HR: 17:00h
AN: V14B-05 INVITED    [Abstracts]
TI: Kinetic competition during chemical and photochemical reactions at iron oxide nanoparticle surfaces
AU: * Gilbert, B
EM: BGilbert@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 90R1116, Berkeley, CA 94720, United States
AU: Waychunas, G A
EM: GAWaychunas@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 90R1116, Berkeley, CA 94720, United States
AU: Banfield, J F
EM: jbanfield@berkeley.edu
AF: University of California Berkeley, Department of Earth and Planetary Sciences, Berkeley, CA 94720, United States
AU: Attenkofer, K
EM: klaus.attenkofer@anl.gov
AF: Argonne National Laboratory, Advanced Photon Source, 9700 S. Cass Avenue, Argonne, IL 60439, United States
AB: The adsorption of aqueous reductants to the surface of ferric iron bearing minerals and the subsequent creation and dissolution of ferrous iron are crucial steps in the geochemical cycling of this transition metal. While conceptual models of reductive dissolution are well established, the details of the interfacial electron transfer step are not well understood at the molecular scale because of the difficulties in probing chemical reactions at the length and time scales of elementary atomic and electronic processes. The goal of our research is to capture, using ultrafast x-ray spectroscopic techniques, the evolution of the chemistry and coordination geometry of surface metal atoms in iron oxide nanoparticles following electron transfer. Although ultrafast x-ray methods are undergoing a period of rapid development, there are numerous technical challenges for studying interfacial reactions of colloidal particles. In particular, the reaction must be initiated using a pulse of laser light in order to synchronize every site; and competing chemical reactions that lead to sample degradation must be minimized. However, addressing these challenges provides broadly relevant insights into kinetic controls on the reactivity of nanoparticles, which will be summarized in this talk. We combined studies of the chemical and photoreductive dissolution of iron oxide nanoparticles in order to indirectly probe the relative rates of competing processes. Of particular importance is the relative rate at which photogenerated structural ferrous iron can reduce surface bound species before detaching without reaction to produce aqueous Fe(II). We find that many elementary processes that occur during (photo)redox reactions of nanoparticles can exhibit a dependence on particle size.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0461 Metals
DE: 1030 Geochemical cycles (0330)
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting