Researchers at King Abdullah University of Science and Technology (KAUST) have invented a hydrogel-based material that is able to capture moisture from low-humidity air, and then release it on demand. The technology could provide a secure new source of drinking water to the world’s most remote, arid regions.
Earth’s air contains almost 13 trillion tons of water, making it a vast renewable reservoir of clean drinking water.
The device utilizes calcium chloride, a cheap, stable, nontoxic salt with an affinity for water. It is this affinity for water which attracts water to the device, until a pool of water eventually forms. However, it is water soluble, which initially presented a challenge as a calcium chloride solution would not be potable. However, KAUST researchers incorporated the salt into hydrogel, which retains its solid state as the calcium chloride captures water. Researchers also added carbon nanotubes into the mix as an expulsion mechanism for the collected water. They chose carbon nanotubes as they efficiently capture heat from the Sun.
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Left outside overnight, the device was able to capture 37 grams of water (one milliliter of water weighs one gram). Relative humidity stood at 60 percent at the time of this experiment. The next morning, following 2.5 hours of natural sunlight irradiation, most of the water was released via the carbon nanotubes and released and collected inside the device.
“The hydrogel’s most notable aspects are its high performance and low cost,” stated Renyuan Li of KAUST’s Water Desalination and Reuse Center. If the prototype were scaled up to produce 3 liters of water per day–the minimum water requirement for an adult–the material cost of the adsorbent hydrogel would be as low as half a cent per day.
The researchers’ work continues for now. Currently they are working on a mechanism which would ensure continuous release of the collected water, rather than it being released in batches. This could also allow the technology to be used to irrigate crops automatically.