Restricting Lattice Flexibility in Polycrystalline Metal–Organic Framework Membranes for Carbon Capture

Abstract

Although polycrystalline metal‐organic framework (MOF) membranes offer several advantages over other nanoporous membranes, thus far they have not yielded good CO2 separation performance, crucial for energy‐efficient carbon capture. ZIF‐8, one of the most popular MOFs, has a crystallographically determined pore aperture of 0.34 nm, ideal for CO2/N2 and CO2/CH4 separation; however, its flexible lattice restricts the corresponding separation selectivities to below 5. A novel postsynthetic rapid heat treatment (RHT), implemented in a few seconds at 360 °C, which drastically improves the carbon capture performance of the ZIF‐8 membranes, is reported. Lattice stiffening is confirmed by the appearance of a temperature‐activated transport, attributed to a stronger interaction of gas molecules with the pore aperture, with activation energy increasing with the molecular size (CH4 > CO2 > H2). Unprecedented CO2/CH4, CO2/N2, and H2/CH4 selectivities exceeding 30, 30, and 175, respectively, and complete blockage of C3H6, are achieved. Spectroscopic and X‐ray diffraction studies confirm that while the coordination environment and crystallinity are unaffected, lattice distortion and strain are incorporated in the ZIF‐8 lattice, increasing the lattice stiffness. Overall, RHT treatment is a facile and versatile technique that can vastly improve the gas‐separation performance of the MOF membranes.

Ultrafast Semi‐Solid Processing of Highly Durable ZIF‐8 Membranes for Propylene/Propane Separation

“…The distinctive phenomenon could be elucidated in terms of enhanced adsorption of C 3 H 6 which hinders the C 3 H 8 transport through ZIF‐8 membrane. On the other side, the as‐synthesized ZIF‐8 membrane possibly possesses rigid framework [7b, 25] . Both the C 3 H 6 and C 3 H 8 permeance decreases with increasing feed pressure, which could be ascribed to non‐linear adsorption isotherms of C 3 H 6 and C 3 H 8 on ZIF‐8 [10a] .…”

Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal–organic framework

“…Metal-organic frameworks are a class of chemically-robust, porous, and oen rigid materials, composed of metal ions or clusters connected by bridging organic linkers. [1][2][3][4] The physical and chemical properties of these materials are highly tunable based on choice of metal and linker, and thus metal-organic frameworks have been proposed for a wealth of applications, [5][6][7][8][9] including catalysis, [10][11][12][13][14][15] sensing, [16][17][18] carbon capture, [19][20][21][22][23] gas separations, [24][25][26] and gas storage. [27][28][29][30][31] Metal-organic frameworks have attracted particular interest as candidate gas storage materials for H 2 and CH 4 that could enable more efficient use of these energy carriers as cleaner fuel alternatives.…”

ZIF‐8 Membrane Separation Performance Tuning by Vapor Phase Ligand Treatment

“…Recently, Babu et al reported the stiffening of ZIF-8 by rapid heat treatment (360 ˚C, few seconds) showing improved CO2/CH4, and CO2/N2 separation performance. [21] Thermal treatment (180 ˚C, 40 min) of LIPS-ZIF-8 in the absence of 2abIm does not result in the shift of the molecular level cut-off to smaller molecules clearly indicating the role of 2abIm linker. It is also possible that the incorporation of the amine group (-NH2) from 2abIm could further promote CO2/N2 and CO2/CH4 selectivity by enhanced CO2 adsorption.…”