Engineering porosity in bifunctional periodic mesoporous organosilicas with MT- and DT-type silica building blocks

Abstract

A series of periodic mesoporous organosilicas (PMOs) with 2-D hexagonal symmetry were synthesized using single-source bifunctional silsesquioxane-type precursors. The frameworks of these PMOs are composed of siloxane–disilsesquioxane (DT²) or siloxy–trisilsesquioxane (MT³) structural units. Three kinds of structure-directing micellar templates, cetyltrimethylammonium chloride, polyoxyethylene(10) cetyl ether, and polyoxyethylene(10) stearyl ether were used to form PMOs from these precursors. These PMOs were found to have pore sizes and surface areas in the range 2.0 to 3.3 nm and 900 to 1200 m² g⁻¹, respectively. PMOs formed with curved morphologies that were comprised of swirling or radial patterns of hexagonal close-packed channels in their bulk and surface regions. Temperature dependent PXRD and ²⁹Si MAS-NMR studies revealed bridging ethylene to terminal ethyl group exchange reactions in which the thermal stability of structural building units followed the order M < D < T < Q.