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This proof-of-concept device, built at MIT, demonstrates a new system for extracting drinking water from the air. The sequence of images at right shows how droplets of water accumulate over time as the inside temperature increases while exposed to the sun. Photo: MIT

A solar-powered water harvester can pull water molecules directly from the air – making drinkable water available even in the desert, according to a new proof-of-concept study in the journal Science.

The new technology, a collaboration between scientists at the University of California at Berkeley and the Massachusetts of Technology, is based on a passive system that draws moisture into a foam-like material and condenses the water even at humidity levels as low as 20 percent, according to the scientists.

The concept is similar to an electric dehumidifier found in many homes – but this one can work without using the extra energy that’s not available in extreme environments, said Omar Yaghi, one of the senior authors, a chemist at UC Berkeley and faculty scientist at Lawrence Berkeley National Laboratory.

“I call it personalized water,” said Yaghi, in a school statement. “One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household.”

Or it could be used to provide life-saving water in the most inhospitable deserts of the world, they added.

Yaghi and the team in California developed the foundational technology at work in the new tool. Metal-organic frameworks employ magnesium, aluminum or other metals in a complex arrangement with organic molecules. The particular MOFs capture different molecules. Three years ago, they developed a combination of zirconium and adipic acid that captures water vapor.

The concept was picked up by collaborators Evelyn Wang at MIT and her team of mechanical engineers, and funded by the Advanced Research Projects Agency of the U.S. Department of Energy. The MIT engineers developed two pounds of miniscule MOF crystals, which were compressed between a solar absorber and a condenser plate.

The air diffuses through the porous MOF. Water molecules bind to the structure. The solar energy drives the captured water vapor toward the condenser, where the liquid collects and drips down, they explain.

The device was able to pull 2.8 liters of water from the air over 12 hours using the 2 pounds of MOF material. The tool was also tested in a real-world scenario: on an MIT rooftop, they said. Yaghi said it could collect 12 ounces of water – about a Coke can’s worth – in under an hour.

Further engineering could refine the tool for use in particular environments. For instance, a technique of fog harvesting near 100 percent humidity is already employed in select areas like Chile and Morocco.

The refinement of the MOF and its collection methods could be key, said Hyunho Kim, a graduate student at MIT and one of the authors.

“By carefully designing this material, we can have surface properties that can absorb water very efficiently at 50 percent humidity, but with a different design, it can work at 30 percent,” said Kim. “By selecting the right materials, we can make it suitable for different conditions. Eventually we can harvest water from the entire spectrum (of water concentrations).”

The technology could be refined for the world’s harshest deserts, they added. For instance, the average humidity of the Sahara Desert, the biggest desert on Earth, is 25 percent. Slightly before dawn this morning, the humidity in Death Valley, the most arid place in the United States, is 19 percent.

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