Perfluorinated Nanoporous Metal–Organic Framework-Based Mixed-Matrix Membranes for CO₂ Capture

The combination of perfluoropolymers with perfluorinated metal–organic frameworks (MOFs) can play an important part in the development of mixed-matrix membranes (MMMs) for the capture of CO2, thanks to the enhanced selectivity toward CO2 and resistance to humidity. Herein, we report the incorporation of the perfluorinated nanoporous MOF F4_MIL-140A(Ce), based on CeIV and tetrafluoroterephthalate, into one of the most representative perfluoropolymers in membrane science, i.e., Hyflon®AD60X, to form a MMM containing 20 wt % of the MOF filler for the separation of CO2 from N2 and CH4. The membrane was characterized by solid-state nuclear magnetic resonance (NMR) spectroscopy, infrared spectroscopy (IR), and gas sorption analysis, finding that the MOF retains its peculiar cooperative mechanism of CO2 adsorption even when embedded in the polymeric matrix. Pure-gas permeation tests on the MMM confirmed the enhancement of selectivity for CO2/N2 and CO2/CH4 gas mixtures, with nonvirtual reduction in permeability. The incorporation of F4_MIL-140A(Ce) into Hyflon®AD60X enhances the CO2/CH4 selectivity from 9.1 to 14.3 and from 6.2 to 7.7 for CO2/N2 separation. The CO2 permeabilities are slightly reduced by less than 5% from 304 to 290 Barrer. Adsorption isotherms, combined with IR and solid-state NMR spectroscopy measurements, suggested that the MMM behavior can be ascribed to the peculiar CO2 adsorption mechanism of F4_MIL-140A(Ce), which is retained even when the MOF is embedded in the polymer matrix.