Microscopic Kinetics of Water Adsorption in Metal–Organic Frameworks

Abstract

Metal–organic frameworks (MOFs) have shown great potential in atmospheric water harvesting, dehumidification, and passive evaporative cooling. Their performance is determined by the water uptake and adsorption kinetics of the MOFs. Here, the water adsorption kinetics in MOFs are systematically investigated using our proposed theoretical framework and experimental measurements. At low relative humidities (RHs), water molecules are adsorbed and diffuse freely in MOFs, as described by the linear driving force assumption and Fick’s law. At high RHs, water condenses into liquid clusters before diffusing, modeled by a two-concentration framework. At medium RHs, both water molecules and clusters coexist in MOFs. Good agreement between experiments and simulations of water uptake and kinetics of UiO-66, CAU-10-H, MOF-801, MIL-101, and MOF-303 demonstrates our theoretical framework fully captures water vapor adsorption processes in MOFs. Our results further show that water adsorption capacity and kinetics are jointly influenced by the porosity, pore radius, and pore geometry factor.