Molecularly Homogenized Composite Membranes Containing Solvent-Soluble Metallocavitands for CO2/CH4 Separation

The rational design of mixed matrix membranes (MMMs) combining appropriate additives and industrial process-able polymers offers a new prospect for highly efficient membrane separations. However, the difficulty in their fabrication due to the lack of processability of most additives and the formation of segregated filler domains in polymer matrices hampers the development and application of MMMs. Herein, we present two new zirconocene-based metallocavitands (ZRA and ZRT) and a series of MMMs fabricated by blending ZRA, ZRT, and MOC-1-NH2 (a zirconocene-based metal-organic cage) with the polyimide (6FDA-DAM), respectively. It was found that ZRA exhibited high thermal stability and good solubility in various solvents, which can be homogeneously mixed with polymers to prepare ZRA-based MMMs without any indication of filler agglomeration. Compared to the pure 6FDA-DAM membrane, a low ZRA-loading MMM (ZRA-2.2%) exhibited better mechanical properties and 50% improved CO2 permeability for CO2/CH4 separation. ZRA-2.2% also exhibited a good performance after 6 months of aging and significantly alleviated the plasticization effect under high pressures. These results suggest the great potential of the ZRA-2.2% for CO2/CH4 separation and that the simple metallocavitands may serve as promising additives in fabricating MMMs for gas separations.