Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 12/12/2003
Publication Date: 12/12/2003
Citation: JOHNSTON, C., LAIRD, D.A., LI, H., TEPPEN, B.J., BOYD, S. PROBING THE NANOSCALE ARCHITECTURE OF MINERAL SURFACES. AMERICAN GEOPHYSICAL UNION. 2003. V. 84(46), FALL MEETING SUPPL., ABSTRACT NO. B11E-01.
Technical Abstract: Soil minerals have been shown recently to have an unexpectedly high affinity for certain types of organic molecules including pesticides, explosives, and related environmental contaminants. Recent laboratory and field studies, for example, have shown that nitroaromatic compounds are strongly sorbed to certain types of expandable clay minerals. For these compounds, sorption by clay minerals may exceed that of soil organic matter and the molecular mechanisms underlying this preference have been the subject of recent investigation. Expandable clay minerals with a low surface charge density and exchanged with potassium ions have been shown to have the highest affinity for these types of organic solutes. Expandable clay minerals have generally been viewed as hydrophilic materials based on their high affinity for water. Recent evidence, however, has shown that the siloxane surface itself has some hydrophobic character. For exchangeable cations with lower hydration enthalpies, such as potassium, the sorbed organic solutes have an opportunity to interact with both the hydrophilic hydrated cation and with nonpolar regions of the siloxane surface. The combined interaction of these two types of surface sites appears to be important for the sorption of both large and small organic solutes. We have recently combined spectroscopic, structural, and quantum chemical methods with sorption isotherms to examine these types of solute-surface interactions in aqueous media for both specimen and soil clays. Examples of solute-hydrophilic and solute-hydrophobic surface site interactions using different probe molecules will be presented.