Accessibility and ion exchange stoichiometry of ionized carboxylic groups in the active layer of FT30 reverse osmosis membrane

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Abstract

We have experimentally determined the concentration of Ba2+ that associates with the accessible ionized R-COO- groups in the polyamide active layer of the FT30 reverse osmosis membrane in the pH range 3.42-10.30. Ba2+ concentrations in the active layer ([Ba 2+]) were measured using the ion-probing/Rutherford backscattering spectrometry procedure reported in our previous work. We found that at all but the lowest experimental pH 3.42, [Ba2+] was lower than the corresponding total concentrations of R-COO- groups; their difference was consistent with steric and charge effects determining the accessibility and association, respectively, of Ba2+ to R-COO- groups. Accordingly, we propose two descriptors, the accessibility ratio (AR) and the neutralization number (NN), to account for the observed difference. AR, the fraction of R-COO- groups accessible to Ba2+ ions, and NN, the average number of RsCOO- groups neutralized per Ba2+ ion, were determined experimentally performing Ag+-Ba2+ ion-exchange tests. The resulting AR = 0.40 indicated that on average only 40% of ionizable carboxylic groups were accessible to Ba2+. [Ba 2+] values calculated using R-COO- concentrations and the AR and NN concepts were in agreement with experimental [Ba2+] results.

Original languageEnglish (US)
Pages (from-to)5042-5048
Number of pages7
JournalEnvironmental Science and Technology
Volume43
Issue number13
DOIs
StatePublished - Jul 1 2009

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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