Fe‐ SO 3 − ‐metal–organic cage‐based mixed matrix membrane for enhanced helium separation

Abstract Metal–organic cages (MOCs) represent emerging fillers for constructing advanced mixed matrix membranes (MMMs) due to their intriguing properties of soluble discrete molecules and versatile cavity structures. However, research on such MMMs targeted at He/CH 4 separation is still limited mainly caused by the lack of MOCs with suitable metal nodes and organic ligands. Herein, we adopted an MOC with dual adsorption sites of Fe open metal site and electronegative SO 3 − groups, where the reversible adsorption of CH 4 selectively impeded CH 4 permeation. This peculiarity enables the prepared Fe‐SO 3 − ‐MOC–PI membrane to exhibit He/CH 4 selectivity of 43.38 and He permeability of 376.3 Barrer, respectively, which is 186% and 174% higher than the pristine PI membrane. The overall performance is also ranked among the reported other MMMs. The feasibility of scaled‐up fabrication combined with stable performance over a prolonged gas permeation test underscores the application potential of Fe‐SO 3 − ‐MOC‐based MMM in He separation.