Adsorption of alcohols by smectites: III. Nature of the bonds

In previous papers of this series it was shown that it is possible to determine both the amount of methanol adsorbed in the interlamellar space of charge-deficient Ca-montmorillonite or of homoionic clays and the amount of methanol occluded in a system of micropores between clay particles. This paper deals with the distinction between methanol molecules in the cation coordination shell within the interlamellar space from those not directly influenced by the cation. An OH stretching band at about 3520 cm−1 or an OD stretching band in the 2600–2650 cm−1 region permits this distinction. At 35°C and at relative methanol vapour pressures between 0·1 and 0·9, one molecule of CH3OD is influenced directly by Na+, 2 molecules are influenced by Ba2+, 1·3–1·8 molecules by Li and 4 molecules by Ca2+. Thus, only 20–50% of the adsorbed alcohol molecules may be within the coordination shell of the cation in the interlamellar space.