(608f) Binary Adsorption of CO2 and H2o on Uio-66 and Amine-Functionalized Uio-66 Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are being examined for a variety of different gas adsorption applications. In many of these applications adsorption occurs in a mixed gas stream, but due to the difficulty of completing mixed-gas adsorption isotherm measurements, there is only a limited amount of experimental isotherm data. The absence of binary adsorption isotherm data limits detailed understanding of complex surface adsorption behavior. Of the various gas separations that are commonly examined, the adsorption of CO₂ on porous solids is of particular interest because this process frequently takes place in a humid gas stream, and yet is commonly studied in dry gas conditions. The presence of humidity in this adsorption process is complex, and in some cases, the impact of humidity on the process is difficult to predict. With this in mind, we have experimentally measured the binary adsorption of CO₂ and H₂O on UiO-66, UiO-66-NH₂, and validated these results to molecular simulations of the binary adsorption isotherms. Then we extended the computational analysis to examine UiO-66 with other amine functional groups and determined the impact of MOF defects on the binary adsorption isotherms. The results show that defects have a significant impact on how water and CO₂ adsorb on the MOF. In some cases, adsorption is enhanced at low pressures, but in other cases these enhancements do not exist. To understand the enhancement in more detail, we utilized simulations and showed that in one MOF water can bridge OH terminated defect sites, which increases the interactions of CO₂ with the adsorbent and enhances CO₂ adsorption. The results highlight the importance of mixed gas adsorption measurements when examining materials for gas separations.