First evidence of multiple octahedral A1 sites in Na-montmorillonite by 27Al multiple quantum MAS NMR
Takahashi, Takafumi (Nippon Steel Corporation. Advanced Technology Research Laboratories)
Kaneshashi, Koji (Nippon Steel Corporation. Advanced Technology Research Laboratories)
Saito, Koji (Nippon Steel Corporation. Advanced Technology Research Laboratories)

Date:	2008
Abstract:	The configuration of hydroxyl groups around the octahedral cations of 2:1 phyllosilicate minerals has long been an important question in clay science. In the present study, Al multiple quantum (MQ) magic angle spinning nuclear magnetic resonance (MAS NMR) was applied to the local structural analysis of octahedral Al positions in a purified Na-montmorillonite. Three octahedral Al sites (Al, Al, and Al) are distinguished by Al 5QMAS NMR, whereas these sites are not differentiated by Al MAS and 3QMAS NMR. The isotropic chemical shift (δ) and the quadrupolar product (P) were estimated to be 5. 8 ppm and 2. 6 MHz for Al, 6. 2 ppm and 3. 0 MHz for Al, and 6. 7 ppm and 3. 7 MHz for Al, respectively. The three Al sites originated from geometric isomers with cis and trans structures, which have mutually different configurations of the OH groups around the central Al ions. From the view point of symmetry for the OH groups, Al and Al in the upfield region were assigned to cis sites, and Al in the downfield region was assigned to a trans site. The occurrence of multiple Al sites implies that Na-montmorillonite used in the present study has cis-vacant structure in the octahedral sheet. This is a reasonable insight, supported by the chemical composition and the differential thermal analysis data of the Na-montmorillonite.
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Cis ; Hydroxyl ; MQMAS NMR ; Na-montmorillonite ; Octahedral Al ; Trans
Published in:	Clays and Clay Minerals, Vol. 56, Núm. 5 (2008) , p. 520-525, ISSN 1552-8367

DOI: 10.1346/CCMN.2008.0560505

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