Vanadium(V) adsorption onto goethite (α-FeOOH) at pH 1.5 to 12: a surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy


Peacock, Caroline L. and Sherman, David M. (2004) Vanadium(V) adsorption onto goethite (α-FeOOH) at pH 1.5 to 12: a surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy. Geochimica et Cosmochimica Acta, 68, (8), 1723-1733. (doi:10.1016/j.gca.2003.10.018).

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Description/Abstract

We measured the adsorption of V(V) onto goethite (α-FeOOH) under oxic (PO2 = 0.2 bar) atmospheric conditions. EXAFS spectra show that V(V) adsorbs by forming inner-sphere complexes as VO2(OH)2 and VO3(OH). We predicted the relative energies and geometries of VO2(O, OH)2-FeOOH surface complexes using ab initio calculations of the geometries and energetics of analogue Fe2(OH)2(H2O)6O2VO2(O, OH)2 clusters. The bidentate corner-sharing complex is predicted to be substantially (57 kJ/mol) favoured energetically over the hypothetical edge-sharing bidentate complex. Fitting the EXAFS spectra using multiple scattering shows that only the bidentate corner-sharing complex is present with Fe-V and V-O distances in good agreement with those predicted. We find it important to include multiple scattering in the fits of our EXAFS data otherwise spurious V-Fe distances near 2.8 Å result which may be incorrectly attributed to edge-sharing complexes. We find no evidence for monodentate complexes; this agrees with predicted high energies of such complexes. Having identified the Fe2O2V(OH)2+ and Fe2O2VO(OH)0 surface complexes, we are able to fit the experimental vanadium(V) adsorption data to the reactions

2FeOH2++VO2+=Fe2O2V(OH)2++2H+

and
2FeOH+HVO42−=Fe2O2VO(OH)0+2OH−

We also determined the first acid dissociation constant of the Fe2O2VO2H2+ surface complex.
Fits of sorption edges to surface complexation models are ambiguous. This is one of the first studies to provide a surface complexation model of sorption edges that is consistent with both spectroscopic and quantum mechanical constraints.

Item Type: Article
ISSNs: 0016-7037 (print)
Related URLs:
Subjects: Q Science > QE Geology
Q Science > QD Chemistry
Divisions: University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
ePrint ID: 41811
Date Deposited: 05 Oct 2006
Last Modified: 27 Mar 2014 18:26
URI: http://eprints.soton.ac.uk/id/eprint/41811

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