期刊
MAGNETIC RESONANCE IN CHEMISTRY
卷 44, 期 11, 页码 985-988出版社
JOHN WILEY & SONS LTD
DOI: 10.1002/mrc.1899
关键词
Si-29 MAS NMR; T-1 relaxation; microporous materials
The Si-29 T-1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1-6 containing Mn2+ 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 Mn2+ 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 Mn2+ concentrations in terms of incorporation of the Mn2+ 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 (c) 2006 John Wiley & Sons, Ltd.
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