Drinking Water Treatment

Researchers improve humidity-harvesting films

May 24, 2022

A single kilogram of the latest film from The University of Texas at Austin could cost only $2, but produce more than 6 liters of water per day in areas with less than 15% relative humidity.

More than a third of the world’s population lives in drylands, areas that experience significant water shortages. Scientists and engineers at The University of Texas at Austin have developed a solution that could help people in drylands access clean drinking water.

The team developed a low-cost gel film made of abundant materials that can pull water from the air in even the driest climates. The materials that facilitate this reaction cost a mere $2 per kilogram, and a single kilogram can produce more than 6 liters of water per day in areas with less than 15 percent relative humidity and 13 liters in areas with up to 30 percent relative humidity.

The water-capturing film can easily be molded into many different shapes.

The research builds on the team’s previous hydrogel breakthrough. However, the technology was originally only designed for relatively high-humidity environments. The new paper appears in Nature Communications.

“This new work is about practical solutions that people can use to get water in the hottest, driest places on Earth,” said Guihua Yu, professor of materials science and mechanical engineering in the Cockrell School of Engineering’s Walker Department of Mechanical Engineering. “This could allow millions of people without consistent access to drinking water to have simple, water generating devices at home that they can easily operate.”

A prototype device can capture water from the air using the new film.

The researchers used renewable cellulose and a common kitchen ingredient, konjac gum, as a main hydrophilic skeleton. The open-pore structure of gum speeds the moisture-capturing process. Another designed component, thermo-responsive cellulose with hydrophobic interaction when heated, helps release the collected water immediately so that overall energy input to produce water is minimized.

Other attempts at pulling water from desert air are typically energy-intensive and do not produce much. And although 6 liters does not sound like much, the researchers say that creating thicker films or absorbent beds or arrays with optimization could drastically increase the amount of water they yield.

The reaction itself is a simple one, the researchers said, which reduces the challenges of scaling it up and achieving mass usage.

“This is not something you need an advanced degree to use,” said Youhong Guo, the lead author on the paper and a former doctoral student in Yu’s lab, now a postdoctoral researcher at the Massachusetts Institute of Technology. “It’s straightforward enough that anyone can make it at home if they have the materials.”

The process of creating the water-capturing film from its ingredients is quite simple.

The film is flexible and can be molded into a variety of shapes and sizes, depending on the need of the user. Making the film requires only the gel precursor, which includes all the relevant ingredients poured into a mold.

“The gel takes 2 minutes to set simply. Then, it just needs to be freeze-dried, and it can be peeled off the mold and used immediately after that,” said Weixin Guan, a doctoral student on Yu’s team and a lead researcher of the work.

The research was funded by the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA): drinking water for soldiers in arid climates is a big part of the project. However, the researchers also envision this as something that people could someday buy at a hardware store and use in their homes.