Investigation Of Photocatalytic Properties Based On Prepared BiFeO₃ Nanomaterials

Currently,water pollution has become one of the many threats faced by human beings,and how to efficiently treat organic pollutants is an important research topic.Photocatalysis can achieve solar-driven pollutant degradation,and semiconductor photocatalysts have been widely used in photocatalysis technology.As a new type of catalyst,bismuth ferrate（Bi Fe O₃,BFO）with a rhombic chalcogenide structure works in the visible light band which is easily available,with a relatively narrow band gap（2.1-2.8 e V）,and can effectively absorb sunlight wavelengths less than 560 nm.In addition,BFO has excellent chemical stability in the photocatalytic process,and its unique ferromagnetic properties can avoid problems such as secondary pollution.However,pure BFO usually has low photocatalytic efficiency,which cannot satisfy industrial application.The dopants will hinder the compounding of photogenerated carriers and reduce the band gap energy of photocatalysts,expected to significantly improve the photocatalytic performance.Therefore,cobalt and samarium were selected as the doping elements of BFO,pure-phase BFO and doped series of BFO nanoparticle materials were prepared by the sol-gel method.More importantly,the particle size,morphology and doping elements impacted on the enhanced photocatalytic properties were analyzed,and the behind physical mechanism for the increased photocatalytic activity for the doped BFO nanoparticles was eventually discussed.The basic works in the thesis are summarized as follows:1.Preparation of pure BFO and Co and Sm series doped nanoparticles:pure Bi Fe O₃,Bi Fe_1-xCo_xO₃ series（x=0.03,0.05,0.07,0.09）and Bi_1-xSm_xFe O₃（x=0.05,0.10,0.15,0.20）nanoparticles were successfully prepared by the sol-gel method and labeled as BFO,n BFCO（n=3,5,7,9）,n BSFO（n=5,10,15,20）.2.Microstructure and performance characterization of pure and doped BFO nanoparticles:X-Ray diffraction test（XRD）,field emission scanning electron microscopy（FESEM）,and X-ray electron spectroscopy（XPS）were employed to characterize the microstructure of the prepared nanoparticles.With increasing cobalt doping,competing structures hovering between rhombic and orthorhombic structures of n BFCO were observed,and microstructural characterization clearly indicated that7BFCO has rhombic and orthorhombic structures coexisting.In the other aspect,with the increase of samarium doping concentration,a structural shift from rhombic to orthorhombic structure of n BSFO was perceived.3.The enhanced photocatalytic activity and the behind physical mechanism for the pure and doped BFO particles:The light absorption level using an ultraviolet visible spectrophotometer（UV-vis）was conducted to calculate the sample band gap width.The photocatalytic degradation of rhodamine B by different BFO samples in aqueous solution was also studied.The band gap of Co-doped BFO was decreased from 2.04 e V to 1.78 e V.Meanwhile,it was found that 7BFCO was the best ratio for obtaining photocatalytic and magnetic activities,e.g.,a photocatalytic efficiency can reach 98.2%.Similarly,the band gap of samarium doped BFO was reduced from 2.04 e V to 1.92 e V.Also,20BSFO was the best ratio for obtaining photocatalytic activity and magnetic activity in the experiment,with a photocatalytic efficiency of 98.5%.This thesis consists of 33 figures,5 tables and 160 references...