Exploring the Adsorption and Dynamics of Water in Zeolite-Like Metal-Organic Frameworks Using Atomistic Simulations

Recently, zeolite-like metal-organic frameworks (ZMOFs) topologically similar to zeolites have been experimentally synthesized. Unlike many MOFs, ZMOFs maintain their structural integrity in water and therefore are interesting from a practical point of view as candidates for applications in aqueous media. We present a molecular scale description on the behavior of water in a ZMOF. Adsorption of water in the ZMOF is studied, including adsorption capacity and isosteric heat. Water adsorption in ZMOF is a three-stage process similar to that observed in zeolites. As loading increases, diffusivity of water in the ZMOF initially increases, but decreases at high loading. A blue shift is observed in the frequencies of the librational motions for water in the ZMOF. With increasing loading, the “structure-making” capability of adsorbed waters enhances, thus a blue shift in bending peak is observed, which is in perfect agreement with the red shift in stretching peak. The adsorbed waters in ZMOF behave as “zeolitic waters”.