Influence of polymer support on gas transport in ultrathin zeolite membranes

Abstract

Ultrathin membranes, with nanoscale thickness, can offer remarkable separation performance, benefiting applications such as purification, catalysis, and drug delivery. However, interfacial defects and finite-size effects lead to transport obstacles known as surface barriers. Such apparent interfacial barriers are also present in defect-free membranes, and lead to nonuniform fluid transport in the entry region of developing flow. Here, we examine the support effect on gas transport through ultrathin zeolite membranes using atomistic simulations, by considering a composite system comprised of a siliceous Theta-1 zeolite nanosheet with a support layer (one side) and a polymeric coating (both sides). Our simulations reveal that external polymer layers can increase internal barriers and entry length required to achieve fully developed flow within crystal channels for light gases under low confinement. Potential energy profiles show the polymer chains influence molecules located up to 0.8 nm into the inner crystal, increasing further the surface barriers and reducing fluid diffusivities when compared to bare nanosheets. We show that even one support layer leads to internal resistance comparable to that of thin membranes, and that entry-length effects can govern transport. The coated/supported nanosheet exhibits maximum separation performance for thicknesss lying in the range of 7.3–15.2 nm. Additionally, our findings demonstrate that the polymer coating/support layer can control the transport across zeolite-based nanocomposites due to slow trajectories and enhanced interfacial resistances, crucial for designing high-performance ultrathin membranes.