Sea-water
Manchester, England — The water surrounding the Caribbean already provides food and enjoyment for people living in the region and elsewhere. But, now it could also be a source for unimaginable quantities of clean drinking water.
A UK-based team of scientists has created a graphene-based sieve capable of removing salt from seawater, a development that could aid the millions of people grappling with water shortages.
It has previously been difficult to manufacture graphene-based barriers on an industrial scale, but scientists from the University of Manchester, led by Dr. Rahul Nair, solved some of the challenges by using a chemical derivative called graphene oxide. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications.
It has reportedly been difficult to produce large quantities of single-layer graphene using existing methods, and current production methods are costly. Writing in the journal Nature Nanotechnology, Nair nevertheless explained that graphene oxide can be produced by oxidation in the laboratory.
“As an ink or solution, we can compose it on a substrate or porous material. Then, we can use it as a membrane,” he told BBC News. “In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene.”
Graphene oxide membranes have already proved their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn’t 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.
Now, Dr Nair and colleagues demonstrated that placing walls made of epoxy resin 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, according to the BBC report.
When common salts are dissolved in water, they always form a “shell” of water molecules around the salt molecules.
This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing through along with the water.
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