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Published online by Cambridge University Press: 01 February 2011
The analyses of layer structure in Na-montmorillonite have been performed using 27Al MAS and 27Al Multi Quantum (MQ) MAS NMR techniques. In 27Al 5QMAS NMR spectra measured at higher magnetic field of 16.4 T, two peaks were observed at 74.2 and 62.9 ppm. Hence, it has been suggested that the 4-coordinated Al site in Na-montmorillonite has two different structures. For detail assignment of the two peaks due to such 4-coordinated Al sites in Na-montmorillonite, 27Al MAS NMR measurements have been carried out for Na-montmorillonites with different water contents. The ratio of two 4-coordinated Al sites was found to be affected by water in the interlayer space of Na-montmorillonite, because the area ratio of peaks corresponding to two 4-coordinated Al sites changes with the water content, i.e., the peak area at around 69 ppm is increased sensitively with an increase in water content. Moreover, Cross Polarization/MAS (CP/MAS) NMR measurements have been carried out. As a result, the enhancement of peak at around 69 ppm was observed. Therefore, the two peaks observed by 27Al 5QMAS methods are assigned to AlO4 in the vicinity of water bound to tetrahedral sheets and the remote AlO4 from such water, respectively.
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