Direct Evidence of CO 2 Capture under Low Partial Pressure on a Pillared Metal–Organic Framework with Improved Stabilization through Intramolecular Hydrogen Bonding

Direct structural observation of CO 2 ‐loaded MOFs is helpful for revealing the specific binding interactions to allow the design of better CO 2 sorbents, but such direct structural evidence is almost always observed for pure‐component CO 2 under a pressure of 1 atm or more, which does not really represent practical CO 2 capture and separation under low partial pressure (≤1 atm) in the presence of other gases. Herein, a series of isoreticular MOFs [Zn(Trz)(R‐BDC) 1/2 ] (FJU‐40‐R, R=H, NH 2 , Br, or OH) are synthesized. Among them, FJU‐40‐NH 2 exhibits the highest robustness, and good heat and water resistance, attributed to its intramolecular hydrogen‐bonding interactions. A CO 2 /N 2 (15:85, v/v) mixture can be separated efficiently through a column packed bed of FJU‐40‐NH 2 solid. The structures of CO 2 ‐loaded FJU‐40‐NH 2 at 1 atm under various atmosphere conditions, including pure CO 2 , CO 2 /N 2 (15:85, v/v), and air, are observed, and it is found that: 1) the mechanism for CO 2 loading into the cages depends on the CO 2 partial pressure; 2) FJU‐40‐NH 2 can capture CO 2 directly from air, and CO 2 will have priority to occupy hydrophobic cage‐I, whereas hydrophilic cage‐II containing the amino group is occupied by H 2 O molecules; 3) the triazolate C−H groups, rather than the amino groups in past observations in dry ice, act as predominant functional sites here under low CO 2 partial pressure.