Functionalization of large-pore mesoporous silicas with organosilanes by direct synthesis

Abstract

Functionalization of porous solids plays an important role in many technical aspects such as enzyme immobilization. In this study, functionalized large-pore mesoporous materials with a P6 mm symmetry were synthesized by co-condensation of tetraethyl orthosilicate (TEOS) and organosilanes 3-aminopropyltriethoxysilane (APTES), 3-mercaptopropylmethoxysilane (MPTMS), phenyltrimethoxysilane (PTMS), vinyltriethoxysilane (VTES), and 4-(triethoxysilyl)butyronitrile (TSBN) in the presence of nonionic triblock co-polymer Pluronic P123 under acidic conditions. The effect of the organosilanes present in the initial synthesis mixtures on the mesostructural properties of the resultant materials was systematically studied by varying the molar ratios of organosilane to TEOS. Solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and elemental analysis data demonstrated the presence of the functional groups both on the pore surface and inside the solid matrixes. Nitrogen adsorption, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) results showed different levels of disorder of the mesostructures upon incorporation of the functional groups, which are dependent upon the type and amount of the organosilanes present in the initial synthesis mixtures. Among the organosilanes studied, their disruptive effects on the formation of the mesostructure follow VTES < TSBN < PTMS ≅ MPTMS < APTES. Such different effects are interpreted in terms of their different behaviors under acidic synthetic conditions and steric molecular sizes and shapes, which have direct impact on interactions of P123 with silicate species and on micellation of P123 template.