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12-03 :: March/April 2012
nanotimes News in Brief
Fuel Cells // Better Cells by Studying the Defects
© Based on Material by Cornell University R
esearchers at Cornell University (US) show that a knowledge of the surface facets of a gold nano-
rod catalyst is insufficient to predict its reactivity, and research must also consider defects on the surface of the nanorod.
“People measure the activity of a sample and then try to understand by using facet information,” said Peng Chen, associate professor of chemistry and chemical biology. “The message we want to deliver is that surface defects [on the facets] dominate the catalysis.” Instead of particles, Chen‘s research group studied catalytic events on gold “nanorods” up to 700nm long, effectively letting them see how acti- vity varies over a single facet. Gold acts as a catalyst to convert a chemical called Amplex Red into resoru- fin, which is fluorescent. Each time a catalytic event occurs, the newly created molecule of resorufin emits a flash of light that is detected by a digital ca- mera looking through a microscope. A flash typically appears as several pixels, and additional computer processing averages their brightness to pinpoint the actual event to within a few nanometers. The resear- chers call the technique “super-resolution microsco- py.” After flooding a field of nanorods with a solution of Amplex Red, they made a “movie” with one frame every 25 milliseconds. The researchers found more catalytic events near the middle of a rod, tapering off toward the ends and a jump back up at the ends. They also found variation in the amount of activity from one rod to another, even though all the rods
When Amplex Red connects with a gold catalyst the structure is changed to make a fluorescent molecule that immediately emits a flash of light, showing where the catalytic event took place. Right, electron microphoto of a single gold nanorod, encased in a poirus silica shell. The shell keeps rods from clumping together and allows expe- rimenters to use heat to clean away a coating that forms when the rods are created. © Cornell / Peng Chen
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have the same types of facets. To explain the results, they proposed that activity is higher in areas where there are more surface defects. The nanorods are made by growing gold crystals from a small “seed” crystal, growing outward from the center to the ends, Chen explained, and more defects form at the beginning of the process.
Xiaochun Zhou, Nesha May Andoy, Guokun Liu, Eric Choudhary, Kyu-Sung Han, Hao Shen, Peng Chen: Quanti- tative super-resolution imaging uncovers reactivity patterns on single nanocatalysts, In: Nature Nanotechnology, Vol. 7(2012), No. 4, April 2012, Pages 237-241, DOI:10.1038/ nnano.2012.18: