In situ synthesis of polymer grafted ZIFs and application in mixed matrix membrane for CO2 separation

Mixed matrix membranes (MMMs) provide an efficient implementation that overcomes the bottleneck of individual inorganic or polymeric membranes for gas separation, but still face challenges. Here, we put forward a strategy of using in situ synthesized polymer grafted metal organic frameworks (MOFs) to eliminate both interfacial and carrier problems existing in the MMMs. Specifically, polyethyleneimine (PEI) grafted ZIF-8 (PEI-g-ZIF-8) was synthesized in situ by using Zn2+, 2-methylimidazole, and hyperbranched PEI through a rapid method at room-temperature. The chemical composition and porous structure of PEI-g-ZIF-8 were investigated by Fourier transform infrared spectroscopy, powder X-ray diffraction, N2 adsorption–desorption measurement, etc. The results indicated that the synthesized PEI-g-ZIF-8 achieves an enlarged pore volume and aminated surface. The improved interfacial compatibility between PEI-g-ZIF-8 nanoparticles and poly(vinylamine) (PVAm) was confirmed through high-sensitivity differential scanning calorimetry and zeta potential measurements. According to the CO2/gas separation tests, the MMMs incorporating with PEI-g-ZIF-8 achieved 1990 GPU of CO2 permeance and 79.9 of selectivity for CO2/N2 (15/85 vol%) separation, and 1790 GPU of CO2 permeance and 40.7 of selectivity for CO2/CH4 (10/90 vol%) separation, under 0.30 MPa gas pressure.