of pure BiOBr.The excellent photocatalytic degradation performance of ZnFe2O4/BiOBr was due to the fact that ZnFe2O4 as a co-catalyst,which increased the active site of the reaction and expanded the visible light absorption of BiOBr.At the same time,the establishment of the internal electric field not only effectively separated the electron-hole pair of individual ZnFe2O4 and BiOBr,but also retained their excellent redox capability for photocatalytic degradation of pollution.