Synthesis Of BiFeO₃ And BiPO₄ By Hydrothermal Method And Their UV Photocatalytic Properties

Recently, the preparation and photocatalytic properties of bismuth-based photocatalysts have received considerable interest. In this dissertation, we choose bismuth ferrite and bismuth phosphate as the research object. For ferrite bismuth, due to the difficulty in preparing the pure BFO, the application of the multiferroic material is restricted. Based on the systematic study on the traditional co-precipitation, this paper presents the synthesis of pure BFO powders by a modified hydrothermal method. For bismuth phosphate, explored the effect of surfactants on the morphology and the photocatalytic activity of Bi PO4 powder.Firstly, the molar ratio of raw materials in the normal co-precipitation has the critical influence on the synthesis of pure Bi Fe O3, the pure Bi Fe O3 powder has been synthesized at Fe3+:Bi3+ = 1:0.8 through optimizing process factors. O n the other hand, the pure Bi Fe O3 powder can be easily achieved using the reversed co-precipitation method with equal mole Fe and Bi ion at CKOH =3 M. Intensified co-precipitation of Bi3+ and Fe3+ ions by the reverse precipitation method is proposed responsible for the easy formation of pure Bi Fe O3, and the sample synthesized with reversed co-precipitation method showed the higher photocatalytic degradation of MO than that of pure Bi Fe O3 prepared by the the normal co-precipitation method. The existence of Bi2Fe4O9 seriously affected the photocatalytic performance of Bi Fe O3.Secondly, pure Bi PO4 was synthesized by the hydrothermal method in the presence of sodium dodecyl sulfate(SDS), sixteen alkyl three methyl bromide(CTAB), macrogol 4000(PEG4000) and polyvinyl alcohol(PVA). The samples prepared by the hydrot hermal method in the presence of SDS exhibit the best photocatalytic activity. SEM results show that the morphology of Bi PO4 changes from irregular shape to rod- like one after adding small amount of SDS(0.5-2 g/L). Further increase of SDS, the rod-like morphology has been broken. UV photo-decolorization of methylene blue(MB) results show that the rod-like Bi PO4 exhibits the higher photocatalytic activity than that of the powder with irregular morphology. The highest photocatalytic activity is obtained for the rod- like Bi PO4 powder prepared at the concentration of SDS is 2 g/L. The photoactivity of Bi PO4 powder in relationship with the morphology and particles size is discussed in detail.