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drolysis in the water layer. The reaction occurs at
the interface, giving rise to nanocrystals which get
deposited at the interface. The yield and the size
distribution depends upon the reaction parameters
such as reactant concentrations, mode of addition
of the reagents, time, temperature and the viscosity
of the medium. In this communication, we briefly
report the successful preparation of nanocrystals
of CdS and iron oxide by this technique. Clearly,
the method is applicable to nanocrystals of a va-
riety of other materials. A noteworthy feature of
this method is that the particles formed remain at
the interface and tend to form thin films.
UV–Vis and photoluminescence spectra. TEM
images were obtained using a JEOL (JEM3010)
transmission electron microscope operating with an
accelerating voltage of 300 kV. For the preparation
of CdS nanocrystals using Cd(St)2, the stearate was
dissolved in toluene by ultra-sonication followed
by mild warming and the reaction was carried out as
in the case of Cd(cup)2.
In the case of oxide nanocrystals, iron cupferr-
onate was used as the metal source and an aqueous
solution of NaOH as the hydrolyzing agent.
Fe(Cup)3 was prepared by the addition of an
aqueous solution of cupferron to the acidic solu-
tion of ferric alum, (NH4)Fe(SO4)2 ꢀ 12H2O, at 0 °C
under vigorous stirring. The resulting brown pre-
cipitate was washed with dil. HCl and then with
5 M ammonia solution to remove the excess cup-
ferron. The iron complex was recrystallized from
heptane and characterized by thermogravimetry
and infrared spectroscopy. In a typical reaction,
0.0020 g of Fe(Cup)3 was dissolved in 25 ml tol-
uene (0.17 mM), the resulting wine red colored
solution was taken in a 250 ml beaker, 10 ml of
milli-Q water was slowly added by using a dropper
to allow the formation of the two liquid phases.
Once the two layers got stabilized, 20 ml of 4 N
NaOH aqueous solution was injected to the
aqueous layer with minimal disturbance of the two
phases. Slowly the color of the organic phase be-
came faint and the interface acquired reddish
brown color. The reaction was allowed for 5 h.
Scanning electron microscope (SEM) images
were recorded with a JEOL scanning electron mi-
croscope. The as-formed film was lifted from the
interface which was further sputter coated with
gold to improve conductivity. Powder X-ray dif-
fraction patterns were recorded on a Siemens5005
Diffractometer employing the reflection Bragg–
Brentano geometry with Cu Ka radiation (k ¼
2. Experimental
To prepare CdS nanocrystals, cadmium cupf-
erronate or cadmium stearate was used as the cad-
mium source and Na2S as the sulfur source.
Cadmium cupferronate was precipitated by mixing
a cupferron solution in water with aqueous
Cd(CH3COO)2 solution at 0 °C. The product was
thoroughly washed with water and 2.5% ammonia
solution. This was subsequently dried in a hot air
oven at 50 °C. Cadmium stearate Cd(St)2, prepared
by the addition of a Cd(CH3COO)2 solution to an
aqueous solution of sodium stearate at 90 °C, was
used as the Cd source. The stearate was washed
thoroughly with hot water and dried. In a typical
reaction, 0.0045 g of Na2S was dissolved in 30 ml of
water in a 100 ml beaker and 0.0125 g of Cd(cup)2
was dissolved in 30 ml of toluene by ultra-sonica-
tion. A drop of n-octylamine was added to the
Cd(cup)2 solution in order to make it completely
soluble. The effective concentrations of these solu-
tions were 2.0 and 1.0 mM, respectively. The toluene
part was added to the beaker containing Na2S so-
lution slowly. The interface starts appearing yellow
colored within a few minutes and slowly over a pe-
riod of few hours, formation of a CdS film in the
interface can be observed, while both the liquid
phases remain colorless. The toluene layer was re-
placed by fresh toluene. The film was lifted with the
help of a glass slide and the same was used for
characterization. A dispersion of the film in toluene
was used to prepare the transmission electron mi-
croscope grids (after sonication) and for recording
ꢀ
1:5418 A). A part of the film, lifted out of the in-
terface with the help of a glass slide was dried and
placed in the diffractometer for this purpose.
3. Results and discussion
In Fig. 1a we show a film of CdS nanocrystals
formed at the aqueous–organic interface by the