In-situ synthesis Al-fumarate on polyurethane foam as a monolithic desiccant for adsorption heat pump systems

Metal-organic framework (MOF) is considered the most promising adsorbent in adsorption heat pump (AHP) systems, owing to its high water-harvesting capacity and rapid adsorption kinetics. However, the practical implementation of powdery MOF usually suffers from poor recovery and easy agglomeration. In this work, a novel Al-fumarate loaded on polyurethane (PU) foam (PU/Al-fumarate) to construct a monolithic desiccant was designed using an in-situ synthetic self-assembly technology. Two synthesis strategies including mixed solvent thermal method (M method) and low-temperature solution method (L method) were implemented and compared. The influences of different synthesis methods on the MOF loading rate, crystal phase, chemical composition, pore structure, microscopic morphology, and the adsorption/desorption performance of monolithic desiccants were systematically discussed. The results showed that the two synthesis methods had no fundamental effects on the composition and crystal phase of PU/Al-fumarate. However, the M-method design strategy possessed a better MOF loading rate (71.76%), higher specific surface area (722.15 m2·g-1), and more excellent water-adsorption capacity (0.333g·g-1) as compared with the monolithic adsorbent synthesized by L-method technology. Furthermore, the resulting monolithic desiccant designed by the M-method strategy showed low desorption activation energy and good cyclic stability. Therefore, this novel PU foam-based Al-fumarate synthesized by M-method as monolithic desiccant will provide a potential candidate for AHP system.