MIT engineers develop superabsorbent material for efficient water harvesting

Monday - July 3 2023, 02:20 UTC - 1 year ago

MIT engineers have developed a superabsorbent material from hydrogel infused with lithium chloride which can absorb moisture from the air, even in dry conditions. The material could be used as a passive water harvester to collect drinking water in desert and drought-prone areas.

MIT engineers have synthesized a superabsorbent material that can soak up a record amount of moisture from the air, even in desert-like conditions. As the material absorbs water vapor, it can swell to make room for more moisture. Even in very dry conditions, with 30 percent relative humidity, the material can pull vapor from the air and hold in the moisture without leaking. The water could then be heated and condensed, then collected as ultrapure water.

The transparent, rubbery material is made from hydrogel, a naturally absorbent material that is also used in disposable diapers. The team enhanced the hydrogel’s absorbency by infusing it with lithium chloride — a type of salt that is known to be a powerful dessicant. The researchers found they could infuse the hydrogel with more salt than was possible in previous studies. As a result, they observed that the salt-loaded gel absorbed and retained an unprecedented amount of moisture, across a range of humidity levels, including very dry conditions that have limited other material designs.

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

"We’ve been application-agnostic, in the sense that we mostly focus on the fundamental properties of the material," says Carlos Díaz-Marin, a mechanical engineering graduate student and member of the Device Research Lab at MIT. "But now 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." .

Díaz-Marin and his colleagues have published their results in a paper published recently in the journal Advanced Materials. The study’s MIT co-authors are Gustav Graeber, Leon Gaugler, Yang Zhong, Bachir El Fil, Xinyue Liu, and Evelyn Wang.

In MIT’s Device Research Lab, researchers are designing novel materials to solve the world’s energy and water challenges. In looking for materials that can help to harvest water from the air, the team zeroed in on hydrogels — slippery, stretchy gels that are mostly made from water and a bit of cross-linked polymer. Hydrogels have been used for years as absorbent material in diapers because they can swell and soak up a large amount of water when it comes in contact with the material.

"Our question was, how can we make this work just as well to absorb vapor from the air?" Díaz-Marin says.

He and his colleagues dug through the literature and found that others had experimented with mixing hydrogels with various salts. Certain salts, such as the rock salt used to melt ice, are very efficient at absorbing moisture, including water vapor. And the best among them is lithium chloride, a salt that is capable of absorbing over 10 tmes its weight in water.