Defect-Free Mixed-Matrix Membranes with Hydrophilic Metal-Organic Polyhedra for Efficient Carbon Dioxide Separation

Defect-free mixed-matrix membranes (MMMs) were prepared by incorporating hydrophilic metal-organic polyhedra (MOPs) into cross-linked polyethylene oxide (XLPEO) for efficient CO2 separation. Hydrophilic MOPs with triethylene glycol pendant groups, which were assembled by 5-tri(ethylene glycol) monomethyl ether isophthalic acid and Cu-II ions, were uniformly dispersed in XLPEO without particle agglomeration. Compared to conventional neat XLPEO, the homogenous dispersion of EG(3)-MOPs in XLPEO enhanced CO2 permeability of MMMs. Upon increasing the amount of EG(3)-MOPs, the membrane performance such as CO2/N-2 selectivity was steadily improved because of unsaturated Cu-II sites at paddle-wheel units, which was confirmed by Cu K-edge XANES and TPD analysis. Therefore, such defect-free MMMs with unsaturated metal sites would contribute to enhance CO2 separation performance.