In Situ Synthesis of Silica-Coated Magnetite Nanoparticles by Reverse Coprecipitation Method

Abstract

Silica-coated magnetite nanoparticles were synthesized by reverse coprecipitation of Fe2+ and Fe3+ with sodium hydroxide in the presence of sodium silicate solution. Effect of reaction conditions and various amounts of sodium silicate solution on the powder particle characteristics was investigated by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer (LPSA), streaming current potential and vibrating sample magnetometer (VSM) techniques. Also, stability of silica-coated magnetite nanoparticles in the acidic condition has been studied by titration method. FT-IR results revealed that silica chemisorbed on the surface of magnetite nanoparticles by Fe–O–Si bonds. Analysis of the XRD patterns confirmed the formation of magnetite having spinel structure in the presence of sodium silicate solution. FE-SEM micrographs revealed that the mean particle size of spherical magnetite decreased from 50 to less than 25 nm by adding sodium silicate solution. Agglomeration declined when the volume ratio of sodium silicate/sodium hydroxide was 0.1. This was attributed to the coating of magnetite nanoparticles by silica. Coating of magnetite by silica prevents the formation of hydrogen bondings between magnetite and water molecules. Further increase in the sodium silicate concentration revealed a reverse effect.