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Coupling Nanoparticles

Materials: Cycloaddition chemistry yields hybrid metal oxide materials

by Mitch Jacoby
January 23, 2012 | A version of this story appeared in Volume 90, Issue 4

Credit: ACS Nano
Azide-alkyne cycloaddition chemistry forms nanoparticle junctions that support light-induced (blue arrow) charge transfer and separation.
Reaction shows formation of nanoparticle junctions that support light-induced charge transfer and separation.
Credit: ACS Nano
Azide-alkyne cycloaddition chemistry forms nanoparticle junctions that support light-induced (blue arrow) charge transfer and separation.

Multiple types of metal oxide nanoparticles can be coupled via azide-alkyne cycloaddition reactions, thereby forming well-defined and customizable junctions between the particles, according to a study published in (ACS Nano DOI: 10.1021/nn203585r). The work may lead to strategies for synthesizing novel materials with properties tailored for applications in catalysis and photovoltaics.

TiO2, WO3, and oxides of other metals are active photo­catalysts as a result of their electronic structures, which mediate conversion of light into chemical energy. The oxides are also central to dye-sensitized solar cells as a result of their knack for facilitating light-induced charge separation and transfer.

Blending more than one type of metal oxide can lead to hybrid products with enhanced properties relative to the individual starting materials, if the components can be mixed intimately enough. For that reason, several researchers have studied methods for combining oxides by forming various types of physical mixtures. Chemical ways of combining oxides could offer greater control and customization options, yet few studies have focused on developing such methods.

Now, Allison C. Cardiel, Robert J. Hamers, and coworkers at the University of Wisconsin, Madison, have shown that classic cycloaddition reactions can be used to form nanoscale metal oxide junctions. They prepared TiO2 and WO3 nanoparticles functionalized, respectively, with alkyne and azide groups. Then they coupled the particles through a copper-catalyzed cycloaddition reaction. That reaction forms a triazole linkage that supports electron transfer.

Indeed, the team found from laser-driven photo­response measurements that films of the hybrid material support rapid charge transfer. And in a test of the material’s photocatalytic properties, they found that it decomposed methylene blue faster and more actively than the individual components did.

“This hybrid nanostructure is an important advance for understanding the basics of charge transfer, and could help develop and optimize devices such as solar cells and photocatalysts,” comments Jillian M. Buriak, a professor and nanomaterials chemist at the University of Alberta.



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