Effects of ion solvation and volume change of reaction on the equilibrium and morphology in cation-exchange reaction of nanocrystals.
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The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of metal chalcogenide nanocrystals, CdE --> M(x)E(y) (E = S, Se, Te; M = Pd, Pt), were investigated. Since the solvation of cations is an important controllable factor determining the free energy of the reaction, the effect of varying cation solvation conditions on the equilibrium of the reaction was examined. A two-phase solvent environment, where the cations involved in the exchange reaction were preferentially solvated in different phases by using selective cation complexing molecules, was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes such as void formation and fragmentation in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guides to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals.