Study of structural and magnetic properties of superparamagnetic Fe3O4/SiO2 core–shell nanocomposites synthesized with hydrophilic citrate-modified Fe3O4 seeds via a sol–gel approach

This paper describes a simple way for the coating of magnetite nanoparticles (MNPs) with amorphous silica. First, MNPs were synthesized by controlled co-precipitation technique under N2 gas and then their surface was modified with trisodium citrate in order to achieve particles with improved dispersibility. Afterward, magnetite-silica core/shell nanocomposites were prepared by a sol–gel approach, using magnetic fluid including electrostatically stabilized MNPs as seeds. The prepared samples were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, zeta potential analysis and vibrating sample magnetometer (VSM) in order to study their structural and magnetic properties. FT-IR and XRD results imply that resultant nanocomposites are consisted of two compounds; Fe3O4 and SiO2 and TEM images confirm formation of their core/shell structure. TEM images also show increase in silica shell thickness from ∼5 to ∼24 nm with increase in amount of tetraethyl orthosilicate (TEOS) used during the coating process from 0.1 to 0.3 mL. Magnetic studies indicate that Fe3O4 nanoparticles remain superparamagnetic after coating with silica although their Ms values are significantly less than pristine MNPs. These core/shell nanocomposites offer a high potential for different biomedical applications due to having superparamagnetic property of magnetite and unique properties of silica.