(376h) Improved Gas Separation Performance of Mixed-Linker Zeolitic Imidazolate Framework ZIF Membranes Via Post Synthetic Ligand Exchange

Zeolitic-imidazolate frameworks (ZIFs), a subclass of MOFs, consisting of transition metals (Zn, Co, etc.) and imidazole-derived ligands, have drawn attention mainly due to their ultra-micropores (< 5 Å) and relatively high thermal/chemical stabilities.¹ A prototypical ZIF, ZIF-8, consisting of Zn and 2-methylimidazole with sodalite (SOD) zeolitic topology, is one of the most widely studied ZIFs mainly due to its robust synthesis and potential for gas separations due to its well-defined pore size. ZIF-7, consisting of Zn and benzimidazole with SOD, exhibits smaller pore size (ca. 3.2 Å)² than ZIF-8 (ca. 4.0 Å)³, therefore promising for helium or hydrogen separation.⁴

Properties of MOFs including gas transport properties are affected by structures of MOFs. To obtain MOFs with new properties, one can obtain via 1) direct (de novo) synthesis of new MOFs and 2) post-synthetic modifications (PSMs) of existing MOFs. PSMs include post-synthetic ligand and metal exchange⁵. Compared to the complex and sensitive nature of MOF formation process via de novo synthesis,⁶ PSMs are a simple and facile approach to impart new properties since daughter MOFs with new properties can be obtained without compromising the structures of mother MOFs. Recent studies have shown that PSMs can modify pore size and surface properties, thereby separation performances.^7-9

In this talk, we would like to present improved gas separation performances of ZIF-8 membranes via post-synthetic ligand exchange by systematically reducing the effective aperture size of ZIF-8. Mother ZIF-8 membranes prepared by a secondary growth were subjected to post-synthetic linker exchange with ZIF-7 linkers, i.e., benzimidazole. The effects of the PSM on the gas separation performance and water stability of the modified membranes will be discussed.

References

1 Park KS, Ni Z, Côté AP, et al., (2006) “Exceptional chemical and thermal stability of zeolitic imidazolate frameworks”, Proceedings of the National Academy of Sciences, 103 (27), pp 10186-10191

2 Thompson, J. A., Blad, C. R., Brunelli, N. A., Lydon, M. E., Lively, R. P., Jones, C. W., Nair, S., “Hybrid Zeolitic Imidazolate Frameworks: Controlling Framework Porosity and Functionality by Mixed-Linker Synthesis”, Chemistry of Materials, 2012, 24 (10), pp 1930–1936

3 Zhang C, Lively RP, Zhang K, Johnson JR, Karvan O, Koros WJ., (2012) “Unexpected Molecular Sieving Properties of Zeolitic Imidazolate Framework-8”, The Journal of Physical Chemistry Letters., 3 (16), pp 2130-2134.

4 Yan‐Shuo Li., YS., Liang, FY., Bux, H., Feldhoff, A., Yang, WS., Caro, J., “Molecular Sieve Membrane: Supported Metal–Organic Framework with High Hydrogen Selectivity”, Angewandte Chemie International Edition., 2010, 122, pp 558-561

5 Tanabe, KK. and Cohen, SM., (2011), “Postsynthetic modification of metal-organic frameworks-a progress report”, Chemical Society Reviews, 40 (2), pp 498-519.

6 Kim, M., Cahill, JF., Fei, H., Prather, KA., and Cohen, SM., (2012) “Postsynthetic Ligand and Cation Exchange in Robust Metal–Organic Frameworks”, Journal of the American Chemical Society, 134 (43), pp 18082-18088

7 Lee, M. J., Kwon, H. T., Jeong, HK., “High‐Flux Zeolitic Imidazolate Framework Membranes for Propylene/Propane Separation by Postsynthetic Linker Exchange”, Angewandte Chemie International Edition, 2018, 57, pp 156-161

8 Karagiaridi, O., Lalonde, M. B., Bury, W., Sarjeant, A. A., Farha, O. M., Hupp, J. T., “Opening ZIF-8: A Catalytically Active Zeolitic Imidazolate Framework of Sodalite Topology with Unsubstituted Linkers”, Journal of the American Chemical Society, 2012, 134 (45), pp 18790-18796

9 Zhang, H., James, J., Zhao, M., Yao, Y., Zhang, Y., Zhang, B., Lin, Y.S., “Improving hydrostability of ZIF-8 membranes via surface ligand exchange”, Journal of Membran