Study On Surface Atomic Structure Regulation And Photocatalytic Performance Of Bismuth Oxide Bromide

Energy shortage,environmental pollution and climate warming are becoming three main problems that restrict the development of human society.Photocatalysis can be considered as an effective energy conversion and environmental pollution treatment potential technology.Photocatalytic materials are the core carrier of photocatalytic technology,so the design of efficient semiconductor catalysts has become the focus of research in the field of photocatalysis.Among many semiconductor photocatalytic materials,bismuth oxybromide（BiOBr）with the unique layered structure has attracted the field of view of researchers.However,BiOBr also has many shortcomings,such as insufficient visible light absorption,high recombination rate of photogenerated electrons and holes,and short lifespan of photogenerated electrons.These problems greatly limit the application of BiOBr semiconductors in the photocatalysis.Therefore,it is urgent to modify surface structure of BiOBr to improve its photocatalytic activity.This thesis will regulate the surface sutucture of BiOBr by different methods to increase the active sites of BiOBr through surface modification methods using sugar molecules as templates,reduce the recombination rate of photogenerated electrons and holes,and expand the light absorption range by constructing surface defects,thereby enhancing its photocatalytic activity.We use mesoerythritol containing a large number of hydroxyl groups to modify the surface atomic structure of BiOBr,thereby significantly improving the catalytic performance.Here,using bismuth nitrate pentahydrate and potassium bromide as raw materials,and mesoerythritol as a template,BiOBr nanosheets containing surface hydroxyl groups were prepared by a hydrothermal method.The hydroxyl group in mesoerythritol combines with bromide ions during the reaction,leaving a mark on the surface of BiOBr,forming a large number of surface hydroxyl active sites.Compared with BiOBr synthesized using water,the thickness of the BiOBr sheet is greatly reduced and the recombination of photo-generated electrons and holes is effectively inhibited after the addition of mesoerythritol,.The increase of surface active sites and the prolonged lifetime of photogenerated carriers have significantly improved the photocatalytic activity of BiOBr.In order to further study the effects of different surface modifiers on the surface atomic structure and catalytic performance of BiOBr,we used a variety of sugar molecules as templates and used hydroxyl to modify the versatility of BiOBr surface.Different sugars（glucose,fructose,Maltose,sucrose and lactose）are chosen as surface modifiers to study the versatility of this method.Compared with BiOBr prepared by water,the thickness of BiOBr nanosheets is significantly thinner after sugar molecules are introduced,which effectively reduces the migration distance between photogenerated electrons and holes.In addition,the hydroxyl imprints formed on the surface of BiOBr by the hydroxyl groups in sugar molecules also increased significantly.These hydroxyl imprints are suitable to form active group hydroxyl radicals in photocatalytic reactions.The above results show that hydroxyl surface modification is a genernal method to improve the photocatalytic activity of BiOBr.Finally,the narrow visible-light absorption range limits the wide application of BiOBr.In order to expand its visible light absorption range,we introduced its visible light absorption by constructing bromine defects.However,it is very difficult to directly remove Br ions.Thus,we developed an indirect method to construct its vacancies.First,iodide ions are introduced into BiOBr to form a BiOBr_1-xI_xsolid solution.Then,according to the different bond energies of the bismuth-bromide bond and the bismuth-iodine bond,the Bi-I bond is broken by a heat treatment to allow the iodide ions to volatilize and then form defects.The method not only expands the visible light absorption range of BiOBr,but also introduces vacancy defects on its surface,increases the active sites of the reaction,and suppresses the recombination of photogenerated electrons and holes,so that the catalyst exhibits excellent photocatalytic performance.