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Photo: Manchester University
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Graphene is one
of the wonders of the science world, with the potential to create foldaway
mobile phones, wallpaper-thin lighting panels, and the next generation of
aircraft. The new finding at The University of Manchester gives graphene’s
potential a most surprising dimension—graphene can also be used for distilling
alcohol.
In a report
published in Science, a team led by Professor Sir Andre Geim
shows that graphene-based membranes are impermeable to all gases and liquids
(vacuum-tight). However, water evaporates through them as quickly as if the membranes
were not there at all.
This newly found
property can now be added to the already long list of superlatives describing
graphene. It is the thinnest known material in the universe and the strongest
ever measured. It conducts electricity and heat better than any other material.
It is the stiffest one too and, at the same time, it is the most ductile.
Demonstrating its remarkable properties won University of Manchester
academics the Nobel Prize in Physics in 2010.
Now the University of Manchester scientists have studied
membranes from a chemical derivative of graphene called graphene oxide.
Graphene oxide is the same graphene sheet but it is randomly covered with other
molecules such as hydroxyl groups OH-.
Graphene oxide sheets stack on top of each other and form a laminate.
The researchers
prepared such laminates that were hundreds times thinner than a human hair but
remained strong, flexible and were easy to handle.
When a metal
container was sealed with such a film, even the most sensitive equipment was
unable to detect air or any other gas, including helium, to leak through.
It came as a
complete surprise that, when the researchers tried the same with ordinary
water, they found that it evaporates without noticing the graphene seal. Water
molecules diffused through the graphene-oxide membranes with such a great speed
that the evaporation rate was the same independently whether the container was
sealed or completely open.
Rahul Nair, PhD, who
was leading the experimental work, offers the following explanation: "Graphene-oxide
sheets arrange in such a way that between them there is room for exactly one
layer of water molecules. They arrange themselves in one molecule thick sheets
of ice which slide along the graphene surface with practically no friction.
"If another atom
or molecule tries the same trick, it finds that graphene capillaries either
shrink in low humidity or get clogged with water molecules."
"Helium gas is
hard to stop. It slowly leaks even through a millimeter-thick window glass but
our ultra-thin films completely block it. At the same time, water evaporates
through them unimpeded. Materials cannot behave any stranger," comments Geim. "You cannot help wondering what else graphene has in store for us."
"This unique
property can be used in situations where one needs to remove water from a
mixture or a container, while keeping in all the other ingredients," says Irina
Grigorieva, PhD, who also participated in the research.
"Just for a
laugh, we sealed a bottle of vodka with our membranes and found that the
distilled solution became stronger and stronger with time. Neither of us drinks
vodka but it was great fun to do the experiment," adds Nair.
The Manchester researchers
report this experiment in their Science paper, too, but they say they
do not envisage use of graphene in distilleries, nor offer any immediate ideas
for applications.
However, Geim
adds, "The properties are so unusual that it is hard to imagine that they
cannot find some use in the design of filtration, separation, or barrier
membranes and for selective removal of water."
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