Computational screening of functional groups for ammonia capture in metal-organic frameworks

Metal-organic frameworks (MOFs) containing functional groups that strongly bind ammonia could be promising candidates for ammonia capture from air. To identify functional groups that preferentially bind ammonia versus water, we used quantum chemical methods to calculate the binding energies of ammonia and water with 21 different functional groups attached to aromatic rings, such as are common in MOF linkers. Among the functional groups studied, R-COOCu and R-COOAg are the top two candidates for ammonia capture under both dry and humid conditions. Orbital and charge analyses were performed to provide additional insight into observed behavior and trends. For Bronsted acid functional groups, increasing acidity and dielectric constant promote protonation of ammonia, as expected.