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Interaction-based ion selectivity exhibited by self-assembled, cross-linked zwitterionic copolymer membranes.
Samuel J Lounder1, Ayse Asatekin2
1Department of Chemical and Biological Engineering, Tufts University, Medford, MA 02155.
Summary
Advanced zwitterionic copolymer membranes offer precise ion selectivity for water purification. These membranes demonstrate tunable salt permeability, enabling efficient separation of ions like chloride and fluoride.
Area of Science:
- Materials Science
- Chemical Engineering
- Environmental Science
Background:
- Advanced ion-selective membranes are crucial for water purification and resource recovery.
- Existing membranes often lack the precise control needed for complex separations.
Purpose of the Study:
- To investigate the ion separation capabilities of cross-linked zwitterionic copolymer membranes.
- To understand the role of zwitterion-anion interactions in controlling ion transport.
Main Methods:
- Fabrication of self-assembled zwitterionic copolymer membranes with subnanometer nanochannels.
- Experimental measurement of salt permeabilities for various salts (NaClO4, NaI, NaBr, NaCl, NaF, Na2SO4).
- Modeling of salt flux using a 1D transport model based on Maxwell-Stefan equations.
Main Results:
- Demonstrated salt permeabilities spanning three orders of magnitude, controlled by zwitterion-anion interactions.
- Identified diffusion as the dominant transport mode for 1:1 sodium salts.
- Achieved ultrahigh chloride/fluoride permselectivity (P_Cl/P_F = 24) due to specific zwitterion-ion interactions.
Conclusions:
- Cross-linked zwitterionic copolymer membranes exhibit tunable ion selectivity based on specific interactions.
- These membranes are effective for selective ion passage and retention, such as high chloride passage and fluoride retention from saline mixtures.
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