Novel mesoporous silicates with two-dimensional mesostructure direction using rigid bolaform surfactants

In this paper we describe how pore-structure modification can be achieved in a highly ordered fashion through the use of bolaform surfactants containing a rigid unit in the hydrophobic chain. The silicate mesophase, SBA-8, synthesized using bolaform surfactants at room temperature, is a two-dimensional (2-D) pore structure with a centered rectangular lattice (space group cmm, 1 < a/b < √3), which has no reported lyotropic liquid crystal analogue. SBA-8 is thermally stable in air, and the surfactant can be removed by calcination to yield a mesoporous material with a high surface area (> 1000 m²/g). The unit cell parameter of the silicate mesostructure can be varied by adding gemini surfactants or by changing reaction temperature; a 2-D silicate mesophase (Mα, a/b > √3) and high quality hexagonal MCM-41 (p6mm, a/b = √3) can be obtained. Hydrothermal transformation of SBA-8 into MCM-41 takes place, confirming the intermediate nature of the SBA-8 mesophase.