(228d) Thermodynamic Measurements of Cation Exchange in Chalcogenide Nanocrystals

A variety of methods have been developed to synthesize nanomaterials of various sizes and composition.  Often these methods rely on a hot injection synthesis scheme, but these are generally developed on a case-by-case basis and not appropriate for all compositions of matter. Cation exchange of nanocrystals is a useful method for the modification of well-defined template materials into a number of derivatives with controlled composition and crystallinity that are otherwise unavailable via traditional synthetic methods.  While a general thermodynamic understanding of the processes that occur in cation exchange is established, very little quantitative data of the thermodynamics of cation exchange has been published.

Recently, we have applied isothermal titration calorimetry (ITC) to study the thermodynamics of CdSe cation exchange.  These ITC experiments involve the incremental titration of a cation source into a cell containing CdSe nanocrystals and measurement of the heat evolved.  With incremental titration, the enthalpy and the equilibrium constant for a reaction are simultaneously measured.  We have applied this method to measure how nanocrystal size, cation source (Ag, Cu), and temperature impact the thermodynamics of the reaction.  We will summarize the similarities and differences between the thermodynamics of cation exchange in nanoscale and bulk materials.  The fundamental thermodynamic data measured in this work will enable the development of more informative synthesis-structure relationships in cation-exchange.