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Solar device desalinates water efficiently

Thermal insulator boosts performance by protecting the device’s sunlight absorber from heat loss

by Elizabeth K. Wilson
December 5, 2016 | A version of this story appeared in Volume 94, Issue 48

Micrograph  showing folded graphene oxide film.
Credit: Jia Zhu
A cross-section of the folded graphene oxide film used as a solar absorber in a new desalination device.

A new solar-powered device that takes the salt and minerals out of saltwater works at a higher efficiency than other similar devices (Proc. Nat. Acad. Sci. 2016, DOI: 10.1073/pnas.1613031113). This type of portable, solar-based technology could be a boon for those living in remote areas without clean drinking water.

Scientists are devoting much attention to the development of solar-powered desalination devices because traditional methods for removing salt from saltwater are based on reverse osmosis and use large amounts of energy. Typical solar-powered desalinators aren’t very efficient—often only 30 to 45% of the energy they take in from sunlight results in water vapor generation. This is in part because their solar absorbers, which heat water to evaporation, are in direct contact with the bulk saltwater, which sucks away large amounts of the heat. To mitigate this energy loss, solar desalinators often require additional heat input from external thermal sources or extra help from optical sunlight concentrators.

Now, Jia Zhu, Xiuqiang Li, Weichao Xu, and colleagues at the University of Nanjing have developed a device that employs a thermal insulator. A folded graphene oxide absorber sits on top of the polystyrene foam insulator, which in turn floats on the bulk saltwater. Water from the bulk solution gets taken up by two-dimensional channels in a cellulose film that’s wrapped around the insulator before making contact with the heated absorber. The insulator keeps heat from dissipating into the bulk water. The device has an efficiency of 80%.


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