Novel synthesis of core–shell structured Fe3O4@SiO2 nanoparticles via sodium silicate

Abstract

In this study, core–shell-structured Fe3O4@SiO2 nanoparticles were synthesized using sodium silicate (Na2SiO3), which is more suitable for mass production than the conventional silane precursor tetraethyl orthosilicate (TEOS). In the particle-surface coating process to form a core–shell structure with Fe3O4, the Na2SiO3 was neutralized with HCl(aq) to form silane groups, and the resulting silane groups combined with hydroxyl groups (OH−) present on the surfaces of the Fe3O4 nanoparticles. Because of the core–shell nanostructure of the single particles, the Fe3O4 nanoparticles were accompanied by significant changes in their intrinsic physicochemical properties. In addition, it was confirmed that there were differences in the thickness of the SiO2 under different neutralized pH conditions for the coating-layer implementation with Na2SiO3. The behavior of the Fe3O4 nanoparticle characteristics with respect to the SiO2 coating-layer thickness was primarily due to changes in the surface properties, associated with the degree of cathodic increase of the surface charge. An intensified negative surface charge enhanced the dispersibility of the particles in aqueous solution with enhanced electrostatic repulsion, which was even higher than that of the conventional TEOS-coated nanoparticles. In addition, the surface coating of SiO2 caused a decrease in magnetization with an increase in the coating-layer thickness, which was comparable to the general tendency associated with increasing the weight per unit particle. However, it was somewhat superior to those of the conventional TEOS method because of the difference in morphology.