Structure and magnetic properties of silica-coated magnetite-nanoparticle composites

Abstract

Magnetite (Fe3O4) nanoparticles and amorphous-silica-coated magnetite-nanoparticle (Fe3O4/a-SiO2) composites have successfully been synthesised using co-precipitation and modified Stöber methods, respectively. Instead of using a commercial product, the Fe3O4 powder was synthesised via co-precipitation method from local ironstone in Indonesia, while the a-SiO2 was obtained from a tetraethyl orthosilicate (TEOS) precursor. The modified Stöber method was utilised to form the Fe3O4/a-SiO2 core/shells. The samples were characterised using x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS), and vibrating sample magnetometer (VSM) techniques. XRD and FTIR data confirmed the formation of single phase Fe3O4 nanoparticles and the Fe3O4/a-SiO2 composites. HRTEM images showed that silica coated the Fe3O4 surface with an increased thickness with the addition of the TEOS. Magnetite-silica multi-core/shells were observed in the HRTEM data examination. EXAFS spectra analysis confirmed that the presence of a-SiO2 shells does not change the crystal and local structures of the magnetite nanoparticles. Room-temperature VSM measurements showed a ferrimagnetic behaviour in both the Fe3O4 nanoparticle and the Fe3O4/a-SiO2 core–shell, with decreased magnetisation appearing with an increased thickness of the a-SiO2 coating.