This invention could turn desert air into water

Saudi researchers have developed a hydrogel that can absorb a lot of water into the air and release it on demand. An invention that could allow the inhabitants of the deserts to hydrate themselves at a lower cost.

An oasis in the desert. Nothing surprising in itself, except when this aquatic haven only starts from … the arid air of the desert! Unbelievable, at first glance, but this is the invention of the research team at the Water Desalination and Reuse Center Peng Wang, King Abdullah University of Science and Technology (KAUST), Saudi Arabia .

As revealed in a publication published in the journal Environmental Science & Technology , the keystone of the system is based on a cheap, stable and low-toxicity substance: calcium chloride. A salt that has a particularly high affinity with water: it is used especially for its absorbing properties in domestic dehumidification systems.

A particularly voracious moisture absorber

” This deliquescent salt [which can melt and liquefy] has such a high affinity for water that it absorbs a great deal of water vapor from  the surrounding air, so much so that a puddle of liquid ends up forming, “ says Renyuan Li, PhD student in Peng Wang’s team. Perfect to absorb moisture from our homes … but a little less to  hydrate from the liquid produced.

The ” puddle”  mentioned by the scientist is indeed made of a particularly indigestible brine, which – highly concentrated – can cause burns, irritation or even gastrointestinal ulceration.

The prowess of the researchers was therefore to design a calcium chloride hydrogel able to maintain its solid state despite the absorption of water, but also to release this water on demand, and only the precious liquid. A challenge that scientists have managed to support by developing a polymer that can retain its solid form until it is heated.

To release the water it contains, it is carbon nanotubes that researchers have added. These nanoscopic assemblies of carbon atoms are indeed particularly effective in converting solar energy into heat. A heat thus used to cause the release of water by the polymer.

First conclusive tests

In order to test their invention, the researchers placed a small amount of polymer – 35 grams to be precise – in an experimental setup. A prototype that, left overnight outside in a relative humidity of 60%, was able to store not less than 37 grams of water. A quantity far from negligible, almost all of which could be extracted from the polymer the next day, after exposure of the prototype to the sun for two hours and a half. A success that opens particularly promising prospects, especially for the inhabitants of the deserts.

” The most remarkable aspects of [our] hydrogel are its high performance and low cost ,  says Renyuan Li. Two parameters that could make the invention stand out as a drinking water production system. Very inexpensive: the researchers estimate that the daily extraction of three liters of water – the minimum vital for an adult – would represent a daily cost of hydrogel only half a penny. What allow the poorest people to benefit from a precious resource, but which is often sorely lacking: water. A true oasis for the deserts of the whole world.

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