Cation Exchange Reactions inIonic Nanocrystals

Dong Hee Son, Steven M. Hughes,Yadong Yin, A. Paul AlivisatosScience,306, 1009 (2004).

Sameh HamzawyMESC9

Outline

Introduction

Experiment

Results and discussion

Conclusion

Complete, fully reversible, and relatively faster cation exchange occurs.

Modification the properties of crystalline materials by the cation exchange of atoms .

Structure and morphology vs. size and shape of the nanocrystal.

Introduction

They chose to work with CdSe nanocrystal.

X. Peng et al., Nature 404, 59 (2000).

Result: A rapid (<< 1 sec) change of solution color. Complete disappearance of fluorescence is observed upon mixing

the solutions.

Experiment and Results Forward Reaction:

Mixing a solution of CdSe NCs in toluene with a small amount of methanolic solution of AgNO3 under ambient conditions.

Ag+ ion solution in a slightly larger amount than necessary.

Methanol favors the forward reaction.

Result:

A slower color change back to that of CdSe nanocrystals and the reappearance of fluorescence are observed over a period of 1 min.

Experiment and Results

Reverse Reaction:

mixing Ag2Se nanocrystals with an excess amount of Cd(NO3)2 in a mixture of toluene and methanol.

For the Forward Reaction : The XRD patterns and optical absorption spectra confirm that the

reaction product is Ag2Se.

Results Analysis

For the Reverse(Recovered) Reaction : XRD patterns, optical absorption, and fluorescence spectra all

indicate that CdSe is recovered from the reverse cation exchange.

CdSe

Ag2Se

Rec.CdSe

TEM images of also indicate that size and shape are preserved for both the initial and recovered CdSe.

Results Analysis

The speed and reversibility of the reaction at room temperature in the nanocrystals is very high,relatively.

As the nanorods become thicker from (A) to (I), the shape change during the cation exchange reaction is suppressed.

Results Analysis

Cation exchange reactions on nanocrystals with highly anisotropic nonequilibrium shapes, such as rods, tetrapods, and hollow spheres.

TEM images of CdSe nanorods of different sizes and their trans formed Ag2Se crystals

Results Analysis

CdS hollow spheres almost maintain overall morphology during the cation exchange.

In the case of CdTe tetrapods, slight expansion of the width is observed.

Results Analysis

changes in size can be accounted for changes in the crystal unit cell symmetry and lattice parameters during the transformation.

The Ag cation exchange reaction in this study, can easily be extended to exchange with other cations under ambient conditions.

Attempts to induce anion exchange have not been successful under similar experimental conditions,

It can be a versatile route for expanding the range of nanoscale materials with divers compositions, structures, and shapes.

Conclusion

Thank you for your attention

Questions ???