Ionization behavior, stoichiometry of association, and accessibility of functional groups in the active layers of reverse osmosis and nanofiltration membranes

Orlando Coronell, Mari I. González, Benito J. Mariñas, David G. Cahill

Research output: Contribution to journalArticle

Abstract

We characterized the fully aromatic polyamide (PA) active layers of six commercial reverse osmosis (RO) and nanofiltration (NF) membranes and found that in contrast to their similar elemental composition, total concentration of functional groups, and degree of polymerization, the ionization behavior and spatial distribution of carboxylic (R-COOH) groups within the active layers can be significantly different. We also studied the steric effects experienced by barium ion (Ba2+) in the active layers by determining the fraction of carboxylate (R-COO-) groups accessible to Ba2+; such fraction, referred to as the accessibility ratio (AR), was found to vary within the range AR = 0.40-0.81, and to be generally independent of external solution pH. Additionally, we studied an NF membrane with a sulfonated polyethersulfone (SPES) active layer, and found that the concentration of sulfonate (R-SO 3-) groups in the active layer was 1.67 M, independent of external solution pH and approximately three times higher than the maximum concentration (≈0.45 ± 0.25 M) of R-COO- groups in PA active layers. The R-SO3- groups were found to be highly accessible to Ba2+ (AR = 0.95 ± 0.01).

Original languageEnglish (US)
Pages (from-to)6808-6814
Number of pages7
JournalEnvironmental Science and Technology
Volume44
Issue number17
DOIs
StatePublished - Sep 1 2010

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Nanofiltration membranes
Osmosis membranes
active layer
Nylons
Reverse osmosis
stoichiometry
Stoichiometry
accessibility
Functional groups
functional group
Ionization
ionization
Association reactions
membrane
Barium
Spatial distribution
Polymerization
Ions
Chemical analysis
sulfonate

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

Cite this

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title = "Ionization behavior, stoichiometry of association, and accessibility of functional groups in the active layers of reverse osmosis and nanofiltration membranes",
abstract = "We characterized the fully aromatic polyamide (PA) active layers of six commercial reverse osmosis (RO) and nanofiltration (NF) membranes and found that in contrast to their similar elemental composition, total concentration of functional groups, and degree of polymerization, the ionization behavior and spatial distribution of carboxylic (R-COOH) groups within the active layers can be significantly different. We also studied the steric effects experienced by barium ion (Ba2+) in the active layers by determining the fraction of carboxylate (R-COO-) groups accessible to Ba2+; such fraction, referred to as the accessibility ratio (AR), was found to vary within the range AR = 0.40-0.81, and to be generally independent of external solution pH. Additionally, we studied an NF membrane with a sulfonated polyethersulfone (SPES) active layer, and found that the concentration of sulfonate (R-SO 3-) groups in the active layer was 1.67 M, independent of external solution pH and approximately three times higher than the maximum concentration (≈0.45 ± 0.25 M) of R-COO- groups in PA active layers. The R-SO3- groups were found to be highly accessible to Ba2+ (AR = 0.95 ± 0.01).",
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AU - Mariñas, Benito J.

AU - Cahill, David G.

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