Graphene Sieve

Graphene 'sieve' filters seawater to create drinkable water

Researchers at the University of Manchester have used a graphene ‘sieve’ to successfully filter salt from seawater to make it drinkable for the first time.

The study, published today in the journal Nature Nanotechnology, found that a graphene-based membrane was capable of blocking salt molecules, while letting water flow through its pores.

Millions of people living in low-income countries lack a reliable source of drinking water. As the impact of climate change increases clean water demand while reducing water supplies, wealthy nations have begun investing in developing new technologies to filter water.

Graphene has been much discussed as a possible component in new filtration technologies, including desalination.

Previously, scientists based at Manchester’s National Graphene Institute had developed a graphene-oxide membrane and shown that it swells when waterlogged. Large molecules such as organic molecules and complex salts were blocked by the membrane.

Recently, the research group have developed a technique which allows them some control over the membrane pore size. This has allowed them to reduce pore size enough to capture common salts – such as sodium chloride – for the first time. When dissolved in water, a ‘shell’ of water molecules surrounds the salt molecules. While water molecules pass through the barrier, the bulky salt molecules are blocked. This makes the membrane ideal for desalination.

Professor Rahul Nair of the National Graphene Institute described this as a “significant step forward”.

“There are realistic possibilities to scale up the described approach and mass produce graphene based membranes with required sieve sizes,” he continued.

Jijo Abraham, a lead author of the study, added that the versatile graphene-oxide membrane is not only useful for desalination, but also “opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.”

It is hoped that filtration systems based around these graphene membranes could be built on a small scale, making them accessible to low-income communities which cannot afford large manufacturing plants.

Graphene sieve for saltwater

Image credit: Graphic News

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