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Harvesting water from desert air

TECHNOLOGY



A team of engineers at the Massachusetts Institute of Technology (MIT) has synthesised a super-absorbent material that can soak up a record amount of moisture from the air. Even in very dry conditions — with 30% relative humidity — this material can pull vapour from the air and hold in the moisture without leaking. The water can then be heated and condensed, and collected as pure water.


The material, which is both transparent and rubbery, is made from hydrogel, a naturally absorbent material that’s also used in disposable nappies. The team enhanced the hydrogel’s absorbency by infusing it with lithium chloride — a type of salt that’s a powerful dessicant, capable of absorbing more than 10 times its own mass in moisture.


If it can be made quickly and at large scale, the gel could be used as a passive water harvester, particularly in the desert and drought-prone regions, where it could continuously absorb vapour that could then be condensed into drinking water. The researchers also say the material could be fit onto air conditioning units as an energy-saving dehumidifier.

“We are exploring widely different problems like how to make air conditioning more efficient and how you can harvest water. This material, because of its low cost and high performance, has so much potential,” says Carlos Dнaz-Marin, a mechanical engineering graduate student and member of the Device Research Lab at MIT. Researchers at the lab are designing novel materials to solve the world’s energy and water challenges.


“It’s the best of both worlds,” says study co-author Gustav Graeber. “The hydrogel can store a lot of water, and the salt can capture a lot of vapour. So it’s intuitive that you’d want to combine the two.”


“The big, unexpected surprise was that, with such a simple approach, we were able to get the highest vapour uptake reported to date. Now, the main focus will be kinetics and how quickly we can get the material to uptake water. That will allow you to cycle this material very quickly, so that instead of recovering water once a day, you could harvest water maybe 24 times a day.”


The team’s findings are published in Advanced Materials.


TOP Artist’s concept


The big, unexpected surprise was that, with such a simple approach, we were able to get the highest vapour uptake reported to date. Now, the main focus will be kinetics and how quickly we can get the material to uptake water.

Gustav Graeber


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