100
A. Khan et al. / Inorganic Chemistry Communications 79 (2017) 99–103
lamp, and achieved the conversion in 90 min [15]. Few research groups
also tested CdS-based composite materials under visible light, including
CdS-TiO , CdS/graphene hybrid and noble metal deposited CdS [16–18].
2
decomposition pattern can be exploited to control size and morphology
of the NPs [26]. In this study, the conversion of two precursors has re-
sulted in two distinct morphologies i.e. nanosheets and nanorods. The
low magnification TEM image of CdS-1 presents very thin sheets like
morphologies (Fig. 1a and b). The sheets seem to be continuous and ex-
tend to several hundred micrometers in length and width. The transpar-
ent image suggests the transmission of electrons through sheets of
thickness less than 5 nm. No evident boundary among the individual
sheets suggests stacking over one another. The TEM image of CdS-2
shows nanorods of almost 80 nm in length and 4–6 nm in diameters
(Fig. 1d and e). Moreover, the nanorods have homogeneous shape and
are structurally uniform. In the HRTEM images (Fig. 1c, and f), a lattice
spacing of 0.33 nm was measured for both morphologies which corre-
spond to the 002 plane of hexagonal CdS confirming their preferential
growth along the c-axis. The formation of different morphologies can
be attributed to different solubility/stability of the precursors used. It
was observed that the precursor CdL-1 completely dissolved at 60 °C
in en and at 70 °C the solution turned slightly turbid due to nucleation
of the CdS monomers resulting in individual CdS dot formation. A grad-
ual increase in the temperature resulted in more CdS dots formation
that probably adopted spherical assembly through common crystallo-
graphic facet {111} and then at the en boiling point (b.p) grew into
sheet-like structure in {111} direction through oriented attachment
[15]. However, due to insolubility of the complex CdL-2 in en upto 117
°C no nucleation was observed. Nonetheless, at en b.p, the precursor
CdL-2 instantly decomposed by a nucleation burst in the earlier mo-
ment of reaction, provided the kinetic drive for anisotropic particles
growth or CdS nanorods [27]. Energy dispersive X-ray spectroscopic
(EDS) analysis has confirmed the presence of Cd and S in the ratio of
1:1 for both nanosheets and nanorods.
We adopted a single source precursor strategy for the synthesis of
CdS NPs by simply refluxing two new cadmium(II) dithiocarbamates
using ethylenediamine (en) as a solvent and thermolyzing agent devoid
of any toxic capping agent/surfactant. The synthesis of the ligand salts,
precursor complexes and their conversion to CdS NPs was carried out
by our previously reported methods [19,20] and is schematically
shown in Scheme 1. The detailed experimental procedure about the
precursor synthesis, their conversion to CdS NPs and photocatalytic
conversion of the p-nitrophenol to p-aminophenol by CdS nanostruc-
tures are given in supporting information.
Complex 1 and 2 were easily synthesized at ambient conditions by
simply mixing the metal salt and ligand. Complex 1 was found soluble
3
in CHCl , DMSO and DMF and hence characterized by NMR, however,
for 2 only FT-IR was done due to insolubility in common organic
solvents.
The bonding nature and coordination mode of the dithiocarbamate
can be assessed by the stretching frequencies. The presence of bands
−
1
−1
at 347 cm
(1) and 334 cm
(2) assignable to Cd\\S stretch [21],
−
1
−1
and a single peak for CS at 991 cm (1) and 967 cm (2) indicated
the bidentate dithiocarbamate-Cd coordination. Furthermore, the
−
1
−1
C\\N stretch observed at 1478 cm (1) and 1513 cm (2), values in
between single and double bonds signifying the resonance phenomena
in the CNSS moiety [22]. The assignment of the proton resonances was
made by their peak multiplicity, intensity pattern and comparison of
the integration values with the expected composition. In the complex
CdL1, multiplets for phenyl protons (7.12–7.32 ppm) and methine pro-
ton (1.4–1.51 ppm), a triplet and quartet for piperidine ring protons
(
3.24 and 1.75 ppm), and a doublet for methylene protons (4.66 ppm,
X-ray powder diffraction analysis has been carried out to understand
the identity and phase purity of CdS-1 and CdS-2 nanostructures (Fig.
2). All the XRD reflections correspond to the hexagonal phase of CdS
consistent with the standard JCPDS card No. 01-077-2306. The diffrac-
tion pattern show that both NPs are devoid of any detectable impurities
or any other CdS phase. Compared to the standard, the 002 reflections in
both diffraction patterns is of highest intensity indicating their preferen-
tial growth along the c-axis. Moreover, broader peaks are indicative of a
small primary particle size.
13
J = 5.0 Hz) was observed. In C NMR, an upfield shift of around
ppm in the SCS peak in complex than the free ligand confirmed the li-
9
gand coordination to metal center [23]. The remaining signals matched
well with the expected composition.
The CdS NPs were obtained from the complexes 1 and 2, single
source precursors (SPs). The presence of metal-chalcogen bond tem-
plate in SPs play a significant role in controlling the stoichiometry and
shape of the nanocrystals [24,25]. Additionally, the different binding
strength of the ligands may be responsible for dissimilarity in the stabil-
ity of precursors or decomposition kinetics; hence this anomalous
UV–Visible absorption measurement is an important technique to
assess the optical properties of the semiconductors NPs. The absorption
Scheme 1. Synthesis of complexes 1 and 2 and their conversion to CdS1 and CdS2 NPs.
Khan, Azam
