A facile and novel approach to magnetic Fe@SiO2 and FeSi2@SiO2 nanoparticles

Fe@SiO2 and FeSi2@SiO2 nanoparticles with core@shell structure have successfully been synthesized by direct silane silicification of Fe2O3 nanoparticles. The as-prepared samples were characterized by N-2 physisorption, X-ray diffraction, transmission electron microscopy, temperature programmed reduction of H-2 X-ray photoelectron spectroscopy, Mossbauer spectroscopy, and superconducting quantum interference magnetometry. It was found that the amorphous SiO2 shell was formed to protect the core against oxidation when the reduced Fe2O3 nanoparticles were silicified by silane. When the reduced Fe2O3 nanoparticles were exposed to air, a Fe2O3 layer was formed. The structure of the core changed from cubic Fe to orthorhombic FeSi2 with increasing silicification temperatures from 350 to 550 degrees C, due to the dissolution of Si atoms into the iron lattice. The magnetic characterization showed that all samples have ferromagnetic nature and the saturation magnetization values drastically decreased with increasing silicification temperature. This novel methodology can be applied to synthesis of Co@SiO2 and Ni@SiO2 with core@shell structure. The as-prepared Fe@SiO2 and FeSi2@SiO2 nanoparticles with core@shell structure can find applications in magnetically separable catalysts, biomedicines, and magnetically recording materials.