Study on the removal of elemental mercury by microspherical Br-doped BiOCl comosite photocatalyst

ZHANG Anchao; ZHANG Jingfan; ZHANG Dan; SUN Zhijun; ZHANG Xu; LIU Yanwen; ZHENG Haikun

doi:10.16186/j.cnki.1673-9787.2022020067

Abstract：Photocatalytic oxidation is an effective technology to control atmospheric mercury pollution.Objec-tives To develop a low-cost visible-light-driven mercury removal catalyst,Methods microspherical BiO-BrxCl1-x composite photocatalysts with different molar contents of bromine(Br)were synthesized by an one-step coprecipitation method,and their photocatalytic performances of Hg0 removal under fluorescent lamp(FSL)were implemented in a wet photocatalytic mercury removal device.The physical and chemical struc-tures of the samples were analyzed by N2 adsorption-desorption,XRD,UV-Vis DRS,SEM,HRTEM,XPS and ESR.Moreover,the charge transfer between BiOCl and BiOBr was studied using density functional theory.Results The results showed that compared with BiOCl and BiOBr,the photocatalytic performances of BiOBrxCl1-x composites were all improved,and the Hg0 removal efficiency of BiOBr0.2Cl0.8 photocatalyst reached as high as 90.3%,which was about 50%than that of pure BiOCl.Compared with NO3-and SO42-,Cl-and CO32-exhibited significant inhibitions on Hg0 removal.The specific surface area of BiOBr0.2Cl0.8 com-posites was slightly higher than that of BiOBr and BiOCl,which would be beneficial for providing more reac-tive sites.With the gradual increase of Br content,the XRD characteristic peak intensity of BiOCl gradually decreased,and the photocatalytic absorption capacity appeared redshift regularly,indicating a strong interac-tion between BiOBr and BiOCl,not a simple mechanical mixing.Both Bi 4f and O 1s of the BiOBr0.2Cl0.8 composite material were shifted towards higher binding energies,indicating that the introduction of Br af-fected the species of Bi and O in BiOCl.The mechanism analysis displayed that the three active species were involved in the oxidative process of Hg0 removal with the high-to-low order of·O-2,h+,·OH.Conclu-sions The improvement of photocatalytic activity was mainly due to the formation of Z-type heterojunction between BiOCl and BiOBr,which effectively enhanced the separation of photo-generated charges.The study provided a new idea for the development of low-cost and efficient bismuth oxyhalide-based photocatalysts for mercury removal.