Metallurgy in a Beaker

MATERIALS CHEMISTRY

Solution route to multimetal nanocrystals has advantages over traditional solid-state syntheses

A solution-phase technique to make multimetallic nanocrystals of high structural complexity has been developed by assistant chemistry professor Raymond E. Schaak and his group at Texas A&M University.

The approach allows materials to be prepared at relatively low temperatures in only a few minutes compared to traditional solid-state reactions involving high-temperature sintering or melting that can take days or weeks to carry out. The technique has the potential to expand the availability of thin films, powders, and crystals of multimetal nanomaterials for applications in catalysis, magnetic storage, shape-memory alloys, and superconductivity.

The technique is a modification of standard nanocrystal synthesis methods that the Texas A&M chemists call metallurgy in a beaker. Schaaks group originally developed the process while working with gold and copper nanoparticles, which aggregate in solution to form nanocomposites that thermally transform at low temperatures into bimetallic nanocrystals. The composition of the compounds can be controlled by the ratio of reactants (J. Am. Chem. Soc. 2005, 127, 3506). The researchers have found the process to be general and have extended it to make trimetallic AuCuSn₂ and AuNiSn₂ nanocrystals that have new structures not observed in bulk systems (J. Am. Chem. Soc. 2005, 127, 7326).

They prepared AuCuSn₂ by heating a solution of HAuCl₄, Cu(C₂H₃O₂)₂, SnCl₂, and poly(vinylpyrrolidone) in tetraethylene glycol to 70 C, then adding dilute NaBH₄ and heating to 120 to 200 C for 10 minutes.

The multimetal materials, Schaak notes, are inherently impure because polymers and stabilizers are needed to form them, but his group has shown that the properties can be comparable to or better than higher purity materials made by high-temperature processes.

Martyn Poliakoff, a chemistry professor at the University of Nottingham, in England, who is familiar with Schaaks work, comments that the strategy is very elegant, with the simplicity that characterizes a really good idea.