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

Abstract

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 ( δ-Na 2Si 2O 5). 1H– 1H 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. 29Si magic angle spinning, 1H→ 29Si CP/MAS NMR and 1H– 29Si 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) 2Si(OH)O −Na +], Q 3 [(SiO) 3Si(OH) and (SiO) 3SiO −Na +] and Q 4 [Si(OSi) 4] groups.