On any given day, you’re surrounded by water suspended in the air as imperceptible vapor. The idea of harvesting this water has deep roots in the sci-fi culture — when we first met Luke Skywalker on the desert planet, Tatooine, he was toiling away on his uncle’s vapor farm — but similar devices have also taken shape in the real world.
One of the biggest challenges engineers face when designing water harvesters is how to keep the device cool. To form water vapor, the device has to be cooler than the air around it. That might mean using a cooling fan, which would prove feasible in areas with easy access to electricity but not in undeveloped regions, where water scarcity is at its worst. Finding another solution is key.
In a study published last week in the journal Science Advances, University of California, Berkeley researchers demonstrated a unique approach to water harvesting that let them extract drinkable water from desert air without the need for external energy. The proof-of-concept device could pave the way for cheaply supplying clean water to arid regions.
“For the first time, we are demonstrating that you can harvest drinkable amount of pure water from the dry desert air every day, using essentially just a simple cheap box, with no additional energy and electricity required other than the natural sunlight,” Omar Yaghi, a professor of chemistry at UC Berkeley who invented some of the underlying technology, told Digital Trends. “All of these are possible because of a revolutionary porous novel material inside the box called metal-organic framework.”
A metal-organic framework (or MOF) is a highly porous material with internal cavities and channels that give it immense surface area. An MOF the size of a sugar cube has the internal surface area of a full football field, Yaghi said. “This high surface area ensures high capacity for the captured water.”
The device developed by Yaghi and his team is, strictly speaking, a box within a box. The internal box is filled with MOFs made up, in this case, of organic material and the expensive metal zirconium. The lid of the outer box is left open at night (when cool, humid air rushes in and is absorbed by the MOF), and closed during the day (when sunlight heats the box, the water molecules escape the MOF, and condense as droplets on the inside of the outer box). From there, Yaghi and his team manually collected the droplets with a pipette.
In a trial in Scottsdale, Arizona, the harvester yielded just about seven ounces of water — not enough to quench someone’s thirst but enough to show feasibility.
“This [device] is especially important for regions where access to clean water is limited,” Yaghi said. “My vision is to achieve ‘personalized water,’ where people in water-stressed regions have a device at home running on ambient solar, delivering the water that satisfy the basic needs of the individuals.”
He acknowledged the many steps ahead before such a device could come to market — including scaling up the device to capture more vapor and experimenting with newer, cheaper MOFs — but Yaghi is optimistic that such technology could someday provide potable water for people in need.
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