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Solution NMR Spectroscopy as a Useful Tool to Investigate Colloidal Nanocrystal Dispersions from the Capping Ligand's Point of View

Published online by Cambridge University Press:  26 February 2011

Jose C Martins ,
Jose C Martins ,
Iwan Moreels  and
Zeger Hens
Jose C Martins
Affiliation:
[email protected] Universiteit Gent Department of Organic Chemistry Krijgslaan 281 S4 Gent B-9000 Belgium 3292644469
Jose C Martins
Affiliation:
[email protected] Universiteit Gent Department of Organic Chemistry Krijgslaan 281 S4 Gent B-9000 Belgium 3292644469
Iwan Moreels
Affiliation:
[email protected] Universiteit Gent Department of Organic Chemistry Krijgslaan 281 S4 Gent B-9000 Belgium 3292644469
Zeger Hens
Affiliation:
[email protected] Universiteit Gent Department of Organic Chemistry Krijgslaan 281 S4 Gent B-9000 Belgium 3292644469
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Abstract

Colloidal semiconductor nanocrystals or quantum dots are an important building block in bottom-up nanotechnology. They consist of an inorganic, crystalline core surrounded by a monolayer of organic ligands. As these ligands can be modified or exchanged for others, they provide a convenient way to give the quantum dots functionality. Here, we show that solution NMR techniques, including diffusion pulsed field gradient spectroscopy, is a very useful tool to investigate the ligands of colloidal nanocrystals. This is demonstrated using InP quantum dots with trioctylphospine oxide ligands as an example. Combining 1H-13C HSQC spectroscopy with pulsed field gradient diffusion NMR, an unequivocal identification of the resonances of the bound ligands is possible. This leads to the determination of the diffusion coefficient of the nanocrystals in solution and allows to verify capping exchange procedures. By calibrating the surface area of the NMR resonances using a solute of known concentration, the density of ligands at the nanocrystal surface can be quantified. We could demonstrate that a dynamic equilibrium exists between bound and free ligands. Analysis of the corresponding adsorption isotherm - determined using 1H NMR - leads to an estimation of the free energy of adsorption and the free energy of ligand-ligand interaction at the nanocrystals surface. Similar investigations are in progress on capped PbSe and ZnO2 nanoparticles. Preliminary results strongly support the generic nature of the approach described for the case of TOPO capped InP nanocrystals.

Keywords

diffusionnuclear magnetic resonance (NMR)colloid
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 984: Symposium MM – Magnetic Resonance in Material Science , 2006 , 0984-MM14-07
Copyright
Copyright © Materials Research Society 2007

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References

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