April 4, 2017

Groundbreaking graphene sieve lets you drink seawater

In a breakthrough that could aid the millions of people living in areas lacking access to a supply of clean drinking water, researchers from the University of Manchester have developed a sieve make from graphene that could be used to efficiently filter salt out of seawater.

The sieve, which is detailed in the latest issue of Nature Nanotechnology, uses a graphene oxide membrane that has already proven effective at filtering out tiny nanoparticles, organic molecules, and larger salts – but not smaller ones. Now, their new filter will be tested against currently-used desalination membranes, according to BBC News.

Originally discovered by a Manchester-led team of researchers 13 years ago, graphene is made up of a single-layer of carbon atoms arranged in a hexagonal lattice. It is considered one of the most promising materials for use in future applications, due largely to its tensile strength and its electrical conductivity, but has been difficult to mass produce, the website noted.

On the other hand, graphene oxide “can be produced by simple oxidation in the lab,” Dr. Rahul Nair, who led the study, told BBC News. What that means that the material is far easier and less expensive to make. “We can compose it on a substrate or porous material. Then we can use it as a membrane,” he said. “In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene.”

That doesn’t mean that it’s a walk in the park, however. As Dr. Nair explained, To make it permeable, you need to drill small holes in the membrane. But if the hole size is larger than one nanometer, the salts go through that hole. You have to make a membrane with a very uniform less-than-one-nanometer hole size to make it useful for desalination. It is a really challenging job.”

Filter could be an alternative to desalination plants in poor countries

As the study authors explained in a statement, previous studies showed that a graphene-oxide membrane would become somewhat swollen if immersed in water, which would allow smaller salts to pass through the membrane. With their new research, they have developed a method to keep that from happening, allowing them to precisely control the size of the pores.

What they did, according to BBC News, is place walls made of epoxy resin on either side of the membrane. This prevented the expansion from taking place, and by making the membrane pores tunable, they have found that the membrane is able to filter out common seawater salts, making it safe for human consumption.

Given that the United Nations predicts that 14 percent of the global population will experience at least some difficulty in obtaining an adequate amount of drinking water by 2025, the Manchester led research team hopes that their technology will be able to improve water filtration and provide a way for poorer countries to desalinate seawater and make it drinkable.

“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,” Dr. Nair said. “We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”

“The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes,” added co-lead author Jijo Abraham, also from the University of Manchester.


Image credit: University of Manchester