The Preparation Of Nanophotocatalyst Based BiFeO₃and BiOBr For Photocatalytic Reduction Of Cr（Ⅵ）

This thesis is aimed at the existence problem in photocatalytic technology, such asthe photocatalysts recovery difficulties, low photocatalytic efficiency, low solarutilization rate. The target is to develop the novel composite photocatalyst with visiblelight response. BiOBr and BiFeO₃were chosen as two typical photocatalyst to designand optimize their photocatalytical properties. The details are summarized briefly asfollows:1. The single-crystalline BiFeO₃nanofibers were successfully fabricated via anelectrospinning method. The resultant nanofibers were characterized byThermogravimetry/Differential Thermal Analysis （TG/DTA）, X-ray diffraction （XRD）,scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, N2adsorption-desorption isotherms, UV–vis diffuse reflectance spectroscopy （DRS）.BiFeO₃nanofibers were used for the photoreduction of Cr（VI）. The BiFeO₃nanofibersshows better photocatalytic activities than those nanoparticles prepared via traditionalsol-gel method, due to the large specific surface area. However, when adding a smallquantity of TA which worked as the reductant and also the holes depletion agent, thereduction rate of Cr（VI） was increased from13%to100%in the potassiumdichromate （20mgL-1） solution with BiFeO₃（1.0gL-1） and TA （2mmolL-1） at pH3.0within80min under the visible-light illumination.. The results demonstrated that theBiFeO₃nanofibers with TA may become promising materials for application in thetreatment of Cr（VI）-containing wastewater.2. BiFeO₃was chemically unstabe in strong acidic conditions （pH≤3）.BiFeO₃/BiOBr composite photocatalyst was synthesised by hydrothermal method usedBiFeO₃nanoparticles prepared by sol-gel method and hexadecyl trimethyl ammoniumbromide （CTAB） as a bromine source at pH=3. The photocatalyst was characterized byX ray powder diffraction （XRD）, scanning electron microscopy （SEM）, UV-Vis diffusereflectance spectroscopy （UV-Vis） and BET. Effects of different molar ratio ofBiFeO₃/BiOBr composite photocatalyst on photoreduction Cr（VI） performance wasstudied under visible light. The experimental results show that the photocatalyticactivityof BiFeO₃/BiOBr composite was better than that of pure BiFeO₃. When themolar ratio of BiFeO₃with BiOBr was1:1, the catalyst activity was highest. Removalrate of Cr （VI） reached over99%in80min.3. The BiFeO₃nanofibers were prepared by an electrospinning method. Then theBiFeO₃nanofibers were added to the AgNO₃solution, and photoreducted to Ag particles under the UV-light. The Ag-BiFeO₃compounds would be obtained. TheAg-BiFeO₃compound was used for the photodegradation of RhB. The experimentalparameters, which influence photodegradation of RhB, such as the dosage of AgNO₃and tartaric acid, the morphology of BiFeO₃, the time of photoreduction to AgNO₃were optimized. The results showed that the Ag-BiFeO₃compounds have the highestphotocatalytic activity under the optimal conditions, which the AgNO₃concentrationwas0.01mol/L,the time of photoreduction was90min in the presence of tartaric acid.