Revealing the Transient Concentration of CO₂ in a Mixed-Matrix Membrane by IR Microimaging and Molecular Modeling

Through IR microimaging the spatially and temporally resolved development of the CO₂ concentration in a ZIF-8@6FDA-DAM mixed matrix membrane (MMM) was visualized during transient adsorption. By recording the evolution of the CO₂ concentration, it is observed that the CO₂ molecules propagate from the ZIF-8 filler, which acts as a transport "highway", towards the surrounding polymer. A high-CO₂ -concentration layer is formed at the MOF/polymer interface, which becomes more pronounced at higher CO₂ gas pressures. A microscopic explanation of the origins of this phenomenon is suggested by means of molecular modeling. By applying a computational methodology combining quantum and force-field based calculations, the formation of microvoids at the MOF/polymer interface is predicted. Grand canonical Monte Carlo simulations further demonstrate that CO₂ tends to preferentially reside in these microvoids, which is expected to facilitate CO₂ accumulation at the interface.