Clay Mineral Surface Geochemistry group
Current Research Team
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Ian C. Bourg |
Top left: Molecular dynamics "snapshot" of water molecules (blue and white), sodium ions (purple), and methane molecules (yellow-brown) intercalated simultaneously between two layers of montmorillonite, a common smectite clay mineral [figure used for the cover of S.A. Auerbach, K.A. Carrado, and P.K. Dutta (eds.), Handbook of Layered Materials Science and Technology, Marcel Dekker, New York, 2004]. Top right: Molecular dynamics snapshot of a water-filled 4-nm-diameter cylindrical pore in a slab of silica glass (yellow, red, and white: Si, O, and H atoms in the silica structure; dark and light blue: water O and H atoms). Silanol OH groups are highlighted as red and white spheres. Center left: Molecular dynamics snapshot of a 40Ar atom (in green) and water molecules located in its first solvation shell. Center right: Molecular dynamics snapshot of the interface between aqueous brine and supercritical CO2 (water O and H atoms in red and white, Na+ and Cl- ions in blue and red, CO2 molecules in gray). The pink line shows the trajectory of a water molecule evaporating into the CO2 phase. Bottom left: Molecular dynamics snapshots of a CO2 hydrate clathrate equilibrated with liquid water at 280, 283, and 289 K (from top to bottom). Bottom right: Molecular dynamics snapshot showing different populations of water molecules in the first two statistical water monolayers on a smectite clay surface (purple, red, and orange: first-layer water molecules donating two, one, or zero hydrogen bonds to siloxane surface O atoms; pink: second-layer water molecules). The dark and light blue spheres are Na+ and Ca2+ outer-sphere surface complexes.
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Laura Hamm |
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Amy Hofmann |
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Michael Holmboe |
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Kideok Kwon |
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Yangyang Liu Postdoctoral Fellow, Earth Sciences Division, Berkeley National Laboratory |
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Aric Newton |
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Laura Nielsen |
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Keith Refson |
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Garrison Sposito |
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Research Goals
Because of their ubiquitous presence in natural materials and their strong surface reactions, nanoparticles produced by weathering or biological processes in natural settings (in particular, clay minerals) figure importantly in a broad range of environmental phenomena, from global climate change to contaminant remediation. Our research is designed to provide molecular-scale information about the surface chemistry of these nanoparticles based on state-of-the-art computer simulation using tested codes and realistic models of layer type minerals. These computer simulations are powerful complements to experimental methods, in that they can reveal the behavior of individual atoms in complex geochemical systems and the manner in which molecular-scale interactions give rise to complex properties such as adsorption, wetting, molecular diffusion, ligand exchange kinetics, nanoparticle electronic structure, and the electrostatic screening of charged surfaces.
Methods
We have been developing an approach to the surface geochemistry of smectite, Si oxide, Mn oxide, and Fe sulfide minerals based on molecular-level simulation. Our research, supported by the DOE-BES program at Lawrence Berkeley National Laboratory, is aimed at understanding the mechanisms by which these minerals interact with water molecules, cations, organic molecules, and supercritical CO2 in aqueous subsurface environments. Our principal techniques, molecular dynamics (MD) and density functional theory (DFT) simulations, are well-established, essential components of research in theoretical physical chemistry.
The underlying approach in MD simulations is to construct potential functions that model all of the known interactions in a system of ions, atoms, and molecules, then devise a strategy for sampling the phase space of the interacting system in order to compute its properties. In a MD simulation, the phase space of the system is sampled through numerical integration of the Newton-Euler equations of motion for each molecular species, which is performed consistently with the suite of potential functions assumed.
In recent years the interpretation of both diffraction and spectroscopic data on clay minerals has been facilitated by a class of independent, first-principles (sometimes termed "ab initio") quantum-mechanical simulations, which now have achieved sufficient accuracy to predict crystallographic properties of clay minerals without recourse to empirical parameterization. The ingredients of this scheme are the atomic nuclei and electrons whose interactions are described by the density functional theory (DFT) formulation of quantum mechanics. DFT-based methods are able to describe structure and bonding properties to a high degree of accuracy, including structural trends. Indeed, these methods represent the only practical quantum-mechanical approach for studying complex materials such as clay minerals and metal oxides.
Our MD calculations utilize the codes MOLDY, developed by K. Refson, and LAMMPS, distributed by Sandia National Laboratories. Our ab initio calculations are performed using a parallel version of the code CASTEP, developed by the UKCP (United Kingdom Car-Parrinello) consortium. Numerical calculations have been carried out under DOE support on Cray XT4, Cray XE6, and IBM iDataPlex supercomputers at the NERSC (National Energy Research Scientific Computing Center).
Research Projects
- CO2-Water Interfacial Tension
- Magnetic Ordering in Mackinawite
- Ion adsorption in the Electrical Double Layer on Smectite Clay Surfaces
- Diffusion in Clay Barriers
- Solute Isotope Fractionation by Diffusion in Liquid Water
- Mn-Vacancy-Induced Photoconductivity of Layer Type Manganese Oxides
- Surface Complexes of Zinc in Birnessite Interlayer
- Nickel Partitioning at Mn(IV) Vacancies in Birnessite
- Proton Adsorption on Smectite Clay Minerals
Recent Publications (2010-2012)
- Hofmann, A.E., Bourg, I.C., DePaolo, D.J., 2012. Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems, Proc. Natl. Acad. Sci. U.S.A. (doi: 10.1073/pnas.1208184109).
- Bourg, I.C., Steefel, C.I., 2012. Molecular dynamics simulations of water structure and diffusion in silica nanopores, J. Phys. Chem. C 116, 11556-11564.
- Nielsen, L.C., Bourg, I.C., Sposito, G., 2012. Predicting CO2-water interfacial tension under pressure and temperature conditions of geologic CO2 storage, Geochim. Cosmochim. Acta 81, 28-38.
- Bourg, I.C., Sposito, G., 2011. Ion exchange phenomena, In: Handbook of Soil Science, Properties and Processes 2nd ed. (Huang, P.M., Li, Y., Sumner, M.E., eds.), CRC Press, Boca Raton, Chapter 16.
- Bourg, I.C., Sposito, G., 2011. Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl-CaCl2) solutions, J. Colloid Interface Sci. 360, 701-715.
- Kwon, K.D., Refson, K., Bone, S., Qiao, R., Yang, W., Liu, Z., Sposito, G., 2011. Magnetic ordering in mackinawite (tetragonal FeS): evidence for strong itinerant spin fluctuations, Phys. Rev. B 83, 064402.
- Kwon, K.D., Refson, K., Sposito, G., 2010. Surface complexation of Pb(II) by hexagonal birnessite nanoparticles. Geochim. Cosmochim. Acta 74, 6731-6740.
- Kwon, K.D., Sposito, G., 2010. Reactivity of biogenic manganese oxide for metal sequestration and photochemistry: computational solid state physics study. J. Miner. Soc. Korea 23, 161-170.
- Peña, J., Kwon, K.D., Refson, K., Bargar, J.R., Sposito, G., 2010. Mechanisms of nickel sorption by a bacteriogenic birnessite, Geochimica et Cosmochimica Acta 74, 3076-3089.
- Bourg, I.C., Sposito, G., 2010. Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media. Environ. Sci. Technol. 44, 2085-2091.
- Bourg, I.C., Richter, F.M., Christensen, J.N., Sposito, G., 2010. Isotopic mass-dependence of alkali metal cation diffusion coefficients in water. Geochim. Cosmochim. Acta 74, 2249-2256.