title: Accessibility and ion exchange stoichiometry of ionized carboxylic groups in the active layer of FT30 reverse osmosis membrane.
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 ([Ba2+]) 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 R-COO- 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+. [Ba2+] values calculated using R-COO- concentrations and the AR and NN concepts were in agreement with experimental [Ba2+] results.
authors: Department of Civil and Environmental Engineering, Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors: Orlando
authors: O
authors: Coronell
authors: Benito I
authors: BI
authors: Mariñas
authors: David G
authors: DG
authors: Cahill
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D005374:Filtration / Q000295:instrumentation / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D009757:Nylons / Q000737:chemistry; D009995:Osmosis; D011108:Polymers / Q000737:chemistry; D013450:Sulfones / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods
chemical_list: D002264:Carboxylic Acids; D007477:Ions; D009757:Nylons; D011108:Polymers; D013450:Sulfones; D014874:Water Pollutants, Chemical; D014867:Water; C017662:polysulfone P 1700; D002244:Carbon