Modification Of BiOBbr-based Nanomaterials And Their Improved Photocatalytic Performance

Recently,the development of photocatalytic technology has displayed huge potential and application prospect in solving the environmental and energy crisis.Nevertheless,the improvement of efficiency of photocatalyst has become a difficult problem to be solved urgently.At present,the regulation of morphology and crystal facet,surface modification,and the construction of heterostructures etc.are main strategy for improving the efficiency of photocatalyst.In this thesis,taking BiOBr as the research object,the fabrication of Z-scheme photocatalyst,regulation of crystal defect and construction of composited materials were achieved to improve the photocatalytic activity of BiOBr in the photodegradation of antibiotics and organic synthesis.The effects of different strategies on the structure,photoelectric property and production of reactive species of BiOBr were investigated.The mechanism of the enhanced photocatalytic activity was also discussed.The main works of this thesis are as follows:1.BiOBr/Bi2O2CO3 and BiO1-xBr/Bi2O2CO3 with rich oxygen vacancy heterostructures were prepared by controlling the reaction time and varying the ratio of precursor.The products were characterized by electron spin resonance(ESR),X-ray photoelectron spectroscopy(XPS),temperature programmed oxidation(TPO)and high resolution transmission electron microscopy(HRTEM).The location,concentration and formation process of oxygen vacancy were analyzed.The photodegradation eff-iciency of ciprofloxacin,bisphenol A and 4-aminopyrine over the prepared heterostructures was evaluated under visible light.It was found that BiO1-xBr/Bi2O2CO3 exhibited much enhanced photocatalytic activity than that of BiOBr/Bi2O2CO3,which could completely mineralize the antibiotics and organic pollutants,while BiOBr/Bi2O2CO3 could not effectively mineralize the target contaminates.The measurement of photoelectric properties and reactive oxygen species,illustrated the fabrication of Z-scheme photocatalytic system in BiOi-xBr/Bi2O2CO3 heterostructures.Oxygen species,acting as the electron mediator,could greatly promote the separation of photogenerated charge carriers.It benefits to the production of superoxide radical(·O2-)on the conduction band of BiO1-xBr and hydroxyl radical(·OH)on the valence band of Bi2O2CO3,thus remaining the high redox ability and improving its photocatalytic performance;2.BiOBr nanosheets with different types of crystal defects were successfully prepared by varying the solvothermal reaction time.The type,concentration and the formation process from surface to inside of defects in different BiOBr nanosheets was analyzed by positron annihilation spectroscopy(PALS),X-ray photoelectron spectroscopy(XPS)and electron spin resonance(ESR)spectra.The production of reactive oxygen species by BiOBr with different defects were evaluated by electron spin resonance(ESR)technique and probe reaction used under visible light.It was found that the type of defects was closely related to the type of reactive oxygen species.BiOBr nanosheets with V’’’BiV·o defect cluster could promote the generation of ·O2-,while BiOBr nanosheets with V·BrV’’’BiV··o defect cluster is beneficial for the generation of 1O2.By using diphenyl sulfide,thioanisole,4-chlorothioanisole,4-methoxy thioanisole,dimethyl sulfide and diethyl ether as the substrate,the photocatalytic activities of BiOBr with different defects for the synthesis of sulfoxide from thioether were determined under the visible light.GC-MS results indicated that thioether could be selectively oxidized to sulfoxide over BiOBr nanosheets with V·BrV’’’BiV··o defect cluster due to the generation of a great number of 1O2 and the yield and selectivity are 71%～81%and 89%～99%,respectively.BiOBr nanosheets with V’’’BiV··o defect cluster resulted in the overoxidation of the substrate due to the production ·O2-.In addition,based on the steady-state fluorescence and phosphorescence and time-resolved fluorescence and phosphorescence,it was proposed that ·O2-was generated via photogenerated electrons involved electron transfer process in BiOBr nanosheets with V’’’BiV··o defect cluster.In BiOBr nanosheets with V·BrV’’’BiV··o defect cluster,photogenerated electrons relaxed to single excited state through intersystem crossing,and then convert 3O2 into 1O2 by energy transfer.3.BiOBr nanosheets were prepared in mannitol by hydrothermal reaction at 150℃ for 3 hours,using bismuth nitrate pentahydrate and sodium bromide as reaction precursors.The prepared BiOBr nanosheets were heat treated in concentrated H2SO4,and then recrystallized in absolute ethyl alcohol,n-amyl alcohol and n-nonyl alcohol,respectively.It resulted in the formation of BiOBr nanosheets,BiOBr/Bi24O3iBr10 composited materials and Bi24O3iBr10 nanorods,respectively.The obtained products were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The photocatalytic activities of the products for the degradation of ciprofloxacin and norfloxacin were evaluated.The results illustrated that BiOBr/Bi24O3iBr10 composited materials exhibited the highest photocatalytic activity for the degradation of antibiotics.The photoelectric properties of the synthesized samples indicated that the formation of composite materials promoted the generation of photogenerated carriers,the separation and transfer of electron and hole.