Synthesis, characterization, and photoluminescence properties of HgSe nanoparticles using a novel mercury precursor by the sonochemical method

Article abstract of DOI:10.1007/s11164-014-1884-2

In this paper, we report the synthesis and characterization of novel mercury selenide (HgSe) nanoparticles by sonochemical method. The HgSe nanoparticles have been prepared using [N,N′-bis(salicylaldehydo)ethylenediamine] mercury(II), [Hg(salen)] complex, as a novel precursor. The effects of the different capping agents, such as sodium dodecyl-benzene-sulfonate, polyethylene glycol, and polyvinyl pyrrolidone on the particle size and morphology of the samples have been investigated. The effect of different parameters, such as: temperature, power of irradiation, and reducing agent were also examined. These nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, X-ray energy dispersive spectroscopy, and Fourier transform infrared spectroscopy.

Full text of DOI:10.1007/s11164-014-1884-2

Res Chem Intermed
DOI 10.1007/s11164-014-1884-2
Synthesis, characterization, and photoluminescence
properties of HgSe nanoparticles using a novel mercury
precursor by the sonochemical method
•
Mahdiyeh Esmaeili-Zare Masoud Salavati-Niasari
Received: 21 July 2014 / Accepted: 20 November 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract In this paper, we report the synthesis and characterization of novel
mercury selenide (HgSe) nanoparticles by sonochemical method. The HgSe nano-
particles have been prepared using [N,N0-bis(salicylaldehydo)ethylenediamine]
mercury(II), [Hg(salen)] complex, as a novel precursor. The effects of the different
capping agents, such as sodium dodecyl-benzene-sulfonate, polyethylene glycol,
and polyvinyl pyrrolidone on the particle size and morphology of the samples have
been investigated. The effect of different parameters, such as: temperature, power of
irradiation, and reducing agent were also examined. These nanoparticles were
characterized by X-ray diffraction, scanning electron microscopy, transmission
electron microscopy, photoluminescence, X-ray energy dispersive spectroscopy,
and Fourier transform infrared spectroscopy.
Keywords Sonochemical synthesis ꢀ Mercury selenide ꢀ Surfactant ꢀ Complex
precursor ꢀ Optical properties
Introduction
In recent years, there has been an increasing interest in semiconductors with
nanosized dimensions in light of being widely studied because of its appropriate
application in industry [1, 2], especially in the field of cadmium and zinc
chalcogenide. Nevertheless, possibly due to the toxicity of mercuride, only a small
number of reports relating to the synthesis of mercury chalcogenides nanoparticles
are discovered. In those reports, some researchers prepared Hg (S, Se, Te)
nanoparticles at room temperature [3, 17–19] while others prepared mercury
M. Esmaeili-Zare ꢀ M. Salavati-Niasari (&)
Institute of Nano Science and Nano Technology, University of Kashan,
PO Box 87317–51167, Kashan, Islamic Republic Iran
e-mail: salavati@kashanu.ac.ir
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M. Esmaeili-Zare, M. Salavati-Niasari
selenide thin layers on transparent polyester sheets by means of chemical bath
deposition [4]. While being concerned with how to synthesize chemical materials
fast and conveniently, they found it a real challenge. The sonochemical method can
be used for solving this problem. It is a quick, synthetic method for many chemical
reactions. Ultrasound has become an important tool in material science in recent
years and has been used in the preparation of novel nanomaterials such as graphene
nanosheets [20, 21]. Because of the unique reaction effect of the ultrasound
irradiation, this method has a rapid reaction rate, controllable reaction conditions,
and the ability to form nanoparticles with uniform shapes, narrow size distributions,
and high purity.
Organic molecules containing imine groups have been interesting to inorganic
chemists because these types of molecules are suitable ligands for transition metals
and have found utility in a broad range of applications. Schiff base metal complexes
have been widely studied because of their appropriate application in industry, and as
antibacterial, anticancer, and herbicidal [5]. Salen ligands are tetradentate,
consisting of two imine nitrogen and two phenolic oxygen donors that coordinate
in the basal plane of the metal ion, and are readily prepared from the condensation
of a salicylaldehyde and a diamine.
We have been interested in the synthesis of metal selenide and metal sulfide
nanoparticles using new inorganic precursors, taking profit of the tools of
organometallic chemistry [6–9]. Using the novel precursor can be useful and can
open a new way for preparing nanomaterials to control nanocrystal size, shape, and
distribution of the particle size.
The present work describes the synthesis of HgSe nanoparticles using
sonochemical method. For this approach [N,N0-bis(salicylaldehydo)ethylenedia-
mine] mercury complex was selected as a new precursor for the first time.
Therefore, in this paper, we report on the HgSe nanoparticles using the
sonochemical method.
Experimental
Materials and physical measurements
Sodium dodecyl sulfate (SDS: 99 % purity) was purchased from Merck, polyeth-
ylene glycol (PEG600, 1L = 1.3 kg, Merck), sodium dodecyl–benzene–sulfonate
(SDBS: 88 % purity, Merck), poly vinyl pyrrolidone PVP-K40- (C6H9NO) n (
n = 40) (99 % purity, Sigma-Aldrich), ethylenediamine (99 % purity, Merck)
selenium tetra chloride (Merck) and mercury acetate (98 % purity, Merck) were
used for synthesize of different morphology of the nanoparticles. All the chemicals
were of the analytical grade and were used without further purification. A
multiwave ultrasonic generator (Sonicator 3000; Bandeline, MS 72, Germany),
equipped with a converter/transducer and titanium oscillator (horn), 12.5 mm in
diameter, operating at 20 kHz with a maximum power output of 100 W, was used
for the ultrasonic irradiation. The ultrasonic generator automatically adjusted the
power level. The wave amplitude in each experiment was adjusted as needed. XRD
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Synthesis, characterization, and photoluminescence properties
patterns were recorded by a Philips X-ray diffractometer using Ni-filtered Cu-Ka
radiation. Scanning electron microscopy (SEM) images were obtained on a LEO
instrument. Transmission electron microscopy (TEM) images were obtained on a
Philips EM208 transmission electron microscope with an accelerating voltage of
100 kV. Fourier transform infrared (FT-IR) spectra were recorded on Shimadzu
Varian 4300 spectrophotometer in KBr pellets. The compositional analysis was
done by energy-dispersive X-ray (EDX, Kevex, Delta Class I). Photoluminescence
(PL) measurement was studied on a Perkin-Elmer fluorescence spectrophotometer.
Synthesis of [Hg(salen)] complex
N,N0-bis-salicylidene-1,2-ethylendiamine; H2salen; (3.7 mmol) was dissolved in 100 ml
methanol; then 100 ml of mercury(II) acetate (0.037 M) was added to the above solution
under stirring. Triethylamine (1 ml, 7.2 mmol) was added and the mixture was heated at
°
80 C for 1 h. The mixture was filtered, and the yellow precipitate was washed with
methanol and dried in a vacuum oven. The melting points of H2salen ligand and
corresponding mercury complex were measured to be 168 [10] and 260–270 °C,
respectively. The higher melting point of the complex is considered to be due to the higher
symmetry and thus more stability of the complex rather than the initial ligand.
Preparation of HgSe nanoparticles
We dissolved 0.2 g of [Hg(salen)] in 100 ml of propylene glycol (PG). Then, 0.1 g
SeCl4 was added to the solution under ultrasonic irradiation for 7 min. The solutions
were then irradiated with an ultrasonic horn for 30 min and added drop-wise
N2H4ꢀH2O. The black obtained precipitate was centrifuged, washed by distilled
water and methanol, and dried in vacuum oven at 60 °C. Preparation of HgSe
nanoparticles under different conditions is listed in Table 1.
Results and discussion
The XRD pattern of the HgSe is shown in Fig. 1. All of the reflections of the patterncan
be indexed to the standard peak of the pure cubic phase of HgSe, which is in suitable
˚
agreement with the reported data (JCPDS No. 73-1668, a = b = c = 6.0720 A). The
patterns of the obtain samples 3, 6, 11, and 12 in different condition (effect of
surfactant, temperature, ultrasonic power, reducing agent) are shown in Fig. 2a–d,
respectively, which have appropriate agreement with the reported JCPDS. This
revealed that the HgSe has a single phase cubic structure. The crystallite size
measurements were also carried out using the Scherrer equation [11],
Kk
Dc ¼
b cos h
where b is the breadth of the observed diffraction line at its half intensity maximum,
K is the so-called shape factor, which usually takes a value of about 0.9, and k is the
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M. Esmaeili-Zare, M. Salavati-Niasari
Table 1 Preparation of HgSe under different conditions
Sample Effect
no.
Surfactant
Temperature Time Ultrasonic Reductant Section
(°C)
(min) power
(W/cm2)
1
Surfactant
–
25
25
25
25
30
30
30
30
30
30
30
15
45
30
30
30
30
60
N2H4ꢀH2O Fig. 5a
N2H4ꢀH2O Fig. 5c
N2H4ꢀH2O Fig. 5d
N2H4ꢀH2O Fig. 5e
N2H4ꢀH2O Fig. 5f
N2H4ꢀH2O Fig. 6a
N2H4ꢀH2O Fig. 6b
N2H4ꢀH2O Fig. 6c
N2H4ꢀH2O Fig. 6d
N2H4ꢀH2O Fig. 7a
N2H4ꢀH2O Fig. 7b
2
SDBS
SDS
60
60
60
60
60
60
60
60
40
50
60
60
3
4
PEG 600
5
PVP 25,000 25
6
Temperature
Time
–
–
–
–
–
–
–
–
–
50
70
25
25
25
25
25
25
7
8
9
10
11
12
13
14
Ultrasonic power
Reducing agent
Sonication
KBH4
Fig. 8a
Zn
Fig. 8b
N2H4ꢀH2O Fig. 9
Fig. 1 XRD pattern of the HgSe nanoparticles (No. 1)
wavelength of X-ray source used in XRD. The estimated crystallite size is about
15 nm.
FT-IR spectrum of the [Hg(salen)] precursor is illustrated in Fig. 3. The broad
band at 3,428 cm-1 is assigned to O–H bonds of hydration water. The peaks at
2,922 and 3,050 cm-1 are responsible for the aliphatic and aromatic C–H bonds,
respectively. The absorption at 1,615 cm-1 is due to the C=N vibration. In addition,
the peak at 1,438 cm-1 is due to the C=C stretching mode. The peak at 757 cm-1 is
123

Synthesis, characterization, and photoluminescence properties
Fig. 2 XRD patterns of the
samples 3, 6, 11, and 12
assigned to bending mode of the phenyl group c (=CH) and two peaks located at
1,146 and 1,178 cm-1 corresponding to the phenolic C–O bond.
The FT-IR spectra of the obtained samples 3, 6, 11, and 12 in different condition
(effect of surfactant, temperature, ultrasonic power, reducing agent) are shown in
Fig. 4a–e. HgSe has no absorption peak in the range of 4,000–400 cm-1 so these
spectra show that products do not have major IR-active impurity.
It was found that the sonochemical reactions occur within the interfacial region,
forming nanocrystals due to very high quenching rate experienced by the products.
Several factors influence the acoustic cavitation such as low vapor pressure, high
surface tension, and high sound speed. The influence of the capping agent,
temperature, time, ultrasonic power, and reducing agent type on the as-prepared
HgSe nanoparticles were investigated (Figs. 5, 6, 7, 8–9). The nanoparticles in the
absence of the capping agent (Fig. 5a) with grain diameter about 15–30 nm have
acceptable distribution. Ultrasonic irradiation creates bubbles, which produces high
temperature and energy after decomposition. This process provides an appropriate
amount of energy for formation of HgSe nanoparticles. TEM image of the as-
synthesized HgSe nanoparticles is shown in Fig. 5b to determine the particle size of
the product. The shape of the obtained products are quasi-spherical with dimensions
about 15–30 nm.
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M. Esmaeili-Zare, M. Salavati-Niasari
Fig. 3 FT-IR spectrum of the Hg(salen) precursor
Fig. 4 FT-IR spectra of the samples 2, 3, 6, 11, and 12
With exchange of the capping agent from SDBS to SDS, PEG and PVP in the
presence of hydrazine as a reductant, the nanoparticles show dense agglomeration
and an increase in the particle size (Fig. 5c–f, Scheme 1). It has been reported that
the presence of capping molecule (such as PEG and PVP) can alter the surface
energy of the crystallographic surface, and promote the anisotropic growth of
nanocrystals and therefore we can see this trend in the case of HgSe [12]. By using
ultrasound irradiation, the formed bubbles collapse, resulting in the generation of
high-speed microjets with very high velocity, which these microjets can generate
HgSe nanoparticles [10].
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Synthesis, characterization, and photoluminescence properties
Fig. 5 a SEM, b TEM images of the as-prepared HgSe in the absence of capping agent (No. 1), SEM
images in the presence of: c SDBS (No. 2), d SDS (No. 3), e PEG (No. 4) and f PVP (No. 5)
The effect of the reaction temperature and time on the morphology of the
products was also investigated (Fig. 6). With increasing the reaction temperature
from 25 (Fig. 5a) to 50 °C (Fig. 6a), the particle size of the nanoparticles increased,
but with enhancement temperature to 70 °C (Fig. 6b), the size and agglomeration of
the nanoparticles decreased, which may be due to an increase in diffusion rate of
bubbles in nucleation region affecting the reactant concentration. Reaction time
effect on the morphology of the nanoparticles, in absence of the capping agent, was
examined (Fig. 6c, d). By increasing the reaction time from 15 (Fig. 6c) to 30 min
(Fig. 5a), the size of the obtained nanoparticles was decreased. With enhancement
of the reaction time to 45 min (Fig. 6d), morphology and size of the samples
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M. Esmaeili-Zare, M. Salavati-Niasari
Fig. 6 SEM images of the prepared HgSe in the presence of hydrazine: a at 50 °C (No. 6), b at 70 °C
(No. 7), c at 25 °C for 15 min (No. 8) and d at 25 °C for 45 min (No. 9) of sonication
changed and agglomeration of the nanoparticles increased, which is consistent with
Oswald ripening.
Figure 7 shows the SEM images of the obtained samples at various powers. It
can be observed that with enhancement of the power from 40 (Fig. 7a) to 50 W
(Fig. 7b), the size and agglomeration of the nanoparticles increase. It was found that
when PG was selected as a solvent, the reaction proceeded smoothly at the power of
40 W. By increasing the ultrasound power to 60 W (Fig. 5a), the agglomeration of
nanoparticles break down and the size of HgSe nanoparticles decrease. Results show
that at higher powers, nucleation stage overcomes the growth stage and smaller
particles will be achieved.
It might be noted that the final temperature and pressure reached after the
collapse of the bubble is proportional to the ultrasonic power. If the ultrasonic
power was increased, the extent of the collapse of the bubble would be greatly
increased, leading to a higher temperature and pressure accordingly, which would
enhance the effect of ultrasonic chemical reactions as a whole. Due to the viscosity
of PG, forming a cavity will require a much higher threshold than water. That might
be one of the reasons why ultrasonic power is lower in water systems than in PG
systems. The implosive collapse of bubbles in PG solvent would result in higher
temperature and pressure than in aqueous solvents. Taking this into account, PG is
an excellent solvent for sonochemical reaction [13].
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Synthesis, characterization, and photoluminescence properties
Fig. 7 SEM images under different powers of ultrasound: a 40 W (No. 10) and b 50 W (No. 11)
Fig. 8 SEM images of the products with different reducing agents: a KBH4 (No. 12) and b Zn (No. 13)
Fig. 9 SEM image of the
sample No. 14
With using strong reducing agents such as KBH4 and hydrazine hydrate, a large
number of nuclei was created and further growth of the nuclei was limited. As a
result, many small particles were obtained (Figs. 5a, 8a). Reduction in the presence
of Zn proceeds only two dimensionally (Fig. 8b). In this experiment, the reaction
that takes place using a chemical reducing agent is the reduction of Se source to
form Se2- ions that subsequently react with Hg2? ions to form HgSe.
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M. Esmaeili-Zare, M. Salavati-Niasari
Scheme 1 Schematic diagram illustrating formation of the HgSe nanoparticles
For investigating of the sonication effect on the morphology of the products, the
blank reaction was performed without ultrasound irradiation. Aggregated nano-
structures are formed in the absence of sonication (Fig. 9). An advantage of using
ultrasound irradiation is that it yields smaller particles and the result shows a growth
in the particle size without ultrasound method.
Figure 10 shows the proton nuclear magnetic resonance (1H-NMR) spectrum of
the complex precursor. The multiple peaks appeared at the chemical shifts of
6.8–7.6 ppm is attributed to the aromatic protons. The sharp peaks appeared at 8.6
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Synthesis, characterization, and photoluminescence properties
Fig. 10 1H-NMR spectrum of the [Hg(Salen)] precursor
and 3.9 ppm could be assigned to the proton of HC=N group and N–CH2,
respectively.
The probable formation process of HgSe nanoparticles under ultrasound waves
(US) in propylene glycol can be summarized as follows [14, 15]:
US
HgðsalenÞ + OHCH2CHðOHÞCH3 ꢁ! Hg2þ + salen2ꢁ
SeCl4 þ OHCH2 CHðOHÞCH3 ! Se4þ þ 4Clꢁ
ð1Þ
ð2Þ
US
OHCH2 CHðOHÞCH3 ꢁ! Hꢀ + HOCHꢀ CHðOHÞCH3
ð3Þ
Hꢀ + Hꢀ ! H2:
Then N2H4 H2O is reacted with Se4?, obtained from solutions of SeCl4, giving
rise to HgSe nanoparticles:
US
Se4þ þ N2H4H2O ꢁ! Se0 þ N2 þ 4Hþ þ H2O
H2 þ Se0 ! Se2ꢁ þ 2Hþ
ð4Þ
ð5Þ
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M. Esmaeili-Zare, M. Salavati-Niasari
Fig. 11 a EDS pattern, b room-temperature photoluminescence spectrum, and c diffuse reflectance
spectrum of the HgSe nanoparticles (No. 1)
Table 2 Characterization comparison of band gap of HgSe nanostructures with other similar works
Band gap (eV)
Method
References
1.55
Emulsion
Liu et al. [24]
0.78
Electrodeposition
Solvothermal method
Mahalingam et al. [25]
RangaRao and Dutta [26]
1.65 (without voltage) and
1.72 (at 700 V)
Se2ꢁ þ Hg2þ ! HgSe:
ð6Þ
Energy-dispersive spectroscopy (EDS) analysis was employed to determine the
composition of the HgSe nanoparticles (Sample No. 1). As shown in Fig. 11a, the
EDS clearly identifies that the nanoparticles are composed of Hg (at.% 51.24 %)
and Se (at.% 48.76 %); they should therefore be attributed to HgSe and further
confirm the purity of products. Room temperature PL spectrum of the HgSe
nanoparticles (Sample No. 1) with excitation at 257 nm is shown in Fig. 11b. A
very broad peak centered at 302 nm (4.109 eV) is shown in the PL spectrum. The
band gap energy of the bulk HgSe crystal Eg is -0.24 eV [16], therefore, the band
gap energy of the as-synthesized HgSe nanoparticles is blue shifted compared to
bulk sample. The large blue-shift in the optical band-gap observed for this sample
compared to bulk mercury selenides can be attributed to strong confinement
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Synthesis, characterization, and photoluminescence properties
Scheme 2 Quantum confinement is responsible for the increase of energy difference between energy
states and band gap
(Table 2. Characterization comparison of band gap of HgSe nanostructures with
other similar works).
Quantum confinement is a change of electronic and optical properties when the
material sampled is of sufficiently small size, typically 10 nm or less. The band gap
increases as the size of the nanostructure decreases (see Scheme. 2). Specifically,
the phenomenon results from electrons and holes being squeezed into a dimension
that approaches a critical quantum measurement, called the exciton Bohr radius. A
stronger confinement leads to a larger separation of the energy levels; as a result, a
higher energy is required to promote an electron from the valance band to the
conduction band.
Conclusions
HgSe nanoparticles were successfully prepared by a facile sonochemical method at
room temperature. Using the surfactants and high temperatures is not necessary for
this synthesis. SEM, TEM, XRD, 1H-NMR, FT-IR, and PL techniques were used to
characterize the structure and purity of the HgSe nanoparticles. The influence of
different parameters such as capping agent, temperature, power of irradiation and
reducing agent type on the morphology of the product was also examined. HgSe is
one of the very interesting II–VI materials to be investigated for its applications in
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M. Esmaeili-Zare, M. Salavati-Niasari
optoelectronic technology including photoconductive photovoltaic, IR detector, IR
emitter, tunable lasers, and thermoelectric coolers [22, 23].
Acknowledgments The authors are grateful to the council of University of Kashan for their unending
effort to provide financial support to undertake this work by Grant No. (159271/242).
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