Amine and fluorine co-functionalized MIL-101(Cr) synthesized via a mixed-ligand strategy for CO2 capture under humid conditions

• MIL-101-NH 2 -F0.5 was synthesized by a mixed ligand strategy. • The adsorbent exhibited moderate isosteric heat of adsorption, high CO 2 selectivity. • Hydrophobicity index of MIL-101-NH 2 -F0.5 was increased compared to MIL-101-NH 2 . • The adsorbent exhibited high hydrothermal stability after steam treatment. The selective capture of CO 2 in humid conditions on metal–organic frameworks is challenging due to competitive adsorption of H 2 O and CO 2 on the active sites. Herein, amine and fluorine co-functionalized MIL-101(Cr) was synthesized and evaluated for use as CO 2 adsorbent to overcome this issue. MIL-101(Cr)–NH 2 -F0.5 (CrA-F0.5) was prepared using a mixed-ligand strategy, and contains 2.9% nitrogen and 0.5% fluorine while maintaining the MIL-101(Cr) structure. Numerically, one 4F ligand per 20 amino ligands was included in the CrA-F0.5 structure. The calculated selectivity for CO 2 /N 2 of CrA-F0.5 is 108 (CO 2 /N 2 = 15/85) at 20 ℃ and 1 bar, and this value was 3.7 and 2.1 times higher than that of MIL-101(Cr) and MIL-101(Cr)–NH 2 , respectively. The results of CrA-F0.5 adsorption of CO 2 indicated that amine and fluorine groups served as adsorptive sites for CO 2 in this structure. The moderate isosteric heat of CO 2 adsorption value (45 kJ mol −1 ) of CrA-F0.5 merits in desorption of CO 2 . The result of a hydrophobicity index test, indicated that CrA-F0.5 was 2.5 times hydrophobic than MIL-101(Cr)–NH 2 . In a CO 2 and N 2 breakthrough test, compared to the dry condition, the CO 2 breakthrough time at 30 ℃ and 1 bar was reduced by 40% for MIL-101(Cr)–NH 2 and by 10% for CrA-F0.5 in 60% relative humidity. The CO 2 and N 2 breakthrough results under humid conditions were consistent with the hydrophobicity index value, and the excellent water repellency of CrA-F0.5 was confirmed. CrA-F0.5 is considered a candidate suitable for CO 2 adsorbent in an actual post-combustion CO 2 adsorption process.