Hematite template route to hollow-type silica spheres

Hollow-type silica spheres with controlled cavity size were prepared from Fe2O3-SiO2 core-shell composite particles by selective leaching of the iron oxide core materials using acidic solution. The spherical Fe2O3 core particles with a diameter range of 20-400 nm were first prepared by the hydrolysis reaction of iron salts. Next, the Fe2O3-SiO2 core-shell particles were prepared by the deposition of a SiO2 layer onto the surface of Fe2O3 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 Fe2O3 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 Fe2O3 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. - Graphical abstract: TEM micrograph of the hollow silica particles. Wall thickness, as estimated by TEM from the ring around the perimeter of the hollow spheres, was ∼10 nm. TEM micrographs of hollow silica spheres show that the sphericity of the core Fe2O3 was preserved