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Quantitative adsorption and local structures of Gallium(III) at the water-alpha-FeOOH interface

Persson, Per LU ; Zivkovic, K. and Sjoberg, S. (2006) In Langmuir 22. p.2096-2104
Abstract
The adsorption of Ga(III) at the water-alpha-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3-11 and surface coverages of 0.9-3.2 mu mol/m(2), Ga(III) was found to adsorb strongly to alpha-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)(4)(-) than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water-a-FeOOH interface, with practically no structural variations as a function of pH or total gallium... (More)
The adsorption of Ga(III) at the water-alpha-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3-11 and surface coverages of 0.9-3.2 mu mol/m(2), Ga(III) was found to adsorb strongly to alpha-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)(4)(-) than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water-a-FeOOH interface, with practically no structural variations as a function of pH or total gallium concentration. Analysis of the first coordination shell required an anharmonic model indicating a distorted geometry of the GaO6 octahedra, with mean Ga-O distances at 1.96-1.98 angstrom. A method based on the continuous Cauchy wavelet transforms (CCWT) was used to identify backscattering atoms in the higher coordination shells. This analysis indicated predominately Fe backscattering, and the quantitative data fitting resulted in three Ga-Fe paths at 3.05, 3.2, and 3.55 angstrom, which correspond to two edge-sharing and one corner-sharing linkage, respectively. The collective results from EXAFS spectroscopy showed that Ga(III) adsorbs to Fe equivalent sites at the surface alpha-FeOOH as an extension of the rows of Fe octahedra in the bulk structure. This interpretation was further corroborated by a Ga-Fe-Fe multiple scattering path at 6.13 A. The quantitative adsorption and proton data were modeled using a surface complexation formalism based on a 1 pK(a) constant capacitance model. In agreement with the EXAFS results, the model obtained included one predominating surface complex with the stoichiometry =-FeOGa(OH)(2)(-0.5) and the stability constant log beta(intr.) = -2.55 +/- 0.04 (equivalent to-FeOH-0.5 + Ga3+ + 2H(2)O equivalent to FeOGa(OH)(2)(-0.5) + 3H(+)). (Less)
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author
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type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
22
pages
2096 - 2104
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:33644884181
ISSN
0743-7463
DOI
10.1021/la052555j
language
English
LU publication?
no
additional info
5
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b087f058-dade-4b3f-9cad-b3a3004af5a1 (old id 4332476)
date added to LUP
2016-04-01 11:48:50
date last changed
2020-02-12 03:46:20
@article{b087f058-dade-4b3f-9cad-b3a3004af5a1,
  abstract     = {The adsorption of Ga(III) at the water-alpha-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3-11 and surface coverages of 0.9-3.2 mu mol/m(2), Ga(III) was found to adsorb strongly to alpha-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)(4)(-) than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water-a-FeOOH interface, with practically no structural variations as a function of pH or total gallium concentration. Analysis of the first coordination shell required an anharmonic model indicating a distorted geometry of the GaO6 octahedra, with mean Ga-O distances at 1.96-1.98 angstrom. A method based on the continuous Cauchy wavelet transforms (CCWT) was used to identify backscattering atoms in the higher coordination shells. This analysis indicated predominately Fe backscattering, and the quantitative data fitting resulted in three Ga-Fe paths at 3.05, 3.2, and 3.55 angstrom, which correspond to two edge-sharing and one corner-sharing linkage, respectively. The collective results from EXAFS spectroscopy showed that Ga(III) adsorbs to Fe equivalent sites at the surface alpha-FeOOH as an extension of the rows of Fe octahedra in the bulk structure. This interpretation was further corroborated by a Ga-Fe-Fe multiple scattering path at 6.13 A. The quantitative adsorption and proton data were modeled using a surface complexation formalism based on a 1 pK(a) constant capacitance model. In agreement with the EXAFS results, the model obtained included one predominating surface complex with the stoichiometry =-FeOGa(OH)(2)(-0.5) and the stability constant log beta(intr.) = -2.55 +/- 0.04 (equivalent to-FeOH-0.5 + Ga3+ + 2H(2)O equivalent to FeOGa(OH)(2)(-0.5) + 3H(+)).},
  author       = {Persson, Per and Zivkovic, K. and Sjoberg, S.},
  issn         = {0743-7463},
  language     = {eng},
  pages        = {2096--2104},
  publisher    = {The American Chemical Society (ACS)},
  series       = {Langmuir},
  title        = {Quantitative adsorption and local structures of Gallium(III) at the water-alpha-FeOOH interface},
  url          = {http://dx.doi.org/10.1021/la052555j},
  doi          = {10.1021/la052555j},
  volume       = {22},
  year         = {2006},
}