Preparation And Photocatalytic Properties Of Polyurethane/Bismuth Oxyhalide Nanocomposite Film

Semiconductor photocatalysis technology has the advantages of high efficiency,low energy consumption,mild reaction conditions and environmental friendliness,which shows great application prospects in the process of organic wastewater treatment.Therefore,it is of great significance to research and develop efficient visible light photocatalytic materials.Bismuth oxyhalide(Bi OX,X=Cl,Br,I)is a typical ternary compound semiconductor.Due to its unique layered structure,suitable band gap width and visible light response,it has attracted much attention in recent years.However,the practical application of micro and nano photocatalysts is seriously limited due to the problems of easy agglomeration and difficult separation and recovery from aqueous phase.Immobilization of nanoparticles on suitable and stable carriers is one of the effective ways to solve this problem,but the research work in this field is less reported,the types of carriers are limited,and the preparation method is complex,which can not be applied to the complex and changeable water treatment system.In view of this,a series of porous polyurethane/bismuth oxyhalide nanocomposite membranes with uniform dispersion,easy separation and good stability were prepared by blending,wet phase conversion and in-situ synthesis method with porous polyurethane film as loading matrix,which was easy to prepare and use,and were applied to the treatment of organic pollutants such as Rhodamine B(Rh B)and tetracycline hydrochloride(TC)in water management process.The main results are as follows:(1)A series of PU/SF-BiOX nanocomposite membranes were prepared by wet phase inversion-in situ synthesis method using Bi OX(X=Cl,Br,I)nanocatalyst loaded on PU/SF composite films with porous structure and hydrophilic properties.SEM results show that the Bi OX in the nanocomposite films is a folded structure composed of numerous small nanosheets,which grows on the inner surface of the film without obvious agglomeration.The degradation properties of different types of nanocomposites were PU/SF-Bi OBr>PU/SF-Bi OCl>PU/SF-Bi OI,which was mainly related to the photoresponse ability,indirect photosensitization of dyes and the position of band valence band.The influence of different loading amount of Bi OBr on the performance of composite membrane was investigated.It was found that the effective load space of composite membrane was certain,and the influence of Bi OBr content on the performance of composite membrane reached the upper limit when the space was filled completely.The cyclic test shows that the nanocomposite membrane has good stability.In addition,the PU/SF-Bi OBr nanocomposite film can effectively generate hydroxyl radical(·OH)and superoxide radical(·O₂^-)in the visible light photocatalytic degradation of Rh B,but·O₂^-and h⁺play a dominant role in the photocatalytic reaction.(2)A series of PU/SF-BiOBr@CdS composite films were successfully prepared by blending-wet phase transformation-in situ synthesis method.And the related properties and photocatalytic activity of the nanocomposite films were characterized.The results show that due to the existence of Bi OBr@Cd S composite semiconductor,its can effectively improve the light absorption ability and the electron hole separation ability of a single Bi OBr,so it has higher photocatalytic activity.The optimal load molar ratio of Bi OBr and Cds is 2.5:2.5,and the degradation rate of TC is 70.3%.In addition,the catalyst in the composite membrane did not agglomerate obviously and had good stability.(3)A series of PU/ZnO–BiOBr heterojunction nanocomposite films were prepared by wet phase inversion-in situ synthesis method.And the photocatalytic activity of the films was evaluated by visible light degradation of TC.The results of XRD,FT-IR and SEM showed that the exposure of Zn O particles was covered by the Bi OBr nanosheets in the composite film,and the growth of Bi OBrr was inhibited by the presence of Zn O,which reduced the size of the nanosheets,indicating that there is an interaction and close contact interface between Bi OBr and Zn O.XPS result shows that the chemical environment of each element in the film changes due to the electronic interaction between Bi OBr and Zn O,this further proves the existence of heterojunction structure.UV-vis DRS result shows that PU/Zn O-Bi OBr composite film has better visible light absorption ability and narrower band gap than single phase PU/Zn O and PU-Bi OBr composite film,which makes it show higher photocatalytic activity for TC.With the increase of Bi OBr loading,the degradation performance of the composite membrane increased gradually.However,when enough Bi OBr nanoparticles were formed in the membrane,the performance of the composite membrane did not further improve with the increase of biobr loading.The composite film did not agglomerate obviously,and it still maintained a high degradation ability after repeated recycling.The results of mechanism study show that the PU/Zn O-Bi OBr composite film can effectively produce superoxide radical(·O₂^-)and hydroxyl radical(·OH)under visible light,but the main active species in the reaction process are·O₂^-and hole(h⁺),and a small amount of·OH may participate in the reaction.