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.