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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,...

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Autores principales: Hwang, Seungtaik, Gopalan, Arun, Hovestadt, Maximilian, Piepenbreier, Frank, Chmelik, Christian, Hartmann, Martin, Snurr, Randall Q., Kärger, Jörg
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2018
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.
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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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