Engineering Li/Na selectivity in 12-Crown-4–functionalized polymer membranes

Lithium is a key ingredient in batteries, which are integral components of next-generation automobiles, airplanes, grid energy storage, and electronic devices. Unfortunately, lithium extraction from natural sources is laborious, slow, and costly, motivating the search for more efficient isolation techniques. While polymeric membranes could reduce the cost of lithium recovery, current membrane materials lack sufficient lithium-ion selectivity. To address this challenge, we introduce a class of polymeric membranes that incorporate ion binding sites, which significantly increases the transport selectivity of LiCl over NaCl. These studies provide guidelines and practical considerations for incorporating specific interactants into polymers that mediate selective ion transport. Lithium is widely used in contemporary energy applications, but its isolation from natural reserves is plagued by time-consuming and costly processes. While polymer membranes could, in principle, circumvent these challenges by efficiently extracting lithium from aqueous solutions, they usually exhibit poor ion-specific selectivity. Toward this end, we have incorporated host–guest interactions into a tunable polynorbornene network by copolymerizing 1) 12-crown-4 ligands to impart ion selectivity, 2) poly(ethylene oxide) side chains to control water content, and 3) a crosslinker to form robust solids at room temperature. Single salt transport measurements indicate these materials exhibit unprecedented reverse permeability selectivity (~2.3) for LiCl over NaCl—the highest documented to date for a dense, water-swollen polymer. As demonstrated by molecular dynamics simulations, this behavior originates from the ability of 12-crown-4 to bind Na+ ions more strongly than Li+ in an aqueous environment, which reduces Na+ mobility (relative to Li+) and offsets the increase in Na+ solubility due to binding with crown ethers. Under mixed salt conditions, 12-crown-4 functionalized membranes showed identical solubility selectivity relative to single salt conditions; however, the permeability and diffusivity selectivity of LiCl over NaCl decreased, presumably due to flux coupling. These results reveal insights for designing advanced membranes with solute-specific selectivity by utilizing host–guest interactions. All study data are included in the article and/or SI Appendix.

• Record URL:
  http://dx.doi.org/10.1073/pnas.2022197118
• Record URL:
  http://www.pnas.org/content/118/37/e2022197118.abstract
• Authors:
  • Warnock, Samuel J
  • Sujanani, Rahul
  • Zofchak, Everett S
  • Zhao, Shou
  • Dilenschneider, Theodore J
  • Hanson, Kalin G
  • Mukherjee, Sanjoy
  • Ganesan, Venkat
  • Freeman, Benny D
  • Abu-Omar, Mahdi M
  • Bates, Christopher M
• Publication Date: 2021-9-24

Language

• English

Media Info

• Media Type: Web
• Features: Figures; References;
• Pagination: e2022197118
• Serial:
  • Proceedings of the National Academy of Sciences
  • Volume: 118
  • Issue Number: 37
  • Publisher: National Academy of Sciences
  • EISSN: 1091-6490
  • Serial URL: http://www.pnas.org/

Subject/Index Terms

• TRT Terms: Boundary layer flow; Copolymers; Lithium chloride; Materials by shape or form; Permeability; Sodium chloride
• Subject Areas: Energy; Materials; Transportation (General);

Filing Info

• Accession Number: 01782744
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 24 2021 10:20AM