Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Jꢀaggregate—semiconductor hybrid nanostructures
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
1197
tions in hexane were kept in glassꢀstoppered flasks in a dessicator
filled with a drying agent.
from the sensitizer to AgI participate in the reduction of
interstitial silver ions and formation of latent image cenꢀ
ters. Therefore, the system promising for information storꢀ
age applications appears to be inappropriate for being an
element for converting sunlight into electricity. Hence the
search for other compounds capable of acting as inorganic
components of such hybrid systems becomes topical.
Clearly, the first requirement for such compounds includes
a specific pattern of mutual arrangement of the energy
levels of the components. In addition, it was found that
not all nanocrystals are suitable for forming HOINs. Adꢀ
sorption of the carbocyanine dye DEC occurs efficiently
on hexagonal βꢀAgI nanocrystals and is not observed on
cubic γꢀAgI nanocrystals.18 Also, we did not observe adꢀ
sorption of DEC on cubic CdS, ZnS, CdSe, and PbS
nanocrystals. We took into account the fact that the crysꢀ
tal lattice plays an important role in the assembly of
HOINs and that adsorption of DEC occurs efficiently on
βꢀAgI. Accordingly, in the present study copper iodide
(CuI), lead iodide (PbI2), and silver sulfide (Ag2S) with
lattice constants similar to those of βꢀAgI were chosen as
inorganic components to synthesize HOIN.
Nanocrystals were obtained following known procedures19,20
by mixing two microemulsions (1 : 1, v/v) whose aqueous phases
contained the necessary reactants, viz., AgNO3 and (NH4)2S for
Ag2S nanocrystals; Pb(NO3)2 and KI for PbI2 nanocrystals; and
CuSO4 and KI for CuI nanocrystals. Solutions of AOT reverse
micelles containing salts solubilized in the aqueous phase were
prepared by adding the AOT solutions in hexane to the aqueous
solutions of the corresponding salt. Silver sulfide nanocrystals
were obtained in solutions of SDS reverse micelles. The soluꢀ
tions of SDS reverse micelles containing AgNO3 and (NH4)2S
were prepared analogously using hexanol as coꢀsurfactant to adꢀ
ditionally stabilize the microemulsions.
Aqueous dye solutions were prepared from the dye solution
in ethanol (C = 1•10–3 mol L–1) because the dye occurs only as
the cisꢀmonomer even at high concentrations. To this end,
a precalculated volume of the DEC solution in ethanol was evaꢀ
porated to dryness on a water bath at 65—70 °C; then, the dye
was dissolved in appropriate amount of water to obtain the deꢀ
sired concentration of the solution and kept on a water bath for
1 min at the same temperature. To prepare a reverse micelle
solution, a solution of АOT in hexane was added to the aqueous
dye solution at 65—70 °C. The mixture thus obtained was vigorꢀ
ously shaken until a transparent microemulsion was formed.
Reverse micelle solutions were prepared at different ratios of
molar concentrations W = [H2O]/[surfactant]. For АOT reverse
micelles, the W values were varied by changing the АOT conꢀ
centration in hexane at constant amount of the aqueous phase
(28•10–3 mL of aqueous phase per millilitre of organic phase).
The hydrodynamic radius of an АOT reverse micelle can be
calculated using expression Rh = 0.175W+1.5 (nm). Taking into
account the thickness of the interfacial АOT layer (0.9 nm),21
one has d = 0.35W + 1.2 nm for the diameter of the water pool of
AOT reverse micelles. For SDS reverse micelles, the diameter
of the water pool was determined from empirical data obtained
in Refs 22 and 23.
DEC (тtransꢀisomer)
The aim of the present study is to investigate the forꢀ
mation of hybrid nanostructures comprising an organic
component (carbocyanine dye DEC) and semiconductor
nanocrystals of different composition in reverse micelle
solutions and to establish the principles for controlling
their assembly.
Absorption spectra were obtained with Perkin—Elmer Lambꢀ
da EZꢀ210 and Shimadzu UVꢀ3101PC spectrophotometers in
quartz cells (optical path length was 10 mm) at 18—25 °C. The
standard arm included the cell with the corresponding solvent or
reference micelle solution.
Results and Discussion
Experimental
CuI and PbI2 nanocrystals. As far as we know, the synꢀ
thesis of copper iodide nanoparticles in reverse micelles
using Triton Xꢀ100 as surfactant is the one and only study
on the subject.24 In the present study, CuI nanocrystals
were synthesized with АOT as surfactant. The synthesis
was carried out at equimolar reactant ratio to exclude the
effect of excess ions on the subsequent dye adsorption.
Copper iodide can exist as a number of polymorphs
(Table 1) including cubic γꢀCuI and a layered hexagonal
structure (at room temperature), the wurtziteꢀtype βꢀCuI
(at T > 643 K), and the rock salt type αꢀCuI (at T > 703 K).
The absorption bands of different CuI polymorphs were
determined at 4 K.25 The cubic structure is characterized
by three bands with maxima at 337, 394, and 396 nm. The
The substances used included potassium iodide (99%, Aldrich),
20% aqueous ammonium sulfide (Sigma), silver nitrate (chemiꢀ
cally pure grade), lead nitrate (analytical grade, Spectrokhim),
and copper sulfate (analytical grade, Spectrokhim). Two surfacꢀ
tants, sodium bis(2ꢀethylhexyl)sulfosuccinate C20H37SO7Na
(АOT, Sigma) and sodium dodecylsulfate C12H25SO4Na (SDS,
Sigma), as well as hexanol (chemically pure grade) were used to
stabilize reverse micelles. Ethanol, distilled water, and nꢀhexane
(99%, HPLC grade, Labꢀscan) were used as solvents.
The cyanine dye DEC was kindly provided by Prof. B. I.
Shapiro (M. V. Lomonosov Moscow State Academy of Fine
Chemical Technology).
Lead nitrate and copper sulfate were purified by recrystalliꢀ
zation. To remove water, АOT was predried at 40 °C in vacuo
(10–3 Torr) until constant weight. Hexane and the AOT soluꢀ