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April 18, 2017
Chemists have developed a solar-powered sponge-like device that inhales cool air at night, clams up during the day, and someday could provide millions of people with freshwater in places where there is none.
The device, developed by a research team led by Omar Yaghi, a chemist at the University of California, Berkeley, is made up of metal-organic frameworks (MOFs), compounds made up of metal clusters that can form three-dimensional structures. This unique material is made up of organic, carbon-based molecules that allow structures to have lots of internal space where moisture can condense.
At night, the device is opened and allows air to flow through the porous material that attracts and holds onto water molecules. Then during the day, the device closes, and sunlight beams through the window at the top of the device, generating heat which forces the MOF to release the water as vapor. The vapor then condenses into droplets to the cool surface below. The set up was first tested in the laboratory, then on a rooftop.
Previous approaches to deriving water from the atmosphere have been rather unsuccessful, either requiring extremely humid air or too much electricity to function efficiently. This unpowered device, on the other hand, is reported to pull over a third of a gallon of water out of the atmosphere per day for every pound of MOF it contains (3 liters per kilogram).
A minimum of 1.98 gallons of water per capita should be enough to support most people for one day, according to the World Health Organization. That means an average person would require around 37.5 square meters of MOF to survive.
Here’s Scott K. Johnson, reporting for Ars Technica:
Because the demonstration prototype was a small device, it only captured a small amount of water, but the potential is there. Scaled up to one square meter, this version would harvest roughly 0.2 liters [6.76 fluid ounces] per day. But if the water-absorbing layer is kept thin, it can “fill up” in as little as an hour, so a once-per-day collection cycle is perhaps unnecessarily limiting. Shading the device periodically over the course of a day would increase the number of cycles and get you close to a liter per day per square meter.
One limitation to consider is the sheer price of the water harvesters. Zirconium, a critical component of the device, costs approximately $68 per pound ($150 per kilogram). However, Yaghi and his researchers have already begun experimenting with much cheaper metals, like aluminum, to take its place.
According to Ars Technica, there’s an estimated 3.4 trillion gallons of water floating in the air at any given time. By using solar-powered technology, this device could be the first to effectively utilize untapped atmospheric water. Even the driest parts of the world could soon have the technology to ensure steady water supply to offer relief to billions of people.