Expanding the repertoire of chalcogenide nanocrystal networks: Ag(2)Se gels and aerogels by cation exchange reactions.

Cation exchange is shown to be a simple and efficient method to prepare nanostructured Ag(2)Se gels and aerogels from CdSe gel precursors. Treatment of CdSe wet gels with AgNO(3) yields, for the first time, Ag(2)Se gels, and these are transformed to high surface area, nanostructured aerogels by supercritical fluid drying. The striking similarity in crystallite size, morphology, and surface area characteristics between CdSe and the corresponding Ag(2)Se aerogels supports a mechanism in which the bonding within the gel network remains globally unchanged, even as the structural attributes of the primary particle components are undergoing a dramatic transformation (hexagonal CdSe to cubic Ag(2)Se). Intriguingly, the rapid exchange also enables exquisite control of composition on the macroscale; reduced concentrations of Ag(+) lead to two-component (i.e., CdSe inside, Ag(2)Se outside) heterogeneous structures of mm-cm dimensions. Overall, this methodology offers a simple approach for the generation of porous nanocrystalline metal chalcogenide networks of known or new compositions.