Poly(amphoteric)-Functionalized MXene Nanosheets to Construct Mixed-Matrix Membranes for Efficient Humidified CO2 Separation

The membrane separation approach has garnered considerable interest in the area of CO2 separation due to its advantages of requiring little electricity and a wide range of applications. Here, we report the preparation of pSBMA@Ti3C2Tx nanosheets functionalized with poly(amphiphilic poly(methacryloyloxyethylsulfobetaine) (pSBMA)) by precipitation distillation, weighing of pSBMA@Ti3C2Tx nanosheets with different mass ratios to be added into cross-linked poly(ethylene oxide) (XLPEO), and preparation of a continuous, thin mixed-matrix membrane (MMM). Under gas humidification, the membrane showed the best permeation performance. Due to the richness of hydrophilic organosulfate groups (−SO3–) and quaternary amine groups [−N+(CH3)3] in pSBMA, the overall water content of the MMMs is increased, which greatly improves the CO2 permeability. Enhancing the ratio of bound water augments the membrane's capacity to segregate CO2/N2. Under coordination of water molecules, quaternary amine groups effectively promote the quick delivery of CO2 in the membrane. In the wet state, the XLPEO/pSBMA@Ti3C2Tx-0.2 membrane has a CO2/N2 selectivity of 27.5 and a CO2 permeability of 4953 barrer, an improvement of 87% and 109%, respectively, compared to those of the XLPEO pure membrane, breaking the 2008 Robeson upper limit and approaching the 2019 upper limit. We also studied the change of the gas separation performance of the membrane under different pressures.