Solar-Powered Device Which Can Draw Water out of Air in Desserts

Delia Watkins
April 16, 2017

Using only sunlight, the harvester can pull liters of water from low-humidity air over a 12-hour period.

Describing the results as "a major breakthrough" for harvesting water from air at low humidity, Yaghi says this technology opens the door to what he calls "personalized water", making possible a future where households in poorer countries can make use of the device to produce their own water without having to travel long distances to find it.

Previous attempts to collect water have either been not particularly effective since they require very humid air or they've been energy hogs and thus aren't viable for long-term use. "Current dehumidifiers are powered by electricity, so creating that extra water ends up costing extra energy".

In 2014, Professor Yaghi and his UC Berkeley team synthesised a MOF - a combination of zirconium metal and adipic acid - that binds water vapour. When heated by the sun or another source, water molecules in the trapped air are released and condensed - essentially "pulling" the water out of the air, the scientists said.

The researchers' tests showed one kilogram of the MOF could collect close to three litres of water per day. It is now a prototype, but has passed tests in real-world conditions.

Right now, the MOF can only absorb 20 percent of its weight in water, but other MOF materials could potentially absorb more than 40 percent. If you were wondering, deserts like the Mojave have a humidity level much higher than 20%.

This is the water harvester built at MIT with MOFs from UC Berkeley. The key component is a promising class of synthetic porous materials called metal-organic frameworks, composed of organic molecules stitched together with metal atoms, which Yaghi pioneered (see "A Better Way to Capture Carbon").

"A person needs about a [330ml] can of water per day". The lines in are organic linkers, and the intersections are multi-metallic units. Better yet, the new invention does not require electricity and the researchers are attempting to make the device as cheap as possible. Since Yaghi developed MOFs, over 20,000 different types of MOFs have been created around the world that can hold hydrogen and methane or that can contain petrochemicals in processing plants.

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Omar Yaghi explains how to make a MOF and their tremendous ability to absorb gases and liquids, including water directly from low-humidity air.

The details about this solar-powered harvester are reported in the journal Science. Using this material, MIT has created a water harvester that utilizes only solar power to pull water from the dry air.

According to researchers, there is much room for improvement in this device and it could be scaled up to provide a family with their freshwater needs for the day.

The devices made from MOF are not restricted to water dispensers.

It's not that hard to collect condensation in a humid climate, but squeezing H20 from arid, thin air is another story.

At $150/kg, zirconium is too expensive to use for a mass-produced product meant to be distributed to people living in arid environments, but Yaghi proposes further work that would swap in aluminum, which costs 1% of the cost of zirconium.

"If you want to get to a 30-liter quantity, to demonstrate the real viability of this, you would need to incorporate multiple stacks of this MOF layer into a device", Wang said.

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