C.M. Expt 3.
Synthesis of Amine Capped Zinc Selenide nanoparticles (time dependent growth)
Developed by Karen S. Quaal, Department of Chemistry and Biochemistry, Siena
College, Loudonville, NY. quaal@siena.edu
Synthesis was as reported in the literature1 with the following modifications:
Time: Aliquots were removed at 5-minute time intervals.
Temperature: During degassed/gas cycle, H.D.A was heated to melting, placed
under reduced pressure at 65oC, and cooled under vacuum to 40-50oC.
After three cycles, system placed under vacuum at 60oC.
Under Nitrogen, system heated to 320oC and injection of Zn/Se/TOP solution was
introduced.
Nanoparticles were grown at 270oC.
Temperature Controller: 5o/minute temperature intervals.
Sample Aliquots: Quenched in 1 mL room temperature toluene.
Preparation of ZnSe nanoparticles: (kinetic or time dependent growth). (Student
prep)
Zn/Se/TOP working solution:
The working solution is made in a glovebox, by mixing 1.26 mL (delivers 0.98mg of
Et2Zn) of a previously prepared solution containing 350 mg of Et2Zn in 4.5 mL
trioctylphosphine (TOP). To this is added 1 mL of the 1M Se/TOP solution. This
mixture is diluted with an additional 2.74 mL of TOP (density 0.831 g/mL) to reach a
total volume of 5mL.
Using standard airless techniques, 15 mL (density 0.813 g/mL) of Hexadecylamine
(H.D.A.) was dried and degassed at 65ºC for three vacuum/nitrogen cycles and then
placed under vacuum for 30 minutes at 40-50ºC. The system was placed under nitrogen
and heated to 320ºC. The Zn/Se/TOP working solution was injected quickly into the hot
H.D.A and the temperature of the reaction was lowered to 270ºC. A yellow color
developed as the nanocrystals were grown at 270ºC. When the reaction reached 270ºC, a
small aliquot was removed and quenched in 1 mL toluene. The growth of the
nanocrystals was verified by the presence of the first exciton peak in the UV spectrum.
Subsequent aliquots of the reaction were removed at specific (~5 min.) time intervals and
quenched in 1 mL toluene until the growth stabilized. The remaining ZnSe was isolated
by precipitation in methanol and centrifugation.
The aliquots were analyzed by UV/visible and fluorescence spectroscopy. A plot of
Quantum Dot diameter vs. time was examined2.
and bubbler
Figure 1. Apparatus for the Synthesis of Quantum Dots. Glassware consists of a 14/20
three-neck 25 mL RB flask, two “piggy-backed” 14/20-air condensers, a 14/20-tee
connector, 2 stopcocks to control the system’s atmosphere, and a 14/20-glass insert,
referred to as a thermowell which is of sufficient length to rest in the melt. The
temperature probe is inserted in the thermowell and connected to a temperature controller,
which controls the heating mantle.
Note: Two “piggy-backed” 14/20-air condensers are used to minimize the amount of
H.D.A. or TOPO that condenses on the inside of the glassware even though the reactions
are performed at temperatures lower than suggested in the literature. Due care must be
taken to insure the system is not clogged, and that nitrogen is free flowing so the risk of
heating a “closed system” is avoided. Finally, the two-stopcock system, although less
sophisticated than a manifold, is much easier to clean.
References:
1. Hines, M. A., and Guyot-Sionnest, P., Bright UV-Blue Luminescent Colloidal ZnSe
Nanocrystals. The Journal of Physical Chemistry B, 1998, 102, 19.
2. Cumberland, S. L., Hanif, K. M., Javier; A., Khitrov, G. A., Strouse, G. F., Woessner,
S. M., Yun, C. S., Inorganic Clusters as Single-Source Precursors for Preparation of
CdSe, ZnSe, and CdSe/ZnS Nanomaterials, Chem. Mater. 2002, 14, 1576-1584.