Mixed matrix membrane based N2/CF4 separation intensified by “window-cage dual sieving” strategy

The perfluorocarbons (PFCs), such as CF 4 , serving as crucial plasma etching gases, have caused a significant threat to the global greenhouse effect. Therefore, the enrichment and recycling of CF 4 is particularly important. However, since the CF 4 /N 2 mixture used for plasma etching with CF 4 content lower than 10 vol %, it is urgently necessary to develop N 2 -preferred transmissible membranes. Herein, cyclic crown ethers with hollow cavity were proposed to be encapsulated within ZIF-7 cages to sieving N 2 and CF 4 by “window-cage dual sieving”, while minimizing the sacrifice of N 2 permeance. Specifically, due to its larger size than the window size of ZIF-7, 15-crown-5 (15C5) was physically restricted into ZIF-7 cages, achieving permanent size sieving. As characterized by TEM and BET results, with the 15C5 modification ratio increasing, the ZIF-7 cage size was tuned from 0.46 nm to 0.43 nm, leading to improved N 2 /CF 4 selectivity. Meanwhile, the ether-oxygen bonding of 15C5 enhanced the interfacial compatibility between the 6FDA-DAM polymer matrix and ZIF-7, improving the filler loading as high as 50 wt%. The resultant 15C5 3 @ZIF-7/PI MMMs at filler loading of 40 wt% achieved N 2 permeability and N 2 /CF 4 ideal selectivity of up to 83.2 Barrer and 6.79, which were improved by 253.0 % and 223.3 %, compared to the pure PI membrane. Together with the good long-term stability and mechanical properties, 15C5@ZIF-7/PI MMMs provide a bright prospect in the membrane based recovery of PFCs for industrial applications.