A library of 20 UiO-66-derived metal-organic frameworks (MOFs) was synthesized in a combinatorial approach involving mixed ligand copolymerization and two post-synthetic modifications (PSMs) in tandem. These MOFs exhibit excellent water stabilities in a pH range of 1 to 12, together with high CO2 uptake capacities and selectivities revealed by the analysis of 147 isotherms, which make them promising adsorbents in adsorption-based CO2 separations such as post-combustion CO2 capture and natural gas upgrading.