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ATR-FTIR spectroscopic characterization of coexisting carbonate surface complexes on hematite

January 1, 2005

The speciation of carbonate adsorbed to hematite in air-equilibrated aqueous solutions has been studied using ATR-FTIR spectroscopy. Samples were measured over a range of pH conditions, at 0.1 M NaCl and at low ionic strength, and in H2O and D2O solutions to permit a multispecies analysis of the data. Second-derivative analyses and fits to the spectra indicate the presence of two major and two minor surface-bound carbonate species. The two major complexes coexist at near-neutral pH and low ionic strength. One of these two complexes is relatively sensitive to ionic strength, being displaced at 0.1 M NaCl, whereas the other is not. Comparison of experimental to DFT/MO-calculated frequencies suggest these two major species to be (a) a monodentate binuclear inner-sphere carbonate surface complex, and (b) a fully or partially solvated carbonate (CO32-) species that is symmetry broken and appears to reside in the structured vicinal water layers at the hematite-water interface, retained by hydrogen bonding and/or other forces. Minor carbonate complexes include diffuse layer CO32- and an unidentified inner-sphere species. Both of the dominant species observed here are likely to be significant controls of the surface charge and sorptive properties of Fe-oxides. Copyright ?? 2005 Elsevier Ltd.

Citation Information

Publication Year 2005
Title ATR-FTIR spectroscopic characterization of coexisting carbonate surface complexes on hematite
DOI 10.1016/j.gca.2004.08.002
Authors J.R. Bargar, J.D. Kubicki, R. Reitmeyer, J.A. Davis
Publication Type Article
Publication Subtype Journal Article
Series Title Geochimica et Cosmochimica Acta
Series Number
Index ID 70029034
Record Source USGS Publications Warehouse
USGS Organization