Sodium thiosulfate-assisted synthesis of NiS2 nanostructure by using nickel(ii)-Salen precursor: Optical and magnetic properties

Article abstract of DOI:10.1039/c4dt02232g

A NiS₂ nanostructure with a protective layer of Ni²⁺ and SO₄^2- ions around it has been successfully synthesized using the Ni(ii)-Salen (Salen = N,N′-bis(salicylidene)ethylenediamine) complex via a simple solvoth

Full text of DOI:10.1039/c4dt02232g

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Sodium thiosulfate-assisted synthesis of NiS2
nanostructure by using nickel(II)-Salen precursor:
optical and magnetic properties†
Cite this: Dalton Trans., 2014, 43,
16745
Raziyeh Akbarzadeh, Hossein Dehghani* and Fatemeh Behnoudnia
2+
2−
A NiS
thesized using the Ni(II)-Salen (Salen = N,N’-bis(salicylidene)ethylenediamine) complex via a simple solvo-
thermal approach in the presence of anhydrous sodium thiosulfate (Na ) as sulfur source and
2
nanostructure with a protective layer of Ni and SO
4
ions around it has been successfully syn-
2 2 3
S O
stabilizer. Unexpectedly, no one kind of pure nickel sulfide nanostructure was prepared using the Ni(II)-
Salophen complex or some of the simple mono and bidentate Ni(II) complexes as starting materials and
the obtained products were a mixture of nickel sulfides. In the photoluminescence spectrum of the pre-
pared NiS
with emission minima was located at 800 nm. The as-synthesized NiS
ferromagnetic behaviour at room temperature, which has small remanent magnetization and saturation
magnetization compared to bulk NiS . These changes might be attributed to the existence of a protective
layer of nickel and sulfate ions around the NiS nanostructures that was confirmed by Energy-dispersive
2
, two peaks were evident at 400 and 420 nm with emission maxima, and one broad peak
2
nanostructure displays a weak
2
2
X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy. The prepared
nanostructure has been characterized structurally, electrochemically, optically and magnetically by avail-
able methods like X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Transmission
electron microscopy (TEM), Energy-dispersive X-ray spectroscopy, Fourier transform infrared and Raman
spectroscopy, Cyclic voltammetry (CV), Photoluminescence (PL) spectroscopy and vibrating sample
magnetometer (VSM).
Received 25th July 2014,
Accepted 15th September 2014
DOI: 10.1039/c4dt02232g
www.rsc.org/dalton
5
–8
sonic irradiation. In particular, the solvothermal method is
a convenient method, because using this method the high
Introduction
It is known that metal sulfides exhibit interesting electronic purity, size- and shape-controlled nickel sulfide nanostructures
properties, and thus have several technological applications. can be easily formed. Cubic pyrite NiS dodecahedrons and
Many unique and interesting properties, in contrast to their microspheres have been synthesized in ethylenediamine–
bulk species, have been exhibited for this class of materials glycol mixed solvent at 200 °C using NiCl ·6H O and sulfur, as
such as higher luminescence efficiency, superior mechanic precursors, by a solvothermal approach. The thermal stability
2
2
2
9
1
–3
toughness, and lowered lasing threshold. Among the family of the pyrite NiS dodecahedrons has been studied and they
2
of metal sulfides, nickel sulfides, as important inorganic func- can act as an excellent precursors for the synthesis of porous
tional materials, have attracted considerable attention because NiO microspheres by calcination in air atmosphere. Nickel sul-
of practical applications, such as paramagnetic–antiferro- fides exhibit magnetic phase behavior. For example, Ni S has
3
4
magnetic (PM–AFM) phase-changing materials, metal–insula- a metallic character and exhibits itinerant electron ferro-
tors, magnetic resonance imaging, magnetic refrigeration and magnetism. In contrast, NiS is an insulating antiferromagnetic
as possible transformation harden the window glass. Many molecule despite the half-filled e band and is consequently
2
3
,4
g
1
0,11
methods have been introduced to synthesize nanomaterials considered to be a Mott insulator.
such as hydrothermal synthesis, microwave irradiation, ultra- phase diagram in magnetic and transport properties.
It consists of a very rich
1
2,13
NiS
2
has applications as a cathode material in rechargeable lithium
batteries, as a counter electrode for dye sensitized solar cells
Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan,
Kashan, I. R. Iran. E-mail: dehghani@kashanu.ac.ir; Fax: +98 361 591 2397;
Tel: +98 361 5591 2386
14–17
and as a hydrogenation catalyst.
useful in sensors and IR detectors.
It is also potentially
It has been pointed out
18,19
that Schiff bases are among the most popular ligands because
†
Electronic supplementary information (ESI) available: Additional experimental
results as discussed in the text (Fig. S1–S3). See DOI: 10.1039/c4dt02232g
of their easy formation and rich coordination chemistry with a
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2
0,21
large variety of metal ions.
Considerable research efforts KBr pellets. The Raman spectrum was measured with a SEN-
−
1
have been devoted for the synthesis of new complexes with TERRA laser Raman spectrometer in the range 200–3500 cm
2
2,23
transition and main group metal ions.
bases, such as H Salen and H Salophen ligands, have exten- sample was measured on a Hitachi 850 fluorescence spectro-
sive applications in the fields of synthesis and catalysis.
Tetradentate Schiff at room temperature. The photoluminescence (PL) of the
2
2
2
4–26
photometer at room temperature. A computerized electro-
These types of ligands contain two imine groups and two phe- chemistry system (Sama 500 potentiostat (Isfahan, Iran)) was
nolic oxygen donors. This arrangement of atoms has provided used to investigate the electrochemical behavior of the
the condition to synthesize square planar metal complexes obtained NiS nanostructure. In addition, magnetic character-
2
that very well stabilize transition metal centers. These types of ization of the nickel sulfide nanostructures was performed to
complexes are flexible and can adopt a variety of structures to measure their magnetic properties at room temperature by a
provide several active site environments allowing different oxi- BHV-55 (Riken, Japan) vibrating sample magnetometer (VSM).
2
7,28
dation reactions.
bond to various metals to form soluble and luminescent
complexes. In contrast to nanomaterials synthesized from H Salen was prepared according to the literature pro-
2 2
H Salen and H Salophen ligands can be
Synthesis of Schiff base ligands
2
2
9,30
inorganic solids, the synthesis of nanostructure metal com- cedure.
In brief, a solution containing one equivalent of
pounds based on organic-metal complexes, as precursors, ethylenediamine (50 mmol) in ethanol was slowly added to a
appears to be surprisingly scarce. In this work, we adapted a stirred solution of the two equivalents of salicylaldehyde
simple solvothermal route for the preparation of NiS nano- (100 mmol) in ethanol. The reaction mixture was refluxed for
2
structures by the direct reaction of the Ni(II)-Salen complex 1.5 h and the yellow Schiff base ligand precipitated. After
and Na S O as sulfur source and stabilizer in DMF solvent. cooling, the ligand was filtered and washed with cold ethanol
2
2 3
2 2 4 2
2
For comparison, Ni(II)-Salophen, NiCl ·6H O, NiSO ·6H O and and dried. The Schiff base of H Salophen was prepared accord-
Ni(CH COO) ·4H O were used in the same conditions. Accord- ing to the same procedure, but 1,2-phenylenediamine was
3
2
2
ing to the effect of the precursor on the type and purity of the used instead of ethylenediamine and the color of product was
products, an easy synthesis of tetradentate Schiff bases was orange.
performed. On the other hand, because of the diversity of
nickel sulfides, the interesting finding in our study is the
Synthesis of the complexes
ability of the aliphatic tetradentate Ni(II)-Schiff base complex
The complexes presented in Fig. S1a and b† were synthesized
(Ni(II)-Salen) to synthesize one type of pure nickel sulfide
as follows: a stirring solution of Ni(II) acetate tetrahydrate
nanostructure, as opposed to the aromatic tetradentate Ni(II)-
Schiff base complex (Ni(II)-Salophen) or simple mono and
bidentate Ni(II) complexes. A full description of the reaction
mechanisms is discussed in this paper.
(
(
2 mmol) and appropriate equivalents of Schiff base ligand
2 mmol) in 50 ml ethanol were refluxed for 1.5 h. The pro-
gress of the reaction was monitored by TLC until the ligand
spot disappeared. The mixture was cooled and the obtained
solid was filtered, and then washed with cold ethanol, diethyl
3
0,31
ether and dried.
Experimental
Preparation of NiS nanostructures
2
Common reagents such as ethylenediamine, salicylaldehyde,
nickel(II) chloride hexahydrate (NiCl ·6H O), nickel(II) sulfate
NiS
2
nanostructures were synthesized by the reaction of Ni(II)-
2
2
Salen complex (0.46 mmol) and Na S O (0.46 mmol) in 15 ml
2
2 3
hexahydrate (NiSO
Ni(CH COO) ·4H O), anhydrous sodium thiosulfate (Na
N,N-dimethylformamide (DMF) and N,N-dimethylacetamide
DMA) were procured from Merck and used without further
4
·6H
2
O), nickel(II) acetate tetrahydrate
(
DMF) solvent. The reaction mixture was stirred, and then
(
3
2
2
2 2 3
S O
),
transferred into an autoclave (25 ml) and maintained at 150 °C
for 15 h. After cooling to room temperature, the black products
were filtered and washed several times with double distilled
water, absolute ethanol and hexane. Finally, the prepared
product was dried in air at 60 °C for 6 h.
(
purifications. Absolute ethanol, double distilled water and
hexane were used during the preparation of powders. Powder
X-ray diffraction (XRD) measurements were performed using a
Phillips X’ Pert PRO equipped with a Cu Kα source having a
scanning range of 0°–80° Bragg’s angle. The morphology of
the synthesized products was directly observed by a Philips
Results and discussion
XL-30 ESEM Scanning electron microscope (SEM) equipped Fig. 1a shows the typical XRD pattern acquired from the NiS
with an Energy-dispersive X-ray spectroscopy (EDS). The Trans- nanostructure with a protective layer of Ni and SO4 ions
mission electron microscopy (TEM) images were obtained by around it, which was synthesized using Ni(II)-Salen complex
2
2
+
2−
dispersing the sample in ethanol and placing a drop of dis- and Na
persion on a carbon coated copper grid in a Zeiss EM10C 15 h. All the diffraction peaks belong to anorthic (triclinic)
instrument operating at 80 kV. Fourier transform infrared NiS (JCPDS 73-0574) with pure crystallinity. No additional
FTIR) spectra were recorded with a Magna 550 Nicolet instru- peaks corresponding to metallic nickel or any other forms of
2 2 3
S O as starting materials in DMF solvent at 150 °C for
2
(
−1
ment, in the spectral range between 4000 and 400 cm , using nickel sulfides were observed in the XRD pattern, indicating
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2
Fig. 1 XRD patterns of the NiS nanostructure synthesized using Ni(II)-
Salen complex and Na
times (a) 15 h (b) 48 h.
2 2 3
S O as the starting material for different reaction
Fig. 3 SEM images of the products synthesized using the Ni(II)-Salen
complex, obtained after different reaction times (a, b) 8 h, (c, d) 15 h and
2
the high purity of the obtained NiS . The absence of nickel
sulfate peaks indicates the possibility that nickel sulfate is
present only as an amorphous phase. As shown in Fig. 1b, it
(e, f) 48 h.
was noticeable that when the reaction time increased to 48 h 8.3 keV correspond to nickel, while those at 0.5 and 2.3 keV
all the diffraction peaks could also be indexed to anorthic NiS2 correspond to oxygen and sulfur, respectively. The sulfur peak is
(
2
JCPDS 73-0574). This result proved that a time increment attributed to sulfide in the NiS nanostructure; however,
2
−
above 15 h has no specific effects on the resultant product and sulfur and oxygen peaks are due to SO
anions around the
4
the peaks corresponding to NiS had a high intensity and no nanostructures.
2
additional peaks were observed. The roughness in the baseline
of XRD pattern was because of the amorphous silica.
Fig. 3 shows the SEM images of the samples obtained by
mixing Ni(II)-Salen complex and Na for 8 h, 15 h, and
S O
2 2 3
Furthermore, the chemical composition of the prepared 48 h, respectively. It can be seen in Fig. 3a and b that the
sample was determined by EDS analysis. Fig. 2 presents the sample obtained after 8 h has non-uniform nanoparticle mor-
EDS spectrum of the NiS
nanostructure obtained using the phology with several tens of nanometers in size, which act as
2
Ni(II)-Salen complex and Na S O as the starting materials at the building block units. The product obtained after 15 h has
2
2 3
1
50 °C for 15 h. It can be clearly seen that the as-prepared a special structure with an average diameter of about 200 nm,
sample consisted of Ni, S and O. The peaks at 0.9, 7.5 and which consists of very small particles that tend to coalesce
(
SO
Fig. 3c and d). Such special morphology might because of the
2
−
4
anions and adsorbed water molecules around the nano-
structure. As can be seen in Fig. 3e and f, a similar morphology
is observed for the NiS samples obtained by increasing the
time to 48 h. From the SEM images of NiS nanostructures,
2
2
it was observed that the nanostructures were almost uniform
in size.
5
The particle size was evaluated by the Scherrer formula:
Kλ
D ¼
β cos θ
where D is the average dimension of crystallites; K is the Scher-
rer constant, (K = 0.89); λ is the wavelength of the Cu Kα radi-
1
ation (0.1541 nm), θ is the Bragg angle of the peak and β is
the corrected half-width of the diffraction peak. The average
Fig. 2 EDS spectrum of the NiS
2
nanostructure synthesized using Ni(II)-
2
crystalline size of the NiS synthesized after 15 h was calcu-
lated to be approximately 28.6 nm using this formula.
Salen complex and Na
of 15 h.
2 2 3
S O as the starting materials for a reaction time
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2
Fig. 4 TEM images of the NiS nanostructure synthesized using Ni(II)-
Salen complex and Na
of 15 h.
2 2 3
S O as the starting materials for a reaction time
2
Because the SEM images of the NiS nanostructure typically
show the aggregation of particles, supplementary TEM
measurements were carried out. Fig. 4 shows the TEM images
of the product obtained after 15 h of reaction. It is noticeable
that TEM images establish that most of the very small NiS2
particles (<20 nm) tend to coalesce and the nanoparticles
formed by the interconnected crystallites might be due to the
2
−
layer of SO4 anions, which act as stabilizer and adsorbed
water molecules, which surround the NiS particles.
2
2
The FTIR spectrum of the prepared NiS nanostructure
after a reaction time of 15 h is shown in Fig. 5a and it contains
a broad peak for asymmetric and symmetric stretching
−
1
vibrations of the adsorbed water molecules at 3429 cm and a
−
1 32
bending vibration band for water at 1627 cm
.
The absorp-
−
1
−1
tion bands at 1107 cm and 613 cm can be attributed to
Fig. 5 (a) FTIR and (b) Raman spectra of the as-prepared NiS
2
nano-
2
−
33
vibrations of SO
4
ν(S–O) and ν(O–S–O), respectively. As structure after a reaction time of 15 h (The Raman peaks of NiS , sulfate
2
expected, the FTIR spectrum confirmed the presence of sulfate ions and adsorbed water molecules are shown as blue, red and green
arrows, respectively).
anions directed toward water around the as-prepared nano-
structure. For further confirmation and characterization, the
Raman spectrum of the typical NiS2 nanostructure obtained
after a reaction time of 15 h with an average diameter of
Table 1 List of the vibrational frequencies (cm− ) derived from the
spectrum shown in Fig. 4b
1
roughly 200 nm was also carried out at room temperature, as
shown in Fig. 5b. The peaks at 279, 306, 410, 557 and
Prepared NiS2
NiSO powder
4
6
76 cm− are related to NiS and the peaks at 968, 1152, 1301
1
NiS
position (cm
2
powder peak
nanostructure peak
peak position
2
−
1 4
−1
−1 33,36
−
1
)
position (cm
)
(cm )
and 1562 cm correspond to sulfate anions around the nano-
structure. In addition, the broad peak between 1500–1700 cm
and the small peak at 3253 cm , could be attributed to the 274
−1
235
279
308
410
557
676
968
1152
−1
3
5
73
15
bending and symmetric stretching vibration of the adsorbed
3
4
water molecules. The Raman peaks of NiS nanostructures
2
562
with no protective layer, which were synthesized by Wang
970
−
1 35
1075
1176
1211
et al., appeared at 210, 262, 518 cm
.
The observed
1
1
301
562
vibrational modes resulting from the spectrum are also shown
in Table 1. For comparison, the literature data are also listed
4
,33,36
in the table.
Fig. 5b and Table 1, the Raman modes of the as-prepared NiS2 interactions. Thus, the Raman spectrum obtained at room
nanostructure, are significantly shifted towards a higher wave- temperature identified that the product was a NiS nanostruc-
number (blue shift) compared to NiS powders previously ture along with a stabilizer layer of sulfate anions and
Therefore, the reason for these changes in adsorbed water molecules around it.
Raman shifts is probably because of the small size of the To find the different effects of aliphatic and aromatic tetra-
particles in the special structural morphology of NiS and dentate Ni(II)-Schiff base complexes when used as precursors,
the shifts can be mainly attributed to the existence of the the reaction was carried out using similar procedure by the
As can be seen from the data shown in
2
2
4
,33,35
reported.
2
2
+
2−
protective layer of Ni and SO
4
ions and adsorbed water substitution of Ni(II)-Salophen complex, which was an aro-
molecules around the nanostructures and to intermolecular matic tetradentate Ni(II)-Schiff base complex with the Ni(II)-
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Table 2 Experimental parameters for the products synthesized using (JCPDS 86-2280) and a trace of hexagonal NiS (JCPDS 75-0613),
the Ni(II)-Salophen complex at 180 °C
and did not show any remarkable changes. The corresponding
XRD pattern is shown in Fig. 6c. Therefore, increasing the
amount of Na S O is not effective in the preparation of a pure
2 2 3
Solvent nickel sulfide. As shown in Fig. 6d, if the concentration of
Concentration
of Ni(II) comp.
(mmol)
Ni(II) comp.:
Na
(mole ratio)
2 2 3
S O
Sample
Time/h
Ni(II)-Salophen complex increased to 0.80 mmol (S8), in addition
the peaks associated to Ni S (JCPDS 76-1813), the peaks
3 4
S1
S2
S3
S4
S5
S6
S7
S8
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.80
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
3 : 4
1 : 1
8
15
24
8
15
24
15
15
DMF
DMF
DMF
DMA
DMA
DMA
DMA
DMF
related to rhombohedral NiS (JCPDS 86-2280) and hexagonal
NiS (JCPDS 75-0613) appeared, but with a low intensity.
However, it was concluded that no pure nickel sulfide nano-
structures were produced by using the Ni(II)-Salophen complex
as the precursor under these conditions.
The SEM images of the samples obtained by mixing the Ni(II)-
Salophen complex and Na S O in 15 ml DMF at 180 °C for
2
2 3
8
h (S1), 15 h (S2) and 24 h (S3) are shown in Fig. S2a–c,†
respectively. Fig. S2d–f,† are related to the SEM images of the
prepared Ni S in DMA, while other reaction conditions were
Salen complex. Table 2 shows applied synthesis conditions
such as solvent, time, concentration and mole ratio of the
starting materials, for the preparation of nickel sulfide nano-
structures using the Ni(II)-Salophen complex. It should be
noticed that no products are obtain at 150 °C in the presence
of Ni(II)-Salophen complex and the reaction requires higher
temperature of about 180 °C. This was because of the reso-
3
4
fixed, i.e. (S4), (S5) and (S6). From the image, it can be
observed that the products have an erratic and non-uniform
surface (except for the product obtained after 15 h of reaction
time in DMA (Fig. S2e†) that has a more uniform and homo-
geneous particle size distribution in comparison to samples
obtained after 8 h and 24 h). For these reaction times, the
nanoparticles agglomerated. Fig. 7 presents the SEM images of
the sample obtained by mixing 0.8 mmol Ni(II)-Salophen
complex in 15 ml DMF at 180 °C for 15 h (S8) in which porous
and homogenous structures composed of nanosheets are
observed.
nance effect in the H Salophen structure, which made the
nickel center more stable than in the H Salen structure.
2
2
Fig. 6a presents a typical XRD pattern of the sample
obtained by mixing the Ni(II)-Salophen complex and Na S O
2 3
2
in 15 ml DMF at 180 °C for 15 h (S2). The reflection peaks can
be indexed as the mixture of cubic Ni3S4 (JCPDS 76-1813),
rhombohedral NiS (JCPDS 86-2280) and hexagonal NiS (JCPDS
Surprisingly, from the FTIR spectrum related to the sample
obtained by mixing 0.8 mmol Ni(II)-Salophen complex at
7
5-0613). By changing the solvent to DMA and fixing other
reaction conditions (S5), the XRD pattern indicates that the
product is the mixture of cubic Ni S (JCPDS 76-1813), rhombo-
−
1
1
6
80 °C for 15 h (S8), in Fig. S3,† the bands at 1120 cm and
3
4
14 cm− confirms the existence of sulfate anions, and the
1
hedral NiS (JCPDS 86-2280) and a trace of hexagonal NiS
JCPDS 75-0613), as can be seen in Fig. 6b. Increasing the
mole ratio of Ni(II)-Salophen complex : Na S O from 1 : 1 to
−
1
−1
two remaining bands at 3427 cm and 1612 cm agree with
the adsorbed water molecules, around the as-synthesized
products.
(
2
2 3
3
: 4 in 15 ml DMA (S7) displays that the sample was also com-
If we fix all the reaction conditions, but change the
posed of cubic Ni3S4 (JCPDS 76-1813), rhombohedral NiS
Ni(II)-Salen complex to NiCl
CH COO) ·4H O), the products are a mixture of NiS and Ni S
3 4
2 2 4 2
·6H O, NiSO ·6H O or (Ni-
(
3
2
2
and no one type of pure nickel sulfide nanostructures are
obtained. Therefore, as can be seen in Fig. 8, all the reflection
peaks can be indexed to rhombohedral NiS (JCPDS 86-2280)
and cubic Ni S (JCPDS 76-1813). Furthermore, a trace of
3 4
hexagonal NiS (JCPDS 75-0613) appeared in Fig. 8a and b
Fig. 6 XRD patterns of the products synthesized by using the Ni(II)-
Salophen complex and Na
2
S
2
O
3
as the starting materials under different
Fig. 7 SEM images of the sample synthesized by using 0.80 mmol of
conditions (a) S2 (b) S5 (c) S7 (d) S8.
Ni(II)-Salophen complex (S8).
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anism. Consequently, the reaction processes can be described
as follows:
(
a) The product synthesized from the Ni(II)-Salen complex:
NiðSalenÞ þ 2DMF ! ½NiðSalenÞðDMFÞ2ꢀ ð1Þ
2
ꢁ
½
NiðSalenÞðDMFÞ ꢀ þ 4S2O3
!
2
ꢁ
ð2Þ
ð3Þ
2
2ꢁ
NiS # þ3SO4 þ 4S þ Salen þ 2DMF
NiS þ S ! NiS2
(
b) The products synthesized from the Ni(II)-Salophen
complex:
NiðSalophenÞ þ 2DMF ! ½NiðSalophenÞðDMFÞ2ꢀ
ð4Þ
ð5Þ
ð6Þ
2
ꢁ
½
NiðSalophenÞðDMFÞ ꢀ þ 4S2O3
!
2
Fig. 8 XRD patterns of the products synthesized at 150 °C for 48 h
using (a) nickel chloride (b) nickel sulfate (c) nickel acetate, as the start-
ing material.
2
ꢁ
2ꢁ
NiS # þ3SO4 þ 4S þ Salophen þ 2DMF
Salophen2 þ 2H2O Ð H2-Salophen þ 2OHꢁ
ꢁ
ð7Þ
and a trace of cubic Ni (JCPDS 04-0850) is also observed in
Fig. 8c.
On the basis of the results described above, we propose
the possible growth mechanisms of different products. In the
reaction between tetradentate Ni(II)-Schiff base complexes
and Na S O in the DMF solvent, two solvent molecules
2 2 3
occupy the empty sites of square planar Ni(II)-Salen and Ni(II)-
Salophen complexes at the early stage of the reaction. More-
ð8Þ
ð9Þ
Ni þ 2NiS2 ! Ni3S4
We suppose that the formation mechanism of the nickel
sulfides from NiCl ·6H O, NiSO ·6H O or Ni(CH COO) ·4H
complexes with Na S O are similar to Ni(II)-Salen or Salophen
over, Na
and then the Na SO is further converted to Na S and Na SO
4
2 2 3 2 3
S O decomposes to Na SO and S upon heating,
2
2
4
2
3
2
2
O
2
3
2
2
2
2 3
through
a disproportionation process. In this reaction
complexes, but the required nickel for the production of Ni3S4
is obtained in the DMF solvent that has a larger tendency for
the reduction of Ni , which can be explained in equations as
process, first, NiS was obtained, and then in the reaction with
2
+
sulfur, it was transformed to NiS . The type of nickel sulfides
2
3
8,39
obtained strongly dependent on the starting materials. Using
follows:
Ni(II)-Salen as the precursor, at 150 °C, results in pure NiS
2
Ni2 þ HCONMe2 þ H2O ! Ni þ Me2NCOOH þ 2Hþ ð10Þ
þ
3
7
nanostructure. On the basis of our previous report, it is
2
+
2−
likely that the obtained Ni and SO4 ions and adsorbed
water molecules act as the stabilizing agents for the nano-
structures and create a rigid protective layer around the nano-
Me2NCOOH ! CO2 þ Me2NH
ð11Þ
It was noticeable that using tetradentate Ni(II)-Schiff base
2
+
structures, which could promote shape control on the growth complexes, the reduction of Ni in the DMF solvent was
of NiS nanostructures. However, in the presence of the Ni(II)- impossible because the square planar structure of these com-
2
Salophen complex, as mentioned above, no product was plexes stabilize the central nickel(II) ion very well. According to
obtained at 150 °C and by increasing the temperature to these data, the schematic synthetic process for the preparation
1
80 °C, a mixture of Ni
These changes may be attributed to the decomposition of
Salophen to starting materials, at this temperature, because obtained after a reaction time of 15 h was investigated using
the phenyl ring in the formed 1,2 phenylenediamine was oxi- cyclic voltammetric in a potential range from 0.0 to 0.6 V using
3
S
4
and two types of NiS was obtained. of nickel sulfide compounds is shown in Fig. 9.
The electrochemical behavior of the NiS2 nanostructure
H
2
2
+
−1
dized and caused the reduction of Ni to Ni. Therefore, Ni3S4 different scan rates (5, 10, 20 and 30 mV s ) at room tempera-
nanostructures were produced by combining Ni and two ture and in a 3 M KOH aqueous solution, as shown in Fig. 10.
equivalents of NiS
path using the Ni(II)-Salen complex, nickel production did not wire as counter electrode, an Ag/AgCl as the reference electrode
occur and Ni was not observed in the final product. Another and a working electrode, which was prepared by dropping an
method to prepare Ni is by combining NiS and two equiva- ultrasonically redispersed NiS nanostructure in pure ethanol
lents of NiS. Because the reaction using the Ni(II)-Salen onto the glassy carbon electrode (2 mm diameter). As seen in
complex produced NiS and NiS , but did not produce any Fig. 10, under the influence of applied voltage and with a
Ni
so this method was not suitable for our proposed mech- 5 mV s− scan rate, a broad oxidation peak around 0.35 V and
2
. It is noteworthy that during the reaction A conventional three-electrode cell was used with a platinum
3 4
S
3
S
4
2
2
2
1
3 4
S
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Fig. 9 Schematic diagram illustrating the formation of nickel sulfide
compounds.
2
Fig. 11 Photoluminescence spectrum of the as-prepared NiS nano-
structure, obtained after a reaction time of 15 h, dispersed in methanol.
The inset shows the clearer broad peak in the near IR region.
S (3s, 3p) or Ni (3d) levels down to the Ni–S hybridization
4
0
levels.
The magnetic property of NiS
of pyrite-type materials that exhibit antiferromagnetic pro-
2
belongs to a large system
4
1
perties. In 1961, Neel et al. proposed that fine particles of an
antiferromagnetic material should exhibit magnetic properties
4
2
such as superparamagnetism and weak ferromagnetism. The
Fig. 10 Cyclic voltammetry of the as-prepared NiS
a reaction time of 15 h within a 0.0 to 0.6 V range at different scan rates
5, 10, 20 and 30 mV s−1) at room temperature and in 3 M KOH
2
nanostructure after
magnetic hysteresis loop of the NiS nanostructure synthesized
2
after a reaction time of 15 h, shown in Fig. 12, presents a week
ferromagnetic behavior. This reveals that the as-prepared NiS2
nanostructures have small remanent magnetization, saturation
(
electrolyte.
magnetization and great coercivity (H
c
= 123 Oe), compared
to bulk NiS2 (H = 78 Oe) and similar to the values of NiS
c
2
a reduction peak at about 0.28 V were observed, which
nanostructures without any protective layer, a decrease in the
remanent magnetization and saturation magnetization was
2
+
3+
were associated with the oxidation of Ni to Ni and with
3
+
2+
the subsequent reduction of Ni to Ni , respectively. More-
over, the figure shows that the current intensity and potential
of the redox peaks are increased by increasing the scanning
rate.
−
1
−1 35
observed (M = 0.025 emu g and Ms = 0.292 emu g ).
r
Fig. 11 shows the room temperature fluorescence spectra of
the NiS nanostructure prepared for 15 h, excited at 325 nm.
2
There is a broad emission for the NiS nanostructure in which
2
the top of the emission peak is separated into two peaks
located, respectively, at 400 and 420 nm. The separated peaks
might be attributed to the presence of structural defects
within the sample due to electronic transitions. A second
broad PL emission band with very low intensity, more clearly
shown in inset picture of Fig. 11, was observed in the near IR
region (about 800 nm). The observed emissions can then be
related to the intra-band transitions that occur on the NiS
2
band structure during excitation. Linganiso et al. proposed
that the NiS2 luminescence characterized at wavelengths of
4
00 and 420 nm could result from the de-excitation between S
(3p) levels and Ni (3d) levels, whereas those features around
Fig. 12 A magnetization–magnetic field (M–H) plot at room tempera-
8
00 nm could be attributed to the de-excitations from either ture of the as-prepared NiS
2
nanostructure after a reaction time of 15 h.
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3
7
According to the previous report, the reason for these
4 X. F. Zhou, L. Lin, W. Wang and S. Y. Wang, J. Cryst.
Growth, 2011, 314, 302.
changes may be the size effect and could be mainly attributed
to the presence of the protective layer on the NiS
nanostructure.
2
5 W. Dong, L. An, X. Wang, B. Li, B. Chen and W. Tang,
J. Alloys Compd., 2011, 509, 2170.
3
7,43
6
W. Zhang, L. Xu, K. Tang, F. Li and Y. Qian, Eur. J. Inorg.
Chem., 2005, 2005, 653.
7
H. Pang, C. Wei, X. Li, G. Li, Y. Ma, S. Li, J. Chen and
J. Zhang, Sci. Rep., 2014, 4, 3577.
Conclusions
Although there have been numerous studies on the NiS
2
nano-
8 N. Chen, J. H. Zeng, F. Q. Li, W. Q. Zhang and Y. T. Qian,
J. Cryst. Growth, 2002, 235, 505.
9 S. L. Yang, H. B. Yao, M. R. Gao and S. H. Yu, CrystEng-
Comm, 2009, 11, 1383.
structures precipitation using sodium thiosulphate as a sulfur
source, this study focus on the use of sodium thiosulfate as
both the sulfur source and the stabilizer to produce a new type
of the NiS
magnetic properties. In this work, NiS2 nanostructures have
been successfully prepared via a facile solvothermal method 11 P. G. Niklowitz, P. L. Alireza, M. J. Steiner, G. G. Lonzarich,
2
nanostructures with diverse chemical, optical and 10 K. D. M. Rao, T. Bhuvana, B. Radha, N. Kurra and
N. S. Vidhyadhiraja, J. Phys. Chem. C, 2011, 115, 10462.
using the Ni(II)-Salen complex and Na
The key insights obtained from the our study are that the pure
NiS
Ni(II)-Salen complex, which is an aliphatic tetradentate Ni(II)-
Schiff base complex, but it is difficult to obtain a pure phase of 13 T. Thio and J. W. Bennett, Phys. Rev. B: Condens. Matter,
nickel sulfides using an aromatic tetradentate Ni(II)-Schiff 1995, 52, 3555.
2
S
2
O
3
in DMF solvent.
D. Braithwaite, G. Knebel, J. Flouquet and J. A. Wilson,
Phys. Rev. B: Condens. Matter, 2008, 77, 115135.
2
nanostructure can be synthesized from the precursor 12 G. Krill, P. Panissod, M. F. Lapierre, F. Gautier and
C. Robert, J. Phys., 1976, 37, 23.
base complex, such as the Ni(II)-Salophen complex or simple 14 G. Andersen and P. Kofstad, Oxid. Met., 1995, 43, 173.
mono and bidentate Ni(II) complexes, such as NiCl ·6H O, 15 H. S. Jarret, W. H. Cloud, R. J. Bouchard, S. R. Butler,
2
2
NiSO
4
·6H
2
O and Ni(CH
3
COO)
2
·4H
2
O complexes, under our
C. G. Frederick and J. L. Gillison, Phys. Rev. Lett., 1968, 21,
reaction conditions. It can be pointed out that the existence of
Ni and SO4 ions and adsorbed water molecules, thereby 16 H. M. Mulmudi, S. K. Batabyal, M. Rao, R. R. Pranhakar,
617.
2
+
2−
create a protective layer around the NiS
has been assessed by EDS, FTIR and Raman spectroscopy, in
2
nanostructure, which
N. Mathews, Y. M. Lam and S. G. Mhaisalkar, Phys. Chem.
Chem. Phys., 2011, 13, 19307.
the current study, playing a crucial role in the chemical and 17 S. T. Oyama, J. Catal., 2003, 216, 343.
magnetic properties of the NiS nanostructure. A corollary to 18 R. S. Mane and C. D. Lokhande, Mater. Chem. Phys., 2000,
this rule is that the saturation magnetization (M ) and rema- 65, 1.
nent magnetization (M ) of the as-prepared NiS nanostructure 19 S. Leitz, G. Hodes, R. Tenne and J. Manassen, Nature, 1987,
2
s
r
2
−
1
−1
were found to be 0.292 emu g and 0.025 emu g , respecti-
vely, when compared to bulk NiS and NiS nanostructures 20 P. A. Vigato and S. Tamburrini, Coord. Chem. Rev., 2004,
without any protective layer, resulted in lower values of M and 248, 1717.
. Additionally, it was interesting that a time increment 21 D. A. Atwood, Coord. Chem. Rev., 1997, 165, 267.
higher than 15 h did not structurally and morphologically 22 W. H. Leung, E. Y. Y. Chan, E. K. F. Chow, I. D. Williams
affect the nanostructure. On the basis of these calculations, and S. M. Peng, J. Chem. Soc., Dalton Trans., 1996, 1229.
the choice of the Ni(II)-Salen complex and Na as starting 23 D. A. Atwood and M. J. Harvey, Chem. Rev., 2001, 101, 37.
materials is critical for preparing the target product and the 24 M. Palucki, G. J. Mc Cormick and E. N. Jacobsen, Tetra-
synthetic strategy might lead the way for the preparation of hedron Lett., 1995, 36, 5457.
other inorganic nanomaterials having different properties and 25 T. Yamada, K. Imagawa, T. Nagata and T. Mukaiyama, Bull.
morphologies, by using such precursors. Chem. Soc. Jpn., 1994, 67, 2248.
The authors are thankful to the University of Kashan for 26 W. Adam, J. Jeco, A. Levai, C. Nemes, T. Patonay and
326, 863.
2
2
s
M
r
2 2 3
S O
supporting this work by grant no. 159183/20.
P. Sebok, Tetrahedron Lett., 1995, 36, 3669.
27 B. Ortiz and S. M. Park, Bull. Korean Chem. Soc., 2000, 21,
405.
28 K. Yamamoto, K. Oyaizu and E. Tsuchida, J. Am. Chem.
Soc., 1996, 188, 12665.
Notes and references
1
Y. N. Xia, P. D. Yang, Y. G. Sun, Y. Y. Wu, B. Mayers, 29 S. L. Barnholtz, J. D. Lydon, G. Huang, M. Venkatesh,
B. Gates, Y. D. Yin, F. Kim and Y. Q. Yan, Adv. Mater., 2003,
25, 353.
C. L. Barnes, A. R. Ketring and S. S. Jurisson, Inorg. Chem.,
2001, 40, 972.
1
2
3
J. Hu, T. W. Odom and C. M. Lieber, Acc. Chem. Res., 1999, 30 L. F. Lindoy, W. E. Moody and D. Taylor, Inorg. Chem.,
2, 435. 1977, 16, 1962.
S. Nagaveena and C. K. Mahadevan, J. Alloys Compd., 2014, 31 M. Sonmez, M. R. Bayram and M. Celebi, J. Coord. Chem.,
82, 447. 2009, 62, 2728.
3
5
16752 | Dalton Trans., 2014, 43, 16745–16753
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
3
2 P. Jeevanandam, Y. Koltypin and A. Gedanken, Nano Lett., 39 I. Pastoriza-Santos and L. M. Liz-Marzan, Pure Appl. Chem.,
001, 1, 263. 2000, 72, 83.
3 K. Nakamoto, Infrared Spectra of Inorganic and Coordination 40 E. C. Linganiso, S. D. Mhlanga, N. J. Coville and
2
3
Compounds, John Wiley, New York, 1997.
4 Q. Sun, Vib. Spectrosc., 2009, 51, 213.
5 W. Wang, S. Y. Wang, Y. L. Gao, K. Y. Wang and M. Liu,
Mater. Sci. Eng. B, 2006, 133, 167.
B. W. Mwakikunga, J. Alloys Compd., 2013, 552, 345.
41 M. Matsuura, Y. Endoh, H. Hiraka, K. Yamada,
A. S. Mishchenko, N. Nagaosa and I. V. Solovyev, Phys. Rev.
B: Condens. Matter, 2003, 68, 094409.
3
3
3
3
6 E. Avzianova and S. D. Brooks, J. Aerosol Sci., 2014, 67, 207.
7 R. Akbarzadeh and H. Dehghani, Dalton Trans., 2014, 43,
42 Low Temp. Phys., ed. L. Neel, C. Dewitt, B. Dreyfus and
P. D. De Gennes, Gordon and Beach, New York, 1962,
p. 413.
5
474.
3
8 D. Ajloo, B. Yoonesi and A. Soleymanpour, Int. J. Electrochem. 43 X. H. Chen, H. T. Zhang, C. H. Wang, X. G. Luo and
Sci., 2010, 5, 459. P. H. Li, Appl. Phys. Lett., 2002, 81, 4419.
This journal is © The Royal Society of Chemistry 2014
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