Graphene sieve could make seawater drinkable
Discovering the world's strongest material 02:25
(CNN)Researchers
in the United Kingdom have developed a graphene-based sieve that can
filter salt out of seawater, a development that could provide drinking
water to millions of people around the globe.
The applications could be a game-changer in countries where access to safe, clean, drinkable water is severely limited.
Graphene
-- an ultra-thin sheet of carbon atoms organized in a hexagonal lattice
-- was first identified at the University of Manchester in 2002 and has
since been hailed as a "wonder material," with scientists racing to
develop inexpensive graphene-based barriers for desalination on an
industrial scale.
Now, the team at Manchester has used a compound of graphene, known as graphene oxide, to create a rigid sieve that could filter out salt using less energy.
Overcoming hurdles
In recent years, there had been some success in water filtration using graphene oxide to sift out other smaller nanoparticles and organic molecules.
But
researchers had struggled to move forward after finding that the
membrane's pores would swell up when immersed in water, allowing
particles to continue to pass through.
Rahul Nair's team at Manchester now claims it has discovered how to control of the expansion and size of the pores.
Writing Monday in the Nature Nanotechnology journal,
the team revealed it was able to restrict pore-swelling by coating the
material with epoxy resin composite that prevented the sieve from
expanding. This means common salt crystals could continue to be filtered
out, while leaving behind uncontaminated, clean, drinking water.
The
discovery is "a significant step forward and will open new
possibilities for improving the efficiency of desalination technology,"
Nair said in a statement from the university.
"This
is the first clear-cut experiment in this regime. We also demonstrate
that there are realistic possibilities to scale up the described
approach and mass produce graphene-based membranes with required sieve
sizes," he added.
Global implications
Boosting global access to water is critical. By 2025, 14% of the global population will suffer from water scarcity, the United Nations predicts.
In addition, climate change is expected to wreak havoc on urban water
supplies, with decreased rainfall and rising temperatures expected to
fuel demand.
Super substance may yield tech 'miracles' 01:41
Cities have been investing heavily in diversifying their water supplies,
including developing new desalination technologies to make seawater
potable. But existing, industrial-scale desalination plants can be
costly and normally involve one of two methods: distillation through
thermal energy, or filtration of salt from water using polymer-based
membranes.
These techniques have drawn criticism from environmentalists, who argue they involve large amounts of energy, produce greenhouse gases and can be harm marine organisms.
What's next?
The
graphene-oxide breakthrough has been welcomed by scientists in the
field as a promising development, but some are cautious of the next
steps.
"The
selective separation of water molecules from ions by physical
restriction of interlayer spacing opens the door to the synthesis of
inexpensive membranes for desalination," wrote Ram Devanathan of the
Pacific Northwest National Laboratory, in an accompanying news-and-views article in the journal.
More
work still needs to be done to test the durability of the barriers and
to confirm the membrane is resistant to "fouling by organics, salt and
biological material," he said.
Water
treatment with membranes that separate water molecules from ions,
pathogens and pollutants has been proposed as an energy-efficient
solution to the freshwater crisis, Devanathan added.
"The
ultimate goal is to create a filtration device that will produce
potable water from seawater or waste water with minimal energy input."
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