In metal–organic framework (MOF) chemistry, polar functionalities greatly affect the gas adsorption properties. However, synthesis of MOFs with desired functionality is very challenging because many chemical functionalities cannot be achieved under the conditions for MOF assembly. Herein, a facile synthesis of new functionalized two-dimensional MOFs with preferential CO2 capture is presented, which uses two successive synthesis steps: 1) rational design and template-free synthesis of the parent MOF with designated pendant amino groups and 2) postsynthetic modification of the active amino groups with acetic acid and trimesoyl chloride functionalities. The only variation in structure arises from the functional groups of these materials. Experimental results demonstrate that the three 2D layered MOFs have remarkable thermal stability and moisture resistance, which are particularly advantageous for practical CO2 capture. Although their surface areas are moderate (270–340 m2 g−1), they still have excellent CO2 adsorption capacity (up to 2.9 mmol g−1 at 1 bar and 273 K) comparable to that of previously reported MOFs with much higher surface areas. Based on first-principles calculations, it is shown that the acidic carbonyl functionalities in addition to the amino groups are also favorable to bind CO2 molecules. The adsorption sites generated from polar functionalities are key factors leading to high CO2 uptake.