One-step synthesis of silica-coated magnetite nanoparticles by electrooxidation of iron in sodium silicate solution

Silica-coated magnetite nanoparticles have been synthesized successfully using a one-step electrochemical method. In this method, pure iron in a dilute aqueous sodium silicate solution that served as a silica precursor was electrooxidized. We show that the presence of silicate can significantly enhance the purity of the magnetite formed. Impurities in the form of FeOOH (found in the magnetite prepared in water) are not found. The magnetite nanoparticles produced by this method are nearly spherical with a mean size ranging from 6 to 10 nm, which is lower than the size of particles prepared in water, and this size range depends on the applied voltage and the sodium silicate concentration. The magnetite nanoparticles exhibit superparamagnetic properties with saturation magnetization ranging from 15 to 22 emu g^-1, which is lower than the saturation magnetization of the Fe₃O₄ bulk materials (M_s = 92 emu g^-1). This facile method appears to be promising as a synthetic route for producing silica-coated magnetite nanoparticles.