Dual-site engineering in EDTA-modified Mg-MOF-74 for effective CO2 capture under humid conditions

An ultramicroporous variant of Mg-MOF-74 is synthesized through a mixed-linker strategy incorporating ethylenediaminetetraacetic acid (EDTA) as exotic linker. • An exclusive H 2 O adsorption site is created based on the uncoordinated oxygen atoms of EDTA. • The hydrogen-bonding network within EDTA-modified frameworks enhances CO 2 adsorption by 14.3 % via the formation of carbonates. • Incorporating EDTA molecules increases the CO 2 /N 2 selectivity by a factor of 2.28 compared to pristine Mg-MOF-74. • The EDTA-modified Mg-MOF-74 outperforms the pristine Mg-MOF-74 with a two-fold enhancement in CO 2 uptake under humid conditions. Mg-MOF-74 ([Mg 2 (DOBDC)]) represents a high-performance solid adsorbent for carbon capture, however, its CO 2 uptake decreases significantly under humid flue gas conditions due to competitive adsorption between H 2 O and CO 2 molecules. Herein, a mixed-linker modification strategy is employed by integrating ethylenediaminetetraacetic acid (EDTA) into the Mg-MOF-74 framework. This approach preserves the original one-dimensional pore structure while altering the coordination environment of Mg 2+ sites, reducing their coordination number to five. The resulting structure with uncoordinated oxygen atoms from EDTA serves as exclusive adsorption centers for H 2 O thereby protecting the CO 2 adsorption capacity. The optimized MOFs exhibits a high CO 2 adsorption capacity (6.4 mmol/g, at 1 bar) and outstanding CO 2 /N 2 selectivity (346). In humid CO 2 /N 2 (15:85, v:v, at 314 K, RH% = 86%) breakthrough experiment, the EDTA-modified frameworks maintain stable CO 2 uptake (3.92 mmol/g), consistent with dry performance, whereas the pristine Mg-MOF-74 shows a great reduction (2 mmol/g). In-situ FTIR further reveals that the incorporation of EDTA facilitates the formation of hydrogen bonding and carbonate species, synergistically enhancing the moisture resistance of MOF materials. Moreover, the modified material retains stable breakthrough times over six consecutive adsorption-desorption cycles under high-humidity conditions, demonstrating its great potential for scalable industrial carbon capture applications.