Theoretical studies on the role of water in ionic liquids at ZIF (IL@ZIF) complex and its effect on selective CO2 separation

Abstract

One of the major problems we have always faced and still facing is the vast amount of toxic gases expelled into the atmosphere mainly during the manufacture of many of the day-to-day commodities we all use. The selective adsorption and storage of gases from various industrially important gaseous mixtures are studied in order to find a suitable method as a sustainable solution for this concern. This study is conducted in order to get a perspective on the gas separation and storage capabilities of large framework molecules like zeolitic imidazolate frameworks (ZIFs) by incooperation of ionic liquids (ILs). Here, the gas adsorption efficiency of IL@ZIF-8 composite materials is studied in the presence of a single water molecule. We have selected 1-butyl-3-methylimidazolium [BMIM]+ cation along with five different anions as the ILs. We used both hydrophilic and hydrophobic ILs in this study. The IL@ZIFs complexes are prepared by adding ILs in two different approaches to the ZIF pore. A single water molecule is added into the previously optimized geometries of IL@ZIF in the first method (Approach-I), while we added water and an IL to the ZIF simultaneously in the second method (Approach-II). The selection of the different approaches for water addition helps to gather information about the interaction pattern of water with the IL and ZIF and also of these molecules with one another in the presence of water. We used these complexes to study their adsorption capabilities towards CO2 and also their selectivity nature towards CO2 in a binary mixture of CO2 and N2. Computational approaches such as density functional theory (DFT) and grand canonical Monte Carlo (GCMC) are used in this study.