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submitted on 15.07.2019 and posted on 16.07.2019by 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.