Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates

Abstract

The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake exhibited by salt-based sorbents makes them attractive for AWH, especially in low relative humidity (RH) environments. Salt-based sorbents often have relatively high desorption heat, rendering water release an energy-intensive process. We proposed a hygroscopic gel, PAM hydrogel controlled incorporated with LiCl, capable of effective moisture harvesting from arid environments. The interactions between the hydrophilic hydrogel network and the captured water enable the PAM-LiCl to accumulate more free and weakly-bonded water molecules, significantly lowering the desorption heat compared with conventional neat salt sorbents. Benefiting from the affinity for swelling of the polymer backbones, the developed PAM-LiCl achieves a high water uptake of ca. 1.1 g/g at 20% RH with fast sorption kinetics of ca. 0.008 g g⁻¹ min⁻¹ and further demonstrates a daily water yield up to ca. 7 g/g at this condition. These findings provide a new pathway for synthesis of materials with efficient water absorption/desorption properties, to reach energy-efficient water release for AWH in arid climates.