Structural Transformation And Related Physical Properties Of Iron Oxide Nanocomposite

Fe2O3 and Fe3O4 are two important kinds of functional materials, and their physical and chemical properties can be tuned by size and morphology. They can be transformed each other by thermal treatment at different gas atmosphere. They have very important applications in many aears such as biomedicine, gas sensing, photocatalysis, electrochemical energy storage and magnetic memory. However, homogenous material can not meet the demands of all the different groups. Therefore, many methods have been developed to synthesize composites for multifunction, thereby increasing their application fields. The physical properties and structural transform of Fe2O3 were investigated in the thesis.α-Fe2O3/ZnO core/shell nanorods were fabricated by a wet chemical method, and their ethanol sensing properties were investigated. It is found that the core/shell nanorods exhibit enhanced sensing properties compared to the bareα-Fe2O3 nanorods. The enhanced sensing mechanism was proposed in terms of the semiconductor theory; the heterojunction barrier ofα-Fe2O3/ZnO core/shell nanorods can be changed into Fe3O4/ZnO core/shell nanorods under hydrogen atmosphere. Because the core/shell nanorods are ferromagnetic, the heterointerface presented between core and shell region, and the thickness of ZnO shell is in nanometer scale, the core/shell nanorods have very strong electromagnetic response, which can be used as absorber for electromagnetic wave. At the same time, the corresponding mechanism was analyzed.α-Fe203/Sn02 core/shell nanorods were synthesized by a wet chemical method using two different precursors. The thickness of SnO2 layer for the core/shell nanorods obtained byβ-FeOOH precursor was about 10 nm. The core and shell contacted tightly each other, and formed heterojunction, resulting in that the core/shell nanorods exhibited very high ethanol sensing properties. However, spaces presented between the core and shell regions for the composites prepared by usingα-Fe2O3 nanorods as precursor. The hetrojuction could not be formed between the core and shell materials, leading to the weak ethanol sensing properties. Porous Fe3O4/SnO2 core/shell nanorods could be obtained after theα-Fe2O3/SnO2 core/shell nanorods were treated under hydrogen atmosphere, and their electromagnetic response properties were investigated. In addition, SnO2/α-Fe2O3 hierarchical nanostructures where the SnO2 nanorods grow on the side surface ofα-Fe2O3 nanorods as multiple rows were synthesized via a wet chemical process. The growth mechanism on the hierarchical nanostructures was investigated by changing the reaction conditions. Fe3O4/TiO2 core/shell nanorods were prepared by the hydrolysis of Ti(SO4)2 usingα-Fe2O3 nanorods as precursor. Their structural transformation was investigated at different temperatures, and the ethanol sensing property of those structures was studied. It is found that they exhibit gas-sensing behavior different from other oxide heterostructures. The corresponding sensing mechanism was proposed in terms of semiconductor theory. In addition, Fe2TiO5 nanostructures can be obtained if the nanocomposites are thermal treated at higher temperature (800-1000℃) under ambient atmosphere. Finally, the electromagnetic response of Fe3O4/TiO2 core/shell nanorods was investigated. It is found that the TiO2 layer played a role on decreasing eddy effect, which may open a way for the application of the magnetic materials in electromagnetic wave absorption.