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
43
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:
http://dx.doi.org/10.1038/nnano.2012.18
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79