(A) study on synthesis of mesoporous silica and titania via a nonsurfactant-templating route and their applications

Abstract

Compared to a surfactant-templating route, a nonsurfactant-templating route is convenient, versatile, low-cost, environmentally friendly and nontoxic method. Although mesoporous materials synthesized via the nonsurfactant-templating route do not have well-defined and long-range ordered structure, they give a high surface area, high pore volume and well-connected pore structure in three dimension. For the types of applications intended for mesoporous materials, the high surface area and three-dimensionally interconnected pore structure are desirable, but full structural order is not crucial as shape-selectivity effects are not involved in most of its applications. From this point of view, the nonsurfactant-templating route is considered to be promising synthetic method of mesoporous materials. In chapter 3, 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 at room temperature. After the elimination of citric acid via thermal treatment at $500^\circ C$, 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, high specific surface area $(800-900 m^2/g)$ and pore volume $(0.6-1.4 cm^3/g)$. Compared to a polymeric silica-citric acid system, the colloidal silica-citric acid system showed an increase in the controllable pore size and thermal stability. The silica nanospheres as framework with highly branched structure led to the rigid structure of the framework and the thicker pore wall, resulting in the improved thermal and structural stabi...