Influence of Amount of Fe(III) precursor and Water in Ethanol on Shell Thickness of SiO2@FexOy

Monodisperse spherical colloidal particles with core–shell structures, such as SiO₂@shell, are the focus of extensive research. However, those coated with iron oxide (SiO2@FexOy) have received comparatively little attention, rendering them a promising area for further research. The present study investigates the process of formation of a thin iron oxide shell from an iron nitrate ethanolic solution. The results of this study indicate that the formation of the shell appears to initiate by the attachment of iron cations to specific, though unidentified binding sites on the silica surface. Once these sites are fully occupied, further incorporation of iron appears to cease. In order to examine how synthesis conditions affect shell thickness, a 2² factorial design was utilized to vary the water content in ethanol and the concentration of the iron precursor. Shell thickness was estimated from the diameters of particles measured in scanning electron microscopy images. The results indicate that, subsequent to the initial binding of iron to the silica surface, alterations in the amount of water or the concentration of the precursor do not result in the continued growth of the shell. This finding suggests that the primary factor impeding shell formation is the number of available binding sites on the silica surface.