Study improves understanding of method for creating multi-metal nanoparticles
Raleigh, NC--A new study from researchers at North Carolina State University (NC State) sheds light on how a technique that is commonly used for making single-metal nanoparticles can be extended to create nanoparticles consisting of two metals, and that have tunable properties. The study also provides insight into the optical properties of some of these nanoparticles.
Tuning the optical properties of nanoparticles is of interest for security applications, as well as multiple industrial and environmental applications having to do with chemical reactions.
The researchers created core/shell nanoparticles with a gold core and silver shell, as well as alloy nanoparticles. They also characterized the optical properties of these nanoparticles.
Improving on digestive ripening
The nanoparticles were synthesized using a technique called "digestive ripening." The technique has been used to create single-metal particles for approximately a decade, but there have been limited studies of core/shell and alloy nanoparticles created using digestive ripening. The comprehensive nature of this latest study may make it more common, though.
"Our detailed evaluation of this synthetic approach should help other researchers explore other kinds of binary metal nanoparticles," says Joe Tracy, an assistant professor of materials science and engineering at NC State and co-author of a paper describing the study.1
Digestive ripening relies on the use of ligands, which are small organic molecules with parts that bond directly to metals. The ligands are usually anchored to the metal cores of the nanoparticles and prevent the nanoparticles from clumping together, which allows them to be suspended in solution. Digestive ripening occurs when the ligands are able to transport metal atoms from the core of one nanoparticle to another - resulting in a more homogenous size distribution among the nanoparticles.
The researchers used digestive ripening to create a solution of gold nanoparticles of similar size. When they introduced silver acetate into the solution, the ligands transported silver atoms to the surfaces of the gold nanoparticles, resulting in nanoparticles with gold cores and silver shells.
The nanoparticles were then transferred into a second solution, containing a different ligand. Heating this second solution to 250° C caused the metals to diffuse into each other, creating nanoparticles made of a gold-silver alloy.
The researchers also created gold-silver alloy nanoparticles by skipping the shell-creation step, introducing silver acetate into the second solution, and raising the temperature to 250° C. This "shortcut" method has the benefit of simplifying control over the gold-to-silver ratio of the alloy.
REFERENCE:
1. Matthew S. Shore et al., Small, first published online: 13 Dec. 2010; DOI: 10.1002/smll.201001138.
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John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.