Drought-prone regions may benefit from the development of a hydroscopic hydrogel that can efficiently capture moisture from the air. The capacity of polyacrylamide (PAM) hydrogels for water uptake has been enlarged by MIT researchers through the inclusion of lithium chloride salt, a powerful desiccant, into the moisture-harvesting material.

The salt-reinforced PAM hydrogel was demonstrated to absorb and retain an unprecedented amount of moisture across a range of humidity levels, including very dry conditions that have limited other material designs. Even in very dry conditions, with 30% relative humidity, the material can pull vapor from the air and hold in the moisture without leaking. The contained liquid can then be collected as pure water after being heated and condensed.

The researchers conducted prolonged swelling experiments to achieve greater salt loadings, which in turn lead to higher water uptakes, than achieved in similar studies. After soaking in salty solution for 30 days, hydrogels incorporated up to 24 g versus the previous record of 6 g of salt/g of polymer. These samples were observed to swell and absorb more moisture at all humidity levels and to capture 1.79 g of water/g of hydrogel at relatively low humidity levels.

In addition to atmospheric water harvesting, the water-collecting system described in Advanced Materials might also find use in passive cooling, thermal energy storage and space conditioning applications.