Isolation of CdSe Quantum Dot Nanoparticles

Procedure adapted by Tommy Garting, Lund University, from A.M. Munro et al., Microchim Acta, 160, 345-350 (2008). Luminescence samples of quantum dots resuspended in hexane prepared by Jenny Gilbertson and Tommy Davis.

This procedure separates oleic acid terminated CdSe quantum dot nanoparticles from the octadecene solvent in which they were prepared.

Clicking a thumbnail on this web page (http://chemistry.beloit.edu/edetc/nanolab/CdSe_isolate/index.html) shows a movie of that step.

Procedure

Wear eye protection

Chemical gloves required

Transfer the octadecene CdSe quantum dot suspension to a micro centrifuge tube. Add 100% ethanol. Cap.

Shake to get an emulsion.

Add a matched tube and the freshly shaken sample tube to opposite sides of a centrifuge, or use an even number of sample tubes. Spin at 3000 rpm for 5 minutes.

Carefully remove the ethanol layer. An oil often appears in the pipet tip. Option: obtain the infrared spectrum of the oil.

The removed ethanol solution is cloudy.

Add a second ethanol wash.

Shake to mix and immediately repeat the centrifuge step.

Carefully remove the ethanol.

Add a third ethanol wash.

When shaking no longer gives a suspension then further centrifugation is not needed.

Pour off the ethanol.

Different size quantum dots isolated by the same procedure.

The quantum dots can be resuspended in an organic solvent (chloroform was used here.)

Suspensions of different size quantum dots in an organic solvent (chloroform was used here.)

Observe the resuspended quantum dots under long wave UV light (hexane was used as the solvent.)

Questions

1. What is the identity of the oil that is removed from the quantum dots? How do you know?
2. What is the absorption wavelength or color of the quantum dots you isolated?
3. How can CdSe exhibit so many different colors?

Materials

CAUTION: Avoid physical contact with cadmium selenide since cadmium compounds are carcinogens. If chloroform is used avoid contact or inhalation since it is a likely human carcinogen.

• CdSe quantum dots in octadecene (preparation)
• 100% Ethanol
• Hexane (or chloroform)
• microcentrifuge and tubes
• Pasteur pipets and bulbs
• Vials
• UV light source

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