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 fieldbased 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/N-2 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 solubilitydriven 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.

Automated summary

The study challenges the assumption that avoiding interfacial porosity is always necessary for high gas-separation performance in MOF/polymer mixed matrix membranes. By investigating the NUS-8/PIM-1 MMM, researchers found that microvoids at the interface can actually enhance CO2 interactions and improve selectivity, leading to a new solubility-driven separation mechanism. This discovery has the potential to change current paradigms and pave the way for more efficient gas separation membranes.