Last October, the team at the University of California at Berkeley traveled to the Arizona desert to put their latest prototype water harvester in the backyard of a home and began to absorb any electricity other than air from the sun. The successful field test of their larger new generation harvester proved the team's prediction in early 2017: the water harvester can extract drinking water every day/day at very low humidity and low cost, which is very suitable for people. Living in areas of the world that are dry and water-deficient.

“There is no such thing,” Omar Yaghi said, inventing the technology of the harvester. “It can operate at ambient temperatures and the surrounding sunlight, and collects moisture in the desert without additional energy input. This journey from the lab to the desert allows us to turn an interesting phenomenon into a science. ""

Yaghi, James and Neeltje Tretter chairs from the Department of Chemistry at the University of California, Berkeley, and a professor at the Lawrence Berkeley National Laboratory, whose team will report on the first scene of a water harvesting harvester in the June 8 issue of Science . The test results progress .

In Scottsdale, tests that reduced relative humidity from as much as 40% at night to as low as 8% during the day proved that harvesters should easily add more water-absorbing agent (a highly porous material called metal-organic framework). Or MOF. Researchers expect that using MOF (MOF-801), which is currently made of expensive metal zirconium, they will eventually be able to harvest about 200 milliliters (about 7 ounces) of water per kilogram (2.2 pounds) of MOF or 3 ounces per pound. water.

But Yaghi also reported that he has developed a new aluminum-based MOF called MOF-303 that is at least 150 times cheaper and captures twice as much water in laboratory tests. This will enable the new generation of harvesters to produce more than 400 milliliters (3 cups) of water per day from one kilogram of MOF, equivalent to half the amount of 12 ounces of soda per pound per day.

Yaghi said: "The commercialization of this has caused great interest, and several startups have begun to use water collection equipment by developers." Aluminum MOF makes this water production very practical because it is cheap. ”

Yaghi also collaborated with Dr. Turki Saud Mohammad Al Saud, President of the Science and Technology City of Abdul Aziz, Riyadh, Saudi Arabia, on the technology to study the Center for Excellence in Nanomaterials and Clean Energy.

Superabsorbent MOFs

Yaghi is a pioneer in metal-organic frameworks with so many internal passages and holes that the sugar cube-sized MOF may have an internal surface area of six football fields. The surface area readily absorbs gases or liquids, but it is also important that they are quickly released upon heating. Various types of MOFs have been tested to charge more gas into the storage tanks of hydrogen fuel vehicles, absorb carbon dioxide from the chimney and store methane.

A few years ago, Yaghi created the MOF-801, which is easy to absorb and release moisture. Last year he tested a small amount of water on a simple harvester to see if he could capture the moisture in the ambient air at night and use the sun. Heat it out and use it again. The harvester was manufactured by MIT's collaborators using less than 2 grams of MOF, proving that the concept is effective: although researchers cannot collect or accurately measure water, the window is atomized in the sun.

Earlier this year, the same harvester was transported to the desert and worked similarly, although only water droplets were again used as proof of concept.

For this new paper, UC Berkeley graduate student Eugene Kapustin and postdoctoral fellows Markus Kalmutzki and Farhad Fathieh collected and measured moisture and tested the latest generation of collectors under different humidity, temperature and solar intensity conditions.

The harvester is essentially a box inside a box. The inner box is fitted with a 2 square foot MOF grain bed that opens to the air to absorb moisture. This is mounted on a two-foot plastic cube with a transparent top and side. The top is open at night to allow air to flow in and out of contact with the MOF, but is replaced during the day so the box can warm up like a greenhouse, draining water from the MOF. The released water condenses inside the outer box and falls to the bottom, and the researchers collect it with a straw.

Extensive field testing provides a blueprint that allows engineers to configure harvesters for different conditions in Arizona, the Mediterranean, or anywhere else based on a specific MOF.

Yaghi said: “The key development here is that it operates at low humidity because this is the case in the arid regions of the world.” Under these conditions, the harvester collects moisture even at dew points below zero.

Yaghi is eagerly awaiting the next field test , which will test the aluminum-based MOF and plan to die in the late summer, with a daytime temperature of 110 degrees Fahrenheit, a nighttime stay of 70s, and a nighttime humidity of 25%.

Further exploration: the device extracts water from dry air and is powered only by the sun

For more information: F. Fathieh et al., “Practical Water Production in Desert Air”, Science Advances (2018). Advances.sciencemag.org/content/4/6/eaat3198

Read more at: https://phys.org/news/2018-06-trials-next-generation-harvester-fresh-air.html#jCp