Solvothermal growth of NiS single-crystalline nanorods

Article abstract of DOI:10.1016/j.jallcom.2009.02.154

Nanorods of NiS were successfully prepared by a solvothermal synthetic route using S and Ni powders as reagents in ethylenediamine (en) solvent at the temperature of 200 °C. The as prepared NiS nanorods were characterized by X-ray diffraction (XRD), field

Full text of DOI:10.1016/j.jallcom.2009.02.154

Journal of Alloys and Compounds 481 (2009) 450–454
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Solvothermal growth of NiS single-crystalline nanorods
Pengfei Yanga, B. Songb,c, R. Wua, Yufeng Zhenga, Yanfei Suna, J.K. Jiana,∗
a College of Physical Science and Technology, Xinjiang University, No. 14, Shengli Road, Urumqi, Xinjiang, 830046, PR China
b Institute of Physics, Chinese Academy of Sciences, Beijing 100080, PR China
c Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Nanorods of NiS were successfully prepared by a solvothermal synthetic route using S and Ni powders
as reagents in ethylenediamine (en) solvent at the temperature of 200 ◦C. The as prepared NiS nanorods
were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM)
and transmission electron microscopy (TEM). It was found that the nanorods have diameters and lengths
in the region from 80 nm to 120 nm, and from 2 ␮m to 3 ␮m, respectively. The NiS nanorods are single
crystals with millerite structure. On the basis of the experimental results and corresponding literatures,
a possible growth mechanism of the NiS nanorods crystals is discussed.
Received 23 January 2009
Received in revised form 26 February 2009
Accepted 26 February 2009
Available online 17 March 2009
Keywords:
Nanostructures
Crystal growth
© 2009 Elsevier B.V. All rights reserved.
Scanning and transmission electron
microscopy
1. Introduction
urated with CO2 [16]. Yu and Yoshimura prepared various phases of
nickel sulfides through the reactions between Ni substrate or Ni2+
In the past few decades, inorganic nanocrystals with controlled
size and shape have drawn much attention from both fields of sci-
ence and technology due to their unique properties and potential
applications in nanodevices [1–3]. In particular, one-dimensional
nanostructures such as nanowires, nanorods, and nanotubes are
currently hot focus because of their special properties [4–6].
Metal sulfides are a kind of materials with great technology-
importance. Among them, nickel sulfides have been paid much
attention because of their potential applications [7]. Until now,
many methods have been employed to prepare novel structure of
NiS. It was reported that organic-monolayer-coated NiS nanorods
and triangular nanoprisms were synthesized using a solventless
thermal decomposition of nickel thiolate precursors in the pres-
ence of octanoate [8]. NiS layer-rolled structures was synthesized by
Jiang et al. in aqueous ammonia solution [9], and nickel sulfides was
synthesized in aqueous solution by Jeong and Manthiram [10]. The
solvothermal and hydrothermal methods have been also developed
to prepare nickel sulfide nanocrystals with various morphologies
[11–13]. Qian’s group reported three-dimensional flower-like archi-
tectures of ␤-NiS were successfully prepared via a hydrothermal
route in the presence of thisodium citrate and ammonia [14]. In
addition, multiple morphologies of nickel sulfides, including hier-
archical dendrites, nanobelts, could be directly grown on nickel foils
[15]. Shen et al. synthesized NiS nanorods in hydrazine hydrate sat-
and sulfur in different solvents, and observed NiS nanowhiskers
co-existing with other nickel sulfides [17]. Examining the previous
reports in details, it can be found that the phases and morphologies
would be affected by the form of nickel source and S source.
To the best of our knowledge, no work on the preparation of
nickel sulfide using S powder and Ni powder as reagents has been
reported up to now. In addition, it would be valuable to explore
an additive-free solution route to prepare uniform NiS nanorods.
Herein, we presented a convenient solvothermal route to prepare
single-crystalline nanorods of NiS directly using S and Ni powders
as starting reagents in pure en solvent, and investigated the effects
of the molar ratio of Ni to S on the phases and morphologies of the
products. The probable growth mechanism of the NiS nanorods was
discussed too.
2. Experimental
All reagents are analytic grade and used without further purification. In a typi-
cal procedure, 0.01 mol of S (99.7%) and 0.01 mol of Ni powder (99.5%) were added
into Teflon-lined stainless-steel autoclave filled with en to 80% of its total capacity
(50 ml), and stirred for 15 min. Then the autoclave was sealed and maintained at
200 ◦C for 28 h. After cooled to room temperature naturally, there were black partic-
ipates collected on the bottom of the autoclave, and were repeatedly washed with
deionized water and alcohol to remove soluble inorganic and organic impurities.
The final products were obtained after dried at 50 ◦C for 6 h in atmosphere.
The crystal structures of the products were examined by X-ray diffraction (XRD)
using a Japan Mac science 18kvw X-ray diffractionmeter with Cu K␣ radiation
(ꢀ = 0.1541 nm). The morphologies, microstructures of the products were charac-
terized by a field emission scanning electron microscopy (FE-SEM, Philips XL-30)
equipped with a energy dispersive X-ray spectroscopy (EDX), and a transmission
electron microscopy (TEM, JEOL 2010).
∗
Corresponding author. Tel.: +86 991 8583183; fax: +86 991 8582405.
E-mail address: jikangjian@gmail.com (J.K. Jian).
0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.02.154

P. Yang et al. / Journal of Alloys and Compounds 481 (2009) 450–454
451
Ni9S8, were observed in the XRD pattern. Fig. 2(a) and (b) are low
and high magnification SEM images of the products revealing its
morphological feature. It can be seen that the products consist of
lots of nanorods which are self-assembled to form flower-like mor-
phology. The nanorods are straight with smooth surfaces, and have
diameters in the region from 80 nm to 120 nm, and lengths are from
2 ␮m to 3 ␮m. EDX (Fig. 2(c)) analysis was employed to determine
the chemical compositions of the products. Nickel and sulfide ele-
ments were detected with a molar ratio of about 1:1 (Ni:S), which
further confirms that the products are NiS. The trace amount of
C element in the EDX spectrum originates is from the carbonous
holder which is used to support the product in the test. TEM was
employed to further examine the morphology and the microstruc-
tures of the products. Fig. 3(a) and (b) are TEM morphological image
and the corresponding HRTEM image of an individual nanorod. The
TEM bright field image (Fig. 3(a)) clearly reveals the nanorod is
straight and smooth again. The HRTEM image (Fig. 3(b)) presents
clear lattice strings with spacing of 0.295 nm corresponding to mil-
lerite NiS (1 0 1) plane, indicating the single crystal nature of the
nanorod.
Fig. 1. XRD pattern of the product prepared at 200 ◦C in en with 0.01 mol S and
0.01 mol Ni for 28 h.
It was found that the molar ratio of Ni to S (noted as MNi:MS)
affected the phases and morphology of the products greatly.
Fig. 4(a–d) shows the XRD pattern and the SEM images of the
products prepared at 200 ◦C for 28 h with the molecule ratio of
MNi:MS = 1:3. The XRD pattern shown in Fig. 4(a) can be indexed
to the cubic NiS2 based on the reported data (ICDD PDF No.
65–3325). It should be noted that all the peaks have slight shift
(about 0.03–0.08◦) to low angle compared with the corresponding
standard data, which implies the lattice deformation of the NiS2
3. Results and discussion
Fig. 1(a) shows the XRD pattern of the products prepared at
200 ◦C for 28 h with the molecule ratio of Ni:S = 1. All peaks can
be well indexed to rhombohedral structured NiS with space group
of R3m and the cell parameters a = 9.61 Å, c = 3.16 Å, which shows
a good agreement with the literature data displayed in the lower
pattern of Fig. 1(b) (ICDD PDF No. 12-0041). No obvious diffraction
peaks from other nickel sulfides such as Ni2S3, Ni3S4, Ni3S2 and
Fig. 2. SEM images (a and b) and EDX pattern (c) of the products prepared with 0.01 mol S.

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P. Yang et al. / Journal of Alloys and Compounds 481 (2009) 450–454
Fig. 3. TEM (a) and HRTEM (b) image of the products prepared at 200 ◦C for 28 h with 0.01 mol S and 0.01 mol Ni in en.
prepared here. In addition, there is a very weak peak at 48.79◦,
which may be due to other nickel sulfides with trace amount. The
XRD analysis indicates that the main phase of the product is cubic
NiS2. SEM observations reveal that the sample is composed of NiS2
particles with diameter of 400–500 nm (Fig. 4(c)) and few big well-
faceted crystals with lateral size of about 4 ␮m (Fig. 4(d)).
As shown above, single crystal NiS nanorods were prepared with
0.01 mol S and 0.01 mol Ni in en at 200 ◦C, while cubic NiS2 parti-
Fig. 4. XRD pattern (a) and SEM images (b–d) of the NiS2 prepared at 200 ◦C for 28 h when MNi:MS decrease to 1:3 in en.

P. Yang et al. / Journal of Alloys and Compounds 481 (2009) 450–454
453
Fig. 5. XRD pattern (a) and SEM image (b) of NiS2 prepared by the reaction between 0.01 mol NiS and 0.01 mol S in en at 200 ◦C for 20 h.
cles were synthesized When MNi:MS decreased to 1:3 with other
experimental parameters fixed.
products is cubic NiS2 and the SEM image (Fig. 5(b)) shows the
morphological feature of the products is sub-micron particles. The
results demonstrate that the starting NiS nanorods have been all
converted into cubic NiS2 particles, and both of their phase and mor-
phology changed. In the process, the excessive S2− ions first reacted
with the NiS nanorods surface constantly and NiS2 species was pro-
duced accordingly in local location of the NiS nanorod. Because
of the different crystal structure between rhombohedral NiS and
cubic NiS2, those NiS2 species would divorce from the surface of
NiS nanorods, which destroyed the one-dimensional structure of
NiS nanorods. The NiS species went into en solvent, nucleated and
grew, leading to the formation of NiS2 particles. Thus, NiS2 particles
are the final stable product when S is excessive.
The formation of sulfides under solvothermal growth has been
extensively studied [18–19]. In the solvothermal reaction of sul-
fur with metal powder in organic solvents, it is believed that the
solvent acts as a structure-directing molecule that is incorporated
into the inorganic framework first and then escapes from it to form
nanocrystallites with desired morphologies [20].
Up to now, en, as an important molecule precursor, has been
successfully applied to grow nanorods of some important materials
such as ZnS [21], CdS [22], etc. In our work, Ni2+ ions produced from
Ni powder at the elevated temperature prefer to coordinate with
en molecules to form a relatively complex [Ni(en)3]2+ (the stability
constants log ˇ3 = 18.33) as follows [17].
4. Conclusions
Ni → Ni + 2e−
Ni2++3en → [Ni(en)3]2+
(1)
(2)
In summary, NiS nanorods were prepared directly by a solvother-
mal route using S powder and Ni powder as starting materials in
en at 200 ◦C for 28 h. The X-ray diffraction (XRD) analysis indicated
that the products were rhombohedral structured NiS. SEM and TEM
characterizations revealed that the products were composed of a
large amount of nanorods with high crystallinity. It was found that
the molar ratio of Ni to S affected the phases and morphology of
the products greatly. The en molecules played a structure-directing
role for the growth of the nanorods.
[Ni(en)3]2+ have three coupling rings, and the stability of the com-
plexes is expected to decrease with the increase of the temperature.
At a proper temperature, sulfur may coordinate to the complex,
and formed the inorganic–organic compounds [17]. With rising of
temperature and prolonging of reaction time, en molecules were
released from the inorganic–organic compounds, and then NiS was
formed as follows.
[Ni(en)3]2++S2− → NiS + 3en
(3)
Acknowledgement
According the previous study on the growth of CdS nanorods in
en solvent [22], the formation of NiS nanorods prepared here
may undergo the following stages: (1) the formation of chain-
This work is supported by the National Natural Science Foun-
dation of China (grant No. 50862008), the National Basic Research
Program of China (973 Program) with grant No. 2007CB936300, and
Xinjiang University starting fund (No. BS060110).
like [Ni(en)3]2+ complex through the coordination of en to Ni2+
;
(2) S2+ react with the chain-like [Ni(en)3]2+ complex to form the
inorganic–organic compounds; (3) en molecules were released
from the compounds, and then NiS nanorods were left. The result
presented here demonstrates that en could provide a template for
NiS one-dimensional structure and make the crystals grow pref-
erentially in a certain direction. So it can be concluded that en is
favorable to the formation of NiS nanorods.
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