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The protonation state of small carboxylic acids at the water surface from photoelectron spectroscopy

Ottosson, Niklas; Wernersson, Erik; Soderstrom, Johan; Pokapanich, Wandared; Kaufmann, Susanna; Svensson, Svante; Persson, Ingmar; Öhrwall, Gunnar LU and Bjorneholm, Olle (2011) In Physical Chemistry Chemical Physics 13(26). p.12261-12267
Abstract
We report highly surface sensitive core-level photoelectron spectra of small carboxylic acids (formic, acetic and butyric acid) and their respective carboxylate conjugate base forms (formate, acetate and butyrate) in aqueous solution. The relative surface propensity of the carboxylic acids and carboxylates is obtained by monitoring their respective C1s signal intensities from a solution in which their bulk concentrations are equal. All the acids are found to be enriched at the surface relative to the corresponding carboxylates. By monitoring the PE signals of acetic acid and acetate as a function of total concentration, we find that the protonation of acetic acid is nearly complete in the interface layer. This is in agreement with... (More)
We report highly surface sensitive core-level photoelectron spectra of small carboxylic acids (formic, acetic and butyric acid) and their respective carboxylate conjugate base forms (formate, acetate and butyrate) in aqueous solution. The relative surface propensity of the carboxylic acids and carboxylates is obtained by monitoring their respective C1s signal intensities from a solution in which their bulk concentrations are equal. All the acids are found to be enriched at the surface relative to the corresponding carboxylates. By monitoring the PE signals of acetic acid and acetate as a function of total concentration, we find that the protonation of acetic acid is nearly complete in the interface layer. This is in agreement with literature surface tension data, from which it is inferred that the acids are enriched at the surface while (sodium) formate and acetate, but not butyrate, are depleted. For butyric acid, we conclude that the carboxylate form co-exists with the acid in the interface layer. The free energy cost of replacing an adsorbed butyric acid molecule with a butyrate ion at 1.0 M concentration is estimated to be > 5 kJ mol(-1). By comparing concentration dependent surface excess data with the evolution of the corresponding photoemission signals it is furthermore possible to draw conclusions about how the distribution of molecules that contribute to the excess is altered with bulk concentration. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Chemistry Chemical Physics
volume
13
issue
26
pages
12261 - 12267
publisher
Royal Society of Chemistry
external identifiers
  • wos:000291885300017
  • scopus:79959387375
ISSN
1463-9084
DOI
10.1039/c1cp20245f
language
English
LU publication?
yes
id
89512f8f-a00e-45cd-a56a-bfc0b508279e (old id 2036077)
date added to LUP
2011-07-26 14:10:45
date last changed
2017-10-22 04:22:58
@article{89512f8f-a00e-45cd-a56a-bfc0b508279e,
  abstract     = {We report highly surface sensitive core-level photoelectron spectra of small carboxylic acids (formic, acetic and butyric acid) and their respective carboxylate conjugate base forms (formate, acetate and butyrate) in aqueous solution. The relative surface propensity of the carboxylic acids and carboxylates is obtained by monitoring their respective C1s signal intensities from a solution in which their bulk concentrations are equal. All the acids are found to be enriched at the surface relative to the corresponding carboxylates. By monitoring the PE signals of acetic acid and acetate as a function of total concentration, we find that the protonation of acetic acid is nearly complete in the interface layer. This is in agreement with literature surface tension data, from which it is inferred that the acids are enriched at the surface while (sodium) formate and acetate, but not butyrate, are depleted. For butyric acid, we conclude that the carboxylate form co-exists with the acid in the interface layer. The free energy cost of replacing an adsorbed butyric acid molecule with a butyrate ion at 1.0 M concentration is estimated to be > 5 kJ mol(-1). By comparing concentration dependent surface excess data with the evolution of the corresponding photoemission signals it is furthermore possible to draw conclusions about how the distribution of molecules that contribute to the excess is altered with bulk concentration.},
  author       = {Ottosson, Niklas and Wernersson, Erik and Soderstrom, Johan and Pokapanich, Wandared and Kaufmann, Susanna and Svensson, Svante and Persson, Ingmar and Öhrwall, Gunnar and Bjorneholm, Olle},
  issn         = {1463-9084},
  language     = {eng},
  number       = {26},
  pages        = {12261--12267},
  publisher    = {Royal Society of Chemistry},
  series       = {Physical Chemistry Chemical Physics},
  title        = {The protonation state of small carboxylic acids at the water surface from photoelectron spectroscopy},
  url          = {http://dx.doi.org/10.1039/c1cp20245f},
  volume       = {13},
  year         = {2011},
}