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Reducing the Pore Size of Covalent Organic Frameworks in Thin-Film Composite Membranes Enhances Solute Rejection

submitted on 15.07.2019 and posted on 16.07.2019 by Amanda Corcos, Gabrielle Levato, Zhiwei Jiang, Austin Evans, Andrew Livingston, Benito Marinas, William Dichtel
Three imine-linked covalent organic framework (COF) films are incorporated as active layers into separate thin-film composite (TFC) membranes and tested for their ability to reject an organic pollutant surrogate and salt from water. The synthesized membranes consist of a polyacrylonitrile (PAN) membrane supporting a TAPB-PDA-H, TAPB-PDA-Me, or TAPB-PDA-Et COF thin film. The latter two COFs direct six methyl and ethyl substituents per tiled hexagon into the pores, respectively, while maintaining the same topology across the series. These substituents decrease the effective pore size of the COF compared to the parent TAPB-PDA-H COF. The TAPB-PDA-Me membrane rejects Rhodamine-WT (R-WT) dye and NaCl better than the TAPB-PDA-H membrane, and the TAPB-PDA-Et membrane exhibits the best rejection overall. The solution-diffusion model used to analyze this permeation behavior indicates that there is a systematic difference in rejection as subsequent pendant groups are added to the interior of the COF pore. These findings demonstrate the concept of tuning the selectivity of COF membranes by systematically reducing the effective pore size within a given topology.


NSF CBET-1706219

NSF DGE-1324585

DOE DE-AC02-05CH11231



Email Address of Submitting Author


Northwestern University



ORCID For Submitting Author


Declaration of Conflict of Interest