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September 24, 2009

How to Guide for Controlling the Structure of Nanoparticles and Another Guide for Nanotubes

1. University of North Carolina engineers have produced a ‘How-To’ Guide for Controlling the Structure of Nanoparticles.

researchers from North Carolina State University have learned how to consistently create hollow, solid and amorphous nanoparticles of nickel phosphide, which has potential uses in the development of solar cells and as catalysts for removing sulfur from fuel. Their work can now serve as a “how-to” guide for other researchers to controllably create hollow, solid and amorphous nanoparticles – in order to determine what special properties they may have.

The study provides a step-by-step analysis of how to create solid or hollow nanoparticles that are all made of the same material. “It’s been known that these structures could be made,” says Dr. Joe Tracy, an assistant professor of material science engineering at NC State and co-author of the paper, “but this research provides us with a comprehensive understanding of nanostructural control during nanoparticle formation, showing how to consistently obtain different structures in the lab.” The study also shows how to create solid nanoparticles that are amorphous, meaning they do not have a crystalline structure.


Abstract “Nickel Phosphide Nanoparticles with Hollow, Solid, and Amorphous Structures”
Published: Online, September 16, 2009, Chemistry of Materials

Abstract: Conversion of unary metal nanoparticles (NPs) upon exposure to O, S, Se, and P precursors usually produces hollow metal oxide, sulfide, selenide, or phosphide NPs through the Kirkendall effect. Here, nanostructural control of mixed-phase Ni2P/Ni12P5 (represented as NixPy) NPs prepared through thermolysis of nickel acetylacetonate using trioctylphosphine (TOP) as a ligand and phosphorous precursor is reported. The P:Ni mole ratio controls the NP size and is the key factor in determining the nanostructure. For P:Ni mole ratios of 1-3, Ni NPs form below 240 °C and subsequently convert to crystalline-hollow NixPy NPs at 300 °C. For higher P:Ni ratios, a Ni-TOP complex forms that requires higher temperatures for NP growth, thus favoring direct formation of NixPy rather than Ni. Consequently, for P:Ni mole ratios greater than 9, amorphous-solid NixPy NPs form at 240 °C and become crystalline-solid NixPy NPs at 300 °C. For intermediate P:Ni mole ratios of ~6, both growth mechanisms give rise to a mixture of hollow and solid NixPy NPs. Similar results have been obtained using tributlyphosphine or triphenyphosphine as the phosphorous source, but trioctylphosphine oxide cannot serve as a phosphorous source.


2. Case Western Reserve University researchers mixed metals commonly used to grow nanotubes and found that the composition of the catalyst can control the chirality. [a recipe for controlling carbon nanotube growth]



Linking catalyst composition to chirality distributions of as-grown single-walled carbon nanotubes by tuning NixFe1-x nanoparticles



Chirally pure single-walled carbon nanotubes (SWCNTs) are required for various applications ranging from nanoelectronics to nanomedicine1. Although significant efforts have been directed towards separation of SWCNT mixtures, including density-gradient ultracentrifugation 2, chromatography3 and electrophoresis4, the initial chirality distribution is determined during growth and must be controlled for non-destructive, scalable and economical production. Here, we show that the chirality distribution of as-grown SWCNTs can be altered by varying the composition of NixFe1-x nanocatalysts. Precise tuning of the nanocatalyst composition at constant size is achieved by a new gas-phase synthesis route based on an atmospheric-pressure microplasma. The link between the composition-dependent crystal structure of the nanocatalysts and the resulting nanotube chirality supports epitaxial models and is a step towards chiral-selective growth of SWCNTs.


20 pages of supplemental information

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