Scientists develop a ‘sieve’ of graphene that transforms sea water into drinking water
BBC News science editor
Illustration showing how the graphene oxide membrane can separate salt from sea water
A team of researchers at the University of Manchester in the UK has created a graphene “sieve” that can remove salt from seawater. The invention has the potential to help millions of people without direct access to safe drinking water.
Graphene is one of the crystalline forms of carbon, such as diamond and graphite.
The sieve created by scientists is made using a chemical derivative, graphene oxide, and can be highly efficient in salt filtration. It will now be tested in comparison to existing desalination membranes.
The results of the research were published in the scientific publication Nature Nanotechnology.
Graphene was discovered in 1962 but was little studied until it was rediscovered, isolated and characterized by researchers at the University of Manchester in 2004. It consists of a thin layer of carbon atoms arranged in a sort of hexagonal lattice.
Its unusual properties, such as its elastic force and electrical conductivity, have made it one of the most promising metals for future applications.
But so far, it has been difficult and expensive to produce graphene barriers on an industrial scale with existing methods.
Rahul Nair, who led the research, reveals, however, that graphene oxide can be made easily in the laboratory.
“In the form of solution or paint, we can apply it on a porous material and use it as a membrane. In terms of material cost and production scale, it has more potential advantages than graphene in a layer. ”
“To make the normal layer of graphene permeable, you have to make small holes in it, but if those holes are larger than one nanometer, the salts escape through them. It would be necessary to make a membrane with a very uniform hole with less than one nanometer so that it can be used in the desalination. Is very difficult.”
The membranes made of graphene oxide proved to be capable of filtering nanoparticles, organic molecules and even salts of larger crystals. But until now, they could not be used to filter common salts, which require even larger sieves.
Earlier works showed that graphene oxide membranes became slightly swollen when immersed in water, which allowed smaller salts to pass through their pores along with water molecules.
Now, Nair and his colleagues have shown that placing walls made of epoxy resin on either side of the graphene membrane is enough to curb this swelling.
This also allowed scientists to adjust the properties of the membrane, allowing more or less salt, for example.
By 2025, the UN estimates that 14% of the world’s population will face water shortages.
While the effects of climate change continue to reduce the reservoirs that supply the cities, richer countries also invest in desalination technologies as an alternative.
Currently, desalination plants around the world use membranes made of polymers.
“Our next step is to compare graphene oxide membranes with the most sophisticated material available on the market,” says Rahul Nair.
But in an article accompanying the research in Nature Nanotechnology, Ram Devanathan of the Pacific Northwest National Laboratory in the US said more study would be needed to actually produce low-cost graphene oxide membranes And on an industrial scale.
The British team has yet to demonstrate the durability of the membrane during prolonged contact with sea water and ensure that it is resistant to the accumulation of salts and biological material – the phenomenon requires that today’s desalination barriers be cleaned or Replaced periodically.