The effect of alcohol type on the thickness of silica layer of Co₃O₄@SiO₂ core-shell particle

Silica layer was deposited on the spherical Co₃O₄ particles, which were prepared by the thermal decomposition of cobalt nitrate, by the hydrolysis and condensation of tetraethylorthosilicate (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB) in alcohol (methanol, ethanol, propanol or butanol). The products were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric/differential thermal analysis (TG-DTA), UV–vis absorption spectroscopy, and vibrating sample magnetization (VSM). The result showed that the spherical Co₃O₄ particles with the average diameter of 242 nm were coated with silica layer (the thickness of 12–27 nm). The thickness of the silica shell varied depending on alcohols, methanol gave thicker silica shell than ethanol, butanol and propanol. Irrespective of the thickness of the silica shell, all the present Co₃O₄@SiO₂ core-shell particles showed a soft ferromagnetic with narrow hysteresis loops, not much different from that of pristine Co₃O₄, suggesting possible applications as magnetic particles with modified surface properties. The core-shell particles were stable in acidic solution (pH = 1) to extend the potential of magnetic Co₃O₄.