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Posted: Mar 31, 2006

Novel platinum nanostructures

(Nanowerk News) Greatly expanding on previously reported work on platinum nanostructures, researchers at Sandia National Laboratories just released a new paper describing a range of novel platinum nanostructures with potential applications in fuel and solar cells as well as nanotags in biomedicine.
Their paper, titled "Foamlike Nanostructures Created from Dendritic Platinum Sheets on Liposomes" was published in the March 22, 2006 online edition of Chemistry of Materials.
John Shelnutt is leading the research effort at Sandia to manipulate the nanoscale structure of platinum in order to have control over the size, porosity, composition, surface species, solubility, stability, and other functional properties of platinum nanostructures. His Sandia colleague Dr. Yujiang Song primarily conducted the work reported in this article.
Shelnutt told Nanowerk: "Such control means that the redesigned platinum could be used in many new applications, including catalysis, sensors, and optoelectronic and magnetic devices."
Because platinum has many technological applications, such as in sensors and as catalyst in various applications, but is in limited supply and quite expensive, researchers are developing methods for reducing the precious metal content of these catalysts.
Shelnutt explains: " One way to minimize platinum usage is to increase catalytic efficiency by nanostructuring the platinum metal. As catalytic or device efficiency may depend on both the size and the shape of the platinum material, the preparation of nanostructured platinum with specific structural features is an area of considerable interest."
In their latest paper, Shelnutt and his team describe how liposomes with and without incorporated porphyrin photocatalysts can be used to generate a range of novel platinum nanostructures, ranging from small uniform dendritic sheets to large circular dendritic sheets to various foamlike platinum structures composed of convoluted dendritic sheets.
SEM image of foamlike platinum nanospheres grown in the presence of 120nm unilamellar liposomes. (Reprinted with permission from ACS)
"These nanofoams are an extraordinary example of a self-supported platinum material" says Shelnutt, "retaining its dendritic structure after the removal of the surfactant and drying."
By characterizing the material, the researchers found that nanostructured platinum foams behave in qualitatively the same way as polycrystalline platinum. In addition, the foam nanospheres possess an electroactive surface area that is similar to that of platinum black.
Shelnutt describes the platinum foams as having electroactive surface areas and electrocatalytic activities comparable to those of platinum black, but rather than consisting of a distribution of nanoparticles that may be unconnected, these dendritic foamlike materials are nanostructured and behave somewhat like polycrystalline platinum.
"For example" says Shelnutt, "the platinum nanospheres should be highly conductive over hundreds of nanometers, that is, the diameters of the nanospheres, making them very attractive from the standpoint of electro-catalytic reactions such as in fuel cell applications."
Together with their previous work, this presents a comprehensive study of the use of liposomal templating and the photocatalytic seeding strategy to produce a variety of novel dendritic platinum nanostructures. With their methods refined, the synthesis of pure forms of flat dendritic nanosheets and various foam nanostructures (nanospheres and monoliths) has been made possible.
In his earlier work Shelnutt was mainly focused on the synthesis of nanoscale spherical platinum dendrites using micelles as templates, but he also showed that dendritic platinum sheets of nanoscale thickness could be formed under similar solution conditions when liposomes were used as templates.
Two relevant previous publications by Shelnutt and colleagues are the recent "Platinum nanodendrites" in the March 14, 2006 edition of Nanotechnology and "Controlled Synthesis of 2-D and 3-D Dendritic Platinum Nanostructures" in the Jan. 21, 2004 edition of Journal of the American Chemical Society.
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