Accessibility and Ion Exchange Stoichiometry of Ionized Carboxylic Groups in the Active Layer of FT30 Reverse Osmosis Membrane

详细信息    查看全文

• 作者：Orlando Coronell ; Benito J. Mariñ ; as ; David G. Cahill
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：July 1, 2009
• 年：2009
• 卷：43
• 期：13
• 页码：5042-5048
• 全文大小：400K
• 年卷期：v.43,no.13(July 1, 2009)
• ISSN：1520-5851

文摘

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.