Observation of hydroxyl groups by O-17 solid-state multiple quantum MAS NMR in sol-gel-produced silica

O-17 NMR parameters (C-Q, eta, delta(iso) and T-1) are reported for both Si-O-Si and Si-OH fragments within a silica gel. The Si-OH units have a wide spread of parameters but are typically characterised by a very short T-1 (similar to 0.1 ms) and C-Q < 200 kHz. These observations have extremely important implications for the quantification of such units in these gels and related glassy materials by O-17 NMR. In light of these observations, the O-17 NMR experiments have been optimised and a distinct resonance from the OH group is observed in 1D static and magic angle spinning (MAS) NMR measurements as well in the multiple quantum (MQ) experiment. (C) 1999 Elsevier Science B.V. All rights reserved