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Sodalite zeolitic-imidazole frameworks (ZIFs) show great potential due to their effective aperture sizes suitable for small gas separations. Numerous efforts have, therefore, been made in tuning their effective aperture sizes to control and enhance their molecular sieving properties. Herein, we present a new strategy to finely tune the effective aperture size of CdIF-1, a cadmium-substituted ZIF-8 analogue, based on thermal amorphization. Among several ZIF-8 analogues screened, CdIF-1 was found to be the only one that could be thermally amorphized. The controlled amorphization reduced the long-range structural order while preserving the short-range order, thereby systematically densifying the ZIF structure and consequently affecting its effective aperture. Meanwhile, it was found that amorphization enhanced the flexibility of the framework, resulting in accessible pores at temperatures above 273 K. As compared to its crystalline counterpart, partially amorphized CdIF-1 showed significantly improved diffusion and adsorption selectivities of n -C 4 H 10 /i-C 4 H 10 ( i.e. , 1.5 → 40.7 and 1.1 → 4.9, respectively), likely due to the amorphization-induced tuning of its effective aperture size.
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Ultrahigh-field 67 Zn NMR reveals short-range disorder in zeolitic imidazolate framework glasses
The structure of melt-quenched zeolitic imidazole framework (ZIF) glasses can provide insights into their glass-formation mechanism. We directly detected short-range disorder in ZIF glasses using ultrahigh-field zinc-67 solid-state nuclear magnetic resonance spectroscopy. Two distinct Zn sites characteristic of the parent crystals transformed upon melting into a single tetrahedral site with a broad distribution of structural parameters. Moreover, the ligand chemistry in ZIFs appeared to have no controlling effect on the short-range disorder, although the former affected their phase-transition behavior. These findings reveal structure-property relations and could help design metal-organic framework glasses.
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- Award ID(s):
- 1855176
- PAR ID:
- 10141518
- Publisher / Repository:
- American Association for the Advancement of Science (AAAS)
- Date Published:
- Journal Name:
- Science
- Volume:
- 367
- Issue:
- 6485
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- p. 1473-1476
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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