Solar powered
device
to clean
greenhouse gases
Researchers have developed an artificial
photosynthetic system to
convert carbon dioxide into useful products like
plastics,
pharmaceuticals and liquid fuels using solar power
A
potentially game-changing breakthrough in artificial photosynthesis
has
been achieved with the develop ment of a system that can capture
carbon
dioxide emissions before they are vented into the atmosphere
and
then, powered by solar energy, convert that carbon dioxide
into valuable chemical products, including
biodegradable plastics,
pharmaceutical
drugs and even liquid fuels. Scientists with the
US
Department of Energy's Lawrence Berkeley National Laboratory
(Berkeley
Lab) and the University of California (UC) Berkeley
have
created a hybrid system of semiconducting nanowires and bacteria
that
mimics the natural photosynthetic process by which plants use the
energy
in sunlight to synthesise carbohydrates from carbon dioxide
and water. However, this new artificial
photosynthetic system synthesizes
the combination of carbon dioxide and water
into acetate, the most
common
building block today for biosynthesis. “We believe our system
is a revolutionary leap forward in the field
of artificial photosynthesis,“
says
Peidong Yang, one of the leaders of this study. “Our system
has
the potential to fundamentally change the chemical and oil industry
in
that we can produce chemicals and fuels in a totally renewable way,
rather
than extracting them from deep below the ground.“
The
research appears in the journal Nano Letters. The more carbon dioxide
that
is released into the atmosphere the warmer the atmosphere becomes.
The
artificial photosynthetic technique developed by the researchers solves
the
storage problem by putting the cap tured carbon dioxide to good use.
“In
natural photosynthesis, leaves harvest solar energy and carbon dioxide is
reduced
and combined with water for the synthesis of molecular products that
form
biomass,“ says Chris Chang, an expert in catalysts for energy conversions.
“In
our system, nanowires harvest solar energy and deliver electrons to bacteria,
where
carbon dioxide is reduced and combined with water for the synthesis of
a
variety of targeted, value-added chemical products.“
HOW
IT WORKS
By
combining biocompatible lightcapturing nanowire arrays with select bacteria,
the
new system offers a winwin situation for the environment: solar-powered
green
chemistry using sequestered carbon dioxide.
“Our
system represents an emerging alliance between the fields of materials
sciences
and biology, where oppor tunities to make new functional devices
can
mix and match components of each discipline,“ says Michelle Chang,
an
expert in biosynthesis. “For example, the morphology of the nanowire
array
protects the bacteria like Easter eggs buried in tall grass so that these
usually-oxygen
sensitive organisms can survive in environmental carbon-dioxide
sources
such as flue gases.“
The
system starts with an “artificial forest“ of nanowire heterostructures,
consisting
of silicon and titanium oxide nanowires, developed earlier by
Yang
and his research group. “Our artificial forest is similar to the chloroplasts
in
green plants,“ Yang says. “When sunlight is absorbed, photo-excited electron
whole
pairs are generated in the silicon and titanium oxide nanowires, which
absorb
different regions of the solar spectrum. The photogenerated electrons
in
the silicon will be passed onto bacteria for the CO2 reduction while the
photo-generated
holes in the titanium oxide split water molecules to make
oxygen.“
Once
the forest of nanowire arrays is established, it is populated with
microbial
populations that produce enzymes known to selectively catalyze
the
reduction of carbon dioxide.
For
this study, the team used Sporomusa ovata, an anaerobic bacterium that
readily
accepts electrons directly from the surrounding environment and uses
them
to reduce carbon dioxide. Once the carbon dioxide has been reduced by
S
ovata to acetate.
“We
are currently working on our second generation system which has a
solar-to-chemical
conversion efficiency of three per cent,“ Yang says.
“Once
we can reach a conversion efficiency of 10 per cent in a cost effective
manner,
the technology should be commercially viable.“
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MM21APR15
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