Researchers from the University of Manchester have created a new type of sieve that is able efficiently to remove salt from seawater, a recent study published in Nature Nanotechnology reports.
The development is a graphene-based device that could one day help millions of people who do not have access to clean drinking water. To make it, researchers turned to a chemical derivative known as graphene oxide.
Graphene is an allotrope consisting of a single layer of carbon atoms arranged in a hexagonal lattice. This gives it a wide range of unique properties, such as extraordinary tensile strength and electrical conductivity.
However, manufacturing graphene-based membranes have proven difficult in the past. This is because not only have scientists not been able to create large quantities of the substance, current production routes are quite costly. In contrast, graphene oxide is much easier to produce.
“Graphene oxide can be produced by simple oxidation in the lab,” said co-author Dr. Rahul Nair, a professor at the University of Manchester, according to BBC News. “As an ink or solution, we can compose it on a substrate or porous material. Then we can use it as a membrane.”
In order to make single-layer graphene permeable, researchers needed to drill holes into the membrane. This posed a problem because if those holes were bigger than one nanometer, they would allow salts to pass through. To overcome this, the team placed walls made of epoxy resin — a substance used in glue — on either side of the graphene oxide membrane to stop it from expanding in water. This then restricted the substance and allowed researchers to control how much salt passed through by changing the speed of water as it went through the membrane.
This new research could greatly increase water availability all around the world. The United Nations estimates that 14 percent of the world’s population will encounter water scarcity by 2025 and that number will only climb as time goes on. They hope that one day the sieve — or ones like it — could be used to help reduce that number.
While more work needs to be done before graphene-based membranes can be inexpensively produced at an industrial scale, this new device is the first time scientists have been able to control the spacing of pores in a membrane for desalination purposes. Researchers next plan to compare the device with others on the market to see how it matches up and the ways it could be improved.
“Realization of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” Nair said, in a statement. “This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”