(101g) Linker Doping Strategy for Hybrid Zeolitic-Imidazolate Frameworks and Their Ultrathin Membranes for Tunable Gas Separations

Linker Doping Strategy for Hybrid Zeolitic-Imidazolate Frameworks and Their Ultrathin Membranes for Tunable Gas Separations

Febrian Hillman¹ and Hae-Kwon Jeong*^1,2

¹Artie McFerrin Department of Chemical Engineering and ²Department of Materials Science and Engineering, Texas A&M University, 3122 TAMU, College Station, Texas 77843-3122, United States.

* Corresponding author: hjeong7@tamu.edu

Zeolitic-imidazolate frameworks (ZIFs)¹ have gained much interest due to their potentials in gas separations.^2-6 In particular, ZIF-8 with a cubic SOD zeolite topology comprising of Zn²⁺ ions tetrahedrally bridged by 2-methylimidazole (mIm) linkers has attracted tremendous research interests due to its impressive propylene/propane separation performance.^{2-5, 7-10} However, ZIFs, like any other crystalline materials, have limited available pore apertures. As a consequence, often times the aperture of these ZIFs do not match well with the size of gas mixtures of interest. Hybrid approach by mixing metals and/or linkers^11-16 has been recently investigated to fine-tune the ZIF porosity and surface properties, and potentially extending their separation applications for many important gas mixtures. In general, the hybrid approach requires mixing of isostructural ZIFs to maintain their topology,^{12, 13} thus limiting the options of linkers and metal centers to obtain hybrid ZIFs. Mixing non-isostructural ZIFs can often lead to crystal systems different from the parent, likely presenting a challenge in predicting and obtaining the desired property change on the hybrid frameworks.¹⁷

Linker-doping, as reported here, can be a strategy to expand the option of imidazolate linkers to obtain mixed-linker hybrid ZIFs. Three linkers were investigated to be doped into the ZIF-8 framework: 2-ethylimidazole (eIm), 2-phenylimidazole (phIm), and imidazole (Im). For the first time, we were able to incorporate eIm linker into ZIF-8 using linker doping strategy, which was previously unattainable.¹⁷ The hybrid doped ZIF-8 have altered the “stiffness” of Zn-N bonding as characterized by FT-IR, thereby linker flip-flopping motion of ZIF-8 as analyzed through gas adsorption isotherms. We further developed the doping strategy through nuclei assisted method, referred as nuclei-assisted linker doping (NALD). The NALD strategy can significantly improve the incorporation of dopant linker into the framework. Furthermore, well-intergrown ultrathin eIm-doped ZIF-8 membranes are grown on α-Al₂O₃ substrates, in which the incorporation of eIm affects the morphology and thickness of the polycrystalline membranes improving the permeance of propylene and propane molecules.

References:

1. K. S. Park, Z. Ni, A. P. Cote, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K. Chae, M. O'Keeffe and O. M. Yaghi, Proc. Natl. Acad. Sci. U. S. A., 2006, 103, 10186-10191.
2. H. T. Kwon and H.-K. Jeong, Chem. Comm., 2013, 49, 3854-3856.
3. H. T. Kwon and H.-K. Jeong, J. Am. Chem. Soc., 2013, 135, 10763-10768.
4. Y. Pan and Z. Lai, Chem. Comm., 2011, 47, 10275-10277.
5. Y. Pan, T. Li, G. Lestari and Z. Lai, Journal of Membrane Science, 2012, 390–391, 93-98.
6. S. R. Venna and M. A. Carreon, J. Am. Chem. Soc., 2010, 132, 76-78.
7. H. T. Kwon and H.-K. Jeong, Chem. Eng. Sci., 2015, 124, 20-26.
8. H. T. Kwon, H.-K. Jeong, A. S. Lee, H. S. An and J. S. Lee, J. Am. Chem. Soc., 2015, 137, 12304-12311.
9. K. Eum, C. Ma, A. Rownaghi, C. W. Jones and S. Nair, ACS Applied Materials & Interfaces, 2016, 8, 25337-25342.
10. K. Li, D. H. Olson, J. Seidel, T. J. Emge, H. Gong, H. Zeng and J. Li, J. Am. Chem. Soc., 2009, 131, 10368-10369.
11. F. Hillman, J. Brito and H.-K. Jeong, ACS Applied Materials & Interfaces, 2018, 10, 5586-5593.
12. F. Hillman, J. M. Zimmerman, S.-M. Paek, M. R. A. Hamid, W. T. Lim and H.-K. Jeong, J. Mater. Chem. A, 2017, 5, 6090-6099.
13. J. A. Thompson, C. R. Blad, N. A. Brunelli, M. E. Lydon, R. P. Lively, C. W. Jones and S. Nair, Chem. Mater., 2012, 24, 1930-1936.
14. K. Eum, K. C. Jayachandrababu, F. Rashidi, K. Zhang, J. Leisen, S. Graham, R. P. Lively, R. R. Chance, D. S. Sholl, C. W. Jones and S. Nair, J. Am. Chem. Soc., 2015, 137, 4191-4197.
15. J.-P. Zhang, A.-X. Zhu, R.-B. Lin, X.-L. Qi and X.-M. Chen, Advanced Materials, 2011, 23, 1268-1271.
16. P. Krokidas, S. Moncho, E. N. Brothers, M. Castier and I. G. Economou, Phys. Chem. Chem. Phys., 2018, 20, 4879-4892.
17. X.-C. Huang, Y.-Y. Lin, J.-P. Zhang and X.-M. Chen, Angewandte Chemie International Edition, 2006, 45, 1557-1559.