Synthesis of CdS quantum dots and optimization of conditions in conventional and microwave

heating methods

S. D. Hettiarachchi and T. G. ChasteenDepartment of Chemistry

Nanoparticles• Particles between 1 nm to 100 nm in size• There are many different nanoparticles in shape

and size.

Nanowires

Nanotubes

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www.kurzweilai.net (04.02.2014)

Quantum Dots (QDs)• A quantum dot is a tiny particle of a

semiconductor nanocrystal which shows quantum mechanical properties.

• They can range from 2 to 10 nanometers in diameter. (Size of the smallest grain of sand is around 62500 nm)

• Because of their small size, quantum dots display unique optical and electrical properties.

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• The electronic characteristics of a quantum dot are related to its size.

• It has an ability to produce light as fluorescence

• The color of the light is tunable according to its size.

• Ability to conduct electricity

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Advantages and uses of CdS QDs

• Light emitting diodes

• Solar cells

• Biofluorescent tagging

• Lasers

• Biomedical imaging

www.nanocluster.mit.edu (04.02.2014)

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Imaginary sketch of CdS quantum dot

6A. Abdelhay, D. Billaud, M. Abyan, L. Balan, J. Gaumet, G. Medjadhi, J. Ghanbaja, R. Schneider, ACS Appl. Matter. Interfaces. 4 (2012) 2561- 2569.

G

G G

G

G

G

G

G

Glutathione (GSH)

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Glutathione (GSH) is an important antioxidant in plants, animals, fungi and some bacteria.

It is a tripeptide with a peptide linkage between the carboxyl group of the glutamate side-chain and the amine group of cysteine which is further attached by peptide linkage to a glycine.

Thiol groups are reducing agents, naturally existing in animal cells.

GSSG Figure 2

Figure 1

Glutathione (GSH) capped CdS QDs

• Increase the biocompatibility

• Can be used in mild chemical conditions

• QDs can be synthesized in short time periods.

• GSH is acting as a reducing agent, so there is no need to add any toxic reducing agents.

Pérez-Donoso, J.M.; Monrás, J.P.; Bravo, D.; Aguirre, A.; Quest, A. F.; Osorio-Román, I.O.; Aroca, R.F.; Chasteen, T.G.; Vásquez, C.C. PloS ONE 2012, 7(1), e30741.

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Objectives

• Synthesize CdS QDs in environmentally greener protocols by using GSH as a capping agent

• Optimize the conditions to synthesize the tunable CdS QDs in the conventional heating method and microwave irradiation

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CdS QDs synthesis in different GSH molar ratios

at various temperatures in conventional heating method

Procedure

CdCl2 (4mM Final concentration) Borax Citrate Buffer (pH 9)

Na2S was added

QD nucleation was initiated by raising the temperature up to 40,50,60,70, and 80 0C one at a time

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Added to

1. Vortexed

2. After 5 minutes

Pérez-Donoso, J.M.; Monrás, J.P.; Bravo, D.; Aguirre, A.; Quest, A. F.; Osorio-Román, I.O.; Aroca, R.F.; Chasteen, T.G.; Vásquez, C.C. PloS ONE 2012, 7(1), e30741.

Reduced Glutathione (GSH) was added at different concentrations

Results and Discussion

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Color variations of CdS QDs in 10 mM GSH concentration at 70 0C

1 Hour 2 Hours 3 Hours 4 Hours

5 Hours 6 Hours 24 Hours 48 Hours

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CdS QDs synthesis by the microwave irradiation

Microwave Bomb

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Side view Upper view

Internal parts

Microwave synthesis of CdS QDs

15 Seconds 30 Seconds20 Seconds 25 Seconds

10 Seconds5 SecondsBefore Microwave

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Conclusion

• Synthesis of CdS QDs was successful by using GSH as a capping agent

• For the normal heating process, the optimum condition for the tunable QDs is 10 mM GSH concentration at 70 0C

• By the microwave irradiation it could produce blue to red CdS QDs within 30 seconds

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Acknowledgements• Supervisor Dr. T. G. Chasteen

• Former Members Mr. Tharaka Wansapura and Ms. Desire Lopez

• Dr. José Manuel Pérez Donoso , Universidad de Santiago de Chile, Santiago, Chile

• Mr. Vicente María Durán Toro, Universidad de Santiago de Chile, Santiago, Chile

• Robert A. Welch Foundation 18

Thank you

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