29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations
✍ Scribed by Vladimir I. Bakhmutov; Boris G. Shpeizer; Abraham Clearfield
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 128 KB
- Volume
- 44
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.1899
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✦ Synopsis
Abstract
The ^29^Si T~1~ time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1–6 containing Mn^2+^ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2–4 with relatively small Mn^2+^ contents. Because the relaxation curves for 1–6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn^2+^ concentrations in terms of incorporation of the Mn^2+^ ions into the silica lattice when their concentration is small (≤2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd.