Mercury selenide nanorods: Synthesis and characterization via a simple hydrothermal method

Article abstract of DOI:10.1016/j.poly.2011.01.023

HgSe nanorods have been synthesized through a simple hydrothermal reduction approach. The nanorods formed were ≈45 nm average diameter and ≈3 μm nm in length. X-ray diffraction characterization suggested that the product consists of cubic phase pure HgSe. The as-prepared products were also characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An X-ray energy dispersive spectroscopy (EDX) study further confirmed the composition and purity of the product. The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. The results showed that the capping agent CTAB (cetyltrimethylammoniumbromide) plays a crucial role in the process. Other factors, such as the reaction time, temperature, different capping agent and the reductant type also have an influence on the morphology of the final products to some extent.

Full text of DOI:10.1016/j.poly.2011.01.023

Polyhedron 30 (2011) 1103–1107
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Mercury selenide nanorods: Synthesis and characterization via a simple
hydrothermal method
Mehdi Bazarganipour a, Minoo Sadri b, Fatemeh Davar c, Masoud Salavati-Niasari a,c,
⇑
a Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, Iran
b Department of Chemistry, College of Science, Bu-Ali Sina University, P.O. Box 4135, Hamadan 65174, Iran
c Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 June 2010
Accepted 12 January 2011
HgSe nanorods have been synthesized through a simple hydrothermal reduction approach. The nanorods
formed were ꢀ45 nm average diameter and ꢀ3 m nm in length. X-ray diffraction characterization sug-
l
gested that the product consists of cubic phase pure HgSe. The as-prepared products were also character-
ized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An X-ray
energy dispersive spectroscopy (EDX) study further confirmed the composition and purity of the product.
The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. The
results showed that the capping agent CTAB (cetyltrimethylammoniumbromide) plays a crucial role in
the process. Other factors, such as the reaction time, temperature, different capping agent and the reduc-
tant type also have an influence on the morphology of the final products to some extent.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Hydrothermal
HgSe nanorods
Co-precipitation
Solution-chemical
1. Introduction
In the case of II–VI mercury chalcogenides, very little work ex-
ists to date on either clusters or QDs, although interest in these
Over the last twenty years, a great deal of work has gone into
understanding the properties of matter at the nanometer scale.
One class of mesoscopic system receiving a lot of attention is col-
loidal semi-conductor quantum dots (QDs) or nanocrystals (NCs)
[1–4]. Progress in this area has benefited from the dynamic inter-
play between advances in synthesis, optical characterization and
theory [5]. Despite this synergy, a major bottleneck in this field
has traditionally been the availability of high quality, crystalline
samples with narrow size distributions, high photoluminescence
efficiencies and controlled surface chemistries. II–VI materials, in
particular, have led to new opportunities for a better understand-
ing and to utilize the size-dependent optical and electrical behav-
ior of QDs [6,7] as a result of the discovery in the early 90s by
Murray and others that one could make high-quality QDs through
the thermolysis of pyrophoric organometallic reagents [8,9].
Prior to these advances, however, analogous examples of high
quality II–VI nanocrystalline compounds could already be found
in small clusters of zinc and cadmium chalcogenides of precise
molecular weight. These clusters represent the molecular limit of
QDs and are also some of the first examples of colloidal nanoparti-
cles. They contain less than 100 atoms and typically lie in the size
range between 1 and 2 nm.
materials abounds. Bulk mercury chalcogenides are semi-metals
widely used in infrared sensing applications. Alloys of Hg com-
pounds (Hg1ÀxCdxTe, for example) are particularly important sys-
tems because of the wide range of tunable optical, electrical and
magnetic properties, achieved through compositional tuning (x)
of this material, from pure semi-metallic Hg (S, Se, Te) to narrow
gap Hg1ÀxCdx (S, Se, Te) and ultimately to wider gap semi-
conductor Cd (S, Se, Te). At the same time, such material tunability
can also be explored by making QDs or clusters of these
compounds, exploiting well-known quantum confinement effects
that occur when the physical size of the NC is smaller than the bulk
exciton Bohr radius. Furthermore, the ease of compositional tuning
suggests that a similar parameter space can be investigated, not
only through size, but also through composition, with the creation
of ternary mercury chalcogenide QDs/clusters leading to tunable
absorbing and emitting species spanning anywhere from the
visible into the far-infrared. Such compounds have potential use
as visible/infrared fluorescent tags, lasing/amplifying elements at
1.3 and 1.55 lm, and in remote sensing applications [10].
The existing mercury chalcogenide NC syntheses that have been
reported largely deal with solvothermal or solvent-based ap-
proaches for making these compounds. These approaches entail
sonochemistry [11], microwave-assisted heating [12,13] and the
thermolysis of common mercury precursors [14,15]. Other methods
make use of metal ion impregnated Langmuir Blodgett films [16] or
other restricted environments such as vesicles [17] or sol–gel net-
works [18] to grow HgS QDs. Recently, the hydrothermal method
⇑
Corresponding author at: Department of Inorganic Chemistry, Faculty of
Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, Iran. Tel.: +98
361 591 2383; fax: +98 361 555 2935.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.01.023

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M. Bazarganipour et al. / Polyhedron 30 (2011) 1103–1107
has also been reported to prepare metal chalcogenide nanostruc-
tural materials, which has the potential advantages of relatively
low cost, high purity and controlled morphology [19–24].
2. Experimental
2.1. Materials and physical measurements
In this work, we report on HgSe nanorods prepared by the sim-
pler hydrothermal method, and compare the difference in the
nanostructure of HgSe synthesized with a different reductant type.
All of reagents and solvents were purchased from Merck (pro-
analysis) and were dried using molecular sieves (Linde 4 Å). XRD
patterns were recorded by a Rigaku D-max C III, X-ray diffractom-
eter using Ni-filtered Cu K
copy (SEM) images were obtained on
a
radiation. Scanning electron micros-
Philips XL-30ESEM
a
equipped with an X-ray energy dispersive detector. Transmission
electron microscopy (TEM) images were obtained on a Philips
EM208 transmission electron microscope with an accelerating
voltage of 100 kV.
2.2. Nanostructured HgSe prepared by the hydrothermal method
Hg(NO3)3ÁH2O and SeCl4 were used as the simple precursors in
the hydrothermal synthesis. The precursors, with a stoichiometric
ratio of Hg:Se (0.45:0.45 mmol), were put into a Teflon-lined auto-
clave. The autoclave was then filled with water up to 80% of its vol-
ume (100 ml capacity). After adding sufficient KBH4 (0.2 g) as the
reductant, and CTAB (cetyltrimethylammoniumbromide) (0.15 g)
as the capping agent, the autoclave was sealed immediately and
heated to 180 °C for the synthesis reaction. After reacting for
12 h, the autoclave was cooled down to room temperature natu-
rally. The obtained precipitates were separated by centrifugation,
washed with deionized water followed by ethanol three times,
and dried at 100 °C under vacuum for 24 h. The structure and mor-
phology of the HgSe powders were characterized by XRD and TEM.
Fig. 1. XRD of HgSe prepared in the presence of KBH4 as the reductant and CTAB as
the capping agent at 180 °C for 12 h.
Fig. 2. SEM images of HgSe prepared in the presence of (a) CTAB, (b) PEG 20000, (c) SDBS as the capping agent and (d) TEM images of HgSe prepared in the presence of CTAB
as the capping agent and KBH4 as the reductant at 180 °C for 12 h.

M. Bazarganipour et al. / Polyhedron 30 (2011) 1103–1107
1105
nanorods. In the presence of N2H4 (0.1 ml) as the reductant, rod-
shape is the preferential morphology (Fig. 3a). Meanwhile, in the
presence of Zn (0.08 g) as the reductant, particles are the preferen-
tial morphology (Fig. 3b).
3. Results and discussion
The composition of the as-prepared product was determined by
XRD (Fig. 1). All peaks in the patterns correspond to the reflections
of cubic phase HgSe [space group: F43m (216)], with lattice con-
ꢀ
Strong reductants such as KBH4 and N2H4, in combination with
stirring rapidly, created a large number of nuclei and further
growth of the nuclei was limited. As a result, many small particles
were obtained. Reduction in the presence of Zn proceeds only two-
dimensionally, i.e., at the interface of the Zn powder with the metal
cation solution. The rate of reduction is further limited by the mass
transport of the metal cation solution to the Zn surface. Therefore,
depletion of metal cations near the interface might occur. As a con-
sequence of the rate and surface area limitations, crystal growth is
favored over nucleus formation, with the result of larger particles
[25].
In continuation, the effect of reaction time on the morphology of
the nanorods, in presence of CTAB as the capping agent, was inves-
tigated (Fig. 4a and b). By increasing the reaction time from 6 to
24 h, the nanorods break down and there is dense agglomeration.
The effect of the reaction temperature on the morphology of the
nanorods, in the presence of CTAB as the capping agent, was also
investigated (Fig. 5a and b). On increasing the reaction tempera-
ture from 100 to 150 °C, nanorods were gradually constituted
(Table 1).
stants a = 6.0720 Å (JCPDS 73-1668). No remarkable diffractions
of other phases, such as selenium, mercury or their other com-
pounds, can be found in Fig. 1, indicating that a crystalline HgSe
phase has been formed after the synthesis for all samples. The
broadening of the diffraction peaks indicates that the samples are
nanosized. The average particle size of the sample is about 23 nm,
estimated through the Scherrer formula.
Meanwhile, the influence of the capping agent, reductant type,
time and temperature were investigated on the as-prepared HgSe
nanorods (Figs. 2–5). The morphology and size of the as-
synthesized products were characterized by SEM and TEM. With
exchange of the capping agent from PEG 20000 (0.15 g) to SDBS
(sodium dodecyl-benzene-sulfonate) (0.15 g), and PEG 20000 in
the presence of KBH4 as a reductant, the nanostructures show dense
agglomeration and the particle size increased (Fig. 2a–c). In fact,
these nanostructures appear to be polycrystalline agglomerations
of crystallites. The morphology of the resulting nanostructure was
examined by TEM. From the TEM image (Fig. 2d), HgSe nanostruc-
tures with an average diameter of 25 nm were observed.
X-ray energy dispersive spectroscopy (EDS) analysis measure-
ment was used to characterize the chemical composition of the
products (Fig. 6). The results for HgSe in the presence of KBH4 as
Fig. 3 reveals the reductant type effect on the morphology of the
nanostructure in the presence of CTAB as a capping agent. In this
study, the reductant plays a key role in the morphology of the HgSe
Fig. 3. SEM images of HgSe prepared in the presence of CTAB as the capping agent and (a) N2H4 and (b) Zn as the reductant.
Fig. 4. SEM images of HgSe prepared in the presence of CTAB as the capping agent and N2H4 as the reductant at 180 °C for (a) 6 h and (b) 24 h.

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M. Bazarganipour et al. / Polyhedron 30 (2011) 1103–1107
Fig. 5. SEM images of HgSe prepared in the presence of N2H4 as the reductant and CTAB as the capping agent at (a) 100 °C and (b) 150 °C for 12 h.
Table 2
Table 1
Characterization comparison of HgSe nanorods with other similar works.
The reaction conditions for each chemical system used.
Method
Precursors
Size
Morphology
Thin film
Ref.
Section
Capping agent
Reductant
Temperature (°C), time (h)
Chemical
deposition
Thermal
decomposition 1,2,3-
Hg(NO3)2,
Na2SeSO3
Cycloocteno-
Thickness of
0.8 lm
Particles size
less than
20 nm
[26]
Fig. 2a
Fig. 2b
Fig. 2c
Fig. 3a
Fig. 3b
Fig. 4a
Fig. 4b
Fig. 5a
Fig. 5b
CTAB
PEG 20000
SDBS
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
KBH4
KBH4
KBH4
N2H4
Zn
N2H4
N2H4
N2H4
N2H4
180, 12
180, 12
180, 12
180, 12
180, 12
180, 6
180, 24
100, 12
150, 12
Nanoparticle [27]
selenadiazole,
mercury acetate
Mercury acetate Mainly 30–
and Se powder 40 nm
Mercury nitrate, Approximately Nanoparticle [29]
Se powder 18 nm in size
Sonochemical
Sonochemical
Nanoparticle [28]
have used non-toxic precursors and solvent. With this route, we
have applied various capping agents and reductant types, which
is rare in the preparation of HgSe nanorods. The sizes of the HgSe
nanorods seem more convenient than in similar works.
4. Conclusion
In summary, this work has demonstrated a new approach for
the controllable growth of HgSe nanorods via reductant exchange
(Table 1). This route to HgSe nanorods is simple, convenient and
effective, and holds potential for the large-scale synthesis needed
for commercial applications. Most important of all, this new ap-
proach can yield a rod-like morphology of HgSe directly, without
mechanical crushing and sieving as is need for a solidified melt,
which may result in enhanced thermoelectric properties being
exhibited.
Acknowledgment
Authors are grateful to the Council of the University of Kashan
for providing financial support to undertake this work.
Fig. 6. EDS spectrum of HgSe prepared in the presence of KBH4 as the reductant and
CTAB as the capping agent at 180 °C for 12 h.
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