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Gas Permeation Through Single-Crystal ZIF-8 Membranes

preprint
submitted on 10.01.2019 and posted on 10.01.2019 by Chen Chen, Aydin Ozcan, A. Ozgur Yazaydin, Bradley P. Ladewig
Abstract
Grain boundaries are an unavoidable microstructural feature in intergrown polycrystalline metal-organic framework (MOF) membranes. They have been suspected to be less size-selective than a MOF’s micropores, resulting in suboptimal separation performances – a speculation recently confirmed by transmission electron microscopy of MOF ZIF-8. Single-crystal membranes, without grain boundaries, should confine mass transport to micropores and reflect the intrinsic selectivity of the porous material. Here, we demonstrate the feasibility of fabricating single-crystal MOF membranes and directly measuring gas permeability through such a membrane using ZIF-8 as an exemplary MOF. Our single-crystal ZIF-8 membranes achieved ideal selectivities up to 28.9, 10.0, 40.1 and 3.6 for gas pairs CO2/N2, CO2/CH4, He/CH4 and CH4/N2 respectively, much higher than or reversely selective to over 20 polycrystalline ZIF-8 membranes, unequivocally proving the non-selectivity of grain boundaries. The permeability trend obtained in single-crystal membranes aligned with a force field that had been validated against multiple empirical adsorption isotherms.

History

Email Address of Submitting Author

bradley.ladewig@kit.edu

Institution

Karlsruhe Institute of Technology

Country

Germany

ORCID For Submitting Author

0000-0002-2135-1913

Declaration of Conflict of Interest

The authors declare no conflict of interest.

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