Starch-derived photoresponsive high-efficientcy hygroscopic hydrogel for all-weather atmospheric water harvesting

Atmospheric water harvesting (AWH) technology, a new strategy to address the scarcity of fresh water, can be used to collect water from ambient air to produce clean water. Materials with moisture absorption-desorption capabilities are the key to AWH technology. Therefore, this paper reports a starch-derived photoresponsive atmospheric water-harvesting material with an acrylic acid (AA)/acrylamide (AM)-grafted starch hydrogel as the backbone, carboxylated carbon nanotubes (FCNTs) as the solar absorber, and lithium chloride (LiCl) as the water absorber. It was found that the hydrogel had good hygroscopicity in the relative humidity range of 25%–90%, and the adsorption capacity reached 8.5 g g−1 at 90% relative humidity. This hydrogel could recycle collected water vapor, and its performance and economy were found to be better than those of most reported atmospheric water harvesting materials. This material is driven by solar energy to release adsorbed water, and more than 94% of the adsorbed water was released quickly over a wide solar intensity range of 0.5–2 kW m−2. When used in the natural environment during the night/day cycle, this hydrogel was reversibly hygroscopic and achieved clean water production. This highlights the potential of biopolymers for atmospheric water harvesting applications.