CO2 is Not Our Enemy: Sun-Powered
Device Converts CO2 Into Fuel
Powered only by natural sunlight, an array of nanotubes is
able to convert a mixture of carbon dioxide and water vapour
into natural gas at unprecedented rates.
Such devices offer a new way to take carbon dioxide from the
atmosphere and convert it into fuel or other chemicals to cut
the effect of fossil fuel emissions on global climate, says
Craig Grimes, from Pennsylvania State University, whose team
came up with the device.
Although other research groups have developed methods for converting
carbon dioxide into organic compounds like methane, often using
titanium-dioxide nanoparticles as catalysts, they have needed
ultraviolet light to power the reactions.
The researchers' breakthrough has been to develop a method
that works with the wider range of visible frequencies within
The team found it could enhance the catalytic abilities of
titanium dioxide by forming it into nanotubes each around 135
nanometres wide and 40 microns long to increase surface area.
Coating the nanotubes with catalytic copper and platinum particles
also boosted their activity.
The researchers housed a 2-centimetre-square section of material
bristling with the tubes inside a metal chamber with a quartz
window. They then pumped in a mixture of carbon dioxide and
water vapour and placed it in sunlight for three hours.
The energy provided by the sunlight transformed the carbon
dioxide and water vapour into methane and related organic compounds,
such as ethane and propane, at rates as high as 160 microlitres
an hour per gram of nanotubes. This is 20 times higher than
published results achieved using any previous method, but still
too low to be immediately practical.
If the reaction is halted early the device produces a mixture
of carbon monoxide and hydrogen known as syngas, which can be
converted into diesel.
"If you tried to build a commercial system using what we have
accomplished to date, you'd go broke," admits Grimes. But he
is confident that commercially viable results are possible.
"We are now working on uniformly sensitising the entire nanotube
array surface with copper nanoparticles, which should dramatically
increase conversion rates," says Grimes, by at least two orders
of magnitude for a given area of tubes.
This work suggests a "potentially very exciting" application
for titanium-dioxide nanotubes, says Milo Shaffer, a nanotube
researcher at Imperial College, London. "The high surface area,
small critical dimensions, and open structure [of these nanotubes]
apparently provide a relatively high activity," he says.