Characterization of Metal-Doped Methylated Microporous Silica for Molecular Separations

Abstract

Novel silica xerogels are prepared and developed by sol-gel method in the present study. The preparation involves cobalt-doping within the organic templated silica matrices, where methyltriethoxysilane (MTES), which contains methyl groups as a covalently bonded organic template is used. The synthesis and surface properties of cobalt-doped methylated microporous silica xerogels with different MTES and cobalt content are revealed by surface and microstructural techniques, such as TGA, FTIR, X-ray and N₂ adsorption measurements. The doping process enhances the thermal stability of the silica xerogels up to ~ 560 °C in oxidizing atmosphere. Besides, this process has no significant effect on the incorporation of the organic template within the silica matrix. As result of the promoted densification of the xerogels either by increasing MTES content and heat treatment, there is structural change of the silica xerogels such as decreasing the micropore volume and broadening of the pore size distribution. Heat treatment and increasing the cobalt oxide content from 5 to 10% weight ratio resulted in samples with approximately the same structural parameters. This suggests that the cobalt particles are homogeneously dispersed in the silica matrix. The novel silica xerogels exhibit trend toward micropores formation suggesting that these doped silica xerogels can be precursor materials for molecular sieve silica membranes applications. Two silica membranes, hydrophobic and cobalt-doped hydrophobic, are prepared and their performance is examined by the study of transport of He, H₂ and N₂. Preliminary results show that the microporous structure obtained in the unsupported cobalt-doped hydrophobic material are preserved after coating inside the tubular support.