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GEOREF RECORD

Solid-state nuclear magnetic resonance study of sepiolite and partially dehydrated sepiolite

Mark R. Weir, Wenxing Kuang, Glenn A. Facey and Christian Detellier
Solid-state nuclear magnetic resonance study of sepiolite and partially dehydrated sepiolite
Clays and Clay Minerals (April 2002) 50 (2): 240-247

Abstract

The assignment of the (super 29) Si CP/MAS-NMR spectrum of naturally-occurring sepiolite clay was re-examined using (super 29) Si COSY and (super 1) H- (super 29) Si HETCOR pulse sequences. Each of the three main resonances at -92.1, -94.6 and -98.4 ppm has been attributed to one of the three pairs of equivalent Si nuclei in the basal plane, and the resonance at -85 ppm to Q (super 2) (Si-OH) Si nuclei. On the basis of the COSY experiment, the resonance at -92.1 ppm is unambiguously assigned to the intermediate, near-edge Si sites. The HETCOR experiment revealed that the resonance at -94.6 ppm cross-polarizes almost entirely from the Mg-OH protons, and therefore is assigned to the central Si position. The remaining resonance at -98.4 ppm correlates strongly to the protons of the structural water molecules and therefore is assigned to the edge Si sites. Nearly complete rehydration was achieved at room temperature by exposing sepiolite samples that had been partially dehydrated at 120 degrees C to water vapor or to D (sub 2) O vapor. The rehydration results support the (super 29) Si NMR peak assignments that were made on the basis of the COSY and HETCOR experiments. The (super 29) Si CP/MAS-NMR spectrum corresponding to the folded sepiolite structure in which approximately one half of the structural water has been removed by heating to 350 degrees C is reported for the first time. The chemical shift values and relative intensities are significantly different compared to the resonances that are observed in the corresponding spectrum of the true sepiolite anhydride. These observations support the earlier claim that sepiolite heated to approximately 350 degrees C exists as a distinct phase to be differentiated from that of the completely dehydrated state.


ISSN: 0009-8604
EISSN: 1552-8367
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 50
Serial Issue: 2
Title: Solid-state nuclear magnetic resonance study of sepiolite and partially dehydrated sepiolite
Affiliation: University of Ottawa, Department of Chemistry, Ottawa, ON, Canada
Pages: 240-247
Published: 200204
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 28
Accession Number: 2002-042851
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200214
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