Two-dimensional (2D) metal-organic frameworks (MOFs) is attractive filler in mixed matrix membranes (MMMs) due to the high aspect ratio and contact opportunity at the filler-polymer interface. However, their oriented alignment in a favorable direction in polymer matrix remains a challenge to fully play the functions from nanosheets. In addition, synthesizing MOFs in the form of freestanding nanosheets has proved challenging. Herein, to our best knowledge, for the first time, we report the facile synthesis of KAUST-7-NH2 nanosheet with one-dimensional channels and an aspect ratio greater than 30. As an anion-pillared ultramicroporous material, KAUST-7-NH2 has 1D channels that are accessible to only relatively small gas molecules (e.g., He, H2, and CO2). The nanosheets are incorporated and aligned in the 6FDA-DAM polymer matrix under the shear force to fully exploit the channel properties of KAUST-7-NH2 with a filler loading up to 50 wt.%. The highly CO2 adsorption and CH4 rejection properties of the (001)-oriented KAUST-7-NH2 nanosheets-based MMMs coupled with the favorable interaction at the filler-polymer interface contribute to the excellent CO2/CH4 separation performance. The resultant membranes show CO2/CH4 selectivity with 66.2% enhancement (surpassed 2008 Robeson upper bound), anti-plasticization up to 17 bar, and long-term stability up to 240 h indicating its good potential for natural gas treatment.

Aligned metal-organic framework nanosheets in mixed-matrix membranes for highly selective CO2/CH4 separation

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