Water Structure and Dynamics in Smectites: X-ray Diffraction and 2H NMR Spectroscopy of Mg-, Ca-, Sr-, Na-, Cs-, and Pb-Hectorite

U. Venkateswara Reddy, Geoffrey M. Bowers, Narasimhan Loganathan, Mark Bowden, A. Ozgur Yazaydin, R. James Kirkpatrick

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Variable-temperature X-ray diffraction and 2H NMR spectroscopy of the smectite mineral, hectorite, containing interlayer Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, and Pb2+ equilibrated at 43% relative humidity (RH) and mixed with 2H2O to form a paste provide a comprehensive picture of the structural environments and dynamics of interlayer 2H2O and the relationships of these properties to interlayer hydration state, the hydration energy and polarizability of the cation, temperature, and the formation of ice-1h in the interparticle pores. The variation in basal spacing shown by the XRD data correlates well with the 2H NMR behavior, and the XRD data show for the first time in hectorites that crystallization of interparticle ice-1h causes a decrease in the interlayer spacing, likely due to removal of interlayer 2H2O. The variation of the 2H NMR behavior of all the samples with decreasing temperature reflects decreasing frequencies of motion for the rotation of the 2H2O molecules around their dipoles, reorientation of the 2H2O molecules, and exchange of the 2H2O molecules between interlayer sites coordinated to and not coordinated to the cations.

Original languageEnglish (US)
Pages (from-to)8863-8876
Number of pages14
JournalJournal of Physical Chemistry C
Issue number16
StatePublished - Apr 28 2016
Externally publishedYes

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Publisher Copyright:
© 2016 American Chemical Society.


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