SAN DIEGO, CALIFORNIA- When Omar Yaghi was growing up in Jordan, outside of Amman, he only received about 5 hours once every 2 weeks. If Yaghi was not up at dawn to turn on the spigots to store water, his cow, and their garden had to go without. Yaghi, a chemist at the University of California, Berkeley, said he and his colleagues have created a solar-powered device that could provide water for millions in water. stressed regions. At its heart is a porous crystalline material, known as a metal-organic framework (MOF), that acts like a sponge: It sucks water vapor out of air, even in the desert, and then releases it as liquid water.
Jorge Andrés Rodríguez Navarro, a MOF chemist at the University of Granada in Spain, says: "This is a real problem. It's just one example of how MOFs can finally get their prime. Yaghi and his colleagues synthesized the first MOF in 1995, and chemists have created thousands of the structures since. Tinkertoy set, connected into a porous network by organic linkers designed to hold close to the hubs and create openings to house molecular guests. By mixing and matching the metals and linkers, researchers found they could tailor the pores to capture gas molecules, such as water vapor and carbon dioxide (CO 2 ). Amanda Morris, a MOF researcher at the Virginia Polytechnic Institute and State University in Blacksburg, says, "We can play games with modifying and knowing exactly where every atom." But because many of the early MOFs were expensive to make and degraded quickly, they did not live up to initial excitement.
In recent years, Yaghi and other MOFs have more robust. More highly charged metals, for example, create stronger bonds that stand up to heat. That has been opened up to look for work as housing, which typically works faster at high temperatures.
One recent market report predicted that the sales of MOFs.
One recent market report predicted that sales of MOFs for applications including storage and canister gas to $ 410 million annually over the next 5 years, up from $ 70 million this year. "Ten years ago, MOFs showed promise for a lot of applications," says Omar Farha, a MOF chemist at Northwestern University in Evanston, Illinois.
One application is Yaghi's, which he hopes to help provide drinking water for the estimated one-third of the world's population living in water-stressed regions. Yaghi and his colleagues first developed a zirconium-based MOF in 2014 that could harvest and release water. But at $ 160 per kilogram, zirconium is too expensive for bulk use. MOF-303, based on aluminum, which costs just $ 3 per kilogram. In the desert of Arizona, Yaghi and his team place their MOF in a small, clear plastic container. They kept it open at night, allowing the MOF to absorb water vapor. MOF to sunlight, which is about 0.2 liters per kilogram of MOF per day.
At last week's meeting of the American Chemical Society and in the 27th August issue of ACS Central Science Yaghi has reported that it has lost more and more productive water harvester. By exploiting MOF-303's ability to fill and empty its pores in just minutes, the team can make the new device complete dozens of cycles daily. Per kilogram of MOF per day from desert air. Yaghi expects further improvements to boost that number to 8 to 10 liters per day. Last year, he said, "Water is harvesting." 22,500 liters per day, enough to supply a small village. "We're making water mobile," Yaghi says.
Other MOF applications are showing promise as well. In the 25 January issue of ACS Applied Nano Materials Farha and his colleagues reported using a MOF to detoxify chemical weapons. The MOF consists of a lanthanum-based framework linked to ring-shaped organic compounds. The compounds, called porphyrins, have been adsorbed on absorbing light and have been used in the air to form a single molecule. In the study, the singlet oxygen in turn could break down molecules of a lab-safe molecular cousin of mustard gas both inside and outside the pores. At the meeting here, Farha's Northwestern colleague Joseph Hupp has reported that he and his colleagues have published a series of zirconium-, hafnium- and cerium-based MOFs that may detoxify nerve agents. Hupp says.
Farha and others have thus encapsulated enzymes inside MOFs, protecting the fragile molecules from harsh environments and enabling them to carry out industrial reactions outside cells. In one example, Farha's team reported in the 26 March issue of Angewandte Chemie that a MOF-caged enzyme called formate dehydrogenase can convert CO 2 to formic acid, a common industrial chemical, at more than three times the rate of the uncaged enzyme, and under green conditions than formic acid is normally made. At the meeting, Thomas Rayder, a graduate student at Boston College, reported building on the idea. He encapsulated a pair of enzymic catalysts in a zirconium-based MOF to drive a series of reactions that convert gaseous CO 2 to methanol, a liquid fuel.
When they were unprotected by the MOFs, Rayder found , the two catalysts did not produce any methanol because they were quickly deactivated, probably by reacting with each other.  Rayder and others still need to be present at the MOFs MOFs can be cheaply reduced to a large scale. But if MOFs can pass those tests, they could offer some of the world's most pressing problems.