New Insights into the Synthesis, Morphology, and Growth of Periodic Mesoporous Organosilicas

Periodic mesoporous organosilicas with two-dimensional and three-dimensional hexagonal as well as cubic ( Pm 3 n ) symmetry were synthesized using bridged silsesquioxane species (RO) 3 Si−CH 2 −CH 2 −Si(RO) 3 as precursors and cetyl- or octadecyltrimethylammonium chloride (C 16 TMACl or C 18 TMACl) as structure-directing species. These materials were characterized by N 2 adsorption, SEM, TEM, and solid-state MAS NMR spectroscopy. 13 C and 29 Si NMR data showed unambiguously that all carbon atoms were covalently linked to Si. The cubic material obtained in the presence of C 16 TMACl and 1,2-bis(trimethoxysilyl)ethane (BTME) first formed into truncated rhombic dodecahedral particles that grew into spheres. The sample prepared in the presence of C 18 TMACl and BTME at 100 °C was entirely comprised of concentrically self-assembled 10-μm hexagonal rods. Using C 16 TMACl in the presence of 1,2-bis(triethoxysilyl)ethane (BTEE) at 95 °C afforded high-quality two-dimensional hexagonal organosilica comprised of unusually long (30−40 μm) faceted empty tubules.