Macroscopic and microscopic gas diffusivity measurements for PIM-COOH/UiO-66-NH2 composite membranes
Name
2025_WW_Gas diffusion manuscript_r1_v2.pdf
Description
Accepted version
Size
1.95 MB
Format
Adobe PDF
Checksum (MD5)
7a4dfa0d7cfd5565e4235a2800064688
Name
2025_WW_Gas diffusion SI_r1_v2.pdf
Description
Supporting information
Size
1.58 MB
Format
Adobe PDF
Checksum (MD5)
46d36df1898dd300d3abc1d7ddbafcd1
Author(s)
Wu, Wan-Ni
Boloki, Omar
Vasenkov, Sergey
Smith, Zachary P
Date Issued
August 2025
Journal
Journal of Membrane Science
Publisher
Elsevier BV
Version
Author's final manuscript
Abstract
Mixed-matrix membranes (MMMs) have been heavily studied due to their compelling performance in gas separation applications. Direct measurement of gas diffusivities in MMMs is essential for constructing reliable transport models, but this measurement remains challenging. This study investigates CH4 and CO2 diffusion in PIM-COOH and a PIM-COOH/UiO-66-NH2 MMM with 30 vol% MOF loading, employing 13C pulsed field gradient nuclear magnetic resonance (PFG NMR) and various macroscopic techniques like the time-lag method and sorption analysis. PFG NMR revealed uniform transport properties across pure PIM-COOH films and MMMs on micrometer scales, indicating well-integrated structures without significant defects or MOF clustering. Macroscopically-measured diffusivities derived from the time-lag method showed strong pressure dependence due to the limitations of applying a linear sorption model to microporous materials. In contrast, corrected secant diffusivities aligned closely with self-diffusivities from PFG NMR and exhibited minimal pressure dependence. Application of another common analysis approach, the use of transient sorption experiments, yielded diffusivities with large uncertainties. This comparative study presents the range of diffusivities found by applying various techniques to capture transport and self-diffusivities, highlighting the need to carefully validate model assumptions for diffusion measurements in microporous polymer and MOF-based membrane materials. Of note, this study highlights the strength of PFG NMR in directly probing microscopic transport.
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Creative Commons Attribution-NonCommercial-NoDerivatives
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DOI of Published Version
https://doi.org/10.1016/j.memsci.2025.124246
