Mixed matrix membranes incorporating two-dimensional ZIF-8 nanosheets for enhanced CO2/N2 separation

•ZIF-8 nanosheets were synthesized by the surfactant-assisted hydrothermal method.•The nanosheets were mainly exposed with small 4 M window on basal planes.•The nanosheets enhanced diffusion-based CO2/N2 separation performance of MMMs.•The enhancement likely stemmed from smaller 4 M window than conventional 6 M window.•Both symmetric and TFC MMMs outdid most of the reported for CO2/N2 separation.