Free Energy Profiles of Monomeric Species in MOFs for Predicting Thermal Stability of MOF–Polymer Systems

Abstract

Metal–organic frameworks (MOFs) and hybrid MOF–polymer systems have been explored for gas separation applications. The pore surface’s environment and interaction with different monomers can help understand the physical properties of hybrid MOFs–polymer systems. In our work, we have focused on understanding the interaction between the pores of UiO-66/UiO-67 and different monomeric species representative of various polymers (ethyl methyl ether, poly(vinyl alcohol), polyvinyl chloride, and polypropylene), which are similar in structure but have different functional groups. We have used advanced sampling techniques to calculate the free energy profile of monomers traversing through the pores. We find that the free energy barrier for different monomers in UiO-66 and UiO-67 is very different and depends on these monomers’ interaction with the pore environment. The pore-limiting diameter of MOFs, the kinetic diameter of the monomers, and the free energy barrier of monomers traversing through the pores of UiO-66 and UiO-67 were used to understand the stability of these MOF–polymer hybrid systems. We find that UiO-66 with poly(vinyl alcohol), poly(vinyl chloride), and polypropylene is predicted to be stable at room temperature compared to UiO-66 with ethyl methyl ether. UiO-67 hybrid polymer systems are predicted to be unstable at room temperature.