Graphene continues to amaze us with its strength and versatility – new interesting applications are discovered for it all the time, and now scientists have found a way to manipulate the miracle material so that it can better filter impurities from water.
Two-dimensional material made of carbon atoms has previously been studied as a way to clean water, but the new method could offer the most promising approach to date. It all comes down to exploiting what is known as van der Waals gaps: the tiny spaces that appear between 2D nanomaterials when they are layered on top of each other.
These nanochannels can be used in a variety of ways, which scientists are now exploring, but graphene thinning causes a filtering problem: the liquid must spend much of its time traveling along the horizontal plane, more rather than the vertical one, which would be much faster.
To solve this problem, the team behind the new study used an elastic substrate to squeeze the graphene layer into a microscopic series of peaks and valleys. This means that the liquid can descend on the side of a peak vertically, rather than hiking on the horizontally open plains (all on a nanoscale, of course).
(Brown University)
“When you start wrinkling graphene, tilt the sheets and channels out of the plane,” says materials researcher Muchun Liu of the Massachusetts Institute of Technology (MIT).
“If you wrinkle it a lot, the channels end up being aligned almost vertically.”
To finish the effect, the graphene and the substrate are fixed in an epoxy substance, before the tops and bottoms of the valleys are cut. It gives the liquid a faster path through graphene, while allowing filtration.
Liu and her colleagues named the new materials VAGME (vertically aligned graphene membranes) and could find uses far beyond making water safe to drink.
“What we’ve got is 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 large to pass through. So you could filter them.”
The next step will be to implement and develop a practical filtration system, but the theory is sound. The material passed one of its first tests, allowing water vapor to flow while capturing larger molecules of hexane.
Finally, these VAGMEs could find uses in industrial or household filtration systems, scientists say – just one of the many promising ways graphene is used in various scientific fields.
As for nanochannels that work between super-thin 2D materials, such as graphene, there is also a lot of potential here, according to experts. The more scientists look at these nanomaterials, the more they discover.
“In the last decade, an entire field has emerged to study these spaces that form between 2D nanomaterials,” says Hurt.
“You can grow things there, you can store things there, and there’s this emerging field of nanofluids where you use those channels to filter some molecules, letting others pass.”
The research was published in Communications about nature.