Sorption of aqueous organic molecules and amino acids on mineral surfaces: determination of binding geometry, local water structure and topological interactions
EMSL Project ID
47556
Abstract
A large frontier in geochemistry is the interaction of organic species with mineral surfaces. Compared to inorganic sorbates which form covalent and hydrogen bonds, organic structures may have partial or dominant hydrophobic interactions with water molecules, multiple charges on a single molecule such as a zwitterion, and complex multi-site interactions with surface functional groups. Additionally, the conformation of the molecule on a surface may differ substantially from the solvated aqueous species. These complexities have relegated most past sorption studies to non-specific binding analysis, though some systematics have emerged, mainly with carboxylic acids. However given the ubiquity of industrial organic pollution, natural organic breakdown products, and pharmaceutical agents in the environment, the need for understanding how organic species interact with mineral surfaces is crucial for predicting their distribution, movement, sequestration and breakdown pathways in ecosystems. The objective of the proposed work is to develop improved systematic knowledge of the binding of amino acids with mineral surfaces as a function of coverage, solution pH and type of mineral surface. We intend to approach this goal using two powerful methods, both of which we have been using for about a decade with solid/water interfaces: Sum-frequency vibrational spectroscopy (SFVS) and surface x-ray diffraction (at the Advanced Photon Source, ANL). SFVS is a unique probe of the solid/aqueous interface that yields direct information on the nature of surface functional groups (such as hydroxyls), and the local water structure, and can be used to determine the vibrational spectrum of sorbed molecular species. A perfect compliment to this method is surface x-ray diffraction by which the details of the solid surface at the aqueous interface can be obtained, including detailed atomic positioning. By using both these techniques and combining them with state-of-the-art advanced simulation methods we expect to clarify the systematics of amino acid binding to two important mineral surfaces hematite/corundum and goethite/diaspore.
The proposed work impacts two of EMSl’s scientific themes. Within “Science of Interfacial Phenomena” the work will gain fundamental new knowledge into organic-inorganic surface binding, including the way in which bound species are organized or ordered by virtue of their interactions with one another. This is essential to predicting organic-organic interactions in a host of systems, both environmental and industrial (e.g. catalysis and synthesis processes). Within “Geochemistry/Biogeochemistry and Subsurface Science” the work will aid predictions about how organic species move in the environment and how they may react with one another at interfaces, or be broken down. This information is extremely important in determining the cycling of anthropogenic pollutants, as well as natural organic species, that affect water quality.
The EMSL provides facilities that are vital to these kinds of investigations. The recently developed high resolution non-linear optical spectrometer system (Hongfei Wang) affords a unique opportunity to measure and interpret the vibrational spectrum of complex sorbed organic molecules using SFVS. Similarly, the cutting edge capabilities of the NWChem suite combined with new developments to improve interface water simulation (Eric Bylaska) give the possibility of realistic sorption geometry predictions for amino acids for the first time.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2012-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members