Simulation studies of water adsorption on MIL-101(Cr) revealing the role of inhomogeneous potential field composed of open metal sites and organic linkers

Abstract

In response to the increasing demand for desiccant-type dehumidifiers, MIL-101(Cr), a metal–organic framework, has garnered attention as a promising adsorbent. This is primarily due to its high water capacity resulting from capillary condensation within its two cage-shaped mesopores, as well as its rapid water adsorption response. However, the exact origins of these characteristics are still not fully understood. In this study, we conducted two types of molecular simulations to investigate the water adsorption on MIL-101(Cr). Firstly, we developed an atomistic model of MIL-101(Cr) that specifically considers the interaction between open metal sites (OMSs) and water molecules. By performing grand canonical Monte Carlo simulations using this model, we discovered that capillary condensation occurs due to the formation of a liquid film that covers the hydrophobic pore surface, driven by the presence of OMSs. Subsequently, we constructed a simplified model that focuses solely on the potential field inhomogeneity of MIL-101(Cr) and conducted grand canonical molecular dynamics simulations to examine the progress of water adsorption. The simulation results indicated that the rapid water adsorption response of MIL-101(Cr) can be attributed to the inhomogeneity of the potential field consisting of hydrophilic OMSs distributed at appropriate intervals and hydrophobic organic linkers.