Harnessing nanoscale densification for controlling gas selectivity in flexible zeolitic imidazolate frameworks
<h2>Summary</h2> Flexible metal-organic frameworks (MOFs) are promising for gas separation due to their molecular recognition capabilities. However, gate-opening behavior in certain flexible MOFs can reduce gas selectivity, enabling simultaneous adsorption of multiple gases. We introduce a binder-free, pressure-free densification process to enhance gas selectivity in flexible zeolitic imidazolate frameworks (ZIF-7 and ZIF-9) by optimizing nanoparticle packing. Unlike powders, the densified ZIF-7 and ZIF-9 retain rhombohedral crystal structures after solvent removal, confirmed via synchrotron powder X-ray diffraction. This process modifies adsorption behavior by introducing a diffusion barrier, enabling diffusivity-driven kinetic separation and enhanced CO<sub>2</sub>/hydrocarbon selectivity. At 0.5 bar, ZIF-7<sub>mono</sub> shows 2×, 4×, and 9.5× higher CO<sub>2</sub> selectivity over C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, and C<sub>2</sub>H<sub>6</sub>, respectively, versus ZIF-7<sub>pwd</sub>. ZIF-9<sub>mono</sub> similarly shows 6.5×, 3×, and 39× improvements over ZIF-9<sub>pwd</sub>. Both monoliths outperform powders in ternary gas mixtures. This study provides a novel strategy to control gate opening and enhance gas selectivity in flexible MOFs for practical separation applications.
Authors
- Tony Pham (ORCID: https://orcid.org/0000-0001-5654-163X)
- Joshua Samuel (ORCID: https://orcid.org/0000-0001-8231-2988)
- Sameh K. Elsaidi (ORCID: https://orcid.org/0000-0002-8326-6984)
- Wenqian Xu (ORCID: https://orcid.org/0000-0002-4815-6253)
- Islam Elzeny
- Xiaobing Hu (ORCID: https://orcid.org/0000-0002-9233-8118)
- Mona H. Mohamed
Institutions
- Northwestern University (US)
- Argonne National Laboratory (US)
- Illinois Institute of Technology (US)
- University of South Florida (US)
- SCI Engineered Materials (United States) (US)
Publication Details
- Journal
- Cell Reports Physical Science
- Published
- 2025-09-01
- DOI
- https://doi.org/10.1016/j.xcrp.2025.102805
- Primary Topic
- Metal-Organic Frameworks: Synthesis and Applications
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Science Foundation
- U.S. Department of Energy
- Northwestern University
- Office of Science
- Materials Research Science and Engineering Center, Harvard University
- Division of Materials Research
- Division of Electrical, Communications and Cyber Systems
- Basic Energy Sciences
- Argonne National Laboratory