Efficient and stable direct air capture with amine-functionalized MIL-100(Cr) metal-organic framework

Metal–organic frameworks (MOFs) are promising for Direct Air Capture (DAC) due to their tunable pore structures, large surface areas, and chemical functionalization. Amine-functionalized MOFs significantly enhance CO 2 adsorption, yet most studies focus on adsorption capacity, with limited research on the impacts of water vapor and oxidative stability in practical DAC applications. Herein, MIL-100(Cr) was modified with polyethyleneimine (PEI), tetraethylenepentamine (TEPA), and diethanolamine (DEA) via impregnation, and their CO 2 capture performance under DAC conditions was systematically evaluated, including adsorption capacity, cyclic stability, water resistance, and oxidative stability. PEI-modified MIL-100(Cr) exhibited the best CO 2 adsorption capacity, achieving 1.21 ​mmol ​g −1 at the same level of amine incorporation and retained over 90 ​% of its initial capacity after 20 cycles. Under humid conditions, the CO 2 adsorption performance of solid amine materials was further improved, due to the enhanced utilization of amine sites, particularly increased accessibility of secondary amines. Furthermore, the PEI-modified MIL-100(Cr) exhibited superior oxidative stability compared to TEPA-modified adsorbents. This study provides valuable insights for optimizing MOF-based adsorbents in practical DAC applications. • MIL-100(Cr) was modified with PEI, TEPA, and DEA by impregnation. • CO 2 uptake over Cr-50%PEI reaches 1.21 ​mmol ​g −1 with better adsorption and stability. • Humid conditions enhance CO 2 adsorption by improving amine efficiency. • Cr-50%PEI exhibits strong coordination and high oxidative stability.