Cation-dipole interactions in clay organic complexes

Abstract

Quantitative gas chromatographic analyses supplemented by X-ray diffraction studies of the adsorption of ethanol and acetone (as model polar organic compounds) on homoionic montmorillonite revealed marked variation in the number of molecules associated with each exchange cation. The results show increasing association in the order K⁺ <Na⁺<Ba²⁺<Ca²⁺. K⁺ and Na⁺ associate with two and three molecules, respectively, of either ethanol or acetone, and the resulting complexes expand to form a monolayer (∼13 Å). Ba²⁺ and Ca²⁺ form both monolayer complexes as well as double layer complexes. In the single layer complexes Ba²⁺ associates with either four molecules of ethanol or four molecules of acetone, Ca²⁺ associates with five molecules of ethanol or four molecules of acetone. In the double-layer complexes the observed cation-molecule ratios are 1 : 8 for both Ba²⁺-ethanol and Ba²⁺-acetone, 1 : 10 for Ca²⁺-ethanol, and 1 : 8 for Ca²⁺-acetone.

The striking dependence of ethanol and acetone adsorption on the nature of the exchangeable cation suggests that cation-dipole interactions play an important role in the adsorption process. Structural models of the organic complexes are presented.