Bidirectional Diffusion of Ammonium and Sodium Cations in Forward Osmosis: Role of Membrane Active Layer Surface Chemistry and Charge.
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| Title: | Bidirectional Diffusion of Ammonium and Sodium Cations in Forward Osmosis: Role of Membrane Active Layer Surface Chemistry and Charge. |
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| Authors: | Xinglin Lu1, Chanhee Boo2, Jun Ma1 majun@hit.edu.cn, Elimelech, Menachem2 menachem.elimelech@yale.edu |
| Source: | Environmental Science & Technology. 12/16/2014, Vol. 48 Issue 24, p14369-14376. 8p. |
| Subjects: | Ion transport (Biology), Semivolatile organic compounds analysis, Ammonium ions, Water quality, Sodium ions, Osmosis, Membrane selectivity (Technology), Surface chemistry |
| Abstract: | Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4+) and sodium (Na+) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also earned out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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