Synthesis Of Magnetic Fe₃O₄ Microparticles And SiO₂/Fe₃O₄ Composite Spheres

Magnetic magnetite particles exhibit some individual properties because of their unique physical and chemical properties, and have a wide range of potential applications in such areas as magnetic recording, ferrofluids, catalytic carrier, biomedicine and pollution control etc. This dissertation focused on the synthesis of magnetic Fe₃O₄ microparticles via self-assembly of Fe₃O₄ nanoparticles which have many excellent properties including monodisperse, well crystallization, higher saturation magnetization, as well as the preparation of magnetic SiO₂/Fe₃O₄ composite spheres.Ferromagnetic Fe₃O₄ nanoparticles were synthesized and then self-assembled into microparticles via a solvothermal method, using FeCl₃·6H₂O as the iron source, sodium oleate as the surfactant, and ethylene glycol as the reducing agent and solvent. The obtained Fe₃O₄ microparticles were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Vibrating sample magnetometer (VSM). The size and morphology of the particles were examined using Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). The Fe₃O₄ microparticles of nearly monodisperse diameters, controllable in the range of 120–400 nm, consist of assemblies of Fe₃O₄ nanoparticles with a diameter of 22 nm. The effects of reaction time, amount of surfactant and NaAc on the products were discussed. Interestingly, by using the pre-synthesized Fe₃O₄ microparticles as the growth substrates, spherical and smooth-looking Fe₃O₄ microparticles with average diameter of 1μm were obtained. A plausible formation process was discussed.Fe₃O₄/silica nanocomposite microspheres have been successfully established by employing a solution-based route via direct decomposition of tetraethyl ortho-silicate (TEOS) in solution under the presence of Fe₃O₄ nanoparticles (NPs) freshly-synthesized by Solvothermal method and Coprecipitaion method, respectively. The route is based on a two-step process, involving: (ⅰ) synthesis of Fe₃O₄ NPs as growth seeds; (ⅱ) formation of Fe₃O₄/silica nanocompounds by direct decomposition of TEOS in the presence of dispersed Fe₃O₄ NPs of (ⅰ) under mechanical stirring at room temperature. The effects of the dosage of TEOS have been investigated. XRD, FTIR, EDS and SEM were used for the characterization of the synthesized products. Morever, a possible formation mechanism of Fe₃O₄/silica nanocompounds was also discussed.