Highly efficient separation of residual carbon dioxide (CO2) from syngas, mainly composed of carbon monoxide (CO) and hydrogen (H-2), could not only make its utilization more energetically efficient but also avoid catalysts poisoning in some industrial applications. In the attempts to address this issue, it is acknowledged that CO2/CO separation is the vital step since H-2 is a nonpolar molecules, difficult to be polarized and could be easily separated from CO2. Herein, we report a novel strategy to graft basic ethylenediamine (ED) molecules onto porous metal-organic frameworks (MOFs) as solid adsorbents for CO2/CO separation via solvent 'squeezing' approach, in which Cu-3(BTC)(2) (BTC = 1,3,5-benzenetricarboxylate) MOF was employed as the pristine MOF. Surprisingly, the ED-grafted Cu-3(BTC)(2) shows unprecedented enhancement of CO2/CO selectivity of 226% at 273 K and 861% at 298 K, respectively, in comparison with the solvent-free Cu-3(BTC)(2). Moreover, despite the large isosteric heats of adsorption of CO2 on the ED-grafted Cu-3(BTC)(2), it could be easily regenerated at moderate temperature. This work provides an efficient and facile method to functionalize MOFs for CO2 capture. (C) 2017 Elsevier Ltd. All rights reserved.