Scientists at the University of Manchester have come up with a new graphene-based water filter that can make drinkable water from salty water, an invention that could have a massive impact on water shortage worldwide.
Graphene is made from a single layer of graphite and composed of hexagonally-arranged clusters of carbon atoms only one-atom thick but possessing surprising advantages in terms of strength, flexibility and electrical conductivity. This “two-dimensional” material was first isolated in 2004 by researchers at the University of Manchester and has since been studied for a variety of uses, from nanosensor technology to solar cells and batteries to surgical tools and paint.
Since discovered, scientists have eyed graphene for its potential to act as a micro-filter, with various projects displaying graphene’s ability to filter out very small particles and organic compounds. Yet until now, the ability to filter out common salts from water had so far eluded researchers. The new results involve a graphene-oxide membrane whose pore size can be controlled so as to sieve out even smaller salts from salty water and make it safe to drink, with the researchers finding that their graphene sieve can filter out 97 per cent of salts.
“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.” says Jijo Abraham of the National Graphene Institute at the University of Manchester and study co-author.
Researchers were not only able to control the pore size on the graphene-oxide filter, the filtration process ran especially quickly, an advantage for desalination systems. “When the capillary size is around one nanometre, which is very close to the size of the water molecule, those molecules form a nice interconnected arrangement like a train,” Rahul Nair, lead author, also of the National Graphene Institute, to the BBC. “That makes the movement of water faster: if you push harder on one side, the molecules all move on the other side because of the hydrogen bonds between them. You can only get that situation if the channel size is very small.”
For decades, scientists had pondered the reality of one-layer-thick sheets of graphite — the material found in common pencil lead — but had been stymied as to how the single layer compound could be isolated. In a now-famous DIY approach to science (which won them a Nobel Prize), two researchers at the University of Manchester used everyday sticky tape to extract thin layers of graphite from a larger graphite sample. They found that by repeatedly sticking and unsticking the tape, thinner and thinner layers could be created, until eventually they arrived at flakes of the 2D graphene.
The lead in your pencil cannot be turned into graphene, however, as only high-quality flake graphite can do the job. Currently, China is the world’s largest supplier of graphite, which is fast becoming a high-demand commodity due to its use in consumer electronics and lithium-ion batteries. Other countries hoping to benefit from the upcoming graphite boom are India, Brazil and Canada.