Metal-Organic Frameworks: Technology Solving the Water Crisis

Device extracts litres of water from low humidity air using only sunlight. Image Credit: MIT, Professor Evelyn Wang. Creative Commons License: CC BY-NC-ND 3.0

Professor Omar Yaghi, a chemist at the University of California, Berkeley, has teamed up with engineering Professor Evelyn Wang from the Massachusetts Institute of Technology, to produce an energy-neutral device, capable of harvesting what Yaghi likes to call “personalised water”.

Over 20 years ago Yaghi invented metal-organic frameworks (MOFs). These incredible materials are a combination of metals, like magnesium or aluminium, and organic molecules to form a rigid, porous structure, which is perfect for storing liquids or gases. Researchers all over the globe have now developed more than 20,000 types of MOF, including one produced by Yaghi in 2014 that is capable of capturing gaseous water.

Yaghi combined zirconium metal with adipic acid to create an MOF that is capable of capturing water vapour.  Yaghi then teamed with engineer Wang who turned this incredible material into a fully functioning, energy-neutral water harvester.  Wang and her team sandwiched one kilogramme of the MOF crystals between a solar absorber and a condenser plate, both of which are in a chamber open to the air.  The water vapour in the air binds to the sandwiched MOF crystals, which sunlight then heats up.  This process of solar heating drives the water towards the condenser plate – which is able to work at the ambient temperature to condense the vapour into liquid water1.

As well as requiring only the power of the sun, this water harvester works in humidity as low as 20%.  These properties mean the technology has great potential to solve the challenges of water harvesting. “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,” said Yaghi. The current prototype is already able to absorb 20% of the MOFs weight in water.  Although, Wang wants to increase water yields by more than double by screening other types of MOF. In conclusion, Wang claims that “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”.

Edited by Richard Murchie




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