Structure and reactivity of Pb(II) on hydrated hematite and goethite, studied via density functional theory

GEOC 5

Cynthia S. Lo, cynthia.lo@nist.gov1, Kunaljeet Tanwar, ftkjt@uaf.edu2, Sanjit K. Ghose, ghose@cars.uchicago.edu3, Anne M. Chaka4, and Thomas P. Trainor2. (1) Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive Stop 8380, Gaithersburg, MD 20899-8580, (2) Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK 99775, (3) GSECARS, Consortium for Advanced Radiation Sources, University of Chicago, Building 434A, Advanced Photon Source, 9700 South Cass Avenue, Argonne, IL 60439, (4) Physical and Chemical Properties Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8380, Gaithersburg, MD 20899-8380
Chemical processes occurring at the metal oxide-water interface play a major role in controlling the sequestration, transport, and bioavailability of contaminant metal ions in soil and aquatic environments. Developing a molecular scale understanding of the factors that dictate surface reactions is a key factor in developing more robust models of interfacial processes in the environment. Our work is focused on the development of structural models for specific mineral-water interface systems, and investigating the atomic and electronic structural influence on reactivity with respect to the adsorption of aqueous metal cations. The system(s) under investigation in this study are the low index faces of α-Fe2O3 (hematite) and α-FeOOH (goethite) and the sorption of the priority contaminant metal Pb(II). The interaction of water with the metal oxide surfaces is expected to result in reactive surface functional groups that are substantially different from those present on the stoichiometric or clean surface present under ultrahigh vacuum conditions. Therefore, the initial aspect of our work is to understand the influence of water on the resulting surface structure. We used density functional theory and ab initio thermodynamics to investigate the structures and energetics of the hydroxylated α-Fe2O3 (hematite) and α-FeOOH (goethite) surfaces in order to predict the most stable terminations. These results are in good agreement with surface structures determined using crystal truncation rod x-ray diffraction methods. We also investigated the nature of Pb(II) sorption to these surfaces to examine the influence of surface structure on the structure and energetics of sorbate binding. Our results show that the DFT-predicted lowest energy configurations are consistent with experimental results performed on parallel systems.
 

Frontiers in Geochemistry: Commemorating the 25th Anniversary of the ACS-Geochemistry Division
9:00 AM-11:55 AM, Sunday, 10 September 2006 Moscone Center -- Room 262, Oral

Sci-Mix
8:00 PM-10:00 PM, Monday, 11 September 2006 Moscone Center -- Hall D, Sci-Mix

Division of Geochemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006