A gel that turns hot air into drinking water

A team of US researchers has made a hydrogel that can suck clean water out of the air in very hot conditions.

The energy-efficient material could be used to provide drinking water in places where access is limited.

“With our new hydrogel, we’re not just pulling water out of thin air. We’re doing it extremely fast and without consuming too much energy,” says Professor Guihua Yu, a researcher in materials science and engineering professor at the University of Texas at Austin, US.

Hydrogels are 3D networks, often made from long polymer molecules, capable of holding large amounts of water.

They’re being used in medical, electronic and engineering research, and scientists have considered “thermoresponsive” hydrogels – which are temperature-sensitive – good candidates for atmospheric water harvesting.

But until now, they’ve not been efficient enough at either trapping water from the surrounding air, or releasing it when needed.

This research, published in PNAS, details a combination of hydrogel ingredients that overcomes the inefficiency.

The new substance draws water out of the atmosphere when it’s cool. Then, when the temperature gets to about 40°C, it releases the water. Typically, higher temperatures have been needed to make these hydrogels work.

Depending on humidity, each kilogram of gel can draw 3.5-7 kilograms of water out of the air.

“What’s really fascinating about our hydrogel is how it releases water. Think about a hot Texas summer — we could just use our temperatures’ natural ups and downs, no need to crank up any heaters,” says Yu.

The researchers’ success revolves around “microgels” – tiny particles inside the hydrogel – which make it more efficient.

“By transforming the hydrogel into micro-sized particles, we can make the water capture and release ultrafast,” says Weixin Guan, a graduate student in Yu’s lab.

“This offers a new, highly efficient type of sorbents that can significantly enhance the water production by multiple daily cycling.”

Next, the researchers are figuring out how to scale the technology up and improve its cost and efficiency.

“We developed this device with the ultimate goal to be available to people around the world who need quick and consistent access to clean, drinkable water, particularly in those arid areas,” says Yaxuan Zhao, a graduate student in Yu’s lab.