H₂, N₂, and CH₄ Gas Adsorption in Zeolitic Imidazolate Framework-95 and -100: Ab Initio Based Grand Canonical Monte Carlo Simulations

Abstract

A multiscale approach based on ab initio and grand canonical Monte Carlo (GCMC) simulations is used to report the H₂, N₂, and CH₄ uptake behaviors of two zeolitic imidazolate frameworks (ZIFs), ZIF-95 and -100, with exceptionally large and complex colossal cages. The force fields describing the weak interactions between the gas molecules and ZIFs in GCMC simulations are based on ab initio MP2 level of theory aimed at accurately describing the London dispersions. We report the total and excess gas uptakes up to 100 bar at 77 and 300 K. Our results unravel the interplay between the uptake amount, pore volume, guest molecule size, temperature, chlorine functional group, and isosteric heat of adsorption in ZIFs. We found that while the uptake capacity of ZIF-100 outperforms ZIF-95 for small molecules (H₂), ZIF-95 offers a superior adsorption capacity for large molecules (CH₄). Moderately sized molecules (N₂) exhibit a more complex uptake behavior depending on the temperature. Furthermore, we show that the induced dipole interactions, such as those caused by −Cl functional groups, play a vital role on gas adsorption behaviors. This work provides the first report on the N₂ and CH₄ uptake of ZIF-95 and -100 using ab initio based GCMC simulations