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Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks
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,...
Autores principales: | , , , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
MDPI
2018
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6017190/ https://www.ncbi.nlm.nih.gov/pubmed/29543777 http://dx.doi.org/10.3390/molecules23030668 |
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author | Hwang, Seungtaik Gopalan, Arun Hovestadt, Maximilian Piepenbreier, Frank Chmelik, Christian Hartmann, Martin Snurr, Randall Q. Kärger, Jörg |
author_facet | Hwang, Seungtaik Gopalan, Arun Hovestadt, Maximilian Piepenbreier, Frank Chmelik, Christian Hartmann, Martin Snurr, Randall Q. Kärger, Jörg |
author_sort | Hwang, Seungtaik |
collection | PubMed |
description | 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, 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. |
format | Online Article Text |
id | pubmed-6017190 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2018 |
publisher | MDPI |
record_format | MEDLINE/PubMed |
spelling | pubmed-60171902018-11-13 Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks Hwang, Seungtaik Gopalan, Arun Hovestadt, Maximilian Piepenbreier, Frank Chmelik, Christian Hartmann, Martin Snurr, Randall Q. Kärger, Jörg Molecules Article 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, 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. MDPI 2018-03-15 /pmc/articles/PMC6017190/ /pubmed/29543777 http://dx.doi.org/10.3390/molecules23030668 Text en © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). |
spellingShingle | Article Hwang, Seungtaik Gopalan, Arun Hovestadt, Maximilian Piepenbreier, Frank Chmelik, Christian Hartmann, Martin Snurr, Randall Q. Kärger, Jörg Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title | Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title_full | Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title_fullStr | Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title_full_unstemmed | Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title_short | Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks |
title_sort | anomaly in the chain length dependence of n-alkane diffusion in zif-4 metal-organic frameworks |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6017190/ https://www.ncbi.nlm.nih.gov/pubmed/29543777 http://dx.doi.org/10.3390/molecules23030668 |
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