Computational Investigation of Acid Base, Surface Complexation, and Oxidation/Reduction Reaction Mechanisms on Iron Oxide and Iron Silicate Surfaces (Felmy Rustad BES, PNNL SCOPE #22130).
EMSL Project ID
6090
Abstract
This project is directed at providing a molecular scale understanding of surface complexation reactions occurring at oxide, oxyhydroxide, and silicate mineral surfaces through the use of molecular modeling calculations. The molecular modeling calculations are used to help identify key molecular level structures and bond energies, which in turn are used to develop improved thermodynamic models of macroscopic adsorption processes. In previous years we have successfully utilized this approach to better understand proton binding and surface charge development at iron oxide surfaces. Last year our efforts were focused on construction and use of high performance computing techniques to address the effect of solvent and electrolyte on acid-base reactions occurring on iron oxide surfaces. This work involves performing virtual titrations of the iron oxide surfaces with NaOH-NaClO4-HClO4 solutions. In pure solutions this work reveals a secondary hydroxylation involving binding of secondary hydroxyls in the near surface layer, providing a novel insight into the molecular structure of the double layer. In addition, these simulations reveal the inertness of low-lying surface functional groups due to removal from the solvent. Finally, we have observed the enhanced development of sodium ion pairing on magnetite, which may account for its anomalously low PZC.New Scope Nov 13, 2005 from JF Boiley:The object of this research is to investigate the generation of charge at the metal oxide/water interface using the cryogenic
capabilities of the PHI Quantum 2000 XPS of the Interfacial and Nanoscale Science Facility. The cryogenic XPS technique is a powerful method that can obtain the composition of solid/solution interfaces equilibrated at room temperature by analyzing
fast-frozen wet solids at liquid nitrogen temperature. In this project the centrifuged pastes of hematite colloidal aqueous suspensions will be used to investigate the effects of pH and ionic strength on the water, hydroxyl, sodium and chloride
composition of the surface. These analyses will address important issues regarding the generation of charge at solid/solution interfaces including (1) the possible correlation between the generation of surface hydroxyls with the adsorption of counterions, (2) the hydration state of counterions as well as (3) the surface coverage of counterions. The study of shifts in binding energies the O 1s spectra in the sample heated to room temperature will also enable the study of the built-in electric potential of the solid/solution interface arising from the charge surface functional groups.
This research will also provide the Interfacial and Nanoscale Science Facility the opportunity to test the assumptions behind the
cryogenic XPS technique by attempting to reproduce data obtained with a sample previously analysed on a Kratos Axis Ultra electron spectrometer at Ume University (Sweden).
Project Details
Project type
Exploratory Research
Start Date
2003-11-18
End Date
2006-09-29
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Faculty of 1000 Biology: evaluations for McLean JS et al 2008 Feb 2 (2) :121-31
http://www.f1000biology.com/article/id/1104258/evaluation
Faculty of 1000 Biology: evaluations for McLean JS et al ISME J 2008 Feb 2 (2) :121-31 http://www.f1000biology.com/article/id/1104258/evaluation
"Majors PD, JS Mclean, and RA Wind. 2006. "NMR microscopy of dental biofilm metabolism." Proc. ISMRM, 14: 2013."
Majors PD, JS Mclean, ON Ona, JC Scholten and RA Wind. 2007. "Hyphenated nuclear magnetic resonance technologies for microbial physiology studies." Presented by Paul D. Majors (Invited Speaker) at Irish Branch of the Society for General Microbiology Conference, Limerick Ireland, April 20 2007. PNNL-SA-54446."
McLean JS, ON Ona and PD Majors. 2008. "Correlated biofilm imaging, transport and metabolism measurements via combined nuclear magnetic resonance and confocal microscopy." ISME Journal 2(2), 121-131, doi:10.1038/ismej.2007.107.
McLean JS, PD Majors, CL Reardon, CL Bilksis, SB Reed, MF Romine and JK Fredrickson (2008). “Investigations of Metabolism and Structure within Shewanella oneidensis MR-1 Biofilms,” Journal of Microbiological Methods 74(1): 47-56, doi:10.1016/j.mimet.2008.02.015 .
Rustad JR, KM Rosso, and AR Felmy. 2004. "Molecular Dynamics Investigation of Ferrous-Ferric Electron Transfer in a Hydrolyzing Aqueous Solution: Calculation of the pH Dependence of the Diabatic Transfer Barrier and the Potential of Mean Force." Journal of Chemical Physics 120(16):7607-7615.