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Gas Permeation Through Single-Crystal ZIF-8 Membranes

submitted on 10.01.2019, 13:11 and posted on 10.01.2019, 17:12 by Chen Chen, Aydin Ozcan, A. Ozgur Yazaydin, Bradley P. Ladewig
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.


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Karlsruhe Institute of Technology



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Declaration of Conflict of Interest

The authors declare no conflict of interest.