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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOGEOCHEMICAL PROCESSES INFLUENCING FORMATION AND STABILIZATION OF SOIL ORGANIC MATTER AND SOIL STRUCTURE Title: Hydrophobic Contributions to the Sorption of Organics from Water to Smectites

Authors
item Teppen, Brian - MICHIGAN STATE UNIVERSITY
item Li, Hui - MICHIGAN STATE UNIVERSITY
item Laird, David
item Johnston, Cliff - PURDUE UNIVERSITY
item Boyd, Stephen - MICHIGAN STATE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 7, 2007
Publication Date: June 7, 2007
Citation: Teppen, B., Li, H., Laird, D.A., Johnston, C., Boyd, S. 2007. Hydrophobic contributions to the sorption of organics from water to smectites. Program of Abstracts 2006 Annual Meeting of Clay Minerals Society. p. 255.

Technical Abstract: One mechanism by which swelling clay minerals can interact with aqueous organic solutes is the hydrophobic force. Smectite interlayers present the extreme case of vicinal water, with a thin, salty water film between two opposing surfaces. This interlayer water is clearly a different phase from bulk aqueous solution, with lower entropy, mobility, and dielectric constant but larger enthalpy and viscosity. As such, hydrophobic organic solutes are likely to partition into this “subaqueous” interlayer phase when the hydrophobic forces outweigh other forces that oppose organic sorption, or when hydrophobic forces augment other forces that favor organic sorption. Several case studies will be presented to illustrate the role and magnitude of these hydrophobic forces in the sorption of aqueous organics to otherwise inorganic smectites.In cation exchange, hydrophobicity is the dominant factor in the “selectivity” of smectites for larger organic cations relative to inorganic cations and smaller organic cations. Two thermodynamic datasets will be shown to support this assertion. Indeed, the clay itself may be indifferent to which organic cation is present except at high loading rates. For neutral organic solutes that can form reasonably strong complexes with smectites, hydrophobic forces seem to enhance sorption. Interlayer water is most perturbed, and its properties farthest from those of bulk water, when present as a monolayer. We will discuss several examples where hydrophobic solutes that are weakly sorbed under other circumstances can be strongly sorbed into the special phase constituted by a monolayer of water between two smectite surfaces. Furthermore, when hydrophobic solutes are present, this monolayer can become the preferred state of the smectite-organic-water system, even at high water activity.

Last Modified: 12/20/2014
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