Super-Absorbent Gel Pulls Fresh Water Out of Thin Air

Super-Absorbent Gel Pulls Fresh Water Out of Thin Air

As the world becomes increasingly hot, fresh and clean water is an increasingly hot commodity. Agricultural demand, climate change, pollution, and other factors are converging to make water scarcity a problem in the present, and it’s likely to get worse in the future.

So, how do we manage it? One group of scientists has a suggestion: pull water out of the air.

Researchers have developed a super-absorbent gel, made from affordable materials, that can suck moisture out of low-humidity air. When heated, the gel releases that moisture as fresh water. One kilogram of gel can theoretically produce nearly 6 litres of water at 15% relative humidity and more than 13 litres of water at 30% humidity, according to a study published in the journal Nature Communications. For reference, the Southwest’s Mojave desert generally ranges between 10% and 30% humidity.

“This new work is about practical solutions that people can use to get water in the hottest, driest places on Earth,” said Guihua Yu, one of the researchers, in a press release. Yu is a materials engineer at the University of Texas at Austin. “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,” he added in the statement.

The researchers made the gel from a derivative of the compound cellulose (which is found in all plant cells), a specific fibre extracted from an edible tuber known as konjac, and absorbent lithium chloride salt. The liquid materials were mixed, poured into a mould, left to set for 2 minutes, and then freeze-dried into a thin sheet. All the materials needed to make 1 kilogram of the dried gel would cost under $US2 ($3), according to the study.

“The synthesis of this gel is very simple,” Youhong Guo, a chemical engineer at MIT and study co-author, told Gizmodo. “Which means everyone can make it [easily],” she added.

Once set and dried, the thin gel sheets became saturated with moisture in about 20 minutes. To extract that water as actual, drinkable liquid, the researchers then heated the gel in a closed chamber and collected the condensation. They found that about 70% of the captured water was released within 10 minutes of heating the gel at 60 degrees Celsius.

The team tested the gel’s absorbance and release of water at different ratios of ingredients and at different humidities. They also compared the gel’s water absorbance and release capacity with other absorbent materials.

There’s lots of other stuff out there that pulls water from the air. For instance, you’ve probably encountered those silica packets inside snack bags and electronics boxes. If you’ve lived somewhere humid, you know that regular table salt absorbs water pretty well, too. Heck, french fries lose their crisp over time because of atmospheric water absorption. But this new material is different in a few key ways.

For one, it both absorbs water very efficiently and lets go of it relatively easily. Those same silica packets have to be heated to 180 degrees Fahrenheit before they release water, and other desiccants need even higher temperatures. It’s also non-toxic and doesn’t add harmful chemicals to the collected water. Finally, unlike some other materials, the gel doesn’t seem to degrade with repeated use, reported the scientists.

However, as nifty as the gel is (and as useful as it could be in the future), we’re far from a world where the material magically solves the water crisis.

The researchers ran their tests with mere milligrams of gel and water, then extrapolated those results to kilograms, which might not be a direct translation to reality. It’s possible that the water absorption and release capacity changes when the gel is used in larger amounts, explained Ruzhu Wang in an email to Gizmodo. Wang is an engineer at Shanghai Jiao Tong University in China who has worked on similar water-harvesting technologies previously and was not involved in the new research.

Plus, the scientists worked with very thin films (about 0.01 centimeters thick) of gel in the lab. Thin sheets are better for surface area exposure, quickly absorbing water and quickly heating up to release water. “But if this water harvesting technology wants to be used on a mass scale, using such a thin material remarkably increases the total volume of the device, making it less compact and portable,” said Wang. The researchers propose that their gel could be used in larger blocks. Yet so far, they haven’t tested that design.

Even so, Wang still believes the new result are “encouraging.” He emphasised that the studied gel material is noteworthy because of how little energy input it takes to produce and use. It is “significant to achieve water harvesting in a sustainable and low-carbon way, in the terms of both material synthesis and energy demand.”

And ultimately, Wang said the new study “has brought nearly impossible freshwater generation [in] the ultra-dry climate closer to reality.” There you go: Science, making the impossible more possible.