Ingenious ‘crumpled’ graphene could be the most promising water filter yet

Graphene continues to dazzle us with its strength and versatility – exciting new applications are constantly being discovered for it, and now scientists have found a way to manipulate the wonderful material so that it can better filter impurities from water.

The two-dimensional material made up of carbon atoms has already been studied as a means of cleaning water, but the new method may offer the most promising approach to date. It is all due to the exploitation of what is called van der Waals gaps: the small spaces that appear between 2D nanomaterials when they are superimposed.

These nanochannels can be used in different ways, which scientists are currently exploring, but the thinness of graphene poses a problem for filtration: the liquid has to spend much of its time traveling along the horizontal plane, rather than vertically. which be much faster.

To solve this problem, the team behind the new study used an elastic substrate to grind the graphene layer into a microscopic series of peaks and valleys. This means that the liquid can descend vertically down the side of a peak, rather than crossing open plains horizontally (all at the nanoscale, of course).

(Brown University)

“When you start crumpling the graphene, you tilt the sheets and channels out of the plane,” says materials scientist Muchun Liu of the Massachusetts Institute of Technology (MIT).

“If you bend it a lot, the channels end up lining up almost vertically.”

To finish the effect, the graphene and the substrate are fixed in an epoxy substance, before the tops of the peaks and the bottoms of the valleys are cut. It gives the liquid a faster path through graphene while still allowing filtration.

Liu and his colleagues gave the new materials the name VAGME (vertically aligned graphene membranes), and further down they could find uses far beyond making water drinkable.

“We end up with a membrane with these short, very narrow channels through which only very small molecules can pass,” says chemical engineer Robert Hurt of Brown University.

“So, for example, water can pass through, but organic contaminants or some metal ions would be too big to pass. So you can filter them.”

The next step will be to put this into practice and develop a practical filtering system, but the theory is solid. The material passed one of its first tests by allowing water vapor to pass through, while trapping larger hexane molecules.

Scientists say these WAVEs could eventually find uses in industrial or household filtering systems – one of the many promising ways to use graphene in various scientific fields.

As for the nanochannels that operate between super-thin 2D materials such as graphene, there is a lot of potential there too, experts say. The closer scientists look at these nanomaterials, the more they discover.

“Over the last decade, a whole field has emerged to study these spaces that form between 2D nanomaterials,” says Hurt.

“You can grow things in there, you can store things in there, and there’s this emerging area of ​​nanofluidics where you use these channels to filter out some molecules while letting others through.”

The research was published in Nature communications.