Ethylene-bridged periodic mesoporous organosilicas with Fm3m symmetry (original) (raw)

Journal of Materials Chemistry, 2005

Abstract

ABSTRACT Divalent surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]2+2Br- (C16-3-1) was exploited as a structure directing agent (SDA) for the synthesis of highly ordered periodic mesoporous organosilicas (PMOs) from 1,2-bis(triethoxysilyl)ethane (BTEE) as organosilica source under basic conditions. The mesophase structure/symmetry and the phys. parameters could be controlled/optimized by adjusting synthetic parameters such as surfactant and base concn., hydrothermal aging temp. and time, and crucially the type (charge, shape, aliph. tail chain length) of the surfactant. Cubic PMO[KIT-5]-n reveals a face-centered Fm3m symmetry similar to that of the previously reported purely siliceous material KIT-5. Under the applied reaction conditions, lower aging temps. generally afforded PMO[KIT-5] materials with increased BET surface area (max. 840 m2 g-1) and pore vol. (max. 0.93 cm3 g-1), however, similar pore size (ca. 3.0 nm). Lower divalent surfactant concns. (C16-3-1) caused a mesophase transformation from cubic Fm3m to hexagonal P6mm symmetry. Upon relative increase of the base (NaOH) concn., the PMO mesostructure transformed from hexagonal to cubic, then from cubic to hexagonal symmetry. Surfactants [CH3(CH2)17N(CH3)2(CH2)3N(CH3)3]2+2Br- (C18-3-1), [CH3(CH2)15N(CH3)2(CH2)3-N(C2H5)3]2+2Br- (C16-3-2), and [CH3(CH2)15N(CH3)3]+Br- (C16) were found to encode for PMO[SBA-1]-n and PMO[MCM-41]-n with cubic Pm3n (former) and hexagonal P6mm symmetry (latter two), resp. All these periodic mesoporous organosilicas were characterized by powder x-ray diffraction (PXRD), nitrogen physisorption, FTIR spectroscopy, 13C and 29Si solid state NMR spectroscopy, SEM, and transmission electron microscopy (TEM). [on SciFinder (R)]

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