Transition-metal salt-containing silica nanocapsules elaborated via salt-induced interfacial deposition in inverse miniemulsions as precursor to functional hollow silica particles.

ABSTRACT

Aqueous core-silica shell nanocapsules were successfully prepared using liquid droplets containing transition-metal salt as templates in inverse miniemulsions. The formation of the silica shell was attributed to the interfacial deposition of silica species induced by the presence of the transition-metal salt. In addition to the control of the particle morphology, the incorporated transition-metal salts could be used to derivatize the particles and confer additional functionalities to the hollow silica particles. To demonstrate the derivatization, the magnetic hollow silica particles were prepared by converting iron salts to magnetic iron oxides by heat treatment. The particle morphology, size, and size distribution were characterized by transmission electron microscopy and scanning electron microscopy. The results show that the particle properties strongly depend on the type and the amount of salts, the amount of tetraethoxysilane (TEOS), the pH of the droplets, and the ratios of 2-hydroxyethyl methacrylate to aqueous HCl solution. The specific surface area and pore properties were characterized by N2 sorption measurements. The pore properties and specific surface area could be tuned by varying the amount of salt. Levels of elements and of iron oxides in the magnetic hollow particles were measured by energy-dispersive X-ray spectroscopy. Iron was distributed homogenously with silicon and oxygen in the sample. The magnetization measured by a magnetic property measurement system confirmed the successful conversion of the iron salts to magnetic iron oxides.