Progress and potential of metal-organic frameworks (MOFs) as novel desiccants for built environment control: A review

The regulation of the balance of the sensible and latent loads remains a critical problem for built environment control. Unlike the traditional vapor compression system that features high-energy consumption and environmental-unfriendly processes, desiccants represent an alternative air-conditioning method that takes advantage of the low-grade energy, decreases the energy consumption and even employs use of water vapor. Though the desiccant-based systems can achieve spatial moisture transfer through the periodic adsorption/desorption process, however, the water-stable desiccants with high water uptake and mildly reversible adsorption are required, and the traditional desiccants cannot meet these requirements. In this respect, metal-organic frameworks (MOFs), possessing a variety of structures and precise functional ability to optimize their properties, are promising porous materials exhibiting high potential for rational design and sorption-based applications. In this review, intrinsic properties and prevalent water adsorption mechanisms of the potential micro/mesoporous MOF desiccants have been elucidated. Subsequently, the selection criteria of the promising MOF desiccants for water loading removal from air in the built environment is proposed and some currently available water-stable MOFs based on different working humidity ranges have been analyzed for the potential humidity control from the aspects of microstructure, isotherms and regeneration conditions. Finally, approaches for screening the well-suited MOFs from material and system levels is presented. Overall, the cases of actual applications in the active or passive way have confirmed that MOF-based systems can effectively regulate the humidity load within the desirable range, thus, underlining the high potential of large-scale applications in the near future.