Synthesis and characteristics of NiO nanoparticles by thermal decomposition of nickel dimethylglyoximate rods

Article abstract of DOI:10.1016/j.ssc.2006.01.031

Arrays of NiO nanoparticles have been synthesized via thermal decomposition of nickel dimethylglyoximate precursor. The structure, morphology and properties of the products were characterized by XRD, TEM, SAED and UV-vis spectrophotometry. TEM reveals that one-dimensional arrays consist of NiO nanoparticles. XRD and SAED indicate that these NiO nanoparticles crystallize with a polycrystalline structure. The optical absorption band gap of NiO nanoparticles is 3.51 eV.

Full text of DOI:10.1016/j.ssc.2006.01.031

Solid State Communications 137 (2006) 581–584
www.elsevier.com/locate/ssc
Synthesis and characteristics of NiO nanoparticles by thermal decomposition
of nickel dimethylglyoximate rods
a
a
b
Xueliang Li a, , Xiaoxi Zhang , Zirong Li , Yitai Qian
*
a School of Chemical Engineering, Hefei University of Technology, Hefei, Anhui 230009, People’s Republic of China
b Structure Research Laboratory, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
Received 27 August 2005; received in revised form 15 January 2006; accepted 19 January 2006 by B.-F. Zhu
Available online 7 February 2006
Abstract
Arrays of NiO nanoparticles have been synthesized via thermal decomposition of nickel dimethylglyoximate precursor. The structure,
morphology and properties of the products were characterized by XRD, TEM, SAED and UV–vis spectrophotometry. TEM reveals that one-
dimensional arrays consist of NiO nanoparticles. XRD and SAED indicate that these NiO nanoparticles crystallize with a polycrystalline structure.
The optical absorption band gap of NiO nanoparticles is 3.51 eV.
q 2006 Elsevier Ltd. All rights reserved.
PACS: 81.10.Jt; 81.70.Pg
Keywords: A. Nanostructures; A. Nickel oxide; B. Decomposition experiments; C. X-ray diffraction; D. Optical properties
1. Introduction
methods have been attempted to synthesize nanostructure
nickel oxide, such as thermal decomposition [14], sputtering
[15], electrodeposition [16], AAM template synthesis [17] and
sol–gel techniques [18]. Zhang et al. [19] have synthesized NiO
fibres in the presence of surfactant PVP. Xu et al. [20] have
synthesized NiO nanorods by using precursor thermal
decomposition in the presence of surfactant nonyl phenyl
ether (NP-9/5) and NaCl flux at 1173 K. However, few
attempts have been made to prepare one-dimensional arrays
of NiO nanoparticles. Furthermore, 1D arrays of nanoparticles,
which possess both the advantages of nanoparticles such as
high surface areas and quantum size effects and the function of
arrays, would hold excellent properties and potential appli-
cation. Hence, it is of importance and significance to synthesize
1D arrays of NiO nanoparticles with a facile pathway.
Nanomaterials with the size of 1–100 nm have attracted
considerable interest due to the difference of properties from
bulk phases arising from quantum size effect. In recent years,
one-dimensional (1D) nanostructures, such as nanorods,
nanowires and nanotubes, have received intensively attention
because of both their fundamental importance and the wide
range of their potential applications in many areas [1,2].
Various methods have been developed to fabricate 1D
structured materials such as laser ablation method, CVD
method, hydrothermal method, structure-directing soft or hard
templates, and the self-assembly of spherical nanoparticles by
oriented attachment [3–5].
NiO, as one of the relatively few metal oxides that tend to be
p-type, is a stable wide band gap material and can be used as a
transparent p-type semiconducting layer [6]. As a kind of
functional material, NiO has received much attention recently
due to its attractive application in catalysts, battery cathodes,
gas sensors, electrochromic films, magnetic materials, active
optical fibers and fuel cell electrodes [7–13]. Therefore, many
In this article, we develop a simple and facile method for the
fabrication of arrays of NiO nanoparticles by the thermal
treatment of the rodlike nickel dimethylglyoximate precursor,
and discuss the crystal structure, morphology and optical
properties of 1D arrays of NiO nanoparticles. This method
requires neither complex apparatus, nor any catalysts or any
surfactants as usually needed in other methods.
*
Corresponding author.
2. Experimental details
E-mail address: xueliangli2005@163.com (X. Li).
All the analytical chemicals were purchased from the
commercial market and used without further purification. In a
0038-1098/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2006.01.031

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X. Li et al. / Solid State Communications 137 (2006) 581–584
typical synthesis, 6 mmol of dimethylglyoxime was dissolved
into 25 mL of ethanol to give a homogenous solution. Then this
solution was added dropwise into 25 mL of aqueous solution
containing 3 mmol NiSO4 under magnetic stirring for 1 h. Red
flocculates of nickel dimethylglyoximate were filtered, washed
with distilled water and absolute ethanol several times to
remove the impurities, and then dried in an oven at 80 8C for
4 h. Finally, the obtained nickel dimethylgloximate precursor
was heated to 400 8C at a heating rate of 5 8C minK1 and
calcining at 400 8C for 2 h.
and w385 8C. The first weight loss is mainly attributed to
the decomposition of the nickel dimethylglyoximate, whereas
the second one may be ascribed to two factors. One is the
decomposition of the nickel dimethylglyoximate and the other
is due to the air oxidation of Ni above 300 8C. Experiment
results show the decomposition mixture contains Ni, NiO and
nickel precursor at 300 8C. The total weight loss is about
25.51%, which is close to the theoretical value. The reaction is
completed by 385 8C. Therefore we choose 400 8C as the
calcining temperature.
The crystalline phases of the samples were identified by
X-ray diffraction (XRD) using a rotating-target Japan Rigaku
D/Max-rB X-ray diffractometer equipped with graphite
Fig. 2 shows the XRD patterns of the as-calcining 1D arrays
of NiO nanoparticles at different conditions. The diffraction
angle and intensity of the characteristic peaks of the samples
are well consistent with those of the standard JCPDS card no.
47-1049. All diffraction peaks can be perfectly indexed to the
cubic structure crystalline NiO and readily indexed as (111),
(200) and (220) crystal planes. No characteristic peaks of
impurities or other precursor compounds were observed. XRD
peaks are markedly broadened at relatively lower temperature
and in shorter time, which suggests that the particle size of as-
calcining NiO increases with increasing the calcining time and
temperature. Evaluated from the Debye–Scherrer formula, the
average sizes of the obtained NiO particles at different
calcining temperature and time are 17.6, 45.2, 35.3, 70 nm,
respectively.
˚
monochromatized Cu Ka radiation (lZ1.5406 A). The oper-
ation voltage and current were 40 kV and 80 mA, respectively.
The morphologies of the samples were examined by transition
electron microscopy (TEM, Hitachi, Model H-800) with an
accelerating voltage of 200 kV. TEM samples were prepared
by dropping the ethanol dispersion on a carbon-coated copper
grid. Thermal gravimetric analysis (TGA) of the as-syn-
thesized sample was carried out on a Shimadzu TA-50H
thermal analyser at a heating rate of 10 8C minK1 from room
temperature to 800 8C in air. Optical absorption spectrum was
recorded on a Shimadzu UV-2401PC UV–vis recording
spectrophotometer in ethanol with the wavelength rang of
200–800 nm at room temperature.
The TEM images of the precursor and the oxide are shown
in Fig. 3. Fig. 3(a) is a TEM image of the as-synthesized
precursor at room temperature. It can be seen that the nickel
dimethylglyoximate precursor displays rodlike morphology
with an average diameter of 400 nm and length of several
micrometers. Fig. 3(b) and (c) shows the morphology of NiO
obtained at 400 8C for 2 h, and NiO nanoparticles connected
along the original directions of the rodlike precursor are
observed. The observed average particle size is about 18 nm,
which is consistent with the XRD result. The arrays of NiO
nanoparticles could be ascribed to the shape confinement of the
precursor. The inset of Fig. 3(c) is the corresponding selected
area diffraction (SAED) pattern of the sample. ED patterns
3. Results and discussion
The rod-like nickel dimethylglyoximate precursor was
obtained by the reaction between NiSO4$6H2O and dimethyl-
glyoxime in ethanol and aqueous solution. Then 1D arrays of
NiO nanoparticles were obtained by calcining the precursor. To
study the influence of temperature on morphologies of NiO,
some experiments were investigated by calcining the precursor
at different conditions.
The thermal behavior of the obtained nickel dimethylglyox-
imate precursor was investigated with thermal gravimetric
analysis (see Fig. 1). The TG curve shows that nickel
dimethylglyoximate precursor starts to decompose at about
255 8C. The major weight loss happens rapidly between w300
Fig. 2. XRD patterns of NiO samples calcining at different conditions. (a)
Fig. 1. TGA curve of the obtained nickel dimethylglyoximate precursor.
400 8C, 2 h; (b) 400 8C, 4 h; (c) 500 8C, 2 h; (d) 700 8C, 2 h.

X. Li et al. / Solid State Communications 137 (2006) 581–584
583
in the UV region is attributed to band gap absorption in NiO
[21]. It is well known that optical band gap (Eg) can be
calculated on the basis of the optical absorption spectrum by
the following equation
n
ðAhnÞ Z BðhnKEgÞ
where hn is the photo energy, A is absorbance, B is a constant
relative to the material and n is either two for direct transition
or 1/2 for an indirect transition [22]. Hence, the optical band
gap for the absorption peak can be obtained by extrapolating
the linear portion of the (Ahn)n–hn curve to zero. The inset of
Fig. 4 shows the (Ahn)2 versus hn curve for the sample. The
band gap of the NiO particles is about 3.51 eV, which is similar
to the value (3.55 eV) reported by Boschloo [23]. No linear
relation was found for nZ1/2, suggesting that the as-prepared
NiO nanoparticles are semiconducting with direct transition at
this energy. In the long-wavelength side, the long tail of the
absorption is probably due to the scattered radiation of nickel
oxide clusters of nanoparticles.
Fig. 3. TEM images and SAED pattern of samples: (a) the precursor of nickel
dimethylglyoximate; (b and c) NiO obtained at 400 8C for 2 h, inset was the
corresponding SAED pattern; (d) NiO obtained at 400 8C 4 h; (e) NiO obtained
at 500 8C for 2 h, inset was the image with large magnification; (f) NiO
obtained at 700 8C for 2 h.
4. Conclusions
In summary, a simple and facile method to synthesize arrays
of NiO nanoparticles by the thermal treatment of the rodlike
nickel dimethylglyoximate precursor is developed. The
calcining time and temperature have less effect on the
morphology of NiO arrays. With increasing the calcining
time and temperature, the size of particles became larger. The
optical absorption band gap of the NiO nanoparticles was
3.51 eV. We expect that this method of precursor thermal
decomposition can be extended to synthesize 1D arrays of
other kinds of metal oxides using corresponding precursors.
recorded on different particles were essentially the same and
the diffraction rings match the XRD peaks very well, which
indicates that the nanoparticles are polycrystalline. To study
the thermal stability of one-dimensional NiO arrays, we
calcined nickel dimethylglyoximate precursor at different
time and temperature. From the Fig. 3(d)–(f), we can see that
the size of the NiO nanoparticles increases as the increase of
calcining time and temperature. When the calcining tempera-
ture reaches 700 8C, the image indicates that NiO nanoparticles
present apparent aggregation due to sintering (see Fig. 3(f)).
The calcining temperature and time have less effect on the
morphology of the NiO arrays and the particle sizes of different
samples are consistent with the XRD results, respectively.
Fig. 4 shows the optical absorption spectrum of the NiO
nanoparticles calcined at 400 8C for 2 h. The strong absorption
Acknowledgements
This work was financially supported by the Natural Science
Foundation of Anhui Province of China (No. 050440303). The
author would thank Mr Shupei Tang and Mr Anping Liu for
their help in XRD and TEM measurements, respectively.
References
[1] S. Iijima, Nature 354 (1991) 56.
[2] M.H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber,
R. Russo, P. Yang, Science 292 (2001) 1897.
[3] X.Y. Chen, X.X. Li, Y. Jiang, C.W. Shi, X.L. Li, Solid State Commun.
136 (2005) 94.
[4] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim,
H. Yan, Adv. Mater. 15 (2003) 353.
[5] X.Y. Chen, X.F. Zhang, C.W. Shi, X.L. Li, Y.T. Qian, Solid State
Commun. 134 (2005) 613.
[6] H. Sato, T. Minami, S. Takata, T. Yamada, Thin Solid Films 236
(1993) 27.
[7] M.M. Natile, A. Glisenti, Chem. Mater. 15 (2003) 2502.
[8] C.H. Chen, J. Liu, M.E. Stoll, G. Henriksen, D.R. Vissers, K. Amine,
J. Power Sources 128 (2004) 278.
Fig. 4. Optical absorption spectrum and (Ahn)2–hn curve (inset) for NiO
[9] I. Hotovy, J. Huran, L. Spiess, S. Hascik, V. Rehacek, Sens. Actuators, B
57 (1999) 147.
nanoparticles.

584
X. Li et al. / Solid State Communications 137 (2006) 581–584
[10] H. Kamal, E.K. Elmaghraby, S.A. Ali, K. Abdel-Hady, J. Cryst. Growth
262 (2004) 424.
[16] K. Nakaoka, J. Ueyama, K. Ogura, J. Electroanal. Chem. 571 (2004)
93.
[11] T. Seto, H. Akinaga, F. Talano, K. Koga, T. Orii, M. Hirasawa, J. Phys.
Chem. B 109 (2005) 13403.
[17] Y. Lin, T. Xie, B.C. Cheng, B.Y. Geng, L.D. Zhang, Chem. Phys. Lett.
380 (2003) 521.
[12] P. Lunkenheimer, A. Loidl, Phys. Rev. B 44 (1991) 5927.
[13] R.C. Makkus, K. Hemmes, J.H.W.D. Wir, J. Electrochem. Soc. 141
(1994) 3429.
[18] Y.R. Park, K.J. Kim, J. Cryst. Growth 258 (2003) 380.
[19] C.F. Zhang, J. Zhan, J.H. Wu, C.J. Li, Trans. Nonferrous Met. Soc. China
14 (2004) 713.
[14] X. Wang, J.M. Song, L.S. Gao, J.Y. Jin, H.G. Zheng, Z.D. Zhang,
Nanotechnology 16 (2005) 37.
[20] C.K. Xu, G.D. Xu, G.H. Wang, J. Mater. Sci. 38 (2002) 779.
[21] D. Adler, J. Feinlieb, J. Phys. Rev. B 2 (1970) 3112.
[22] A. Hagfeldt, M. Gratzel, Chem. Rev. 95 (1995) 49.
[23] G. Boschloo, A. Hagfeldt, J. Phys. Chem. B 105 (2001) 3039.
[15] Y.M. Lu, W.S. Hwang, J.S. Yang, H.C. Chuang, Thin Solid Films
420–421 (2002) 54.