Synthesis And Characterization Of Magnetic Fe Core-shell Nanocomposite

The properties of nanometer-sized magnetic particles of iron have been studied extensively both experimentally and theoretically. Although these particles show promise for practical applications such as catalysis, magnetic recording, magnetic fluids, and biomedical applications, their utility has been limited due to easy aggregation and uncontrollable oxidation. Freshly synthesized iron nanoparticles often ignite spontaneously upon exposure to air or undergo a rapid exothermic reaction with oxygen under ambient aerobic condition.In this paper, the preparation of metalα-Fe particles by reduction of ferrous ion using KBH₄ in simple ethanol-water system with the presence of surfactant was successfully performed. We have also studied the influence of different reaction conditions on the diameter of final Fe nanoparticles. The results showed that the proper reaction condition were: Reactant concentration 10g/L, volume ration of ethnol to water 7:1, temperature 40℃, reacting time 30min. From the dispersed effect we could see that the macromolecule surfactant had a perfect effect on the Fe dispersion. SAED, XRD, and TEM were applied to characterize the product, which indicated that some of the finnal products wereα-Fe but some were spathic and others might be uncrystalline, the diameters were between 20nm to 50nm.Freshly synthesized iron nanoparticles often ignite spontaneously upon exposure to air or undergo a rapid exothermic reaction with oxygen under ambient aerobic condition. One method for controlling the oxidation is to coat the particles, creating a core-shell structure. This core-shell structure maintains the favorable magnetic properties of metallic iron and the shell can protect the nanoparticle from oxidation and reduce the dipole interaction. Furthermore, the coating could provide the nanomagnets with several other benefits such as compatibility in biological system, functionality and high suspension stability under different solution. Reasons that easy control the deposition process, controllable porosity and optical transparency, make silica an ideal, low-cost material to tailor the surface properties, while basically maintaining the physical integrity of the underlying core nanocrystals.In this paper, we used the "st(o|¨)ber" method by using the TEOS'hydrolysis and nanosized Fe as the "seeds" to make a smooth SiO₂ shell coating on the Fe core. The results showed that the final products were core-shell structure; the diameter of Fe cores was from 20nm to 30 nm; the SiO₂ shell were nearly 10nm. The TG-DSC results showed that SiO₂ coated Fe nanoparticles had much higher antioxidant ability than the pre-products, so the SiO₂ layer could effectively protect the iron core from further oxidation and reduce the dipole interaction.