Preparation of nanosized nickel particles by hydrothermal method

Article abstract of DOI:10.1246/cl.2004.146

The reduction of Ni (OH)₂ to ultrafine Ni metal powder under hydrothermal condition with ethylene glycol was investigated. The reduction proceeded gentlly at about 160°C and did not pollute the environment. The particle size obtained was about

Full text of DOI:10.1246/cl.2004.146

146
Chemistry Letters Vol.33, No.2 (2004)
Preparation of Nanosized Nickel Particles by Hydrothermal Method
Feibao Zhang, Yuantao Chen, Jiazheng Zhao,y and Hulin Liꢀ
College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China
yState Key Laboratory, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
(Received October 21, 2003; CL-030993)
The reduction of Ni (OH) 2 to ultrafine Ni metal powder un-
der hydrothermal condition with ethylene glycol was investigat-
ed. The reduction proceeded gentlly at about 160 ꢁC and did not
pollute the environment. The particle size obtained was about
10 nm.
Ultrafine Ni metal powders are attracting more and more at-
tention in recent years in the field of function materials, i.e. cat-
alysts, magnetic materials, conducting inks, and ferrofluids.1–3
Various preparation methods have been reported. Derry and
Whittemore4 reported at the second International Symposium
of Hydrometallurgy in 1973 that Ni powders were obtained in
a pressure reduction system from slurries of Ni (OH) 2 generated
from sulfate solution using H2 at 170 to 250 ꢁC. Che et al.5 got
submicron particles by hydrogen reduction at temperatures over
300 ꢁC. Hedge et al.6 had found that nanocrystalline nickel pow-
der could be produced in ethylene glycol using hydrazine as the
reducing agent at elevated temperature. Chou and Huang7 have
developed a method by which nanosized nickel colloid was syn-
thesized by using nickel chloride as the precursor, hydrazine as
the reducing agent, and palladium as the nucleation agent. All of
these methods were very useful and of widespread importance,
but some limitations such as the elevated temperature, high cost
or low yield should be circumvented for practical utilities.
Therefore, developing a synthesis method of ultrafine Ni metal
powder with mild condition and low cost is still the most impor-
tant goal of material scientists. In this paper, we report a novel
strategy to synthesize Ni powders under hydrothermal condi-
tionsꢁin ethylene glycol. The reduction proceded gently at about
160 C and no other poisonous reagents were needed. To our
knowledge, there are few reports about synthesizing Ni powders
based on the hydrothermal method. This method may be a new
way to synthesize metal nanoparticles.
20
30
40
50
60
70
80
90
2θ/degree
Figure 1. XRD patterns for the sample.
acterized using an X-Ray diffractometer as shown in Figure 1.
All these diffraction peaks, including not only the peak po-
sitions but also their relative intensities, can be perfectly indexed
into the crystalline structure of Ni. The result is in accordance
with the standard spectrum (JCPDS, NO. 04-0850).
The spherical size of the crystalline was calculated from the
major diffraction peak (111) using the well-known Scherrer’s
formula (Eq 1), by assuming the factors, viz. instrumental
0:89ꢁ
D ¼
ð1Þ
B cos ꢂ
Where ꢁ is wavelength (1:5418 ꢃ 10ꢄ10 m), B is the full
width at half maximum of the peak, and ꢂ is the Bragg’s angle
of the XRD peak. The grain size was found to be about 10 nm.
The morphology of the powders was observed by TEM as
shown in Figure 2. The Ni powders were dispersed very well
and the morphology of which could be obviously observed. It
can be seen that Ni crystals are uniformly spherical and their
average size is about 10 nm, which is consistent with that esti-
mated from the XRD data. The selected area electron diffraction
A mixture of NiCl2ꢂ6H2O (0.5 g) and NaOH was put into a
Telfon-lined autoclave of 30-mL capacity. The mole ratio of the
alkali to nickel, [OH]/[Ni], was 4.0. The autoclave was filled
with ethylene glycol up to 80% of its capacity, maintained at
160 ꢁC for 12 h, and then cooled to room temperature on stand-
ing. The products were filtered and washed with distilled water
and absolute ethanol in sequence. Finally the black products
ꢁ
were dried at 50 C. The structure and morphology properties
of products were characterized by several techniques. Powder
X-ray diffraction (XRD) data were collected using a Rigaku
D/MAX 2400 diffractometer with Cu Kꢀ radiation
ꢀ
(ꢁ ¼ 1:5418 A). A transmission electron microscope (TEM: Hi-
tachi 600, Japan) was used to observe the morphology and de-
gree of agglomeration.
Figure 1 shows the X-ray powder diffraction pattern of the
product. It is identified as a pure Ni powders (JCPDS NO. 04-
0850). The crystalline structure of Ni powders was further char-
(A)
(B)
(C)
Figure 2. TEM images of Ni powders. (A) Light field; (B) dark
field; (C) SAED.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.2 (2004)
147
(SAED) results taken from one of Ni powders indicate that the
Ni is monocrystalline and match well with the XRD results.
The dark field confirmed that the obtained Ni nanocrystals had
well-defined crystallinity.
lize the metal powders. A great advantage of the method is that
pure Ni powders can be produced without using Pt or Pd catalyst
for nucleation. Given the generality of this approach, we hope to
extend our synthetic method to prepare other metal nanoparti-
cles.
Hegde et al.7 have prepared Ni nanoparticles in the Ni
ꢁ
(OH)2/EG/PVP system in an oil bath at about 200 C using Pt
or Pd catalyst for nucleation and PVP as a stabilizer of small
Ni metal particles. They succeeded in preparing nickel nanopar-
ticles having spherical shape. In contrast with their work, Ni
powders were prepared with ethylene glycol hydrothermally in
our study. The particle size of the Ni nanoparticles prepared in
present work was ten times smaller than those reported by
Hedge. We also carried the experiment with different mole ratio
of the alkali to nickel, [OH]/ [Ni]. It should be emphasized that
Ni particles can be formed via the hydrothermal method unless
the mole ratio of the alkali to nickel is higher than 4.0. Thus
the growth process of Ni particles by the hydrothermal method
would be different from that of the conventional method. Hydro-
thermal method may cause different nucleation and growth of Ni
particles with excessive alkali.
This work was supported by the National Natural Science
Foundation of China.
References
1
‘‘Materials Handbook,’’ ed. by G. S. Brady, H. R. Clauser,
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H. Weller, Angew. Chem., Int. Ed. Engl., 32, 41 (1993).
R. Derry and R. G. Whittemore, ‘‘2nd Int. Symp. Hydromet-
alurgy,’’ (1973), p 42.
5
6
S. L. Che, K. Takada, K. Takashima, O. Sakurai, K.
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33 (1997).
In conclusion, this report proposed a simple one-step way to
synthesize Ni particles. Well-dispersed Ni powders with size 10–
20 nm and spherical shape have been prepared based on the hy-
drothermal method. No polyol has been used to protect or stabi-
7
K. S. Chou and K. C. Huang, J. Nanopart. Res., 3, 127
(2001).
Published on the web (Advance View) January 14, 2004; DOI 10.1246/cl.2004.146