Structures And Photocatalytic Properties Of Bismuth Ferrite Semiconductors

With the development of global industrial technology, human made brilliant achievements in various fields but facing the serious problem of environmental pollution at the same time, and the enviromental poblem even began to threaten people’s health and other biological survival. An effective degradation of organic pollutants wicth are the main source of water pollution has become a hot topic that was widely discussed. Photocatalytic technology has the advantages of low energy consumption and no secondary pollution, and the current focus point of the research is to improve the utilization efficiency of solar energy, which has a important practical significance to solve the environmental pollution and energy shortage problems.Bismuth Ferrite based compounds(Bi Fe O3,Bi2Fe4O9 and Bi25 Fe O40) as a narrow band gap semiconductor, has an exciting light response in the range of visible light wavelength, which indicates that it has potential applications in the field of photocatalysis.In this paper, we have combined first principles calculation and hydrothermal synthesis methods and systematically studied the structures and optical absorption and photocatalytic properties of Bismuth Ferrite based compound semiconductor, and also studied the effect of Ag metal particles accumulation on the semiconductor surface. Finally, the degradation efficiency of organic pollutants of the three kinds of compounds was compared.First principles calculation results show that the Bi FeO3 is a direct band gap semiconductor, with a band gap of 2.013 eV; after doping Ag,Bi FeO3 transformed to be an indirect bandgap semiconductor and the band gap decreased to 1.301 e V; Bi2Fe4O9 is an indirect band gap semiconductor and the band gap values is 1.922 e V; Bi25FeO40 is a direct band gap semiconductor and the band gap value was 1.817 ev. By analyzing the outer electron distribution of Bi Fe O3 and Bi2Fe4O9, it is found that Fe-O forms a covalent bond, and Bi-O forms an ionic bond. The photoelectric properties of Bi Fe O3, Bi2Fe4O9 and Ag doped Bi FeO3 show obvious optical absorption properties in the visible range.The pure phase Bi Fe O3, Bi2Fe4O9 and Bi25FeO40 powders were prepared by hydrothermal method. The optimum synthesis process of three kinds of semiconductor materials was respectively found. For Bi FeO3, the KOH concentration is 8.5M, the temprature is 200℃ and the reaction time is 12h; For Bi2Fe4O9 the KOH concentration is 4M, the temprature is 200℃ and the reaction time is 6h; For Bi25FeO40, the KOH concentration is 4M, the temprature is 80℃ and the reaction time is 12 h.The optical absorption tests showed that the band gap value of Bi Fe O3, Bi2Fe4O9 and Bi25FeO40 is 1.93 e V and 1.4 and 1.7 ev(Bi2Fe4O9 is double band gap materials) and 1.63 e V. This result matches well with the first principles calculation of the band gap. Photocatalytic test results show that the three have a strong photocatalytic degradation of methylene blue solution. Bi25 Fe O40 powders performed the highest efficiency of light catalytic, because the concentration of methylene blue solution decreased to 87.2% at 120 min under light irradiation with the help of Bi25 Fe O40; The second is Bi Fe O3 powder with Ag small particles on its surface,of which the efficiency reached 87.0%; Bi2Fe4O9 nano powder is slightly inferior than that of the others,of wihich the efficiency reached 81.3%.In addition, materials computation methods can accurately predict some physical and chemical properties of materials and we can combine it with experimental researches to shorten the cycle of the development of new materials, which is of great significance for the development and applications of new materials.