Is Porosity at the MOF/Polymer Interface Necessarily an Obstacle to Optimal Gas-Separation Performances in Mixed Matrix Membranes?

Current MOF/polymer mixed matrix membranes (MMMs) design relies on the assumption that it is necessary to avoid interfacial porosity in order to achieve high-level gas-separation performances, but is this assumption valid in all cases, for all separation mechanisms? This communication proves that this is not always true by considering NUS-8/PIM-1, a prototypical MMM for CO2 capture. Our molecular simulations approach integrating quantum calculations, force field-based Monte Carlo, and equilibrium/non-equilibrium molecular dynamics simulations, revealed that a porosity generated at the NUS-8/PIM-1 interface in the form of microvoids favors the interactions between CO2 and the NUS-8 surface and therefore contributes to ensure a high CO2/N2 and CO2/CH4 selectivity for the corresponding MMM, preserving the pure NUS-8 membrane value and exhibiting a high flux for CO2. This high-level performance is achieved by means of a solubility-driven separation mechanism, as opposed to previously studied diffusion-driven separations where the interface porosity had been shown to deteriorate the MMM separation performance. We believe that these results will change the current paradigm in the field of MOF/polymer MMMs, paving the way toward new strategies for the development of highly efficient membranes for gas separation.