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Researchers from Saudi Arabia have developed a hydrogel that can absorb the moisture from the air to produce low-cost drinking water.
You have probably encountered it while unpackaging your latest gadget—a bag full of transparent beads made of a material called silica gel, which is used to prevent the rust and decay of electronic devices thanks to its moisture-absorbing capabilities. Such a material would be an excellent candidate to harvest moisture in the air in arid regions or places without a fresh water supply. That was the reasoning behind the innovative project launched by the scientists at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. Their system, based on a modified hydrogel, can harvest its own weight in water, even in low moisture conditions. To get there, however, this technological project has had to overcome a few obstacles.
Their solution makes use of calcium chloride, a chemical compound extremely good at absorbing moisture. In fact, a layer of this salt can become a puddle of water at room temperature. This property is called deliquescence or hygroscopy. Calcium chloride, however, poses a challenge: the resulting water is brine. Thus, the scientists leveraged its absorption qualities but embedding this salt in hydrogel bubbles that would keep it in a solid state. Next, in order to enable the release of the harvested water, they added a small proportion of carbon nanotubes (0.42% of the total weight). These structures are extremely efficient at capturing solar radiation, i.e. the heat needed for the evaporation of water.
For their first test, they just used 35 grams of the material, which harvested 37 grams of water overnight. Then, the next morning they left it under the sun and, after two and a half hours, the hydrogel had already released the water inside the chamber of the device.
In other articles, we have mentioned a range of water-harvesting devices, from harp systems to prototypes making use of metal-organic materials. Nevertheless, many of them are cumbersome or costly. In contrast, this Saudi hydrogel uses a highly efficient technique, as collecting three liters of water could cost as little as half a dollar cent per day. Enough to cover the daily needs of an adult.
The hydrogel devised by the scientists at KAUST is an excellent water harvester, but it is nowhere close to the absorption properties afforded by an innovative material developed at the National University of Singapore (NUS). This team has followed a different approach by using zinc oxide to create a material which can absorb more than 2.5 times its weight in water. Once applied to a wall as a coat of paint, this zinc oxide hydrogel can reduce the relative humidity of a room by 20% in seven minutes. Besides its applications as a dehumidifier, this new material could also have applications for electronics.