Preparation Of Modified Bismuth Bromide And Its Photocatalytic Properties

With the progress of science and technology,human society has stepped into the modern civilization gradually.For the rapid development of economy,many environmental problems emerged and need to be solved urgently.In human production and daily life,some organic pollutants which are difficultly degraded naturally are released into the environment,destroying the balance of ecosystem,and eventually accumulate to the human body through drinking water,atmosphere and food chain,which pose a serious threat to human survival,reproduction and social development.At present,researchers have developed physical,chemical and biological methods to treat environmental pollutants.Semiconductor photocatalysis technology,as a green environmental pollution control mean,which can convert solar into chemical energy,and then effectively catalyzed degradation of the organic pollutants.While,Bismuth bromide oxide（BiOBr）,a kind of visible-light-driven photocatalyst has attracted considerable study attention in recent years due to its unique structural properties,good photoelectric properties,simple preparation measure and good chemical stability.In addition,BiOBr can catalyze O₂to produce amount of reactive oxygen species to mineralize organic pollutants highly.Unfortunately,it is found that BiOBr still has some shortcomings,such as small specific surface area,low separation efficiency of photogenerated carriers and poor dispersion stability,ect.In this paper,the structure and properties of BiOBr were regulated by changing the solvent conditions during preparation,and different methods were used to modify BiOBr.The photocatalytic degradation performance and reaction mechanism of BiOBr prepared under different conditions for organic pollutants were studied to reveal the regulation mechanism of different modification methods on the photocatalytic performance of BiOBr.The main contents and conclusions are as follows:1.BiOBr photocatalysts were solvothermally synthesized by Bi（NO₃）₃·5H₂O and tetrabutylammonium bromide（TBAB）in ethanol solution with different volume fractions（0%,20%,50%,80%and 100%）,which were named BiOBr₀,BiOBr₂₀,BiOBr₅₀,BiOBr₈₀and BiOBr₁₀₀respectively.The as-prepared samples were characterized by X-ray diffraction（XRD）,tunneling scanning electron microscopy（SEM）and ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis DRS）,ect.The results indicated that the crystal phase,morphology and surface charge distribution of BiOBr were affected by ethanol concentration.The catalytic degradation rate of Rh B by BiOBr increased first and then decreased with the increase of ethanol consumption in visible light,BiOBr₅₀showed the most excellent photo-degradation activity for Rh B.Zeta potential which is positively correlated with photocatalytic activity affects the transfer of electrons to the interface and the dispersion stability,occupying a significant role in photocatalytic performance,and it found that superoxide radical(O₂^·-)generated from activating O₂was the dominant active species during the photosensitization process of Rh B and BiOBr.2.BiOBr was synthesized by hydrothermal method using[Bi（ON₃）₃·5H₂O]and cetylpyridine bromide（CPB）as Bi and Br sources.At pH=3.3,the synthesized BiOBr was soaked in Na F solution of 0.01 mol/L,0.1 mol/L and 0.3 mol/L to obtain the three fluorided catalysts,named BiOBr-F_0.01,BiOBr-F_0.1and BiOBr-F_0.3,respectively.The samples were characterized by XRD（X-ray diffraction）,SEM（Scanning electron microscopy）,UV-Vis DRS（UV-Vis diffuse reflectance spectra）,XPS（X-ray photoelectron spectroscopy）and FL（Fluorescence spectrum）.The photocatalytic activity of the catalysts was evaluated by the degradation of an organic dye Rhodamine B（Rh B）under visible-light（λ≥420 nm）irradiation.The results indicated that the structures and properties of the catalysts were changed with the concentration of NaF increased.For example,Mineralization of Rh B was decreased after fluoride modification,while the decolorization rate of Rh B was improved when using BiOBr-F_0.1as catalyst.Reactive oxygen species（ROS）participating in the degradation of Rh B were examined and the generation of superoxide radical(O₂^·-),hydroxyl radical（·OH）and photogenerated hole（h⁺）were identified in the photocatalytic system.Compared with BiOBr,the mineralization rate of BiOBr modified by NaF decreased,which was attributed to the decreased production of ROS;the decolorization of Rh B was accelerated using BiOBr-F_0.1due to the fast deethylation,making the maximum absorption peak of Rh B blue-shift.3.BiOBr was synthesized by solvothermal method using bismuth nitrate pentahydrate[Bi（NO₃）₃·5H₂O]and sodium bromide（Na Br）as Bi and Br sources and ethanol as medium.Using terephthalic acid（PTA）and zirconium tetrachloride（ZrCl₄）as raw materials,N,N-dimethylformamide（DMF）as medium,UIO-66 was coated on the surface of BiOBr by solvothermal method to prepare BiOBr@UIO-66 catalysts with different composite ratios（5%,10%,30%,50%）.The physical structure and properties of the catalysts were analyzed by X-ray diffraction（XRD）,attenuated total reflection fourier transform infrared spectroscopy（ATR-FTIR）,tunnel scanning electron microscopy（SEM）,BET-N₂adsorption-desorption（BET）,ultraviolet-visible diffuse reflection spectroscopy（UV-Vis DRS）and fluorescence emission spectroscopy（FL）.With the increase of composite ratio,the infrared absorption of UIO-66 was enhanced,indicating that UIO-66 was successfully coated on the surface of BiOBr.Compared with BiOBr,the composite catalyst has more abundant pore structure,larger specific surface area,smaller average pore size and larger pore volume.The absorption ability for visible light enhanced,and the separation efficiency of electrons and holes improved.At the same time,the dispersion stability of the composite catalyst was further improved.Compared with BiOBr,the degradation efficiency of RhB by the composite catalyst is higher.Among them,30%BiOBr@UIO-66is the best,and its kinetic rate constant is 2.38 times as fast as BiOBr.BiOBr and 30%BiOBr@UIO-66 can’t activate O₂to produce O₂^·-,but the latter can oxidize H₂O to produce·OH.The capture experiments show that the main active species of Rh B degradation by BiOBr are O₂^·-,h⁺,while 30%BiOBr@UIO-66 are·OH,O₂^·-and h⁺.The composites can improve the oxidation ability of H₂O under visible light,enhancing the degradation efficiency of RhB significantly.