HR: 17:45h
AN: V14B-08    [Abstracts]
TI: X-ray Spectroscopic Tools for Structural Determination of Cr(VI)-Treated Iron Nanoparticles
AU: * Manning, B A
EM: bmanning@sfsu.edu
AF: San Francisco State University, Department of Chemistry and Biochemistry, San Francisco, CA 94132, United States
AU: Kiser, J
EM: jkiser@sbcglobal.net
AF: San Francisco State University, Department of Chemistry and Biochemistry, San Francisco, CA 94132, United States
AU: Ruiz, A
EM: inkgeist@yahoo.com
AF: San Francisco State University, Department of Chemistry and Biochemistry, San Francisco, CA 94132, United States
AB: Chromate (Cr(VI)) is a highly soluble groundwater contaminant of environmental concern. We are developing and investigating zero-valent iron nanoparticles (nano-Fe) for possible use in remediation of Cr(VI). In this paper we focus on the application of X-ray techniques to determine the electronic environment and solid phase chemistry of Cr and Fe in Cr(VI)-and Cr(III)-treated nano-Fe. Results from X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES) confirmed that Cr(VI) was quantitatively reduced to Cr(III) by nano- Fe. Parallel experiments with 100-mesh Fe filings as a model system show similar Cr(VI) reduction properties but with a somewhat different Fe(III) corrosion product. Detailed analysis of XPS O 1s line spectra revealed that both Cr(III)- and Cr(VI)-treated nano-Fe yielded a predominantly Cr(III) hydroxide product. The Cr local atomic structure in Cr(III)- and Cr(VI)-treated nano-Fe was determined using extended x-ray absorption fine structure spectroscopy (EXAFS) and revealed octahedral Cr(III) with Cr-O interatomic distances between 1.97-1.98 angstroms for both Cr(III) and Cr(VI) treatments. A pronounced second Cr-Cr (and/or Cr-Fe) interatomic shell at 3.01 angstroms was also detected. Our results suggest that the reaction product of Cr(VI)-treated nano-Fe is an insoluble, poorly ordered Cr(III) precipitate and/or a mixed-phase Cr(III)/Fe(III) hydroxide.
DE: 0461 Metals
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 1065 Major and trace element geochemistry
DE: 1806 Chemistry of fresh water
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting