The capture of carbon dioxide (CO2) from dilute streams characterized by high relative humidity, such as flue gas from coal- and natural gas-fired power plants, represents a viable strategy for mitigating large-scale CO2 emissions. While metal–organic frameworks (MOFs) have long been regarded as high-capacity CO2 adsorbents, their performance often declines under humid conditions. This decline arises either from competitive adsorption between CO2 and H2O at the same binding sites or from the intrinsic lack of hydrolytic stability in many MOFs. We have developed a series of novel MOF materials that maintain, or even enhance, their CO2 adsorption capacity in the presence of water vapor compared to dry conditions. Our design strategies included the incorporation of aluminum cations and closely spaced aromatic ligands (adsorbaphores) as MOF building blocks, chemical functionalization of the ligands with polarizable groups to strengthen CO2–MOF interactions, and decoration of MOF pores with ammonia molecules coordinated to sets of open metal sites spaced at short distances. CO2 and H2O vapor adsorption isotherms, along with CO2 breakthrough curve measurements, confirmed the enhanced CO2 capture performance of these materials under humid conditions, while spectroscopic and X-ray diffraction analyses provided insights into the molecular-scale mechanisms responsible for the observed behavior.
