Engineers at Caltech have created tiny structures inspired by the shape of cactus spines to create a material able to harvest drinkable water from the air during the day and night. The new system combines two water-harvesting technologies into one device. The material is a micro-architected hydrogel membrane able to produce water through solar steam-water generation and fog collection.
The fog collection system works at night, gathering water from low-lying clouds along seacoast that is heavy with water droplets. The technology can coalesce and collect the droplets from the clouds turning the fog into drinkable water. Solar steam collection is a water-collection technique that works well in coastal areas because it can also purify the water.
This technology works during the day and uses heat from the sun to cause water to evaporate into steam which can be coalesced into drinking water. The two technologies operate under vastly different conditions and typically require different materials to work. Caltech’s device combines both into a single system able to generate clean drinking water 24 hours a day.
The scarcity of water is one of the major challenges that scientists and engineers are trying to overcome worldwide. Engineers based the design of their system on cactus needles which are uniquely adapted to survive dry climates. For their system, the spines are called “micro-trees,” and they’re able to attract microscopic droplets of water suspended in the air.
The droplets slide down to the base of the spine, where they coalesce with other droplets into heavy drops that eventually converge in a reservoir of water for drinking. In the day, the hydrogel membrane absorbs sunlight to heat up water trapped underneath it, turning it into steam. The steam then condenses on a transparent cover where it’s collected for drinking. The team captured 35 milliliters of water from fog using a test system with a size between 55 and 125 square centimeters. During the day, the material collected about 125 milliliters of water from solar steam.