Preparation of core-shell SiO₂/Fe₃O₄ nanocomposite particles via sol-gel approach

Core-shell structural SiO₂/Fe₃O₄ nanocomposite particles with adjustable magnetic properties were prepared via a sol-gel process, in which the hydrolysis and condensation of TEOS were conducted on the surface of Fe₃O₄ nanoparticles under the aid of basic catalyst. The effects of the volume ratio of alcohol to water, the concentrations of ammonium and TEOS on the appearances and properties of the nanocomposite particles were investigated. The mechanism of the formation of SiO₂/Fe₃O₄ nanocomposite particles was analyzed. Results show that silica shell is mainly formed from the aggregative growth of silica primary particles on the surface of Fe₃O₄ nanoparticles. With increasing the concentration of TEOS in the range of 0-0.02mol/L, the silica shell thickness increases on the condition of 0.3mol/L of NH₄OH and 4:1 ratio of alcohol to water. Although the saturation magnetization of the nanocomposite particles decreases with the thickness of silica shell increasing, the coercive force of the particles is almost unchanged. And more, the nanocomposite particles remain favorable superparamagnetism.