To stir or not to stir: formation of hierarchical superstructures of molecularly ordered ethylene-bridged periodic mesoporous organosilicas

The effect of stirring during the synthesis of mesoporous organosilica materials prepared via surfactant (cetyltrimethylammonium bromide, CTAB) mediated assembly of distilled 1,2-bis(triethoxysilyl)ethylene (BTEE) under basic conditions has been probed. A variety of hierarchical superstructures of periodic mesoporous organosilicas that contain molecularly ordered ethylene groups were obtained by simply varying the extent of stirring (i.e., agitation of the synthesis gels). Under static conditions, large (> 10 mu m in diameter) hierarchical cake-like particles made up of loosely or closely aggregated rods were obtained as the predominant particle morphology; virtually no other particle morphology was observed. Fast stirring conditions generated spongy flower-like particles that extended for up to 160 Pm. Intermediate stirring conditions resulted in a mixture of smaller cake-like particles and elongated rope-like particles that are made up of closely aggregated rods. Despite remarkable differences in the morphology of the hierarchical periodic mesoporous organosilicas, their structural ordering, textural properties and the molecular ordering of ethylene groups were comparable. The formation of hierarchical superstructures did not affect the accessibility and reactivity of the ethylene groups as demonstrated by their successful bromination.