permaculture

[Lawrence London <lfljvenaura@gmail.com>]

Water harvesting from air with metal-organic frameworks powered by natural
sunlight | Science
http://science.sciencemag.org/content/early/2017/04/12/science.aam8743
Atmospheric water is a resource equivalent to ~10% of all fresh water in
lakes on Earth. However, an efficient process for capturing and delivering
water from air, especially at low humidity levels (down to 20%), has not
been developed. We report the design and demonstration of a device based on
porous metal-organic framework-801 [Zr6O4(OH)4(fumarate)6] that captures
water from the atmosphere at ambient conditions using low-grade heat from
natural sunlight below one sun (1 kW per square meter). This device is
capable of harvesting 2.8 liters of water per kilogram of MOF daily at
relative humidity levels as low as 20%, and requires no additional input of
energy.

http://www.sciencemag.org/news/2017/04/new-solar-powered-device-can-pull-water-straight-desert-air

Crystalline materials similar to these can now harvest water vapor from the
air.
Yaghi Laboratory at UC Berkeley
This new solar-powered device can pull water straight from the desert air

By Robert Service <http://www.sciencemag.org/author/robert-service>Apr. 13,
2017 , 2:00 PM

You can’t squeeze blood from a stone, but wringing water from the desert
sky is now possible, thanks to a new spongelike device that uses sunlight
to suck water vapor from air, even in low humidity. The device can produce
nearly 3 liters of water per day for every kilogram of spongelike absorber
it contains, and researchers say future versions will be even better. That
means homes in the driest parts of the world could soon have a
solar-powered appliance capable of delivering all the water they need,
offering relief to billions of people.

The new water harvester is made of metal organic framework crystals pressed
into a thin sheet of copper metal and placed between a solar absorber
(above) and a condenser plate (below).
Wang Laboratory at MIT

There are an estimated 13 trillion liters of water floating in the
atmosphere at any one time, equivalent to 10% of all of the freshwater in
our planet’s lakes and rivers. Over the years, researchers have developed
ways to grab a few trickles, such as using fine nets to wick water from fog
banks, or power-hungry dehumidifiers to condense it out of the air. But
both approaches require either very humid air or far too much electricity
to be broadly useful.

To find an all-purpose solution, researchers led by Omar Yaghi, a chemist
at the University of California, Berkeley, turned to a family of
crystalline powders called metal organic frameworks, or MOFs. Yaghi
developed the first MOFs—porous crystals that form continuous 3D
networks—more than 20 years ago. The networks assemble in a Tinkertoy-like
fashion from metal atoms that act as the hubs and sticklike organic
compounds that link the hubs together. By choosing different metals and
organics, chemists can dial in the properties of each MOF, controlling what
gases bind to them, and how strongly they hold on.
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Over the past 2 decades chemists have synthesized more than 20,000 MOFs,
each with unique molecule-grabbing properties. For example, Yaghi and
others recently designed MOFs that absorb—and later release—methane, making
them a type of high-capacity gas tank
<http://science.sciencemag.org/content/346/6209/538> for natural
gas–powered vehicles.

In 2014, Yaghi and his colleagues synthesized a MOF that excelled at
absorbing water, even under low-humidity conditions. That led him to reach
out to Evelyn Wang, a mechanical engineer at the Massachusetts Institute of
Technology (MIT) in Cambridge, with whom he had previously worked on a
project to use MOFs in automobile air conditioning. After synthesizing the
new zirconium-based MOF, dubbed MOF-801, Yaghi met Wang at MIT and said,
“Evelyn we have to come up with a water-harvesting device.” She agreed to
give it a shot.
Device pulls water from the air

At night setup soaks up water vapor from air, and uses heat from the sun to
release it as liquid water during the day.
V. Altounian/*Science*

The system Wang and her students designed consists of a kilogram of
dust-sized MOF crystals pressed into a thin sheet of porous copper metal.
That sheet is placed between a solar absorber and a condenser plate and
positioned inside a chamber. At night the chamber is opened, allowing
ambient air to diffuse through the porous MOF and water molecules to stick
to its interior surfaces, gathering in groups of eight to form tiny cubic
droplets. In the morning, the chamber is closed, and sunlight entering
through a window on top of the device then heats up the MOF, which
liberates the water droplets and drives them—as vapor—toward the cooler
condenser. The temperature difference, as well as the high humidity inside
the chamber, causes the vapor to condense as liquid water, which drips into
a collector. The setup works so well that it pulls 2.8 liters of water out
of the air per day
<http://science.sciencemag.org/lookup/doi/10.1126/science.aam8743> for
every kilogram of MOF it contained, the Berkeley and MIT team reports today
in Science.

“It has been a longstanding dream” to harvest water from desert air, says
Mercouri Kanatzidis, a chemist at Northwestern University in Evanston,
Illinois, who wasn’t involved with the work. “This demonstration … is a
significant proof of concept.” It’s also one that Yaghi says has plenty of
room for improvement. For starters, zirconium costs $150 a kilogram, making
water-harvesting devices too expensive to be broadly useful. However, Yaghi
says his group has already had early success in designing water-grabbing
MOFs that replace zirconium with aluminum, a metal that is 100 times
cheaper. That could make future water harvesters cheap enough not only to
slake the thirst of people in arid regions, but perhaps even supply water
to farmers in the desert.

**Update, 14 March, 12:28 p.m.: This item has been updated to reflect the
fact that the device pulls nearly 3 liters of water out of the air for
every kilogram of the water-absorbing material that is used.*



http://zeenews.india.com/science/this-new-solar-powered-device-can-harvest-water-from-dry-air-1996552.html