Super-Hygroscopic Calcium Chloride/Graphene Oxide/Poly(N-isopropylacrylamide) Gels for Spontaneous Harvesting of Atmospheric Water and Solar-Driven Water Release.

Although atmospheric water harvesting is a promising approach for extracting clean water in water deficient areas, most atmospheric water collectors require additional energy for releasing the water absorbed. It is still challenging to improve both moisture absorption capacity and desorption efficiency of moisture water collectors. Inspired by clean solar energy and the large humidity difference between day and night, super-hygroscopic calcium chloride (CaCl)/graphene oxide (GO)/poly(N-isopropylacrylamide) (PNIPAM) gels are designed for spontaneous collection of atmospheric water in a wide range of relative humidity (RH) followed by solar-driven release of the water absorbed. An optimal CaCl/GO/PNIPAM hygroscopic gel possesses a hierarchical porous structure with directional water transport channels, facilitating water capture and release, thus exhibiting a high moisture absorption capacity of up to 3.6 g g at an RH of 90%. Driven by simulated sunlight, the solar-thermal energy conversion effect of the GO component triggers a unique hydrophilic-hydrophobic conformational transition and shrinkage of the PNIPAM for efficient release of the water absorbed. The integration of the spontaneous harvesting of atmospheric water and the solar-driven water release makes the super-hygroscopic gels promising for efficiently utilizing atmospheric water for special applications where water is desperately necessary but unavailable.