Vibrational Probe Studies of Water Interactions with Montmorillonite

C. T. Johnston1, G. Sposito2 and C. Erickson1
1 Department of Soil and Water Science, University of Florida, Gainesville, Florida 32611
2 Department of Soil Science, University of California, Berkeley, California 94720

Abstract: Interaction of water with montmorillonite exchanged with Na+, K+, Co2+, and Cu2+ cations as a function of water content was examined using an FTIR/gravimetric cell designed to collect spectroscopic and sorption data simultaneously. Correlation of water desorption isotherms with infrared spectra of the clay-water complex showed that the position of the HOH bending band of water decreased as a function of water content. The largest decreases in frequency were observed for Cu2+ and Co2+; smaller decreases were found for Na+ and K+. In addition, the molar absorptivity of sorbed water increased upon decreasing the water content. The decrease in frequency and the concomitant increase in molar absorptivity were attributed to polarization effects on the sorbed water molecules by exchangeable cations. The interference fringes of a self supporting clay film permitted d-spacings to be determined optically and, therefore, changes in frequency, molar absorptivity, and water sorption behavior to be related directly to changes in interlayer spacing. The d-spacings obtained from the interference fringes were consistently larger by approximately 0.5 Å than those determined using powder XRD.

Key Words: Cation exchange • Desorption isotherm • FTIR • Gravimetric • Montmorillonite • Physisorption • Water

Clays and Clay Minerals; December 1992 v. 40; no. 6; p. 722-730; DOI: 10.1346/CCMN.1992.0400611
© 1992, The Clay Minerals Society
Clay Minerals Society (www.clays.org)