Synthesis, Property And Application Of Hierarchical Structured Fe₃O₄Micro-and Nanomaterials

In recent years, magnetic nanomaterials have aroused much interestdue to their unique properties. Especially, hierarchical structuredmagnetic nanomaterials have been essentially researched owing to theirexistence of large activated surface areas. The development andapplication of Fe₃O₄magnetic nanomaterials with hierarchical structuresis of great significance. In this dissertation, we mainly studied thesynthesis of hierarchical structured Fe₃O₄nanomaterials and theircomposites, and the transformation of hierarchical structured Fe₃O₄frompolycrystalline to single crystal under heating. The as-synthesizedmagnetic nanomaterials were characterized, and their applications werealso studied such as heavy metal ions adsorption and electrochemicalenergy storage. The main results are summarized as follows:1. Monodispersed hierarchical Fe₃O₄microspheres were preparedthrough a solvothermal method. The Fe₃O₄microspheres exhibitferromagnetic properties at room temperature and can be convenientlycollected via an external magnet. Different from bulk Fe₃O₄, thesehierarchical Fe₃O₄microspheres can be applied to remove Pb²⁺ions fromwaste water. Furthermore, the interaction between Fe₃O₄and toxic metalions is reversible, which means that the adsorbed Pb²⁺ions can beremoved from Fe₃O₄in weak acidic water with the assistance ofultrasound radiation. It is noteworthy that the adsorption ability of theFe₃O₄microspheres is so strong that any further modification of theFe₃O₄microspheres is unnecessary.2. The hierarchical Fe₃O₄microspheres that synthesized via asolvothermal method was applied as raw material, and Fe₃O₄@Cnanocomposites were prepared through the hydrothermal carborization ofglucose on the surfaces Fe₃O₄microspheres. The Fe₃O₄@Cnanocomposites were characterized by X-ray diffraction （XRD）, fieldemission scanning electron microscopy （FESEM）, and transmissionelectron microscopy （TEM）. The electrochemical energy storage performances of the Fe₃O₄@C microspheres were investigated by Cyclicvoltammetry （CV）、Galvanostatic charge–discharge （CD） and Cyclic life.The results show that the Fe₃O₄@C microspheres possess a specificcapacitance of110.8F g1at a current density of0.5A g1with a potentialwindow of between1.0and0.5V, which shows good electrochemicalenergy storage performances. After2000electrochemical cycles, theFe₃O₄@C electrode still remaining95.6%of the highest specificcapacitance, indicating its good cycle stability.3. Monodispersed hierarchical Fe₃O₄microspheres were preparedthrough a simple solvothermal method. After dried, they were put into atube-furnace and then calcined under the protection of argon flow. Theinfluence of calcining temperature and time on the morphology of thefinal product was studied. The products were studied by X-ray diffraction（XRD）, field emission scanning electron microscopy （FESEM）,transmission electron microscopy （TEM）, and vibrating samplemagnetometer （VSM）. The results show that single crystal Fe₃O₄can beobtain under a calcining temperature （500℃） that is far below the meltingpoint of bulk Fe₃O₄for2h. The magnetic property of product wastransformed from superparamagnetism into ferromagnetism.