Salty hydrogel sucks liters of drinking water a day out of thin air

Salty hydrogel sucks liters of...
A new salty hydrogel can pull fresh water from ambient air very efficiently
A new salty hydrogel can pull fresh water from ambient air very efficiently
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A new salty hydrogel can pull fresh water from ambient air very efficiently
A new salty hydrogel can pull fresh water from ambient air very efficiently

A shortage of drinking water is a key problem in many parts of the world, and it’s a cruel irony that huge amounts are floating around in the air, inaccessible. Researchers at the University of Texas at Austin have now developed a salty hydrogel that can pull plenty of fresh drinking water out of air in relatively low humidity.

As the name suggests, hydrogels are mostly made of water, but that doesn’t stop them wanting more. Their excellent absorbency makes them useful in diapers and bandages, and potentially as dehumidifiers and devices that extract drinking water from the air.

That last application could be particularly useful, but unfortunately the process is a bit slow and inefficient. Adding hygroscopic salts, which are also effective water absorbers, could help, but frustratingly these salts don’t integrate with hydrogels very well.

So for the new study, the researchers set out to find a way to mix the two properly. The key was to start with a polymer made from molecules that are “zwitterionic” – essentially, they contain ions with both positive and negative electrical charges. This allows the it to grab hold of the hygroscopic salts more firmly, and the resulting hydrogel was very efficient at absorbing water from the air around it.

Doing so involves a cycle of absorption and separation. First, the material is left for an hour to suck moisture out of ambient air. Then it’s dried out in a condenser, to wring out and collect the water, before putting it back on absorption duties. Repeating this cycle multiple times didn’t seem to reduce its ability to absorb or release water.

In tests, the salty hydrogel performed extremely well. The team was able to extract 5.87 L (1.55 gal) of freshwater per kilogram of the material per day, from air with a humidity of 30 percent. That’s one of the best performances we’ve seen from a water harvester like this – and we’ve seen a lot of them, usually using metal-organic frameworks as the absorbent material.

With further optimization, these zwitterionic hydrogels could be very useful in providing drinking water to developing and drought-stricken regions.

The research was published in the journal Angewandte Chemie.

Source: Wiley

Ralf Biernacki
"Then it's dried out in a condenser. . ." Evaporated by heat, presumably? Salts are hygroscopic, all right, but it takes a lot to rip fresh water back out of them. You would be converting a water harvesting problem into a desalination problem, which could be even worse.
Water-makers for ocean-going yachts and other vessels could be a quicker path to market, then wealthy arid regions, then poorer regions get the benefit of a mature, already-profitable, much cheaper technology.
Getting the water out of the hydrogel must need some expensive equipment. It is often very poor people who need water. Solar evaporation is easier and cheaper.
I wonder how it compares with the Israeli machine that New Atlas reported on in November.
How about dew harvesting?
Completely passive and apart from filtering needs little or no complex, expensive technological assistance.
Drying out the atmosphere seems like a bad, short sighted idea.