Back to Table of Contents

46970-SE
Complementary Techniques for Resolving the Structure of Environmentally-Significant Poorly Crystalline and Polycrystalline Materials, at the ACS National Meeting, March 2007, Chicago, IL

F. Marc Michel, State University of New York at Stony Brook, Liane G. Benning, University of Leeds, Sytle M. Antao, Advanced Photon Source, Argonne National Laboratory and Peter J. Chupas, Advanced Photon Source, Argonne National Laboratory

Poorly-crystalline and polycrystalline materials commonly form in many of Earth's near-surface aqueous environments and are of substantial interest due to their surface reactivity and potential impacts on the fate and transport of environmental contaminants. This symposium explored how the structure of poorly-crystalline and polycrystalline materials may be resolved by using complementary synchrotron-based and laboratory studies. The materials discussed included iron (hydr)oxides and sulfides, silica nanoparticles, and a variety of other environmentally-relevant compounds that are of great interest due to their high reactivity and ubiquity in certain environments. The aim of this session was to highlight examples where investigators have made progress by combining multiple techniques for probing structure at both the surface and interior of particles.

The morning session began with a talk and discussion about the general strengths and weaknesses of structure probes for poorly crystalline and nanocrystalline materials. Presented as part of this overview were some of the most common techniques currently used for structure solution including pair distribution function (PDF) analysis, extended X-ray absorption fine structure (EXAFS), Mossbauer, and nuclear magnetic resonance (NMR) spectroscopy. In general these methods can yield information regarding interior and surface structure of particles, specific types of order/disorder, site distortion, and valence configuration. Subsequent talks during the morning session included a variety of natural and synthetic compounds ranging from silica nanoparticles to manganese carbonates and oxides to organic macromolecules in soils. Both the structure and reactivity of these compounds were discussed as well as the limitations of the methods utilized for elucidating these fundamental properties.

The focus of the afternoon session was almost exclusively on the chemical, physical, and structural properties of iron oxide and oxyhydroxide nanoparticles. In particular the mineral ferrihydrite, a nanocrystalline iron oxyhydroxide that is an important component in both natural (pristine) and contaminated settings, was discussed in detail. During the afternoon session a new structure model was presented for ferrihydrite that subsequently has attracted substantial interest and attention at the international level.

Funds awarded by the Petroleum Research Fund helped to cover a portion of travel expenses for three participants in the session. Liane G. Benning, professor in experimental biogeochemistry at the University of Leeds in the United Kingdom, both assisted in organizing the session and presented on the first steps in the formation of silica nanoparticles. Jakob Frommer, a Ph.D. student at ETH in Zurich, Switzerland presented on the aging and transformation of chromium hydroxide phases and discussed environmental implications of these findings. Xavier Chatellier, research scientist in biogeochemistry at the CNRS at the University of Rennes in France, presented on his investigations on the properties of iron phosphate nanoparticles. In depth discussion between the presenters and the more than 35 audience members resulted in an interesting and productive session.

Back to top