Now many of you may be wondering why and how the wings of a butterfly can make it into an edition of Technology Tuesday, but little did we know, butterfly wings may be the answer to alternative fuels. Read on to find out how…
Butterfly wings rank among the most delicate structures in nature. Butterfly wings have also given researchers inspiration for new technology that doubles production of hydrogen gas — a green fuel of the future — from water and sunlight.
Tongxiang Fan, Ph.D., stated that finding renewable sources of energy is one of the great global challenges of the 21st century. One promising technology involves producing clean-burning hydrogen fuel from sunlight and water. It can be done in devices that use sunlight to kick up the activity of catalysts that split water into its components, hydrogen and oxygen. Better solar collectors are the key to making the technology practical, and Fan’s team turned to butterfly wings in their search for making solar collectors that gather more useful light.
“We realized that the solution to this problem may have been in existence for millions of years, fluttering right in front of our eyes,” Fan said. “And that was correct. Black butterfly wings turned out to be a natural solar collector worth studying and mimicking,” Fan said.
Scientists long have known that butterfly wings contain tiny scales that serve as natural solar collectors to enable butterflies, which cannot generate enough heat from their own metabolism, to remain active in the cold. When butterflies spread their wings and bask in the sun, those solar collectors are soaking up sunlight and warming the butterfly’s body.
The steep walls of the ridges help funnel light into the holes, Fan explained. The walls absorb longer wavelengths of light while allowing shorter wavelengths to reach a membrane below the scales. Using the images of the scales, the researchers created computer models to confirm this filtering effect. The nano-hole arrays change from wave guides for short wavelengths to barriers and absorbers for longer wavelengths, which act just like a high-pass filtering layer.
The group used actual butterfly-wing structures to collect sunlight, employing them as templates to synthesize solar-collecting materials. They chose the black wings of the Asian butterfly Papilio helenus Linnaeus, or Red Helen, and transformed them to titanium dioxide by a process known as dip-calcining. Titanium dioxide is used as a catalyst to split water molecules into hydrogen and oxygen. Fan’s group paired this butterfly-wing patterned titanium dioxide with platinum nanoparticles to increase its water-splitting power. The butterfly-wing compound catalyst produced hydrogen gas from water at more than twice the rate of the unstructured compound catalyst on its own.
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