Tortuous mixed matrix membranes: A subtle balance between microporosity and compatibility

Machiel van Essen, Raymond Thür, Menno Houben, Ivo F.J. Vankelecom, Zandrie Borneman, Kitty Nijmeijer (Corresponding author)

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Abstract

In this work, the effectiveness of metal-organic frameworks (MOFs) with sheet-like morphologies was assessed as function of the MOF microporosity and MOF-matrix compatibility. Zeolitic imidazolate frameworks (ZIFs, a MOF subclass) with sheet-like/platelet morphologies were incorporated in Matrimid/PBI matrices resulting in mixed matrix membranes (MMMs). The ZIFs were either permeable (ZIF-301) or impermeable (ZIF-95X) for gases with a kinetic diameter bigger than or equal to the kinetic diameter of CO2. Additionally, MMMs containing impermeable graphene nanosheets were fabricated as reference to confirm the ZIF-95X impermeability. The MMMs containing the ZIF-301 nanoplatelets showed enhanced CO2 permeabilities. Analysis of the N2 and CO2 solubility and diffusivity showed that this permeable additive enhances the solubility of both gases, but only increases the N2 diffusivity through the ZIF-301 MMM. This signified that for MMMs with sheet-like MOFs the MOF micropore volume should only be accessible for one gas such that the sheet-like morphology effectively increases the tortuosity for the other species. Contrarily, the MMMs containing impermeable ZIF-95X and graphene showed declined MMM separation performances. Analysis of the N2 and CO2 diffusivities showed the presence of defective interfaces in these MMMs and proved that an increased tortuosity is only effective if the additive-matrix interface is defect free.

Original languageEnglish
Article number119517
Number of pages10
JournalJournal of Membrane Science
Volume635
DOIs
Publication statusPublished - 1 Oct 2021

Bibliographical note

Funding Information:
This work is part of the research program ‘Fuel feedstock production by a combined approach of controlled plasma conversion and membrane separation’ with project number 13584, which is partly financed by the Dutch Research Council ( NWO ). R.T. acknowledges FWO Vlaanderen for a SB PhD grant (1S63317 N).

Keywords

  • CO2-Based separations
  • Mixed matrix membranes
  • Sheet-like and platelet additives
  • Zeolitic imidazolate frameworks

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