Preparation And Property Study Of BiFeO₃ And Bi₂Fe₄O₉ Nanomaterials

BiFeO3 is the only known room temperature multiferroic?ferroelectric and ferremagnetic?material,which shows great potential for ferroelectric memories.Unfortunately,the shortcomings of BiFeO3 mainly lie in the leakage current caused by defects during preparation.This shortcoming is detrimental for ferroelectricity,besides its weak ferromagnetism also significantly limits its memory properties.Until now,most of studies on BiFeO3 concentrated on reducing leakage current and improving ferromagnetism by doping.BiFeO3 is also a kind of semiconductor.Unfortunately,research and application studies based on semiconductor properties are still limited,and further works are necessary.In this work,high sensitive BiFeO3 nanosheets gas sensor was prepared based on the self-polarization effect,semiconducting properties and defects.Besides,one of the common impure phase Bi₂Fe₄O₉ during the synthesis of BiFeO3,was also prepared and studied.Bi₂Fe₄O₉ nano-/micro-particles with different morphologies and different facets-dominant were prepared,and their photocatalytic ability was studied.There are two main experiments in this work:1.Rhombohedral structure BiFeO3 nanosheets with Fe²⁺ defects were prepared and their gas sensing ability was investigated.X-ray diffraction?XRD?and SEM results showed that the prepared nanoparticles are nanosheets,and the corresponding thickness is about 50 nm.This structure showed that the samples are with relatively large specific area.XPS analysis results showed that there was a large part of Fe²⁺defects,which played the role as acceptors and made BiFe0₃ a kind of p-type conductor.The p-type conductivity was consistant with the gas sensing result.Gas sensing experiments showed that the BiFeO3 sample was very sensitive towards trace isopropanol,and its detection limitation reached a level of 5 ppb.The sensing mechanism analysis showed that the self-polarization,build-in potential and Fe²⁺defects is beneficial for improving sensing performance.This research provided a new method to prepare effective gas sensors.2.Bi₂Fe₄O₉ nanosheets and microds orthorhombic structure were prepared by sovolthermal method.Their photocatalytic ability towards methylene blue was studied.The mopholigies and facets-exposure of Bi₂Fe₄O₉ can be tuned and controlled by controlling the preparation conditions in the sovolthermal system.XRD results showed that most of the surfaces of Bi₂Fe₄O₉ nanosheets are consisted by ?001}facets,while that of microrods are mainly consisted by {110} facets.UV-Vis-NIR measurement showed that the band gaps of nanosheets are 1.9 and 1.55 eV,and the band gaps of microrods are 1.7 and 1.45 eV respectively.Since Bi₂Fe₄O₉ is a kind of multi-band semiconductor,it can be used as a kind of potential photocatalyst.The Bi₂Fe₄O₉ microrods showed higher photocatalytic ability towards the photodegradation of mythelne blue.The high photodegradation performance of microrods can be attributed to narrower band gap and different facets-exposure.