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Encapsulation of [bmim+][Tf2N] in different ZIF-8 metal analogues and evaluation of their CO2 selectivity over CH4 and N2 using molecular simulation

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Abstract

Zeolitic imidazolate frameworks (ZIFs), a subfamily of metal–organic frameworks (MOFs), are considered as candidates for the development of energy-efficient and high-performing gas separation processes based on nanoporous materials. A recently reported class of hybrid materials, which consist of ionic liquid (IL) pairs encapsulated in the cages of ZIFs (namely IL@ZIFs), has revealed exceptional CO2 selectivity. Herein, we investigate the effect of the metal center type of the framework on the performance of IL@ZIFs, exclusively using computational methods. We use the highly studied ZIF-8 and prepare metal variants, by replacing the original metal Zn2+ with Co2+, Be2+ and Cd2+. For each ZIF-8 metal analogue, we prepare IL@ZIFs of varying IL composition, by introducing methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim+][Tf2N]) in the ZIF cages. With the use of Monte Carlo simulations, we evaluate the selectivity of both the pristine ZIF-8 metal analogues and the IL@ZIF-8 metal analogues for CO2/CH4 and CO2/N2 mixtures. Our results show that metal variation affects the ZIF performance. Moreover, the IL composition affects the performance; for each IL@ZIF-8 case, there is an optimum IL composition that ensures maximum selectivity for the two mixtures. In an effort to facilitate the evaluation of the IL composition-related performance, we use the available pore volume (APV) parameter. Our analysis reveals that there is a common APV value among all IL@ZIF-8 analogues that dictates the optimum separation performance for both CO2/CH4 and CO2/N2 mixtures. This finding can help towards a better understanding of the design and preparation of these materials.

Graphical abstract: Encapsulation of [bmim+][Tf2N−] in different ZIF-8 metal analogues and evaluation of their CO2 selectivity over CH4 and N2 using molecular simulation

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Supplementary files

Article information


Submitted
15 Feb 2020
Accepted
21 Jun 2020
First published
22 Jun 2020

Mol. Syst. Des. Eng., 2020, Advance Article
Article type
Paper

Encapsulation of [bmim+][Tf2N] in different ZIF-8 metal analogues and evaluation of their CO2 selectivity over CH4 and N2 using molecular simulation

A. M. O. Mohamed, P. Krokidas and I. G. Economou, Mol. Syst. Des. Eng., 2020, Advance Article , DOI: 10.1039/D0ME00021C

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