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Electrochemical adsorption offers a promising approach for the separation of monovalent cations, which is an important but challenging subject in separation science. However, progress in this area has been hampered by the lack of suitable materials with effective ion selectivity. In this work, we present the synthesis of covalent organic frameworks (COFs) functionalized with a series of crown ethers (NCx-TAB-COFs, x donate 12, 15, 18, indicating the size of crown ether) for the efficient and highly selective electrochemical capture of monovalent cations. In our design, crown ether moieties act as confinement sites, imparting high selectivity for different monovalent cations depending on the cavity dimensions of the crown ether present. COFs electrodes prepared using the novel crown-COFs exhibit superior performance for the selective sequestration of monovalent (alkali metal) cations. Notably, 18-crown-6 ether-substituted COF (NC18-TAB-COF) shows a remarkable selectivity (14.26) for K+ over Na+ and a substantial Rb+/Na+ selectivity of 22.4. Furthermore, NCx-TAB-COFs maintain their remarkable selectivity and capacity under mixed-cation conditions. Density functional theory calculations and molecular dynamics simulations suggest that the unexpectedly high selectivity for larger cations is likely due to diverse binding modes in conjunction with the porous structure of the COFs. Given their lower dehydration-free energies and smaller hydrodynamic radii, K+, Rb+, and Cs+ more readily permeate the confined channels of COFs. In contrast, Na+ and Li+, with higher dehydration-free energies and hydrodynamic radii, diffuse into the NCx-TAB-COFs structure at a much slower rate and are bound predominantly to the surfaces of the COFs.

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  This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © 2025 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/jacs.4c16346.

Keyword: Crown ether, Capacitive deionization, Covalent organic framework

Date published: 2025-04-16

Publisher: American Chemical Society (ACS)

Journal:

• Journal of the American Chemical Society (ISSN: 00027863) vol. 147 issue. 15 p. 12460-12468

Funding:

• Ministry of Education, Culture, Sports, Science and Technology
• Exploratory Research for Advanced Technology JPMJER2003

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5847

First published URL: https://doi.org/10.1021/jacs.4c16346

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Updated at: 2026-02-16 18:31:21 +0900

Published on MDR: 2026-04-04 08:24:44 +0900