Novel bis(methylimidazolium)alkane bolaamphiphiles as templates for supermicroporous and mesoporous silicas

A series of bis-cationic bolaamphiphiles were synthesized containing N-methylimidazolium head-groups, separated by alkyl chains of 12, 16 and 24 methylene units. Their critical micelle concentrations were determined with subsequent flooding experiments revealing the tendency for the formation of hexagonal mesophases at high surfactant concentrations. The surfactants were employed as templates for silica formation, at ca. four times their critical micelle concentrations, permitting super-microporous and nanoparticulate mesoporous silicas to be prepared. Silica surface areas ranged from 500 to 1000 m2 g−1, and pore diameters (DTEM) from 10 to 22 Å. Analysis of the materials by small angle X-ray diffraction indicated that, in the case of the template possessing 24 methylene units, the silica obtained exhibited a 2D hexagonal pore arrangement.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis and characterization of novel imidazolium-based bolaform surfactants. ► CMC determination and flooding experiments of these new promising templates. ► Supramolecular templating affording high surface area, nanoporous silicas. ► Structural analysis using SAXS, TEM and nitrogen sorption. ► Template chain length controls morphology and pore-ordering of the silicas.