Incorporating nano-sized ZIF-67 to enhance selectivity of polymers of intrinsic microporosity membranes for biogas upgrading

[Display omitted] •Nano-sized ZIF-67 was synthesized and incorporated into PIM-1 matrix.•The resultant MMMs showed significantly enhanced CO2/CH4 selectivity.•The nano-sized fillers afforded an improved polymer-filler compatibility.•A modified Maxwell model was proposed to elucidate the gas transport behaviors. Membrane-based separations are of energy-efficient and environmentally benign attributes for biogas energy developments. Membranes from polymers of intrinsic microporosity (PIMs) often suffer from low selectivity. In this study, remarkable enhancements in CO2/CH4 selectivity of PIM-1 membranes are achieved by incorporating nano-sized ZIF-67 (ZIF-S) filler with a larger specific surface area and a better compatibility, thereby fortifying the interactions with PIM-1 matrix and effectively alleviating nonselective interfacial voids. For the resulting PIM-1/ZIF-S membranes, a maximum CO2/CH4 selectivity of 21.1 was acquired with 15 wt% loading of ZIF-S, an increase of 69.40% compared with the pristine PIM-1 membrane, along with an associated CO2 permeability above 2800 Barrer. To elucidate gas transport behaviors within membranes, a modified Maxwell model is developed and the calculation results match well with the experimental data. The strategy of incorporating framework nanofillers into membranes may find promising applications in enhancing the selectivity of highly permeable polymer membranes.