Polyethylenimine grafted ZIF-8@cellulose acetate membrane for enhanced gas separation

Mixed matrix membranes (MMMs) combine the advantages of both polymers and inorganic fillers, and hold great promise for industrial gas separation. In this work, to enhance the interfacial compatibility between cellulose acetate (CA) matrix and ZIF-8 crystals, an interfacial design strategy was proposed by grafting polyethylenimine (PEI) onto ZIF-8 particles. The introduction of amine-rich PEI could regulate the surface property and maintain the pore accessibility of ZIF-8 crystals. In addition, the amine groups in PEI could interact with hydroxyl/carbonyl groups in CA chains to suppress the non-ideal voids at the ZIF-8/CA interface. With the aid of PEI, the interfacial compatibility between ZIF-8 and CA is substantially enhanced. Compared with pristine CA and ZIF-8@CA membranes, PEI grafted ZIF-8@CA (PZIF-8@CA) membrane exhibits a better gas separation performance, bearing a CO2 permeability of 150.3 Barrer with CO2/N-2 and CO2/CH4 ideal selectivities of 44.2 and 53.7, respectively. The separation mechanisms are attributed to the superior interfacial property, the good dispersion of ZIF-8 particles, the amine groups in PEI, and the high CO2 solubility of the CA matrix.