Hematite template route to hollow-type silica spheres

Abstract

Hollow-type silica spheres with controlled cavity size were prepared from Fe 2O 3–SiO 2 core–shell composite particles by selective leaching of the iron oxide core materials using acidic solution. The spherical Fe 2O 3 core particles with a diameter range of 20–400 nm were first prepared by the hydrolysis reaction of iron salts. Next, the Fe 2O 3–SiO 2 core–shell particles were prepared by the deposition of a SiO 2 layer onto the surface of Fe 2O 3 particles using a two-step coating process, consisting of a primary coating with sodium silicate solution and a subsequent coating by controlled hydrolysis of tetraethoxysilicate (TEOS). The Fe 2O 3 core was then removed by dissolving with acidic solution, giving rise to hollow-type silica particles. Scanning electron microscopy clearly revealed that the cavity size was closely related to the initial size of the core Fe 2O 3 particle. According to the cross-sectional view obtained by transmission electron microscopy, the silica shell thickness was about 10 nm. The porous texture of the hollow-type silica particles was further characterized by nitrogen adsorption–desorption isotherm measurements.