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Per Persson. Photo.

Per Persson

Director

Per Persson. Photo.

Adsorption of monocarboxylates at the water/goethite interface: The importance of hydrogen bonding

Author

  • K. Noren
  • Per Persson

Summary, in English

The adsorption of monocarboxylates (acetate, benzoate, and cyclohexanecarboxylate) at the water/goethite interface was studied as a function of pH and ionic strength by means of quantitative adsorption measurements and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra were obtained of suspensions prepared in both H2O and D2O. In order to identify the number of predominating surface complexes and to improve the resolution of overlapping peaks the ATR-FTIR spectra were subjected to a 2D correlation spectroscopic analysis. The adsorption envelopes of acetate, benzoate, and cyclohexanecarboxylate are similar and depend strongly on pH and ionic strength, but the pH dependence is also correlated to the slightly different pK(a) values of the monocarboxylic acids. At the molecular level, the ATR-FTIR spectroscopic results reveal two surface complexes: one solvent-surface hydration-separated ion pair and one surface hydration-shared ion pair. The former predominates at circumneutral pH values while the latter forms mainly in the acidic pH range. We find no evidence for direct inner-sphere coordination between the carboxylic oxygens and the Fe(III) ions present at the surface. The identification of surface hydration-shared ion pairs emphasizes the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes at the water/goethite interface. (C) 2007 Elsevier Ltd. All rights reserved.

Publishing year

2007

Language

English

Pages

5717-5730

Publication/Series

Geochimica et Cosmochimica Acta

Volume

71

Document type

Journal article

Publisher

Elsevier

Topic

  • Earth and Related Environmental Sciences

Keywords

  • transform infrared-spectroscopy
  • outer-sphere adsorption
  • mineral/water
  • interfaces
  • organic-matter
  • carboxylic-acids
  • aqueous-solution
  • surface
  • complexation
  • neutron-diffraction
  • electric-fields
  • atr-ftir

Status

Published

ISBN/ISSN/Other

  • ISSN: 0016-7037