One- and two-dimensional solid-state magic angle spinning NMR studies on the hydration process of layered sodium disilicate SKS-6

Three different kinds of silanols, which include isolated silanol, silanol I (with the hydroxyl proton bonded to an oxygen atom in the adjacent layer) and silanol II (with the hydroxyl proton bonded to the non-bridging oxygen at the same silicon atom), are generated during the hydration process of SKS-6 (delta-Na2Si2O5). H-1-H-1 nuclear Overhauser enhancement spectroscopy reveals that the proton of silanol I has an effective chemical exchange or spin diffusion with the proton of hydrogen-bonded water, while the proton of silanol II is likely far away from the other proton-containing species. Si-29 magic angle spinning, H-1 --> Si-29 CP/MAS NMR and H-1-Si-29 phase-modulated Lee-Goldburg decoupled correlation experiments demonstrate that the local environments of the silicon sites in the final hydrated sample are mainly composed of Q(2) [(SiO)(2)Si(OH)O-Na+], Q(3) [(SiO),Si(OH) and (SiO)(3)SiO-Na+] and Q(4) [Si(OSi)(4)] groups. (C) 2003 Elsevier Inc. All rights reserved.