Graphene sieve turns seawater into drinking water
New research
demonstrates the real-world potential of providing clean drinking water for
millions of people who struggle to access adequate clean water sources. The new
findings from a group of scientists at The University of Manchester were
published today in the journal Nature Nanotechnology. Previously
graphene-oxide membranes have shown exciting potential for gas separation and
water filtration.
Graphene-oxide
membranes developed at the National Graphene Institute have already
demonstrated the potential of filtering out small nanoparticles, organic molecules,
and even large salts. Until now, however, they couldn't be used for sieving
common salts used in desalination technologies,
which require even smaller sieves. Previous research at The University of
Manchester found that if immersed in water, graphene-oxide membranes become
slightly swollen and smaller salts flow through the membrane along with water,
but larger ions or molecules are blocked.
The Manchester-based
group have now further developed these graphene membranes and
found a strategy to avoid the swelling of the membrane when exposed to water.
The pore size in the
membrane can be precisely controlled which can sieve common salts out of salty
water and make it safe to drink.
As the effects of
climate change continue to reduce modern city's water supplies, wealthy modern
countries are also investing in desalination technologies. Following the severe
floods in California major wealthy cities are also looking increasingly to
alternative water solutions. When the common salts are dissolved in water, they
always form a 'shell' of water
molecules around the salts molecules. This allows the tiny capillaries
of the graphene-oxide membranes to block the salt from flowing along with the
water. Water molecules are able to pass through the membrane barrier and flow
anomalously fast which is ideal for application of these membranes for
desalination.
Professor Rahul Nair,
at The University of Manchester said: "Realisation of scalable membranes
with uniform pore size down to atomic scale is a significant step forward and
will open new possibilities for improving the efficiency of desalination technology. "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."
Mr. Jijo Abraham and
Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper:
"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." said Mr. Abraham.
By 2025 the UN expects
that 14% of the world's population will encounter water scarcity. This
technology has the potential to revolutionise water filtration across the
world, in particular in countries which cannot afford large scale desalination
plants. It is hoped that graphene-oxide membrane systems can be built
on smaller scales making this technology accessible to countries which do not
have the financial infrastructure to fund large plants without compromising the
yield of fresh water produced.
https://phys.org/news/2017-04-graphene-sieve-seawater.html