Drawing water from dry air

Finding yourself stranded in the desert without any water could become less of a life-and-death problem, thanks to a new device that can pull potable water from air even in humidity as low as 20% (a condition typical for North Africa). The water harvester, constructed by Evelyn N. Wang’s group at MIT, is powered by only sunlight and has at its heart a metal-organic framework, or MOF, developed by Omar M. Yaghi’s group at the University of California, Berkeley (Science 2017, DOI: 10.1126/science.aam8743). In 2014, Yaghi reported a water-grabbing MOF, known as MOF-801, with the structure [Zr₆O₄(OH)₄(fumarate)₆] that could soak up to 25% of its weight in water. He approached Wang about incorporating it in a water-harvesting device. Her group built a prototype with dust-sized crystals of MOF-801 sandwiched between a solar absorber and a condenser plate, which are inside a chamber that’s open to the air. As air flows through the chamber, water attaches to the MOF. Sunlight then heats the MOF, driving the water onto a condenser, where it cools and drips into a collector. Over the course of one day, Wang estimates, a 30-L version of the harvester could collect up to 12 L of water from air, enough to support a single household.