Effect of Negative Surface-Charge Densities of Smectite Clays on the Adsorption Isotherms of Racemic and Enantiomeric Tris(2,2′-Bipyridyl)Ruthenium(II) Chloride

Gilles Villemure1
Centre de Recherche en Photobiophysique, Université du Québec à Trois-Rivières 3351, boul. des Forges, C.P. 500, Trois-Rivières, Quebec G9A 5H7, Canada
1 Present address: Department of Chemistry, University of New Brunswick, Bag Service #45222, Fredericton, New Brunswick E3B 6E2, Canada.

Abstract: The level of adsorption of enantiomeric tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+ by seven different smectite samples was found to be controlled by the total surface area of the clay. The level corresponded to one monolayer. The adsorption of the racemic mixture was lower for all samples, being limited to saturation of the clay's cation-exchange capacity. The addition of NaCl increased the adsorption of the racemic Ru(bpy)32+ to the same level as the enantiomers. The dependence on the clay's surface charge density, expected on the basis of the limited face-to-face aggregation model, was not found. The sharp decrease in adsorption of the enantiomers by low charge-density clays and the corresponding sharp increase in adsorption of the racemate by high charge density clays were not observed. These results do not necessarily invalidate the model. The range of negative charges examined may not have been wide enough. Also, charge distribution in smectite is generally not uniform.

Key Words: Adsorption • Enantiomorphs • Racemic pairs • Smectite • Surface charge • Tris(2,2′-bipyridyl)ruthenium(II)

Clays and Clay Minerals; December 1990 v. 38; no. 6; p. 622-630; DOI: 10.1346/CCMN.1990.0380608
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)