J. Phys. Chem. C 2010, 114, 4515–4526
4515
Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 1. Results from X-ray Diffraction Profile Modeling Eric Ferrage,*,† Bruno Lanson,‡ Laurent J. Michot,§ and Jean-Louis Robert| Laboratoire Hydroge´ologie, Argiles, Sols et Alte´rations, UMR6269-CNRS, UniVersite´ de Poitiers, 40 aVenue du Recteur Pineau, 86022 Poitiers Cedex, France, Mineralogy & EnVironments, LGCA - Maison des Ge´osciences, CNRS - UniVersite´ Joseph Fourier, BP53, 38041 Grenoble cedex 9, France, Laboratoire EnVironnement et Mine´ralurgie, Nancy UniVersity, CNRS-INPL UMR 7569 BP40 54501, VandoeuVre Cedex, France, and IMPMC Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris, France ReceiVed: October 14, 2009; ReVised Manuscript ReceiVed: January 7, 2010
The dehydration of two Na-saturated synthetic saponites with contrasting layer charge was studied by modeling the X-ray diffraction (XRD) patterns recorded along a water vapor desorption isotherm. The interlayer configurations used to reproduce the XRD data over a large angular range include Na+ cations located in the interlayer midplane and H2O molecules normally distributed about one or two main positions for mono- and bihydrated layers, respectively. Although strongly reduced in comparison to natural smectites, hydration heterogeneity was systematically observed for these synthetic saponites, especially along the transition between two hydration states. Using improved models for the description of the interlayer organization, the influence of layer charge on the structure of interlayer water can be precisely assessed. In addition, the comparison with water contents obtained from water vapor gravimetry experiments allows discriminating the relative contributions of H2O molecules from 1W and 2W interlayers (crystalline water) and from the pore space network. Introduction and Background Information Smectites are clay minerals ubiquitous in surface environments, both terrestrial and marine, where they often represent one of the main mineral components. Their structure involves colloidal size (
