Aug 31, 2005
Phasing in nanocrystals
Researchers at Tsinghua University, China, and the National Center for Nanoscience and Nanotechnology of China have come up with a “general strategy” for creating nanocrystals. The phase transfer and separation technique can produce nanocrystals of noble metal, semiconductor and conducting polymer, as well as nanocrystals that are magnetic/dielectric, fluorescent and have optoelectronic or biomedical properties.
“We believe that a general strategy may provide us with a clearer insight into the underlying principle behind the controlled growth of low-dimensional nanostructures,” said researcher Yadong Li.
Li and colleagues demonstrated their technique on noble metals. They used a liquid–solid–solution process in which ethanol reduced noble metal ions at the interfaces of the solid, liquid and solution phases. Typically, the team mixed 20 ml of an aqueous solution of noble metal salt with 1.6 g of sodium linoleate, 10 ml of ethanol and 2 ml of linoleic acid. They treated the mixture for 10 hours at a temperature between 20 and 200 °C depending on the metal and the desired size of nanocrystal.
The system contained three phases – the solid form of sodium linoleate, a liquid phase of ethanol and linoleic acid, and a solution phase of water-ethanol containing noble metal ions. Reduction of the metal ions led to the formation of nanocrystals of noble metal. These underwent a spontaneous phase separation and assembled at the bottom of the container.
In this way the team made nanocrystals of silver, gold, platinum, palladium, ruthenium, rhodium, and iridium. The researchers say the phase transfer process can occur for nearly all the transitional or main group metal ions. By altering the reaction conditions they were able to make nanocrystals of metal oxides such as TiO2 and CuO, composite oxides such as the magnetic CoFe2O4, and various sulphides, selenides and fluorides.
The technique was also able to create dielectric nanocrystals of BaTiO3, rare earth fluorescent nanocrystals and nanorods of the biocompatible material hydroxyapatite, which could have applications in creating artificial bone grafts. What’s more, copper phthalocyanine nanocrystals prepared using the method could have applications as an optoelectronic material.
“The possible applications of the as-obtained nanocrystals in the fields of catalysis, biological labelling, pharmaceuticals and photoluminescence will take our research forward,” said Li. “Subsequent research on the application of this approach to other novel useful compounds might bring additional exciting opportunities in nano-related fields.”
The researchers reported their work in Nature.
About the author
Liz Kalaugher is editor of nanotechweb.org.