Mesoporous silica framed by sphere-shaped silica nanoparticles

Organic template-derived mesoporous silica with narrow pore size distribution was prepared through a colloidal silica-citric acid system. Colloidal silica sol with 5 nm in particle diameter was firstly prepared under base-catalyzed condition via hydrolysis of tetraethyl orthosilicate (TEOS) and condensation reaction. Subsequently, colloidal silica-citric acid nanocomposite solution was synthesized by addition of citric acid to the as-prepared colloidal silica sol. After the elimination of citric acid via thermal treatment at 500 °C, the mesoporous silica was successfully obtained, and its pore size was easily controlled in the range from 2 nm up to 15 nm maintaining the narrow pore size distribution, the high specific surface area (800-900 m2/g) and the pore volume (0.6-1.4 cm3/g). Comparing with a polymeric silica-citric acid system, the colloidal silica-citric acid system showed an increase in the controllable pore size and the structural stability. The sphere-shaped silica nanoparticles as a framework with highly branched structure led to the rigid structure of the framework and the thicker pore wall, suppressing the shrinkage of the silica structure in spite of the large vacancy produced by the removal of citric acid.