Computational investigation of the performance of ZIF-8 with encapsulated ionic liquids towards CO₂ capture^*

* This publication is dedicated to Professor Peter Cummings on the occasion of his 65th birthday. Professor Cummings has been an international leader in the field of computational chemistry, statistical mechanics and molecular simulation for many decades and a great mentor for many younger researchers in the field, including the corresponding author of this work. We wish him many more decades of inspiration and productivity.

Abstract

The effect of Ionic Liquid (IL) encapsulation in Metal Organic Frameworks (MOFs) is extensively studied towards the enhancement of the MOFs as CO₂-selective materials. The influence of the IL anion-cation pair type is investigated through the combination of two different cations, namely 1-butyl-3-methylimidazolium [bmim⁺] and 1-octyl-3-methylimidazolium [omim⁺] and three distinct anions, namely bis-trifluoromethylsulfonyl-imide [Tf₂N⁻], tricyanomethanide [TCM⁻], and tertracyanoborate [B(CN)₄⁻], that can be encapsulated in ZIF-8, resulting in a series of ZIF hybrids (IL@ZIF-8). The study investigates the impact of the anion and the cation on the separation of CO₂ from mixtures with CH₄ and N₂. Monte Carlo simulations of adsorption of the three gases in both the pristine ZIF-8 and in ILs@ZIF-8 reveal that CO₂ capacity increases dramatically for the case of ILs@ZIF-8. Moreover, analysis of the simulations and additional density functional theory calculations show that CO₂/CH₄ (related to natural gas purification) and CO₂/N₂ (related to post-combustion CO₂ capture) mixture selectivity is affected by the distribution, composition and type of the IL pair. Moreover, the sorbent selection parameter, S, and the regenerability factor, R, are used to evaluate the performance of all IL@ZIF-8 analogues along with other known CO₂-selective materials.

GRAPHICAL ABSTRACT

Keywords:

• Metal organic frameworks
• ionic liquids
• gas separation
• CO₂ capture

Acknowledgements

This publication was made possible thanks to financial support from Texas A&M University at Qatar through the Responsive Research Seed Grant program. The statements made herein are solely the responsibility of the authors. We are grateful to the High Performance Computing Center of Texas A&M University at Qatar for generous resource allocation.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Amro M. O. Mohamed http://orcid.org/0000-0002-3620-3876

Salvador Moncho http://orcid.org/0000-0003-1631-5587

Panagiotis Krokidas http://orcid.org/0000-0002-2445-6059

Ioannis G. Economou http://orcid.org/0000-0002-2409-6831

Notes

* This publication is dedicated to Professor Peter Cummings on the occasion of his 65th birthday. Professor Cummings has been an international leader in the field of computational chemistry, statistical mechanics and molecular simulation for many decades and a great mentor for many younger researchers in the field, including the corresponding author of this work. We wish him many more decades of inspiration and productivity.