Credit: © 2007 Wiley

Palladium nanocrystals are effective catalysts for many chemical reactions, including those that involve making carbon–carbon bonds or adding hydrogen to certain compounds. In particular, these properties have led to the use of these metal nanoparticles in catalytic converters to remove harmful pollutants from car emissions. The method by which Pd nanocrystals are usually made, however, involves a fairly toxic organic solvent (ethylene glycol), and restricts the range of nanocrystal shapes to predominantly cubes and cuboctahedra.

Now, Younan Xia and co-workers1 at the University of Washington, Seattle in the US have developed a water-based synthesis of Pd nanocrystals that offers a more environmentally friendly route to these materials. The process is quite straightforward and simply involves heating a mixture of a Pd salt, a stabilizing polymer and citric acid in water. Moreover, the shape of the nanocrystals can be controlled by varying the concentrations of each reagent. Low levels of Pd result in icosahedral nanocrystals, but on increasing the Pd content, octahedral and decahedral structures are formed. The yield of decahedral particles could be improved by increasing the concentration of citric acid.

Significantly, each shape of nanocrystal could be reproducibly prepared in high yields using this method, offering access to decahedral and octahedral structures for which no high-yielding syntheses have been previously developed. It is suggested that these metal nanoparticles could prove useful for applications ranging from catalysis to medicine.