Simultaneously enhanced gas separation performance and long-term stability by thermally treated ZIF-8-based nanocomposite membranes

The challenges of trade-off effect and long-term stability pose huge obstacles in the application of polymer-based gas separation membranes. In this study, we proposed a novel strategy to overcome these problems by in-situ thermally treating ZIF-8/polyimide mixed-matrix membranes (MMMs) at 300 °C. After thermally treatment, the T-ZIF-8 produced some unsaturated Zn site as defects that decreased BET surface area and the shrunk of micropore size as compared with ZIF-8. The MMMs with T-ZIF-8 significantly affects their gas separation performance and long-term stability, in which, the H 2 /CH 4 and CO 2 /CH 4 separation performance of T-ZIF-8/PI(3:10) and T-ZIF-8/PI(6:10) increased from far below the 2008 trade off lines for their PI matrix to approach or even above that. Additionally, both higher permeability and selectivity were observed for T-ZIF-8/PI(6:10) as compared with its precursor for H 2 /CH 4 separation, which was contributed by its higher H 2 diffusion coefficient (3834 vs 580 × 10 -8 cm 2 s −1 ) and H 2 /CH 4 diffusion selectivity (240 vs 154). Furthermore, the T-ZIF-8/PI (1:10) and T-ZIF-8/PI(3:10) MMMs demonstrate less than 15 % H 2 decreasing after 150 days, which is much better than that of the pristine PI membrane (26.7 %). These results probably contributed by the defected ZIF-8 loading induced extra ultra-micropore that caused size sieving effect and strong interaction with polyimide matrix that formed more rigid polymer chains. These findings propose a strategy to effectively enhance the gas separation performance and long-term stability by in-situ introducing the defect MOF in the polymer matrix.