The Preparation of Mesoporous Silica Gel and the Nature of the Modification of Its Surface with Organoalkoxysilane

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Abstract
Mesoporous silica gel with a narrow pore-size distribution at the pore diameter of 200 Å has been prepared upon gelation in the presence of starch. Taking into account the effects on the geometrical properties of its surface, two typical surface-modifying procedures that utilize organoalkoxysilane were characterized. Procedure I retains the mesoporous structure, although the fixed amount of the organofunctional group is rather small. Procedure II introduces a large amount of the organofunctional group to the surface, but is accompanied by a pronounced reduction in both the B.E.T. surface area and the specific pore volume. The observed range of the apparent surface concentration of the organofunctional group and the scanning electron micrographs suggest that the surface is coated with highly crosslinked organosiloxane polymers in the latter case. Despite the contrasts between the two modified surfaces, the similarity of C-13 NMR line shapes, chemical shifts, and spin-lattice relaxation times between the respective surface organofunctional groups indicates that their microenvironment and mobility resemble each other.