Structural stability of metal organic frameworks in aqueous media – Controlling factors and methods to improve hydrostability and hydrothermal cyclic stability

• There are six major factors which control the structural stability of metal organic frameworks (MOFs) in aqueous media.
• There are eight different strategies which can be adopted to improve the hydrothermal stability of MOFs in aqueous media.
• Hydrothermal cyclic stability becomes critical when MOFs are being used as adsorbents in adsorption refrigeration systems.
• Ligand functionalization has been found to be the most effective strategy for improving hydrothermal cyclic stability.

Metal organic frameworks (MOFs) have recently emerged as a center of attention among the class of more traditional porous materials including zeolites, activated carbons, and silica gels, due to their significantly larger pore volumes and tunability of pore geometry. A large amount of literature exists incorporating the gas adsorption and separation characteristics of MOFs; however, only a limited portion has been dedicated to the water adsorption properties of these novel materials. Water adsorption capacities of MOFs are known to substantially exceed those of traditional porous materials, due to which they are continuously gaining increasing attention for potential applications in water desalination and purification, dehumidification, and adsorption cooling technologies. However, a vast majority of these materials is characterized by structural degradation on either immediate or prolonged exposure to moist environments, resulting in partial or complete deterioration of water adsorption characteristics of the framework. This article reviews the various structural parameters which control the dimensional stability of MOFs in aqueous media, as well as different strategies which have been reported in literature for improving the hydrothermal resistance of these materials for potential applications in the industrial sector.

(a) Factors controlling the structural stability of MOFs in aqueous media, and (b) methods used to improve the hydrostability and hydrothermal cyclic stability of MOFs (PECVD = plasma enhanced chemical vapor deposition).Figure optionsDownload as PowerPoint slide