Room Temperature Solid Surface Water with Tetrahedral Jumps of 2H Nuclei Detected in 2H2O-Hydrated Porous Silicates

• Published in: The journal of physical chemistry. B 2004-11, Vol.108 (46), p.17783-17790
• Main Authors: Benesi, Alan J, Grutzeck, Michael W, O'Hare, Bernie, Phair, John W
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp048047k

The nature of water adjacent to solid silicate surfaces in kanemite, rehydrated zeolite A, rehydrated highly porous glass, rehydrated high surface area silica gel, and the hydration products of tricalcium silicate has been investigated with 2H NMR techniques and calorimetry. The room temperature 2H NMR quadrupole echo spectra of all samples show a sharp central resonance that corresponds to 2H2O. The kanemite, porous glass, and silica gel spectra show in addition powder patterns that were assigned, based on previous findings for kanemite, to silanol −OH groups experiencing rapid 3-fold jumps or rotational diffusion about the Si−O bond. The spectrum of hydrated tricalcium silicate shows in addition to the aqueous peak a rigid powder pattern that is assigned to Ca(O2H)2. Spectra obtained at −120 and −150 °C for the kanemite sample show that the qcc values for the aqueous deuterons range from 180 to 210 kHz, as would be expected for the different water environments observed in the X-ray structure of kanemite. Room temperature 2H T 1 data obtained at two magnetic fields for kanemite are exactly matched with theoretical calculations that assume rapid tetrahedral jumps of the 2H nuclei (2.0 × 108 s-1) in a solid-state lattice similar to those observed in 2H2O ice below the freezing point. The T 1 data cannot be matched with isotropic rotational diffusion as would be expected for liquid water. The T 1 data for low loadings of 2H2O in zeolite A are also matched with the tetrahedral jump model. T 1 data for the other samples are consistent with rapid exchange of 2H nuclei or 2H2O molecules between solid-state surface water experiencing rapid tetrahedral jumps and liquid-state water farther from the surface. Heat evolution observed during hydration of all samples is consistent with the heat of fusion expected for a liquid to solid phase transition for the surface water.