Researchers have figured out how to quickly extract large amounts of fresh water from the air using a hydrogel containing hygroscopic salt.

Materials scientist Guihua Yu and his team at the University of Texas at Austin, USA, have developed a salt-compatible hydrogel that can absorb and retain water when combined with hygroscopic salt.

Hydrogels can absorb and store water many times their weight. The underlying polymer increases during this process. But so far, the use of such a property to obtain fresh water from the atmosphere is impractical, since the process is slow and inefficient.

Moisture absorption can be improved by using hygroscopic salts, which can quickly remove large amounts of moisture from the air. But these salts and hydrogels are usually incompatible.

Therefore, the authors of the new work figured out how to create a hydrogel compatible with salt. With it, the team was able to extract almost 6 liters of clean water per kilogram of material. The process took 24 hours. The relative air humidity was 30%.

The basis for the new hydrogel was a polymer made from zwitterionic molecules. Polywitterions carry both positively and negatively charged functional groups, which helped the polymer become more salt sensitive. Initially, the molecular strands in the polymer were tightly entwined, but when the researchers added a lithium chloride salt, the tension dropped and a porous hydrogel formed.

According to the authors, their development will help with the collection of water in arid regions.