Water harvesting from air with a hygroscopic salt in a hydrogel–derived matrix

The extraction of water from air is a promising way to supply fresh water, especially in remote, arid regions. This process can be supported by desiccant materials such as zeolites, metal−organic frameworks, or hygroscopic salts. Here we present a composite material that is able to absorb 660 kg of water per cubic meter of bulk material from air at 10 mbar water vapor pressure and 28 °C. The material consists of calcium chloride incorporated into an alginate-derived matrix. A simple synthesis route leads to spherical beads of the composite with a diameter of approximately 2 mm. This macroscopic structure allows for good vapor permeability through packed beds. The collected water can be released at 100 °C, potentially enabling a solar-driven application. In addition, the synthetic route uses cheap, non-toxic, and easily accessible materials allowing for widespread application.Extraction of water from air is a promising way to secure fresh water supplies in remote, arid regions. Here a composite material consisting of calcium chloride incorporated into alginate-derived beads is described, and shown to reversibly absorb 660 kg of water per cubic meter of material from the air.