In-situ etching MOF nanoparticles for constructing enhanced interface in hybrid membranes for gas separation

Metal-organic frameworks (MOFs) based hybrid membranes have great potential for energy-efficient gas separation. However, the defective interface structure greatly depresses their separation performance. In this work, a distinctive interfacial design strategy via in-situ etching ZIF-8 nanoparticles is proposed to construct hybrid membranes with nearly defect-free interfaces. The nanoscale etching of ZIF-8 nanoparticles in polymer matrix with acid group (PI-COOHx) is well controlled by the amount of carboxyl group and reaction time. Owing to the strong coordination interaction between Zn2+ ions and –COOH groups, the residual ZIF-8 nanoparticles are tightly wrapped by polymer matrix. Molecular simulation was performed to study the in-situ etching ZIF-8 in PI-COOHx matrix in molecular level. The resulted hybrid membranes (PI-COOHx/E-ZIF-8) exhibit simultaneously enhanced permeability and selectivity with increasing filler loading content. Benefiting from the rational interfacial design, the effective loading content of ZIF-8 nanoparticles is up to 50 wt% for PI-COOH20/E-ZIF-8 membrane. The H2, CO2, and O2 permeability of the membrane are 3058.6, 1429.0, and 459.0 Barrer, increasing by 468.5%, 288.3% and 348.2%, respectively, of pristine PI-COOH20 membrane, and the gas selectivity for H2/N2, H2/CH4, O2/N2, and CO2/CH4 gas pairs are greatly improved from 20.3, 23.4, 3.9 and 16.0 of pristine PI-COOH20 membrane to 30.7, 37.6, 4.6 and 17.6. The comprehensive separation performance for H2/N2, H2/CH4, and O2/N2 gas pairs surpass the 2008 upper bound and approach the 2015 upper bound. Meanwhile, the CO2 plasticization resistance of PI-COOH20/E-ZIF-8 membrane also achieves significant improvement from 6 bar of PI-COOH20 membrane to 27 bar. This work provides an effective and robust strategy to effectively enhance the interfacial compatibility of hybrid membranes.