(582b) Water-Bridges Substitute for Defects in Amine-Functionalized Uio-66, Boosting CO2 Adsorption

The search for cheap, effective, and benign methods to separate gases from mixed streams is one of the world's greatest challenges. Metal organic frameworks (MOFs) have proven to be exceptional materials for these separations, in part because of the myriad of structures that can be designed to target specific gases. In practice, however, adsorption often takes place in the presence of other gases, which themselves can co-adsorb, complicating matters. For example, the removal of CO₂ from flue gases or humid cabin air on the International Space Station must account for the presence of water. Here, Ideal Adsorbed Solution Theory (IAST) is unable to predict multicomponent adsorption due to the clear non-idealities. Moreover, the presence of MOF defects can change the nature of the MOF, skewing adsorption. In these cases a proper understanding of the role of defects and functional groups on binary adsorption would significantly aid in the design of better MOFs for gas separations. This work presents a combined experimental and computational study of H₂O/CO₂ adsorption in amine-functionalized UiO-66. Grand canonical Monte Carlo simulations are used to investigate binary adsorption in three variations of UiO-66, each with different linkers. Furthermore, each MOF is investigated as a perfect crystal as well as two additional forms with precise linker defects. Under certain water loadings, it is found that CO₂ adsorption is slightly enhanced. Binary adsorption experiments confirm the peculiar behavior seen from the simulations. A detailed examination of the simulations shows that water-bridges form between metal oxide cores, replacing linker defects. Furthermore, the proximity of these water bridges to the certain features of the MOF lead to this enhancement of CO₂ adsorption. This work provides a deeper understanding of the interaction of water with MOF defects and the resultant co-adsorption of a second gas that could aid in the design of new materials that harness this effect.