sciencehabit quotes a report from Science Magazine: 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, 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. 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. 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 findings were published in the journal Science.
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