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

• Superparamagnetic MgFe2O4 nanoparticles were synthesized by USP method.
• MgFe2O4/SiO2 core–shell structure were formed by sol–gel approach.
• Acidic catalyst such as HCl play key role to form amorphous silica layer.
• Coated nanoparticles are potential for biomedical applications.

This paper describes a simple way for the coating of superparamagnetic magnesium ferrite (MgFe2O4) nanoparticles with amorphous silica layer. First, core MgFe2O4 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 FeOSi. 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 MgFe2O4 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.

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