Structurally stabilized defective ZIF-8 with open " windows " constructed by coordination node occupancy for enhanced CO2 separation

Defective MOFs have presented improved CO2 capture for mixed-matrix membranes (MMMs) due to the enlarged pore size and abundant active adsorption sites. However, the reduced structural integrality and stability urgently need to be solved by requesting a facile and universal construction strategy for their industrial application. Herein, 1-methylimidazole (1-MI) was proposed to compete with 2-methylimidazole (2-MI) for coordination to construct structurally stabilized defective ZIF-8 (d-ZIF-8) with open "windows" and exposed active Zn sites, achieving enhanced adsorption and fast diffusion for CO2. Specifically, due to the similar molecular structure and the same molecular weight of 1-MI and 2-MI, the structural integrality of d-ZIF-8 was maintained, thus the stability was perfect. As characterized by BET results, both the microporous size and mesoporous proportion of dZIF-8 are improved, which is beneficial for fast diffusivity of CO2. From FTIR results, the exposed active Zn sites in d-ZIF-8 are demonstrated, which enhance the CO2 adsorption by 14.8% compared to pure ZIF-8. Meanwhile, the enhancement of Tg further demonstrates that the percentage of defects increases with rising the content of 1MI. Synergized by the enlarged pore size and increased active Zn sites, the prepared d-ZIF-8 (7:3)/Pebax MMM with filler loading of 5 wt% achieves 107.6 Barrer for CO2 P and 85.9 for alpha CO2/N2 . This performance exceeds the 2008 and approaches 2019 upper bound. Meanwhile, the membrane exhibits good long-term stability, indicating the structural stability of the proposed d-ZIF-8.