A promising metal–organic framework (MOF), MIL-96(Al), for CO2 separation under humid conditions

Abstract

The CO₂ adsorption uptake and enthalpies with MIL-96(Al) were assessed in the presence of up to 40% relative humidity via both experiment and simulation. Interestingly at 10% relative humidity, the water equilibrated in the pores of this MOF proffers a significant increase in affinity for CO₂ at 0.2 bar, which is associated with a limited decrease in capacity. This study suggests that at medium RH, water and CO₂ are able to adsorb in different regions of the structure. Indeed, such behaviour is explained by the preferential adsorption of H₂O in cavities containing more hydrophilic groups including Al(1)–H₂O_terminal, Al(3′)–OH_terminal and Al(3)–H₂O_terminal while CO₂ adsorbs in the remaining, less hydrophilic cavities containing μ₂-OH groups. This highlights the interest of using materials with this variety in pore chemistry as one way forward for CO₂ capture in the presence of contaminants such as water.