Silicon-29 nuclear magnetic resonance study of hydroxyl sites on dehydrated silica gel surfaces, using silylation as a probe

A detailed /sup 29/Si NMR analysis is presented on the silylation of a series of heat-treated silica gels by hexamethyldisilizane (HMDS) with the aim of elucidating details of the surface hydroxyl population of the unsilylated samples. It is found that the complete removal of all silanol groups from silica is probably approached only at temperatures higher than those normally employed in silica treatment (i.e., higher than 1000/sup 0/C) and that some molecular water may remain on the surfaces of samples normally considered ''dried'' (e.g., evacuated at 200/sup 0/C). The population and reactivity patterns of surface hydroxyls are considered in terms of reasonable surface and dehydration models.