Fe (oxyhydr)oxides are ubiquitous and exert a primary control on coupled redox cycles and the transport of minor but critical metals. In this regard, detailed information on the local coordination environment of impurities is necessary to understand host phase properties, biogeochemical cycling of micronutrients, the long-term stability of impurity/host phase associations, waste forms, and tailoring natural Fe oxides for industrial uses. Extended X-ray absorption fine structure (EXAFS) spectroscopy is the method of choice for determining the local coordination environment of impurities in a host phase. Nonetheless, and in particular for seemingly incompatible dopants, a lack of appropriate standard structures and a priori knowledge concerning thermal disorder, coordination numbers, and potential defect associations can render traditional shell by shell fitting unreliable. I will describe recent work that used ab initio molecular dynamics (AIMD) informed extended x-ray absorption fine structure (EXAFS) spectroscopy to detail the local coordination environment of U and Zn incorporated in hematite (α-Fe<sub>2</sub>O<sub>3</sub>) and goethite (α-FeOOH). Precise predictions concerning the distribution of Fe vacancies around U(VI) incorporated in hematite were confirmed by high resolution HAADF (high angle annular dark field) – STEM (scanning transmission electron microscopy). These examples demonstrate that AIMD-informed EXAFS can greatly increase our understanding of metal incorporation in Fe (oxyhydr)oxides.

Coupling theory, spectroscopy, and electron microscopy to determine the bonding environments of metal impurities in Fe(III)-(oxyhydr)oxides

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.