Solar Energy Triggered Clean Water Harvesting from Humid Air Existing above Sea Surface Enabled by a Hydrogel with Ultrahigh Hygroscopicity.

Water scarcity is a ubiquitous problem with its magnitude expected to rise in the near future, and efforts to seek alternative water sources are on the rise. Harvesting water from air has intrigued enormous research interest among many groups with Scientific American listing this technology as the second most impactful technology that can bring about a massive change in people's lives. Though desalination offers a huge prospect in mitigating water crisis, its practicality is limited by exorbitant energy requirement. Alternatively, the air above sea water is moisture rich, with the quantity of vapor increasing at the rate of 0.41 kg m-2 . Herein, a method to sustainably harvest water from this moisture rich zone is demonstrated by employing a nanoporous superhygroscopic hydrogel, which is capable of absorbing water from highly humid atmospheres by over 420% (highest) of its own weight. The desorption process from the hydrogel, occurring at 55 °C (lowest), is triggered by natural sunlight (A.M 1.5) thereby ensuing an external energy-less water harvesting approach. The hydrogel exhibits excellent stability even after 1000 absorption/desorption cycles. Through multiple absorption/desorption cycles, it is possible to harvest over 10 L water per kg of hydrogel daily.