Functionalization of SBA-15 by an acid-catalyzed approach: A surface characterization study

The functionalization of a mesoporous ordered silica, SBA-15, by a grafting strategy has been successfully achieved. The derivatized SBA-15 products with trimethylmethoxy silane, vinyltrimethoxy silane and octyltrimethoxy silane have been characterized by BET analysis, DRX analysis, thermogravimetric analysis and NMR techniques. The use of p-toluenesulfonic acid as catalyst and the azeotropic distillation of the alcohol generated in the hydrolysis and condensation of the silanes allowed the incorporation of high amounts of organic loading in shorter times as compared to conventional toluene reflux method. The surface of the resulting materials has been thoroughly analyzed and the concentration of total and residual silanols and silane molecules attached on the surface has been quantitatively determined. Being the as-modified SBA-15 materials hydrophobic as a rule, the accessibility of the residual silanol population, evaluated by a deuterium exchange method and subsequent cross-polarization NMR analysis, depends on the nature of the surface organic layer.