(30a) Restricting Lattice Flexibility in Polycrystalline Metal-Organic Framework Membrane for Efficient Carbon Capture

Agrawal, K. V., University of Minnesota
Babu, D., École Polytechnique Fédérale de Lausanne (EPFL)
Polycrystalline membranes based on metal-organic frameworks (MOFs) are advantageous to their nanoporous counterparts owing to a high degree of structural tunability, relatively fast crystallization kinetics, and higher reproducibility [1]. However, achieving an efficient CO2/N2 and CO2/CH4 separation, crucial for the energy-efficient carbon capture, has remained a challenge [2]. ZIF-8 possesses a crystallographically-determined pore aperture of 0.34 nm, ideal for CO2/N2 and CO2/CH4 separations. However, the lattice flexibility and the gate-opening phenomenon in ZIF-8 is a bottleneck in realizing gas-sieving, critical for the membrane-based postcombustion capture, and selectivities have remained below 5 [3]. In this presentation, I will report a novel post-synthetic treatment, which drastically improves the capture performance of the ZIF-8 films [4]. 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). High CO2/CH4, CO2/N2, and H2/CH4 selectivities of up to 32.5, 29.3, and 175, respectively, and complete blockage of C3H6 is achieved. Spectroscopic and X-ray diffraction studies confirm that while the coordination environment and crystallinity is unaffected, lattice distortion and strain are incorporated in the ZIF-8 lattice, increasing the lattice stiffness. Overall, this method can improve the separation performance of several MOF membranes.


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  4. J. Babu, G. He, M. T. Vahdat, P. A. Schouwink,M. Mensi, K. V. Agrawal, Submitted, under review.