Constructing Dual-Transport Pathways by Incorporating Beaded Nanofillers in Mixed Matrix Membranes for Efficient CO2 Separation

Mixed matrix membranes (MMMs) have attracted significant attention in the field of CO2 separation because MMMs have potential to overcome an undesirable trade-off effect. In this study, the beaded nanofillers of ZIF-8@aminoclay (ZIF-8@AC) were synthesized using an in situ growth method, and they were doped into a Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. The beaded structure was formed by ZIF-8 particles joined together during the process of AC coating on the ZIF-8 surface. ZIF-8@AC played a vital role in the improvement of gas separation performance. It was mainly attributed to the following reasons: First, the inherent micropores of ZIF-8 constructed the internal pathways for gas transport in the beaded nanofillers, benefiting the improvement of gas permeability. Second, the staggered AC layers constructed the external pathways for gas transport in the beaded nanofillers, increasing the tortuosity of gas transport for larger molecules and favoring the improvement of gas selectivity. Therefore, the internal and external pathways of ZIF-8@AC co-constructed the dual-transport pathways for CO2 transport in MMMs. In addition, the abundant amino groups of the beaded nanofillers provided abounding carriers for CO2, facilitating CO2 transport in the dual-transport pathways. Therefore, the CO2 separation performance of Pebax/ZIF-8@AC-1 MMMs was significantly improved. The CO2 permeability and CO2/CH4 separation factor of Pebax/ZIF-8@AC-1-7 MMM were 620 +/- 10 Barrer and 40 +/- 0.4, which were 2.3 and 1.6 times those of a pure Pebax membrane, respectively. Furthermore, the CO2/CH4 separation performance of Pebax/ZIF-8@AC-1-7 MMM overcame successfully the trade-off effect and approached the 2019 upper bound. It is a novel strategy to design a beaded nanofiller doped into MMMs for carbon capture.

Automated summary

This study synthesized beaded nanofillers ZIF-8@AC using an in-situ growth method and incorporated them into a Pebax matrix to fabricate MMMs for efficient CO2 separation. The ZIF-8@AC played a vital role in improving gas permeability and gas selectivity by constructing internal and external transport pathways. The CO2 separation performance of the MMMs was significantly enhanced, overcoming the trade-off effect and approaching the upper bound of 2019.