A facile and novel approach to magnetic Fe@SiO2 and FeSi2@SiO2nanoparticles

Abstract

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 N₂ physisorption, X-ray diffraction, transmission electron microscopy, temperature programmed reduction of H₂, X-ray photoelectron spectroscopy, Mössbauer 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 °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.