Modeling Water and Ammonia Adsorption in Hydrophobic Metal-Organic Frameworks: Single Components and Mixtures

Capturing ammonia under humid conditions is difficult because chemical functionalities that attract ammonia tend to also attract water. In this work, three hydrophobic metal organic frameworks (MOFs) were assessed for ammonia capture under dry and humid conditions. Using grand canonical Monte Carlo simulations, pure water isotherms were calculated and showed good agreement with experiment. The low heats of adsorption for water substantiate the hydrophobic nature of these MOFs. Simulated ammonia isotherms predict that hydrophobic MOFs adsorb similar amounts of ammonia under dry and humid conditions. These results suggest that hydrophobic MOFs could be appropriate candidates for ammonia capture under humid conditions. The simulations also provide detailed information on the behavior of water and mixtures of water and ammonia confined in hydrophobic pores.