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Developing an efficient adsorbent for selective separation and capture of CO2 from CO2/N-2 mixture is an important and challenging issue for mitigating global warming. In this study, we posited that high CO2/N-2 selectivity could be obtained by impregnating polyethyleneimine (PEI) within the pores of NU-1000, a zirconium based metal-organic framework (MOF), since it has a high surface area (similar to 2320 m(2)/g) and free and exposed -OH groups but does not have unsaturated metal sites possibly having strong interactions with N-2 molecules. A series of PEI-impregnated NU-1000 (PEI(x)@NU-1000) materials with varied PEI loadings have been successfully prepared. As reasoned, PEI(50)@NU-1000 showed the highest CO2/N-2 selectivity among the PEI-loaded adsorbents in the literature under similar conditions. Remarkably, it exhibited extremely high CO2/N-2 selectivities (similar to 8000) at low pressures and a very high CO2/N-2 selectivity (661) at a typical pressure of flue gas (1 bar). Furthermore, PEI(50)@NU-1000 could efficiently separate CO2/N-2 mixture under a dynamic flow condition and maintained its CO2 uptakes during three consecutive adsorption and desorption.