Impact of acidic catalyst to coat superparamagnetic magnesium ferrite nanoparticles with silica shell via sol–gel approach

This paper describes a simple way for the coating of superparamagnetic magnesium ferrite (MgFe 2 O 4 ) nanoparticles with amorphous silica layer. First, core MgFe 2 O 4 nanoparticles were synthesized by ultrasonic spray pyrolysis (USP) technique from the aqueous metal nitrate precursor solution. Afterward, silica was coated on the obtained particles surface by a sol–gel approach. In this reaction, tetraethyl orthosilicate (TEOS) were used as precursor of silica and HCl as a catalyst, and it has been found that acidic catalyst plays an important role to form amorphous silica layer on nanoparticle surface without formation any core-free silica particles. The composition, morphology and structure of the products were characterized using different analysis technique such as X-ray diffraction (XRD), field emission electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), electrophoretic scattering photometer, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA), respectively. The results indicate that the product has a core–shell structure, which is combined through the chemical bond of Fe O Si. The silica thickness lies in the range of 30–50 nm with overall dimension of the resulting nanospheres 200–300 nm. Magnetic measurement were carried out on a vibrating sample magnetometer (VSM), and the measurement results indicate that MgFe 2 O 4 nanoparticles remain superparamagnetic after coating with silica although their Ms values is significantly less than uncoated samples. This core/shell nanocomposite can be used for several applications especially in the biomedical field due to having superparamagnetic property of core and unique properties of silica.