Synthesis of Ordered Silicates by the Use of Organic Structure-Directing Agents

Abstract

Microporous, crystalline silicates can be synthesized using organic structure-directing molecules whose function is to organize silicate species into particular arrangements that then spontaneously self-assembles into the final crystalline materials. The porosity is obtained by removal of the organic component. The authors discuss the molecular properties (size, rigidity, hydrophobicity) necessary for the organic component to interact with aqueous silicate species and prepare microporous silicates. It is shown that a strategy to construct large organic molecules in order to prepare large pore crystalline silicates could involve the use of two charge centers if these functionalities are distributed within the molecules such to prevent aggregation in aqueous media. A charge distribution that allows aggregation of the organic molecules at synthesis conditions directs the formation of a locally amorphous, mesoporous silicate rather than a crystalline, microporous material.