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

Author:
  • K. Noren
  • Per Persson
Publishing year: 2007
Language: English
Pages: 5717-5730
Publication/Series: Geochimica et Cosmochimica Acta
Volume: 71
Document type: Journal article
Publisher: Elsevier

Abstract 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.

Keywords

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

Other

Published
  • ISSN: 0016-7037
Per Persson
E-mail: per [dot] persson [at] biol [dot] lu [dot] se

Professor

MEMEG

+46 46 222 17 96

+46 70 266 38 79

E-C350

50

Professor

Centre for Environmental and Climate Research (CEC)

+46 46 222 17 96

+46 70 266 38 79

D350

Ekologihuset, Sölvegatan 37, Lund

50