(144g) Impact of Functional Groups on LiCl Impregnation and Performance of LiCl@ MIL-101 Analogs for Atmospheric Water Harvesting

Supporting hygroscopic salt with porous materials is a promising strategy for atmospheric water harvesting. The impregnated hygroscopic salt enables high water uptake at low relative humidity, while the porous structure allows for water uptake at higher relative humidity, also preventing salt aggregation and leaching after sorption cycles. Previous studies have focused on LiCl loading into large pore water-stable MOFs. Studies on functionalized MOF materials are, however, have been missing. In this work, LiCl was impregnated into MIL-101, and into its amino or hydroxyl functionalized analogs at various salt solution concentrations. The amine groups were introduced by using a modified linker, whereas hydroxyl groups were introduced by immobilizing ethanolamine at the open Cr metal sites of the parent MIL-101. The concentrations of aqueous LiCl solutions were optimized for each MOF material. It has been found that the introduction of the amine functional group promotes salt impregnation, while the hydroxyl group leads to a decreased amount of salt impregnated. The final water uptake depends on the balance between the salt loading and the remaining pore volume for water adsorption. The best performing sample was cycled, and the performance was retained, indicating the stability of these composites. This composite sorbent was then immobilized onto porous Ni foam for future water-harvesting device integration. By using concentrated LiCl and MIL-101 solutions, mechanically stable LiCl@MIL-101/Ni foams were obtained. The initial water uptakes were higher than for powders due to external LiCl excess. The leaching of extra framework salt eventually leads to water uptake comparable to that of the tested powders. Performance was retained after several cycles.