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Graphene Oxide Sieve Could Make Saltwater Drinkable

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A team of researchers in the United Kingdom have come up with a way to turn seawater into drinkable water by using a graphene-based sieve. This development could help millions of people around the world who don’t have access to clean drinking water.

Graphene was isolated and identified by researchers from the University of Manchester in 2004. It is composed of a single layer of carbon atoms arranged in a hexagon-shaped lattice, the BBC reports. Its unusual characteristics include electric conductivity and extreme tensile strength, making it one of the most promising materials for future use.

However, it was been difficult to manufacture graphene-based devices on a large scale. Producing single-layer graphene using current methods such as chemical vapor deposition has been challenging, and quite expensive.

Now, scientists from the same university, led by Dr. Rahul Nair, have found a workaround. They used a chemical derivative called graphene oxide to make a sieve that has the potential to efficiently filter salts from saltwater.

Nair said that compared to graphene, “graphene oxide can be produced by simple oxidation in the lab.” He explained,

As an ink or solution, we can compose it on a substrate or porous material. Then we can use it as a membrane. In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene.

Regarding turning the graphene itself into a sieve, Nair said, “To make it permeable, you need to drill small holes in the membrane. But if the hole size is larger than one nanometre, the salts go through that hole. You have to make a membrane with a very uniform less-than-one-nanometre hole size to make it useful for desalination. It is a really challenging job.”

But graphene oxide membranes, on the other hand, have already proven that they can sift small nanoparticles, organic molecules and large salts. But previously, they could not filter out common salts, which were smaller. Graphene oxide membranes tend to swell when immersed in water, letting smaller salts pass through along with water molecules.

So the researchers placed walls made of epoxy resin on the graphene oxide membrane, stopping the material from expanding. In this way, the scientists were able to tweak the properties of the membrane to allow common salt to pass.

Desalination plants around the world use polymer-based membranes to filter saltwater, and this new graphene oxide sieve will now be tested against them. Nair said, “The next step is to compare this with the state-of-the-art material available on the market.”

The study was published in Nature Nanotechnology.

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