Regulating polymer transport resistance to enhance ZIF-8 contribution in mixed-matrix membranes for CO2/N2 separation

Polymer transport resistance was tuned by controlling the solvent evaporation rate. • Reduced polymer transport resistance promoted a more effective contribution of ZIF-8 transport pathways to CO 2 /N 2 separation. • The 7.8 wt% in situ-grown MMM achieved a CO 2 permeability of 510 Barrer and a CO 2 /N 2 selectivity of 33.0. Beyond filler modification, regulating the polymer structure is also crucial for optimizing gas transport in mixed-matrix membranes (MMMs), yet this aspect remains insufficiently explored. Herein, the solvent evaporation rate was controlled to regulate the transport resistance of Pebax 2533 and elucidate its influence on the transport contribution of ZIF-8 in ZIF-8/Pebax MMMs for CO 2 /N 2 separation. For Pebax 2533 membranes, increasing the evaporation rate reduced both crystallinity and relative fractional free volume, resulting in a non-monotonic variation in CO 2 permeability and a decrease in CO 2 /N 2 selectivity. At a moderate evaporation rate of 2.5 × 10 −5  kg·m −2 ·s −1 , the balance between reduced crystallinity and preserved free volume resulted in lower polymer transport resistance, enabling the contribution of ZIF-8 to be more effectively translated into membrane separation performance. As a result, the in situ-grown MMM containing 7.8 wt% ZIF-8 achieved a CO 2 permeability of 510.0 Barrer and a CO 2 /N 2 selectivity of 33.0, with its CO 2 permeability exceeding that of most reported Pebax-based MMMs. This work demonstrates that controlling solvent evaporation is an effective strategy to regulate polymer transport resistance and enhance the contribution of ZIF-8 in MMMs. Download: Download high-res image (207KB) Download: Download full-size image