A research team led by Paul Alivisatos has shown that the process by which one type of cation (positively charged atoms), is exchanged for another, takes place at a much faster rate in nanocrystals than in crystals of extended size, and is fully reversible in nanocrystals; something that is virtually forbidden in micro-sized or bulk crystals under the same environmental conditions. The discovery illustrates another unexpected property of nano-sized systems and could have substantial implications for the burgeoning nanotechnology industry.

The cation exchange reaction offers a versatile route for expanding the range of nanoscale materials with diverse compositions, structures, and shapes without having to develop new synthetic methods to produce each individual nanostructure. It is expected that the cation exchange reaction in the nanocrystals developed here can easily be extended to exchanges with other cations. To date, however, attempts to induce exchanges of anions (negatively charged ions) have not been successful under similar experimental conditions, possibly because the much larger size of the anions, relative to the cations, makes diffusion more difficult. The speed and reversibility of the reactions with the anions demonstrates, however, that inorganic nanocrystals with many of their atoms on the surface are far more chemically dynamic than previously thought and that they behave in chemical reactions more like more like molecules than like extended solids.