Optimization of a hygroscopic hydrogel device improves efficiency

A small team of engineers from the U.S., Chile and Ireland has found a way to extract more water from drier air, allowing for water production in arid places like the Atacama Desert. Their paper is published in Device.

Instead of looking for ways to improve sorbent materials, the team sought to optimize the way hydrogel-based water-capture systems work.

Scientists believe there will be a global water crisis in the coming years. As the demand for fresh water increases and existing sources become depleted, new sources are required. One popular area of study involves extracting water from the air.

Current techniques involve hydrogels and metal-organic frameworks. In this new effort, the researchers focused their attention on systems that use hydrogels to absorb water in the air during the night when the air contains the most water, and then using solar energy during the day to squeeze the water from the hydrogel into a holding container.

In studying hydrogel processes currently in use, the research team found that the most inefficient part of such systems was the pace at which the hydrogels soak water from the air and they sought to speed up the process.

They came up with an approach 10 times faster than other MOF-based devices that involves making a hydrogel with a cross-linked polyacrylamide polymer with added lithium chloride. Further changes included optimizing the thickness of the hydrogel and the air gap used for collecting water from the hydrogel.

The team tested their device in the Atacama Desert in the heat of summer and found it could provide water at humidity levels as low as 11%. They also found it could produce as much as two liters a day when humidity levels were 30%. In another test, this time from a roof on the campus of MIT, the researchers found the device capable of producing 1.7 L/m²/day in 50% humidity conditions.

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