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Graphene sieve filters seawater into potable water
April 11, 2017, 1:17 pm

Researchers claimed last week that they had created a graphene-based membrane capable of removing salt from seawater, which would now be tested against existing desalination membranes. This sought-after development could aid millions of people without ready access to clean drinking water.

Scientists from the University of Manchester in the United Kingdom say they solved the challenge of manufacturing grapheme-based barriers on an industrial scale, by using a chemical derivative called graphene oxide.

Graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications.

But it has been difficult to produce large quantities of single-layer graphene using existing methods, such as chemical vapor deposition (CVD). Current production routes are also quite expensive.

The researchers say their "graphene oxide can be produced by simple oxidation in the lab and compose it on a substrate or porous material. Then we can use it as a membrane".

Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they could not be used to filter out common salts, which require even smaller sieves.

Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules. Researchers have now demonstrated that placing walls made of epoxy resin (a substance used in coatings and glues) on either side of the graphene oxide membrane was sufficient to stop the expansion.

Restricting the swelling in this way also allowed the scientists to tune the properties of the membrane, letting through less or more common salt for example. The scientists plan to test the graphene oxide sieve against existing industrial membranes used in desalination.

By 2025 the UN expects that 14 percent of the world's population will encounter water scarcity. As the effects of climate change continue to reduce urban water supplies, wealthy modern countries are also investing in desalination technologies.

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