Scientists from the Massachusetts Institute of Technology and University of California Berkeley have developed a solar-powered device capable of harvesting clean drinking water from thin air.
The technology relies on a special foam-like material – a metal-organic framework, or MOF – that “sucks” water into its pores from dry air using ambient solar heat.
In work published in the journal Science, a prototype device tested by the researchers under arid conditions of 20-30 percent humidity drew nearly three litres of water from the air over a 12-hour period.
Drinking water, even in the desert
The technology could feasibly produce clean drinking water nearly anywhere on Earth, and be especially useful in desert regions, where other water harvesting systems cannot be deployed because the air is so dry.
“This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity,” said lead researcher Omar Yaghi from UC Berkeley in an article in the Berkeley News.
“There is no other way to do that right now, except by using extra energy. Your electric dehumidifier at home ‘produces’ very expensive water.”
What is a MOF?
Yaghi invented metal-organic frameworks in the early-1990s. To produce the specialised material, metals like magnesium or aluminium are combined with organic molecules in a nanostructure that resembles atomic scaffolding, with rigid organic molecules linked together with metal ions.
Highly conductive and easily tailored to meet specific chemical tasks, MOFs have been used to boost the efficiency of dye-sensitised solar cells, increase the storage capacity of fuel tanks and capture carbon dioxide from power plants.
MOFs bind with water, harvested via Solar Energy
In 2014, Yaghi built a MOF that binds with water. He then turned to associate professor of mechanical engineering at MIT, Evelyn Wang, to develop a drinking water harvesting system.
The system they came up with consists of around a kilogram of MOF crystals compressed between a solar absorber – a black plate designed to maximise solar heat – and a lower condenser surface which remains at the same temperature as the outside air. As air flows through the foam-like MOF, water molecules attach to the porous cavities inside.
To release the water, sunlight heats the MOF, forcing the bound water molecules to the condenser plate, where it drips into a collector.
“This work offers a new way to harvest water from air that does not require high relative humidity conditions and is much more energy efficient than other existing technologies,” said Wang.
Although the prototype can now absorb 20 percent of its weight in water, Yaghi believes the possibilities offered by MOFs are boundless.
“It’s not just that we made a passive device that sits there collecting water; we have now laid both the experimental and theoretical foundations so that we can screen other MOFs, thousands of which could be made, to find even better materials,” he said.
“There is a lot of potential for scaling up the amount of water that is being harvested. It is just a matter of further engineering now.”
