The Impact of Carbonate on Surface Protonation, Electron Transfer and Crystallization Reactions in Iron Oxide Nanoparticles and Colloids
EMSL Project ID
19826
Abstract
In this proposal we outline a plan to address three key issues of importance in the geochemical behavior of iron oxides and in the geochemical cycling of iron, specifically the influence of ubiquitously present carbonate on electron transfer reactions; solid phase transformations/recrystallization; and on the binding of carbonate to reactive sites on the edges of particles. Certain aspects of these three phenomena, particularly those involving the heterolytic dissociation of water, have recently been the subject of intensive research efforts by the principal investigators on this proposal. Previously, these investigations have been largely restricted to idealized pure phase (i.e. oxide-water) systems. Geochemical systems are of course more complex and some understanding is needed of how to extend these calculations to heterogeneous natural environments. We propose to begin efforts along these lines with the introduction of carbonate. Carbonate was chosen for emphasis since it is ubiquitous in the natural environment, is known to bind strongly to oxide surfaces, is reactive on the time scales of interest in this study, and has a speciation driven by acid-base reactions. It is thus well suited to our goal of developing computational models of the oxide-water interface with reactive protons. Moreover, the geochemical behavior of carbonate strongly influences global climate and CO2 sequestration technologies. This proposal is divided into four specific tasks. In the first task, we extend our current molecular dynamics modeling capability to treat reactions in the Fe(II)-Fe(III)-H2CO3-CO2-HCO3--CO32--OH-H2O system. In the second, we identify and investigate, both experimentally and theoretically, the speciation of carbonate-bearing polynuclear ions in solution and the structure of sequestered carbonate within the oxide phases. Task three involves coupled simulation and experimental studies of the impact of carbonate on the protonation of sites at edges of particles on different iron oxide preparations. In the fourth task we examine the effect of carbonate on the catalytic recrystallization of ferric iron (oxy)(hydr)oxides by Fe(II) adsorbates. Taken as a whole these tasks are designed to answer key questions with regards to specific site binding, electron transfer reactions, and crystallization reactions of iron oxides that impact both the geochemical cycling of iron and CO2 species.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-10-01
End Date
2007-11-05
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Boily JF, and AR Felmy. 2008. "On the protonation of oxo- and hydroxo- groups of the goethite (a-FeOOH) surface: A FTIR spectroscopic investigation of surface O-H stretching vibrations." Geochimica et Cosmochimica Acta 72(14):3338-3357 . doi:10.1016/j.gca.2008.04.022