In this study, a previously reported Zr-MOF UiO-66(Zr)-(COOH)2 with optimal features for CO2 capture was ionized by neutralization with aqueous MOH solutions (M=Li+, Na+, K+). This post synthetic modification route has endowed some of the resulting MOFs with higher CO2 uptake capacity. The CO2/N-2 selectivity of UiO-66(Zr)-(COOK)(2) calculated by Ideal Adsorption Solution Theory (IAST) demonstrates a significant enhancement of 83% compared with the pristine MOF. In addition, dynamic column breakthrough experiments were performed using a binary CO2/N-2 mixed gas with a molar ratio of 15:85 to mimic the flue gas composition. The CO2/N-2 selectivity of UiO-66(Zr)-(COONa)(2) calculated based on breakthrough data is 99.6, which is among the highest CO2/N-2 selectivities obtained experimentally using binary mixed gas breakthrough/co-adsorption experiments. Our results strongly confirm that ionization is an effective way of introducing strong CO2 adsorption sites into MOFs for higher CO2-MOF interactions and better CO2 separation performance. (C) 2014 Elsevier Ltd. All rights reserved.