It’s not that difficult to collect condensation in a humid climate, but squeezing H20 from arid, thin air is another story. One of the most common ways to do it requires an electric dehumidifier, which means using one nonrenewable resource just to capture another. It’s “very expensive water,” senior author Omar Yaghi of Lawrence Berkeley National Laboratory said in a statement.
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.
Yaghi is the inventor of the metal-organic framework (MOF), a tiny grid made of aluminum or magnesium mixed with organic molecules. The hybrid material is both stiff and porous, which makes it an efficient way to collect and store gases and fluids. In the two decades since the MOF’s development, scientists around the world have built tens of thousands of permutations to hold substances like natural gas.
A few years ago, Yaghi and his colleagues at Berkeley built an MOF that could bind water vapor—the first step toward making water from air. They sent the MOF over to MIT engineer Evelyn Wang, who incorporated it into an ingenious water collecting system. Wang and her colleagues compressed microscopic MOF crystals into a film, which they sandwiched between a solar panel and a water-condensing plate. As air flowed through the layers, particles of water vapor caught and stuck in the MOF sheet. Sunlight on the solar panel pushed them forward into the condenser, where they were transformed from gas to liquid.
The new dehumidifier worked even in low-humidity conditions, but the team acknowledges that they’ve still got some work to do. The MOF sheet can currently absorb up to 20 percent of its weight in water; in the future, they hope to double that number.
Still, Yaghi said, “this is a major breakthrough,” and one that lays the foundation for Earth-friendly home appliances. He added, “One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household.”
Source: Water harvesting from air