Amino-Functionalized Porous Organic Cages Assembled Pebax Mixed Matrix Membranes for Enhanced CO₂/N₂ Separation

Membrane separation technology has garnered significant attention for CO2 separation and purification, with mixed matrix membranes (MMMs) emerging as promising candidates due to their advantages of ease of processing, high mechanical strength, and thermal stability. The development of effective fillers for separation performance becomes one of the key foci in this area. In this work, CC3, a type of porous organic cages (POCs), was synthesized and functionalized with two amino-containing materials of different chain lengths. Polyethylenimine (PEI) and diethylenetriamine were used as modification agents to successfully graft amino groups onto the CC3 crystals to form defect-free Pebax mixed matrix membranes containing amino-functionalized CC3. The special porous structure of CC3 increases the gas permeability of the mixed matrix membrane by providing extra channels for the transportation of CO2. Besides, amino groups on functionalized CC3 interact with the chains of Pebax through hydrogen bonding, thus improving the compatibility between filler and matrix. The amino groups can further facilitate the transport of gases across the membrane through reversible reactions with CO2, which is further enhanced under humid conditions. Under optimal conditions, at 1 bar and 30 °C, the CO2 permeability of Pebax/PEI@CC3-MMMs was 342.33 Barrer with a selectivity of 33.38, while Pebax/DETA@CC3-MMMs exhibited a CO2 permeability of 273.34 Barrer and a selectivity of 35.77. This work demonstrates that amino-functionalized POCs (CC3) can effectively enhance the CO2 permeability and the CO2/N2 selectivity, which may provide a way to develop high-performance mixed matrix membranes with superior separation properties.