Hydrogel sucks moisture from the air to get clean water

(Credit: John T/Unsplash)

A new way to harvest water from the humid air above water surfaces with a hydrogel could help address water scarcity.

The new method takes advantage of the huge amount of water that evaporates from water surfaces such as reservoirs and the open sea each day.

The solution lies in a unique zinc-based water-absorbing hydrogel that researchers developed last year. This gel-like material is over eight times more absorbent than commercial drying agents. The new method also only needs natural sunlight to harvest water from the water-saturated hydrogel.

“Our hydrogel can convert moisture present in humid air to water without the need for any external energy input. By harnessing the moisture-rich air that is commonly found above water surfaces, we can collect water, which would otherwise be lost to the environment, for different uses,” says research team leader Tan Swee Ching, an assistant professor from the materials science and engineering department at the National University of Singapore.

Better than the alternatives

Conventional drying agents like silica gel and calcium chloride can only absorb small amounts of water. Extracting water from these agents would require energy intensive processes and high temperatures, which prevent this approach from being cost-effective.

The new hydrogel efficiently absorbs water more than four times its original weight. When used repeatedly over multiple absorption-desorption cycles within a day, the amount of water it collects can reach up to 14 times per kilogram of hydrogel used.

As an added advantage, the hydrogel releases water at a relatively lower temperature of between 45 and 50 degrees Celsius (113 and 122 degrees Fahrenheit), which the team’s setup can achieve. Natural sunlight can extract the water from the hydrogel without an external energy source.

Furthermore, while most commercially available drying agents are only suitable for single use, the hydrogel maintains its absorption capability even after 1,000 absorption-desorption cycles.

How does it work?

As a proof of concept, the research team first built floating devices each containing a small amount of hydrogel placed on a glass plate. They left these devices to float on the water at a beach. Periodically, the researchers retrieved the water saturated hydrogels and transferred them to an enclosed glass box which they then exposed to natural sunlight. When exposed to heat, the temperature in the glass box would increase further, releasing the moisture within the hydrogels as vapors which later condensed on the walls of the glass box. The researchers then collected the condensed water droplets in the glass box.

When they examined the quality of the water they harvested from the hydrogels, the researchers found that the salt content is almost negligible.

“Unlike processes like desalination which are highly energy intensive, water collected using the novel hydrogel requires less treatment for different uses. Our invention also has potential to be scaled up considerably to function as a floating water-capturing farm,” says Tan.

This approach could benefit rural communities where access to clean water remains a challenge. By creatively applying novel solutions, we hope to contribute towards mitigating the global water crisis.”

Taking their research forward, the team is currently looking at ways to optimize the performance of the hydrogel and the water harvesting process. They are also exploring innovative methods to increase absorption capacity of the hydrogel. In addition, the researchers are keen to work with commercial partners to bring this idea to market.

The findings of the study appear in Advanced Materials.

Source: National University of Singapore