ARS | Publication request: Reactions of Organic Molecules with Smectite Surfaces in Aqueous Systems

Submitted to: Meeting Abstract
Publication Acceptance Date: September 23, 2004
Publication Date: September 23, 2004
Citation: Laird, D.A. 2004. Reactions Of Organic Molecules With Smectite Surfaces In Aqueous Systems. Acta Mineralogica-Petrographics, Abstract Series 4, University Of Szeged, Szeged, Hungary. P.64.

Technical Abstract: Understanding of chemical reactions between anthropogenic organic molecules and smectite surfaces in aqueous systems is crucial for understanding the fate of pesticides and other organic contaminants in natural environments. On a macroscopic scale smectites are strongly hydrophilic; however, the hydrophobic/hydrophilic character of smectite surfaces varies dramatically on a molecular scale. The net interaction energy between organic molecules and hydrated smectites, hence sorption affinity, depends on the nature, size and distribution of the hydrated interlayer cations, hydrophilic nanosites and hydrophobic nanosites relative to the stereo chemistry of the organic molecules. The above model provides a framework for understanding reactions between organic molecules and smectite surfaces. Strongly polar organic molecules, such as pyridine, are not sorbed on smectites from aqueous systems. Pyridine is not polar enough to be competitive with water for salvation of the inorganic cations but it is too polar (lacks a nonpolar moiety) to interact with the hydrophobic nanosites. By contrast, weakly polar molecules, such as atrazine and 3-butylpyridine, are sorbed on smectites from neutral aqueous systems. Sorption of weakly polar compounds varies from 0 to 100% depending on the surface charge density and percentage of tetrahedral charge. Nonpolar molecules, such as chlorpyrifos and phenanthrene, are strongly sorbed by smectites from aqueous systems. Sorption of nonpolar molecules, however, is not correlated with surface charge density or percentage of tetrahedral charge. Furthermore, affinity of smectites for nonpolar organic molecules increases with the amount adsorbed, suggesting that such molecules are retained by capillary condensation rather than being sorbed in the interlayers.