Hydratable Core-Shell Polymer Networks for Atmospheric Water Harvesting Powered by Sunlight

The development of technologies to enable fresh water harvesting from atmospheric moisture could help overcome the problem of potable water scarcity. Here, an atmospheric water harvesting (AWH) device is assembled in a core-shell structure, with the core consisting of networks of alginate (Alg) and polyaniline (PANI) and the outer layer consisting of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) modified with sulfonic acid groups (SPNIPAM) to increase the water adsorption at low relative humidity. The resulting hydrogel, modified with lithium chloride (LiCl) for increased water storage capacity (SPNIPAM-Li-PANIAlg), displays a similar lower critical solution temperature to pristine PNIPAM (32 °C) while affording a 15-fold higher water capture ratio, and releases water upon exposure to sunlight at intensities less than 1 kW m^-2 . The developed AWH system is capable of harvesting 6.5 L of water per kilogram in a single daily absorption/desorption cycle under sunlight and can operate at relative humidity levels as low as 17% with no additional external energy input. The thermo-responsive hydrogel SPNIPAM-Li-PANIAlg exhibits excellent stability during natural sunlight-driven absorption/desorption cycles for at least 30 days, and allows sustainable harvesting of over 28.3 L kg^-1 from a moisture-rich environment by means of multiple absorption/desorption cycles.