Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks
- Univ. Leipzig, Leipzig (Germany). Faculty of Physics and Earth Sciences
- Northwestern Univ., Evanston, IL (United States). Dept. of Chemical and Biological Engineering
- Friedrich-Alexander-Univ. Erlangen-Nürnberg, Erlangen (Germany). Erlangen Catalysis Resource Center
Molecular diffusion is commonly found to slow down with increasing molecular size. Deviations from this pattern occur in some host materials with pore sizes approaching the diameters of the guest molecules. A variety of theoretical models have been suggested to explain deviations from this pattern, but robust experimental data are scarcely available. Here in this paper, we present such data, obtained by monitoring the chain length dependence of the uptake of n-alkanes in the zeolitic imidazolate framework ZIF-4. A monotonic decrease in diffusivity from ethane to n-butane was observed, followed by an increase for n-pentane, and another decrease for n-hexane. This observation was confirmed by uptake measurements with n-butane/n-pentane mixtures, which yield faster uptake of n-pentane. Further evidence is provided by the observation of overshooting effects, i.e. by transient n-pentane concentrations exceeding the (eventually attained) equilibrium value. Accompanying grand canonical Monte Carlo simulations reveal, for the larger n-alkanes, significant differences between the adsorbed and gas phase molecular configurations, indicating strong confinement effects within ZIF-4, which, with increasing chain length, may be expected to give rise to configurational shifts facilitating molecular propagation at particular chain lengths.
- Research Organization:
- Univ. of Minnesota, Minneapolis, MN (United States). Nanoporous Materials Genome Center
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; German Science Foundation (DFG); Alexander von Humboldt Foundation
- Grant/Contract Number:
- SC0008688; HA 1893/17-1; KA 953/35-1; FG02-17ER16362
- OSTI ID:
- 1474411
- Journal Information:
- Molecules, Vol. 23, Issue 3; ISSN 1420-3049
- Publisher:
- MDPICopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
New insights into the breathing phenomenon in ZIF-4
|
journal | January 2019 |
Diffusion processes in a poly-crystalline zeolitic material: A molecular dynamics study
|
journal | August 2018 |
Similar Records
Diffusion of methane and other alkanes in metal-organic frameworks for natural gas storage
Study of the mechanism of the cracking of small alkane molecules on HY zeolites