Stony Brook University
Department of Geosciences
Earth and Space Sciences Building (ESS 255)
Stony Brook, NY 11794-2100 USA
fmichel@ic.sunysb.edu
Phone: (631) 632-6839 Fax: (631) 632-8240
F. Marc Michel, CV 2007

We are interested in using advanced experimental techniques at the synchrotron and in the laboratory to develop a molecular-scale understanding of various nanocrystalline materials in environmental geochemical systems. Evaluating reactions and processes at an extrememly small scale first requires the fundamental characterization of all materials of interest. We are using a number of different techniques to evaluate fundamental properties such as atomic structure, particle size, cluster size, surface charge characteristics, morphology, and element oxidation states.

• X-ray and neutron total scattering and pair distribution function (PDF) analysis
• XRD and Rietveld analysis
• Extended X-ray absorption fine structure (EXAFS)
• X-ray absorption near-edge spectroscopy (XANES)
• Quasi-elastic (dynamic) light scattering (DLS)
• X-ray photoelectron spectroscopy (XPS)
• Electron microscopy (SEM and TEM)

Evaluating atomic structure in nanocrystalline materials using traditional powder diffraction analysis techniques (e.g., Rietveld method) is often hindered by the broadening of diffraction maxima resulting from the effects of particle size and disorder. These effects are manifested as a significant diffuse scattering component in a diffraction pattern which contains important information regarding the local atomic arrangement in the structure. Total scattering and pair distribution function (PDF) analysis is therefore a valuable tool for evaluating nanocrystalline materials because the diffuse scattering, as well as the Bragg component, are included in the analysis and therefore information regarding the short-, medium-, and long-range atomic ordering is attainable.

We have recently focused on using X-ray total scattering and the PDF method to probe the atomic structures of a number of nano-sized metal sulfides (e.g., FeS and MnS) and oxides (ferric and aluminum hydroxides). These compounds are abundant in certain near-surface environments and often play important roles in geochemical processes and the fate of contaminants. The atomic structure of a material has implications on its reactivity and other unique properties and is therefore an essential component for completing a fundamental characterization study. These studies have been conducted primarily at the 1-ID and 11-ID beamlines of the Advanced Photon Source at Argonne National Laboratory.

Our characterization of the initial FeS precipitate has revealed that it has an atomic structure nearly identical to crystalline mackinawite. With individual crystallite sizes on the order of 2 - 3 nm this material has a tremendous amount of surface area and is highly reactive. We are currently investigating the interaction of this material with various contaminants in the form of metals and metalloids. The incorporation of such contaminants as impurities in Fe-S phases is of interest and we are also exploring the effect and fate of impurities during subsequent transformations to more stable phases such as pyrite (FeS2).

Michel, F. M., Schoonen, M. A. A., Zhang, X. V., Martin, S. T., Parise, J. B., (2006) Hydrothermal Synthesis of Pure Alpha-Phase Manganese(II) Sulfide without the Use of Organic Reagents, Chem. Mater., 18, pp. 1726-1736.

Michel, F. M., Antao, S. M., Chupas, P. J., Lee, P. L., Parise, J. B., Schoonen, M. A. A., (2005) Short- to Medium-Range Atomic Order and Crystallite Size of the Initial FeS Precipitate from Pair Distribution Function Analysis, Chem. Mater., 17, pp. 6246-6255.

Michel, F. M., Antao, S. M., Celestian, A. J., Ehm, L., Schoonen, M. A. A., Parise, J. B., Liu, G., Strongin, D., Kim, J., Grey, C. P., Han, W., Gillow, J., Chupas, P. J., Lee, P. L., (2006) Similarities in Structure of Coherent Scattering Domains in 2- and 6-Line Ferrihydrite and Effect of Particle Size, Chem. Mater. Submitted.

Liu, G., Debnath, S., Paul, K. W., Han, W., Hausner, D. B., Hosein, H-, A., Michel, F. M., Parise, J. B., Sparks, D. L., Strongin, D. R., (2005) Characterization and Surface Reactivity of Ferrihydrite Nanoparticles Derived from the Ferritin Protein, Langmuir, Submitted.

Michel, F.M. & Schoonen, M.A.A., Cluster size and electrophoretic mobility of the initial FeS precipitate before and after freeze-drying and as a function of pH from dynamic light scattering. In progress-expected 2006.