Facet-Specific Gas Transport Properties of Metal–Organic Frameworks in Polymer Nanocomposites

Abstract Metal–Organic Frameworks (MOFs) hold significant potential for various applications in gas, liquid, and ion separations. However, while MOF-based nanocomposite research is growing, facet-specific studies on molecular transport are rare. Here, a pioneering investigation into facet-specific gas transport in nanocomposites was conducted using ZIF-8, with exposed {110} or {100} facets interacting with a polyimide. Despite their otherwise near-identical properties, the higher energy {100} facet showed more significant MOF–polymer interactions, resulting in substantially stronger binding with the polymer, which was corroborated by DFT calculations. This phenomenon leads to unique gas transport trends: the {110} facet promotes propylene/propane separations, while the {100} facet enhances hydrogen-based (H2/N2, CH4) and ethylene/ethane separation, particularly at subambient temperatures and mainly by diffusion selectivity. This study provides insights into an largely unexplored area of MOF–polymer composites. Gas transport properties are significantly influenced by surface-dependent interactions for MOF–polymer hybrid materials, enabling unique separation properties through simple engineering of the MOF surface.