In silico analysis of argon adsorption and porous properties of Fe-soc-MOF pre-adsorbed with nonpolar and polar fluids

Abstract

© 2020 Elsevier Inc. In this molecular simulation work, we provide a profound insight into the textural and adsorptive properties of a microporous metal-organic framework with soc topology (soc-MOF) using combined argon physisorption and pre-adsorption with fluids having different polarities (CCl4, NH3, and H2O) at 87 K. With different amounts of pre-adsorbed molecules added to the framework, the adsorption isotherms, snapshots, and isosteric heats of argon at 87 K are investigated using the grand canonical Monte Carlo simulation (GCMC), whereas the porous properties are obtained by using the Monte Carlo integration technique (MCI). It is found that insertion of pre-adsorbed molecules has a substantial effect on argon adsorption uptake in the regions of Henry's law and saturation capacity since the accessible pore space becomes smaller in volume and size. By observing the pre-adsorption mechanisms of non-polar (CCl4) and mildly polar (NH3) fluids, it is clear that the pre-adsorbed molecules mainly prefer to locate at the cages due to stronger interaction between Fe sites and pre-adsorbed molecules, followed by pre-adsorption in the channels when the cages are utterly or nearly fulfilled. Therefore, post-adsorption of argon initially occurs in the cages because of the enhancement of interactions between pre-adsorbed molecules existing in the framework, as confirmed by isosteric heat at low loading. Conversely, for highly polar fluids like H2O, pre-adsorption is proceeded by non-selective pore filling. From the analysis at the molecular level, it can be concluded that pre-adsorption could be used as another tool for advanced surface characterization to provide a better understanding of the structural and adsorptive properties of other soc-MOFs and MOFs that have different topological framework types.