Sonochemical preparation of copper sulfides with different phases in aqueous solutions

Article abstract of DOI:10.1016/j.materresbull.2012.12.020

There is a growing interest in the synthesis of nanostructured copper sulfides due to their ability to form compounds with various stoichiometries. We report a sonochemical route for the preparation of copper sulfides with different compositions in aqueous solutions, using different, general and convenient copper sources such as copper acetate, copper hydroxide or basic copper carbonate and thiourea or thioacetamide as sulfur precursors under ambient air. Phase analysis, purity and morphology of the products were studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results revealed that nanoparticles of covellite, CuS, with crystallite sizes between 7 and 18 nm can be obtained by using different precursors and complexing agents and that chalcocite, Cu ₂S, can also be prepared sonochemically.

Full text of DOI:10.1016/j.materresbull.2012.12.020

Materials Research Bulletin 48 (2013) 1184–1188
Contents lists available at SciVerse ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Sonochemical preparation of copper sulfides with different phases in aqueous
solutions
a,
a
b
a,b
*
ˇ
ˇ
ˇ
Matjaz Kristl , Nusa Hojnik , Saso Gyergyek , Miha Drofenik
a Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia
b
ˇ
Jozef Stefan Institute, Department for Material Synthesis, Jamova 39, 1000 Ljubljana, Slovenia
A R T I C L E I N F O
A B S T R A C T
Article history:
There is a growing interest in the synthesis of nanostructured copper sulfides due to their ability to form
compounds with various stoichiometries. We report a sonochemical route for the preparation of copper
sulfides with different compositions in aqueous solutions, using different, general and convenient
copper sources such as copper acetate, copper hydroxide or basic copper carbonate and thiourea or
thioacetamide as sulfur precursors under ambient air. Phase analysis, purity and morphology of the
products were studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and
thermogravimetric analysis (TGA). The results revealed that nanoparticles of covellite, CuS, with
crystallite sizes between 7 and 18 nm can be obtained by using different precursors and complexing
agents and that chalcocite, Cu2S, can also be prepared sonochemically.
Received 26 July 2012
Received in revised form 4 December 2012
Accepted 9 December 2012
Available online 19 December 2012
Keywords:
A. Chalcoge´nides
A. Semiconductors
C. X-ray diffraction
C. Electron microscopy
C. Thermogravimetric analysis (TGA)
ß 2012 Elsevier Ltd. All rights reserved.
1. Introduction
filters [13,14] on windows in warm climates. Copper sulfide thin
films have also been reported as promising gas sensor materials for
Synthesis and characterization of nanosized metal chalcogen-
ides have attracted significant interest in the past decade and is
still the subject of intense investigation due to their unique
thermoelectric, semiconducting and optical properties which
allow various applications in science and technology. It is well
known that the properties of nanomaterials can be very different
from those of the corresponding bulk materials due to the fact that
the number of atoms on the surface is comparable to that inside the
particles [1–3]. It is often possible to control the physical and
chemical properties of nanoparticles by varying their size and
shape, which is an important characteristic in many fields, from
non-linear optics, optoelectronics and photochemistry to catalysis
[4]. Copper sulfides are of particular interest due to their ability to
form compounds with different stoichiometries and different
valence states [5]. It is well known [6] that copper and sulfur form
several stable phases at room temperature, starting from copper
rich chalcocite, Cu2S, to copper poor covellite, CuS, with several
detecting ammonia [15]. Covellite has already been used as
cathode material in lithium batteries [16] and attracts special
interest due to its metal-like electrical conductivity down to liquid
helium temperature and superconductivity at 1.6 K [17].
Many methods for the synthesis of copper sulfides have been
reported, yet the most straightforward of which is the synthesis
from elements at elevated temperatures [18,19]. However, the
required elevated temperatures in traditional solid-state reactions
make size control difficult. Among modern methods, suitable for
preparation of nanosized copper sulfides, microwave-assisted
methods [20,21], thermolysis of molecular precursors [22,23],
hydro/solvothermal syntheses [24–27], microemulsion syntheses
[28] and mechanochemical preparation methods [29,30] have
been reported. In recent years, ultrasound has become an
important tool in the synthesis of nanosized metals, metal oxides,
ferrite nanoparticles and metal chalcogenides. The unique reaction
conditions during the process of acoustic cavitation – high
temperature and pressure, followed by rapid cooling to bulk
temperature [31] – enable the preparation of nanoparticles with
uniform shapes and narrow size distribution. The sonochemical
method has been successfully applied to the preparation of
numerous metal chalcogenides [32], including mercury and
cadmium chalcogenides reported recently by our group [33–35].
The first sonochemical synthesis of CuS/PVA nanocomposites
was reported in 2002 by Kumar et al. [4] by sonochemical
phases of varying stoichiometry with the general formula Cu2ꢀx
S
between those two compositions. Copper sulfides with different
compositions have found applications as solid state solar cells
[7–10], electrodes [11], in catalysis [12] and selective radiation
* Corresponding author. Tel.: +386 2 22 94 415; fax: +386 2 2527 774.
E-mail address: matjaz.kristl@uni-mb.si (M. Kristl).
0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2012.12.020

M. Kristl et al. / Materials Research Bulletin 48 (2013) 1184–1188
1185
irradiation of an ethylenediamine-water solution of copper acetate
and sulfur under an argon flow. Particle sizes between 165 and
225 nm were reported. Wang at al. [36] prepared CuS with an
average diameter of 13 nm via a sonochemical route from an
aqueous solution containing copper acetate and thioacetamide in
the presence of triethanolamine as a complexing agent under
ambient air. Later, CuS was prepared sonochemically in aqueous
solutions from copper acetate and thiourea [37] and from freshly
precipitated Cu(OH)2 and thiourea [38].
The main aim of our research was a systematic approach to the
sonochemical synthesis of copper sulfides. While a variety of
copper sulfides with different stoichiometries are known, only CuS
syntheses by a sonochemical approach have been reported by now.
We tried to synthesize copper sulfides from different copper and
sulfur precursors and to study the influence of different complex-
ing agents on the composition and size of the products. One of the
main goals of the research presented herein was to prepare Cu–S
phases with different compositions by changing the molar ratio of
precursors. To the best of our knowledge, this is the first report on
the synthesis of chalcocite nanoparticles by the sonochemical
method in aqueous solutions.
compositions, the molar ratio n(Cu):n(S) was changed from 1:2 to
3:1. In Synthesis 2, we attempted to prepare copper sulfides from
elemental sulfur: 0.16 g (ꢂ0.005 mol) of elemental sulfur was
dissolved in 50 mL of 1 M NaOH at 80 8C using a magnetic stirrer. In
another beaker, we prepared the cationic precursor solution by
dissolving 0.998 g (ꢂ0.005 mol) of copper acetate in 50 mL of
0.05 M EDTA. The two solutions were mixed and irradiated as
described above. In Synthesis 3, we used freshly precipitated
Cu(OH)2 and thiourea, as reported by Xu et al. [38], but changed the
molar ratio of precursors. Syntheses 4, 5, 6 and 7 were following
the same procedure as Synthesis 1, but instead of copper acetate,
we used copper chloride, copper sulfate, basic copper carbonate
and copper nitrate as copper precursors. Finally, in Synthesis 8, the
method reported by Wang et al. [36], using copper acetate and
thioacetamide, was modified by applying different complexing
agents: 1.996 g (ꢂ0.01 mol) of copper acetate and 0.900 g
(ꢂ0.012 mol) of thioacetamide was dissolved in 50 mL of distilled
water and sonicated (1 h, 70% amplitude) without any complexing
agent and with addition of 5 mL monoethanolamine, triethano-
lamine and EDTA with different concentrations.
Powder diffraction spectra of all prepared products were
measured with an AXS-Bruker/Siemens model D5005 X-ray
powder diffractometer (XRD) equipped with a CuK
˚
source and a graphite monochromator (l = 1.54178 A) in the range
a radiation
2. Experimental
108 ꢃ 2 ꢃ 708, using a step size of 0.028 and time/step = 2 s. The
u
Following copper compounds were used for the syntheses:
copper acetate monohydrate, Cu(CH3COO)2ꢁH2O (99.8%, Kemika
Zagreb), copper chloride dihydrate, CuCl2ꢁ2H2O (99.5%, Sigma–
Aldrich), copper sulfate pentahydrate, CuSO4ꢁ5H2O (99.8%, Baker),
copper nitrate trihydrate, Cu(NO3)2ꢁ3H2O (99%, Sigma–Aldrich),
basic copper carbonate, Cu2(CO3)(OH)2ꢁ½H2O (w(Cu) = 55–57%,
Riedel-de-Ha¨en). The used sulfur precursors were thiourea, H2N–
CS–NH2 (99.8%, Merck), thioacetamide, C2H5NS (99%, Sigma–
Aldrich) and elemental sulfur (99.5%, Merck). EDTA (99.8%, Kemika
Zagreb), monoethanolamine (98%, Riedel-de-Ha¨en) and trietha-
nolamine (99%, Carlo Erba) were used as complexing agents.
In a typical synthesis from copper acetate and thiourea
(Synthesis 1), 1.996 g (ꢂ0.01 mol) of copper acetate and 0.76 g
(ꢂ0.01 mol) of thiourea was dissolved in 50 mL of water in a
100 mL flat-bottomed beaker and sonicated in an ambient
atmosphere for 1 h using a Sonics & Materials VCX 600 sonicator
at 70% amplitude (20 kHz, 80 W/cm2, 1 cm2 Ti direct immersion
horn). The as-obtained black precipitation was centrifuged at 6000
RPM, washed twice with water and once with absolute ethanol and
air-dried for 24 h. In an attempt to obtain products with different
morphology and size of the products were observed by transmis-
sion electron microscopy (TEM). The thermionic electron-source
TEM (JEOL 2100) was operated at 200 kV. For the TEM investigation
the nanoparticles were deposited on a copper-grid-supported
perforated transparent carbon foil. The crystallite size of the
nanoparticles was estimated using the Scherrer formula:
0:94 ꢁ
l
ꢁ cos
ꢁ 57:3
dx ¼
Here,
b
u
l
is the wavelength of the X-ray radiation (nm),
width at half-maximum (FWHM) of the corresponding peak (8) and
is the diffraction angle (8). The effects of instrumental broadening
b the full-
u
were subtracted by measuring an external macrocrystalline
standard under the same instrumental conditions.
Thermogravimetric analysis was carried out on a Mettler TGA/
SDTA 851e system in the temperature range 30–700 8C in open air
and in a nitrogen stream of 100 mL/min with a heating rate of 10 K/
min, using Al2O3 crucibles.
■
600
■
■
■
n(Cu):n(S) = 3:1
■
400
200
■
n(Cu):n(S) = 2:1
▲
▲
■
●
■
▲
▲
30
n(Cu):n(S) = 1:1
n(Cu):n(S) = 1:2
60
▲
▲
0
20
40
50
2θ (º)
Fig. 1. X-ray diffraction patterns of copper sulfide nanoparticles synthesized by ultrasonic irradiation from copper acetate and thiourea by changing the molar ratio. ~ = CuS,
& = Cu2S.

1186
M. Kristl et al. / Materials Research Bulletin 48 (2013) 1184–1188
Fig. 4. TEM image of CuS nanoparticles prepared from copper hydroxide and
thiourea using the molar ratio n(Cu):n(S) = 2:1.
Fig. 2. TEM image of CuS nanoparticles prepared from copper acetate and thiourea
using the molar ratio n(Cu):n(S) = 1:2.
3. Results and discussion
image (Fig. 4) shows spherical particles, which are strongly
agglomerated into clusters with sizes of several hundred nm.
XRD patterns of copper sulfide nanoparticles, prepared from
basic copper carbonate and thiourea, are shown in Fig. 5. Pure
covellite with an average particle size of 8.3 nm can be prepared
using excess amounts of sulfur, while products from syntheses
using equimolar mixtures or excess copper always contain a
mixture of covellite and Cu2(CO3)(OH)2. However, by washing this
mixture with diluted acetic acid, pure covellite with an average
particle size of 7 nm was isolated.
In the last part of our experiments, the role of complexing
agents in the sonochemical synthesis of copper chalcogenides was
studied. The results are shown in Fig. 6: while the product without
a complexing agent is a mixture of copper sulfate and copper
sulfide, all products obtained in the presence of complexing agents
could be identified as pure covellite. The crystallite sizes depend on
the used complexing agent; the smallest particles were obtained
using a 0.05 M aqueous EDTA solution.
It should be mentioned that no copper sulfides could be
prepared in a similar way by sonication from aqueous solutions,
when copper salts of strong acids (chloride, sulfate and nitrate)
were used as copper precursors. The products were mostly whitish
and could not be identified by XRD. The products obtained from
elemental sulfur dissolved in NaOH and EDTA solutions of copper
acetate (Synthesis 2) yielded CuS, contaminated with CuO, even
when performing the sonication in a Suslick cell under nitrogen
flow. The successful syntheses of copper sulfides are summarized
in Table 1.
Fig. 1 shows the XRD pattern of products, obtained from copper
acetate and thiourea (Synthesis 1) using different molar ratio of
precursors. It can be seen that the composition of the product can
be simply changed by applying different molar ratio of precursors:
by using excess amounts of sulfur (n(Cu):n(S) = 1:2), pure covellite,
CuS (PDF No. 00-001-1281) was prepared, while products
synthesized from an equimolar mixture of Cu and S contain both
peaks of covellite and chalcocite, Cu2S (PDF No. 00-003-1071). Pure
Cu2S can be obtained by using excess amounts of copper
(n(Cu):n(S) = 2:1 and 3:1). All products shown in Fig. 1 were
prepared using 1 h sonication time, while changing the sonication
time from 30 min to 2 h has negligible effects on the composition
of products.
The average crystallite size for CuS nanoparticles, calculated by
the Scherrer equation from the (1 1 0) peak (2
For Cu2S, the crystallite size was calculated to be 5.6 nm from the
average of (1 1 1) and (2 2 0) peaks (2 = 27.958 and 46.288,
respectively). The TEM image of CuS in Fig. 2 shows nanoparticles
with an average diameter of 10 nm, which are agglomerated in
bigger clusters.
Fig. 3 represents the XRD patterns of products, synthesized
from freshly precipitated Cu(OH)2 and thiourea in different molar
ratios. By changing the molar ratio n(Cu):n(S) = 1:2 to 2:1, we only
managed to obtain pure CuS with average crystallite sizes 8.9 nm.
All peaks could be indexed as (1 0 2), (1 0 3), (1 1 0), (1 0 4) and
(1 1 6) reflections of hexagonal covellite. The corresponding TEM
u = 48.108), is 8.4 nm.
u
800
(103)
(110)
(102)
600
400
(116)
(104)
n(Cu):n(S) = 2:1
200
n(Cu):n(S) = 1:2
0
20
30
40
50
60
2θ (º)
Fig. 3. X-ray diffraction patterns of copper sulfide nanoparticles synthesized by ultrasonic irradiation from copper hydroxide and thiourea by changing the molar ratio.

M. Kristl et al. / Materials Research Bulletin 48 (2013) 1184–1188
1187
■
■
■
1500
1000
500
0
■
■
■
▲
■
▲
■
▲
▲
n(Cu):n(S) = 1:2
washed with HAc
■
▲
▲
▲
▲
▲
▲
▲
■
n(Cu):n(S) = 1:1
n(Cu):n(S) = 1:2
▲
▲
20
30
40
50
2θ (º)
Fig. 5. X-ray diffraction patterns of copper sulfide nanoparticles synthesized by ultrasonic irradiation from basic copper hydroxide and thiourea by changing the molar ratio.
~ = CuS; & = Cu2(CO3)(OH)2.
▲
▲
▲
▲
1000
500
0
▲
▲
EDTA
MEA
TEA
▼
▼▼
▼
20
30
40
50
60
2θ (º)
Fig. 6. X-ray diffraction patterns of nanoparticles synthesized by ultrasonic irradiation from copper acetate and thioacetamide without a complexing agent (lowest) and using
different complexing agents: ethylenediamine tetraacetic acid (EDTA), monoethanolamine (MEA) and triethanolamine (TEA). ~ = CuS; ! = CuSO4ꢁ5H2O.
While the thermal analysis of bulk copper sulfides is well
known, little information could be found about thermal behavior of
nanosized CuS, so one of the goals of our study was to investigate
the thermal stability of as-prepared covellite and the product
obtained during the decomposition. The results of the thermal
analysis of CuS nanoparticles, prepared from copper acetate and
thiourea (Synthesis 1), are depicted in Fig. 7. The initial mass loss of
nearly 1.2% up to 120 8C was attributed to the loss of adsorbed
water, while the second mass loss of 1.1% between 155 and 230 8C,
with
a peak temperature of 185 8C, may be due to the
Table 1
Precursors and products of the sonochemical syntheses of copper sulfides in aqueous solutions.
Synthesis number
1.
Cu precursor
Cu(CH3COO)2
S precursor
H2N-CS-NH2
Complexing agent
–
Product
Isolated yield (%)
Crystallite size (nm)
CuSa
Cu2Sb
CuS
CuS
CuS
CuS
CuS
CuS
94
91
86
93
95
90
82
89
8.4 ꢄ 0.6
5.6 ꢄ 0.8
8.9 ꢄ 0.5
8.3 ꢄ 0.5
7.3 ꢄ 0.4
7.7 ꢄ 0.5
18.1 ꢄ 1.6
12.8 ꢄ 1.0
c
3.
6.
8.
Cu(OH)2
H2N-CS-NH2
H2N-CS-NH2
C2H5NS
–
Cu2(CO3)(OH)2
Cu(CH3COO)2
–
0.05 M EDTA
0.03 M EDTA
Monoethanolamine
Triethanolamine
a
Molar ratio Cu:S = 1:2.
b
Molar ratio Cu:S = 2:1–3:1.
c
Freshly precipitated from CuCl2 by adding NH3 and NaOH.

1188
M. Kristl et al. / Materials Research Bulletin 48 (2013) 1184–1188
DTG
TGA
4. Conclusions
Copper sulfide nanoparticles with different phases have been
prepared in aqueous solutions using a sonochemical approach. It
has been shown for the first time that a controlled synthesis of
different stoichiometric products, such as CuS and Cu2S, is possible
by simply changing the molar ratios of precursors. The average
crystallite size of the synthesized nanoparticles could be altered by
using different complexing agents. The method has been proved to
be a simple, mild and environment-friendly due to the use of
aqueous solvents.
Δm = -19.9%
5 mg
50
100 150 200 250 300 350 400 450 500 550 600 650
ºC
Acknowledgement
T (ºC)
Fig. 7. TGA curve and first derivative (DTG) representing the decomposition of
The authors acknowledge the use of equipment in the Center of
Excellence on Nanoscience and Nanotechnology–Nanocenter.
sonochemically prepared CuS nanoparticles at
nitrogen.
a
heating rate of 10 K/min in
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mass loss between 230 8C and 700 8C (
agreement with the calculated value for the overall decomposition
of CuS to Cu1.96S ( mcalc = 16.4%).
Dmmeas = 17.6%) is in fair
D