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Submitted on March 14, 2007
Accepted on May 9, 2007
The Structure of Ferrihydrite, a Nanocrystalline Material
F. Marc Michel 1*, Lars Ehm 1, Sytle M. Antao 2, Peter L. Lee 2, Peter J. Chupas 2, Gang Liu 3, Daniel R. Strongin 3, Martin A. A. Schoonen 1, Brian L. Phillips 1, John B. Parise 4
1 Center for Environmental Molecular Science (CEMS), Stony Brook University, Stony Brook, NY 11794, USA; Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA. 2 Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA. 3 Center for Environmental Molecular Science (CEMS), Stony Brook University, Stony Brook, NY 11794, USA; Department of Chemistry, Temple University, Philadelphia, PA 19122, USA. 4 Center for Environmental Molecular Science (CEMS), Stony Brook University, Stony Brook, NY 11794, USA; Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA; Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.
* To whom correspondence should be addressed.
F. Marc Michel , E-mail: fmichel{at}ic.sunysb.edu
Despite the ubiquity of ferrihydrite in natural sediments andits importance as an industrial sorbent, the nanocrystallinityof this iron oxyhydroxide has hampered accurate structure determinationby traditional methods which rely on long-range order. Herewe uncover the atomic arrangement by real-space modeling ofthe pair distribution function (PDF) derived from direct Fouriertransformation of the total x-ray scattering. The PDF for ferrihydritesynthesized using different routes is consistent with a singlephase (hexagonal spacegroup P63mc; a = ~5.95, c = ~9.06 Angstroms).In its ideal form, this structure contains 20% tetrahedrallyand 80% octahedrally coordinated iron and has a basic structuralmotif closely related to the Baker-Figgis -Keggin cluster. Real-spacefitting indicates structural relaxation with decreasing particlesize and also suggests that second-order effects such as internalstrain, stacking faults and particle shape contribute to thePDFs.
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[DOI: 10.1126/science.1144002] |Summary »|Full Text »|PDF »
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