Low Temperature Hydrothermal Synthesis Of Octahedral Fe₃O₄ Submicrocrystals

Magnetite Fe₃O₄ nano- and/or microparticles have been extensively applied in information storage, ferrofluids, sensors, catalysts, and especially biomedical fields due to their special magnetic and electrical properties.In this thesis, Octahedral Fe₃O₄ microcrystals with a relatively high magnetic saturation value have been prepared at a low temperature of 90°C via a hydrothermal approach. Typical octahedral Fe₃O₄ samples were characterized by means of XRD, SEM, TEM, XPS, FTIR, and VSM. The XRD and XPS analyses indicate a cubic phase of the as-prepared Fe₃O₄ submicrocrystals with high crystalline perfection. The SEM and TEM analyses show that the particle size distribution is in the range of 200～300 nm with regularly octahedral morphology. The XPS and FTIR analyses reveal that biocompatible PEG-6000 molecules cover the surface of Fe₃O₄ crystals. The VSM measurements show that the Fe₃O₄ octahedrons have a relatively high magnetic saturation value of 85.5 emu/g and a coercive field of 118 Oe. The formation mechanisms related to Fe₃O₄ octahedral crystals and their linear self-assembly structures are discussed.The effects of reaction parameters on the resulting product were investigated, including the starting materials, oxidizing agent, pH value, reaction temperature, reaction time, and dropping rate of NaOH and KNO₃ aqueous solution.Spherical Fe₃O₄ paticles with size range of 250～330nm were prepared by a solvothermal method in a Teflon-lined static autoclave. Typical spherical Fe₃O₄ samples were characterized with XRD, TEM and VSM. It is found that the crystallinity of spherical particles is lower in intensity than that of octahedrons. Although a higher magnetic saturation value of 90.3 emu/g possessed by the sphericals, a lower coercive field of 60 Oe occurs in comparison with those of octahedrons (85.5 emu/g and 118 Oe).