Interaction-based ion selectivity exhibited by self-assembled, cross-linked zwitterionic copolymer membranes.
basic_science · Level V
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- Record sourced from PubMed, PMID 34493652.
- Also identified by DOI 10.1073/pnas.2022198118 and PMC identifier 8449329.
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Abstract
Water filtration membranes with advanced ion selectivity are urgently needed for resource recovery and the production of clean drinking water. This work investigates the separation capabilities of cross-linked zwitterionic copolymer membranes, a self-assembled membrane system featuring subnanometer zwitterionic nanochannels. We demonstrate that selective zwitterion-anion interactions simultaneously control salt partitioning and diffusivity, with the permeabilities of NaClO<sub>4</sub>, NaI, NaBr, NaCl, NaF, and Na<sub>2</sub>SO<sub>4</sub> spanning roughly three orders of magnitude over a wide range of feed concentrations. We model salt flux using a one-dimensional transport model based on the Maxwell-Stefan equations and show that diffusion is the dominant mode of transport for 1:1 sodium salts. Differences in zwitterion-Cl<sup>-</sup> and zwitterion-F<sup>-</sup> interactions granted these membranes with the ultrahigh Cl<sup>-</sup>/F<sup>-</sup> permselectivity (<i>P</i><sub><i>Cl-</i></sub><i>/P</i><sub><i>F-</i></sub> = 24), enabling high fluoride retention and high chloride passage even from saline mixtures of NaCl and NaF.