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Molecular Structures of Citrate and Tricarballylate Adsorbed on alpha-FeOOH Particles in Aqueous Suspensions

Lindegren, Malin; Loring, John S. and Persson, Per LU (2009) In Langmuir 25. p.10639-10647
Abstract
In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto alpha-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ. infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation... (More)
In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto alpha-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ. infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation spectroscopy formalism that aided the resolution of pH-dependent spectral features. This has enabled the detection of two previously unidentified citrate-goethite surface complexes: one protonated species at low pH, and one inner sphere complex prevailing at high pH and coordinated via a combination of hydroxyl and carboxylate groups. In addition, ail inner sphere complex involving only carboxylate coordination predominating at low pH and an outer sphere complex existing in the circumneutral pH region were identified. The behavior of tricarballylate parallels that of citrate, except no inner sphere surface complex is formed at high pH values, which is in accordance with the lack of an alpha-hydroxyl group. The comparison between citrate and tricarballylate reinforces previous observations showing that inner sphere surface complexes of pure carboxylates at water-iron oxide interfaces are suppressed at high pH values, where outer sphere species are relatively more predominant. It also shows that significant amounts of inner sphere surface complexes of carboxylates; only seem to form in the basic pH region when the ligands contain complementary functional groups, such as the hydroxyl or amine groups. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
25
pages
10639 - 10647
publisher
The American Chemical Society
external identifiers
  • scopus:70349923756
ISSN
0743-7463
DOI
10.1021/la900852p
language
English
LU publication?
no
id
531053e5-5bd2-4374-a6ef-ddb0ca8dfc98 (old id 4332372)
date added to LUP
2014-03-04 09:47:03
date last changed
2017-11-19 03:31:48
@article{531053e5-5bd2-4374-a6ef-ddb0ca8dfc98,
  abstract     = {In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto alpha-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ. infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation spectroscopy formalism that aided the resolution of pH-dependent spectral features. This has enabled the detection of two previously unidentified citrate-goethite surface complexes: one protonated species at low pH, and one inner sphere complex prevailing at high pH and coordinated via a combination of hydroxyl and carboxylate groups. In addition, ail inner sphere complex involving only carboxylate coordination predominating at low pH and an outer sphere complex existing in the circumneutral pH region were identified. The behavior of tricarballylate parallels that of citrate, except no inner sphere surface complex is formed at high pH values, which is in accordance with the lack of an alpha-hydroxyl group. The comparison between citrate and tricarballylate reinforces previous observations showing that inner sphere surface complexes of pure carboxylates at water-iron oxide interfaces are suppressed at high pH values, where outer sphere species are relatively more predominant. It also shows that significant amounts of inner sphere surface complexes of carboxylates; only seem to form in the basic pH region when the ligands contain complementary functional groups, such as the hydroxyl or amine groups.},
  author       = {Lindegren, Malin and Loring, John S. and Persson, Per},
  issn         = {0743-7463},
  language     = {eng},
  pages        = {10639--10647},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Molecular Structures of Citrate and Tricarballylate Adsorbed on alpha-FeOOH Particles in Aqueous Suspensions},
  url          = {http://dx.doi.org/10.1021/la900852p},
  volume       = {25},
  year         = {2009},
}