Quantification of functional groups and modeling of their ionization behavior in the active layer of FT30 reverse osmosis membrane

Orlando Coronell, Benito Jose Marinas, Xijing Zhang, David G Cahill

Research output: Contribution to journalArticle

Abstract

A new experimental approach was developed to measure the concentration of charged functional groups (FGs) in the active layer of thin-film composite reverse osmosis (RO) and nanofiltration (NF) membranes as a function of solution pH. FT30 RO membrane, with a fully aromatic polyamide (PA) active layer sandwiched between a polysulfone support and a coating layer, was used. The experiments consisted of saturating charged FGs with heavy ion probes, and determining the ion probe concentration by Rutherford backscattering spectrometry (RBS). Deprotonated carboxylic groups were saturated with Ag +, and protonated amine groups with WO42-. The ionization behavior of carboxylic and amine groups was modeled based on acid-base equilibrium theory. While the ionization behavior of amine groups was satisfactorily described by one dissociation constant (pKa = 4.74), two pKa values (5.23 and 8.97) were necessary to describe the titration curve of carboxylic groups. These results were consistent with the bimodal pore size distribution (PSD) of FT30 active layer reported in the literature. The calculated total concentrations of carboxylic and amine groups in the active layer of the FT30 RO membrane studied were 0.432 and 0.036 M, respectively, and the isoelectric point (IEP) was 4.7. The total concentration of carboxylic and amine groups revealed that the degree of cross-linking of the PA active layer of the FT30 RO membrane studied was 94%.

Original languageEnglish (US)
Pages (from-to)5260-5266
Number of pages7
JournalEnvironmental Science and Technology
Volume42
Issue number14
DOIs
StatePublished - Jul 15 2008

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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