Fresh Air That’s as Good as Gold

Photo courtesy of Brookhaven National Lab

Brookhaven Lab physicists Peter Sutter, Eli Sutter, and Xiao Tong (left to right) with one of the Center for Functional Nanomaterials instruments used to characterize the new nanoparticle structures.

"A little fresh air will be good for you." So parents say, especially when they're trying to kick a slightly comatose teenager off the couch during summer vacation.

Turns out that a little air can be good for increasing the activity of molecules too, according to researchers at the Office of Science's Brookhaven National Lab (Brookhaven Lab). And that's what the scientists were trying to do, while producing a few benefits for the rest of us.

Specifically, the scientists at Brookhaven Lab's Center for Functional Nanomaterials, were trying to increase the activity of gold. Gold is typically quite unreactive – the chemical equivalent of the teenager who gets up at the crack of 11:00 a.m. and painfully plods over to the couch to play computer games all day. However, with the right incentives, it is capable of astonishing productivity, especially speeding chemical reactions while not being consumed (a process called catalysis).

Gold can be an outstanding catalyst when separated into tiny, discrete nanoparticles. But under even moderate heat – a point that will be important below – gold particles tend to glom together and then shut down. Mixing gold with other metals can help, but sustaining their intense catalytic activity requires a nearly perfect setup.

So the Brookhaven scientists tried what in retrospect was a simple approach: They insisted the gold get some fresh air. Namely, they created nanoparticles of gold and the metal indium, and then exposed them to oxygen. In theory, it wouldn't work. The oxygen and indium would connect, pushing the gold particles together in an unreactive center and driving few chemical reactions. But in practice, adding oxygen caused shells of a gold-indium oxide to form across the surface of the nanoparticles. (A more detailed look at their work can be found in a recent issue of the Proceedings of the National Academy of Sciences http://www.pnas.org/content/early/2013/06/05/1305388110.)

Not only was the new compound highly catalytic, it also kept its structural integrity at high temperatures, such as those found in car engines. That's where the compound has particularly high potential, since it is particularly good at taking carbon monoxide (the colorless, odorless stuff that's especially bad to inhale) and combining it with oxygen to produce carbon dioxide, which is rather more benign.

Enlarge Photo

Image courtesy of Brookhaven National Lab

Transmission electron microscopy (TEM) images of the gold-indium alloy nanoparticles at room temperature. (A) shows an overview of multiple particles, while (D) shows a high-resolution TEM image of one nanoparticle's crystalline gold-indium core surrounded by the amorphous and catalytic oxide shell.

Car engines produce traces of carbon monoxide – it's simply an imperfect part of the burning process – but they use catalytic converters to reduce that pollutant, and others, such as nitrogen oxides. Catalytic converters often use a platinum catalyst to cleanse carbon monoxide from the exhaust, but the gold-indium compound created at Brookhaven Lab could prove cheaper and perhaps more durable.

Researchers may find more uses for that compound, and perhaps related compounds with new and novel uses too. That will be part of their continuing efforts using the unique capabilities of the Center for Functional Nanomaterials and the resources of the Office of Science.

Sometimes, fresh air can be good as gold. Now if it could only speed the sleepy teenager up and off the couch!

The Center for Functional Nanomaterials is one of the five DOE Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the U.S. Department of Energy, Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE's Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please click here.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about Brookhaven Lab, please go to http://www.bnl.gov/world/.

Charles Rousseaux is a Senior Writer in the Office of Science, [email protected].