Graphene continues to dazzle us with its strength and versatility: exciting new applications are being discovered all the time and now scientists have found a way to manipulate wonderful material so that it can better filter water impurities.
Two-dimensional material made up of carbon atoms has been studied before as a way to clean water, but the new method could offer the most promising approach to date. It’s all due to the exploitation of what are known as van der Waals gaps: the tiny spaces that appear between 2D nanomaterials when they are superimposed.
These nanochannels can be used in a variety of ways, which scientists are exploring now, but the thinness of graphene causes a problem for filtration: the liquid must spend much of its time traveling through the horizontal plane, rather than the vertical, which be much faster.
To solve this problem, the team behind the new study used an elastic substrate to drag the graphene layer into a microscopic series of peaks and valleys. This means that the liquid can move vertically to the side of a peak, instead of walking horizontally through the open plains (all at the nanoscale, of course).
(Brown University)
“When you start wrinkling 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 wrinkle it a lot, the channels end up aligning almost vertically.”
To finish the effect, the graphene and substrate are fixed in an epoxy substance, before the tops and bottoms of the valleys are trimmed. It gives liquids a faster path through graphene while allowing filtration.
Liu and his colleagues have given the new materials the name VAGME (vertically aligned graphene membranes) and, below, they could find uses far beyond making water safe to drink.
“What we end up with 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 pollutants or some metal ions would be too large to pass through. So you could filter them out.”
The next step will be to put it into practice and develop a practical filtering system, but the theory is sound. The material passed one of its first tests, as it allowed water vapor to circulate, while trapping larger hexane molecules.
Finally, these VAGME could find uses in industrial or domestic filtration systems, according to scientists, just one of the many promising ways graphene is used in various scientific fields.
As for nanochannels that work between super-thin 2D materials like graphene, there’s a lot of potential here, too, according to experts. The closer scientists look at these nanomaterials, the more they discover.
“In the last decade, a whole field has emerged to study these spaces that are formed between 2D nanomaterials,” says Hurt.
“You can grow things in there, you can store things in there, and there’s this emerging field of nanofluids where you use these channels to filter some molecules and let others through.”
The research has been published in Communications on Nature.