Small molecule bridged MOF-802/polymer mixed-matrix membranes for helium extraction

The inherent nanochannels of mixed-matrix membranes (MMMs) have demonstrated significant potential in molecular sieving-based separations. However, achieving efficient helium (He) separation and purification remains challenging due to the inherent trade-off between selectivity and permeability. To overcome these limitations, rational design of polymer structures and MOF particle and preparation strategy for MMM is imperative. Herein, we proposed a strategy for constructing novel MOF-802/Mi@6FPZ MMMs for efficient He separation and purification. The design employed a tailored system composed of 6FPZ copolyimide (6FDA/mPDA:PABZ), MOF-802, and the small-molecule modulator 2-methylimidazole (Mi) to MMMs. The presence of hydrogen bonding between Mi and 6FPZ polymer, the formation of Zr–N coordination bonds between Mi and MOF-802 verified by ATR-IR spectroscopy, enabled the MOF-802 particles to be dispersed uniformly within the 6FPZ. Notably, the Zr–N bond formation liberated partial –COOH groups, creating additional nanochannels within the MOF-802/Mi@6FPZ to facilitate gas transport. PAL experiments indicated that the optimized MOF-802(20 %)/Mi(10 %)@6FPZ MMMs possess an average channel size of ≈0.40 nm, ideal for the selective separation of He from CH 4 or N 2 . This small molecule bridged MMMs achieved remarkable He/CH 4 and He/N 2 selectivity values of 429.8 and 174.2, respectively, coupled with a He permeability of 177 Barrer far surpassing the 2016 upper bound. This novel design strategy not only addresses critical challenges in He separation but also presents a versatile platform for developing defect-free, high-performance MMMs for a range of gas separation applications.