Nanoscale synthesis and optical features of metallic nickel nanoparticles by wet chemical approaches

Article abstract of DOI:10.1016/j.jallcom.2011.02.164

Nickel nanoparticles (Ni-NPs) were successfully synthesized and attached on indium tin oxide (ITO) substrate by two different methods: from solution reduction process by using sodium borohydride (NaBH₄) as reducing agent in the presence of poly(N-vinilpyrrolidone) (PVP) as protective and stabilizing agents and by polyol process under ethylene glycol EG as a solvent. The results indicated that the samples prepared in aqueous solution show the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of ～31 nm and good size dispersion compared to the preparation in EG that revealed large size ～150 nm. The dynamics of the nanoparticle's growth in the solvents and comparison with optical absorption is presented.

Full text of DOI:10.1016/j.jallcom.2011.02.164

Journal of Alloys and Compounds 509 (2011) 5882–5886
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Nanoscale synthesis and optical features of metallic nickel nanoparticles by wet
chemical approaches
a,∗
b
c
d
Khalid Nouneh , Munetaka Oyama , Raquel Diaz , Mohammed Abd-Lefdil ,
e
a,f
I.V. Kityk , Mosto Bousmina
INANOTECH, Institute of Nanomaterials and Nanotechnology, MAScIR Moroccan Advanced Science, Innovation and Research Foundation, ENSET, Av. Armée Royale, Rabat, Morocco
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8520, Japan
Department of Física Aplicada C-XII, Universidad Autónoma de Madrid, Madrid, Spain
Laboratory of Materials Physics, University Mohammed V, Rabat, Morocco
Electrical Engineering Department, Czestochowa University of Technology, Armii Krajowej 17, Czestochowa, Poland
Hassan II Academy of Science and Technology, Rabat, Morocco
a
b
c
d
e
f
a r t i c l e i n f o
a b s t r a c t
Article history:
Nickel nanoparticles (Ni-NPs) were successfully synthesized and attached on indium tin oxide (ITO) sub-
strate by two different methods: from solution reduction process by using sodium borohydride (NaBH4)
as reducing agent in the presence of poly(N-vinilpyrrolidone) (PVP) as protective and stabilizing agents
and by polyol process under ethylene glycol EG as a solvent. The results indicated that the samples pre-
pared in aqueous solution show the occurrence of face-centered cubic metallic nickel nanoparticles with
a medium diameter of ∼31 nm and good size dispersion compared to the preparation in EG that revealed
large size ∼150 nm. The dynamics of the nanoparticle’s growth in the solvents and comparison with
optical absorption is presented.
Received 11 January 2011
Received in revised form 24 February 2011
Accepted 25 February 2011
Available online 5 March 2011
Keywords:
Nickel nanoparticles
Wet chemical
Surface modification
Nanostructured material
SPR
©
2011 Elsevier B.V. All rights reserved.
Indium tin oxide
1
. Introduction
Various techniques have been used to fabricate Ni-NP such as
modified polyol method [13], sol–gel with additional annealing
treatment [14] and laser ablation technique [15].
In the past two decades, considerable attention has been
devoted to the synthesis of metal nanoparticles (NP) because their
physical and chemical properties differ from those of the bulk
phases and are very promising for optoelectronic, biocatalytic
activity, different kind of sensing etc. [1,2]. The synthesis of metal-
lic NP with homogenous sizes indicates that control of their size
is necessary to evaluate their properties and potential applications
in several areas such as microelectronics, optoelectronics, cataly-
sis, photocatalysis, magnetic materials, information storage, among
others [3–8]. Ni-NPs have also attracted much attention because of
their applications as catalysts, conducting and magnetic materials
On the other side, a variety of reports have focused on the pro-
duction and/or attaching of Ni-NPs on the conductive substrate.
Wu et al. [9] reported fabrication of Ni-NPs by hydrazine reduction
◦
in ethylene glycol at 60 C without soluble polymer as a protec-
tive agent. These results show that the addition of trace of sodium
hydroxide (NaOH) is necessary to produce pure Ni-NP in ethy-
◦
lene glycol and an elevated temperature reaction (at 60 C) was
useful in accelerating the reaction rate. Roy et al. [10] synthe-
sized oxide-coated Ni-NPs with tetragonal crystalline structure by
using borohydride reduction method. The effect of the annealing
in the as-prepared sample was efficient to observe fcc Ni peak and
their subsequent ferromagnetic behavior. Wang et al. [11] prepared
Ni-NPs with mean size equal to about 31 nm covered by hydrox-
yethyl carboxymethyl cellulose (HECMC) layer in solution using
hydrazine reduction. In the latest report, Ni NO with monodis-
perse size (∼50 nm) via a modified hydrazine reduction route in
ethanol without any surfactant introduced well dispersion were
synthesized by Bai et al. [12].
[
9–12]. The synthesis of Ni-NP in pure aqueous solutions is attrac-
tive due to absence of organic pollution and existence of promising
physical and chemical properties.
∗ Corresponding author at: Institute of Nanomaterials and nanotechnology
(
INANOTECH), MAScIR, Rabat, Morocco. Tel.: +212 5 37 57 61 80;
fax: +212 5 37 57 08 80.
E-mail addresses: k.nouneh@inanotech.mascir.com (K. Nouneh),
iwank74@gmail.com (I.V. Kityk).
In previous works, refined seed mediated growth method was
proved to be the effective way to attach densely precious metal
0
925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.02.164

K. Nouneh et al. / Journal of Alloys and Compounds 509 (2011) 5882–5886
5883
on indium tin oxide (ITO) substrate [16–19]. That is, Au, Ag and
Pt NP with moderate distribution which can grow on the ITO sur-
face by the method without using any special binder molecular
agent.
cycles (1, 2, and 3 cycles of 1 h, respectively) and under 12 h and 24 h
seed (Fig. 1D and E, respectively). With one-cycle in situ seed, the
Ni-NPs were found to grow on the surface with a quasi-spherical
shape whose size was extended within the range 8–17 nm. This
result reflects the limited nucleation Ni after 1 h treatment. We also
found that even with increasing in situ time, the attached density
was not highly improved due to the high oxidation ability of Ni-NP
in the seeded solution. To improve the attached density of Ni-NPs
on ITO surface, we proceed to repeat the in situ seeded cycle during
1 h at least two or three times (Fig. 1B and C). When the number
of in situ seeded cycles was increased, the density and the grown
nanostructures of Ni-NPs had significantly changed, and increase in
the grown size of Ni-NPs was observed on the ITO surface keeping a
moderate dispersion as shown in Fig. 1D. The size of each Ni-NP has
varied within the range of 10–30 nm. In contrast, some gathered
clusters of Ni-NPs were observed after six-cycles seeding and if
we keep the ITO substrate during 12 h growth, we observe that,
the surface morphology has been substantially changed to show
the connection or networked nanostructures of Ni-NPs (Fig. 1E).
Fig. 1F shows the FE-SEM image of Ni-NPs/ITO produced by NaBH4
in EG for a growth times of 24 h. It was observed that the attached
density of Ni-NPs was relatively low exhibiting a sparse distribution
of particles on the surface with a large size distribution of about
200 nm.
In the present study, we have found a reproducible synthesis
method based on one-step in situ chemical reduction of Ni(OH)2
−
by using sodium borohydride (NaBH ) in the presence of trisodium
4
citrate as stabilization. The influence of the parameters on the size
of Ni nanoparticles was studied. Such produced samples on ITO
are compared with those obtained by using ethylene glycol (EG) as
both solvent and reducing agent in presence of NaBH . We describe
4
these two methods and we compare the morphology (size, shape
and dispersion) and the physical properties of the as-prepared
samples.
2.
Experimental
The following chemical products were used for synthesis: the nickel nitrate
hexahydrate, Ni(NO3)2, obtained from Aldrich Co., Ltd. while EG, trisodium citrate,
NaBH4 and NaOH, were obtained from Wako Pure Chemicals, Ltd.
ITO thin conducting film deposited on glass has been used as substrate and it was
obtained from Asahi Beer Optical, Ltd. Its sheet resistivity was 150 ꢀ/sq and their
surface sizes are equal to about 1 cm × 1 cm. Before the immersion in Ni precursor
complex solution, the ITO thin films were first cleaned by sonication in acetone and
in ethanol during 15 min each, respectively. After flashing the different ITO plate by
pure water, it was then cleaned by sonication in ultra pure water for 15 min. This
procedure was repeated two times in order to remove dust. Finally, the ITO piece
was dried with a stream of nitrogen gas before use.
The grazing X-ray diffraction (XRD) patterns of the Ni-NPs
on ITO samples are shown in Fig. 2A. We should notice that
◦
the diffraction peaks of ITO are dominant. Peaks at 2ꢂ = 41.89 ,
5
2.1. Growth of nickel by NaBH4 in aqueous solution
◦
8.95 are assigned to hcp Ni (0 0 2) and (0 1 2) planes (JCPDS data
A piece of pre-treated ITO was immersed in Ni precursor complex solution com-
No. 45-1027), respectively. While a peak at 76.31◦ is attributed
posed of 0.5 ml of 0.01 M Ni(NO3)2, 0.1 ml of 0.01 M trisodium citrate and 20 ml H2O.
After stabilizing (∼15 min), 1 ml of fresh ice-cold 0.1 M NaBH4 aqueous solution was
added into the Ni precursor complex solution while stirring for 30 s and then keep
to (2 2 0) fcc Ni phase (JCPDS data No. 04-0850). This indicates
that both hcp and fcc Ni-NPs were simultaneously synthesized
by NaBH4 in aqueous solution case. In addition, we should note
◦
it for 1 h in 28 C. The substrate was taken out of the Ni precursor complex solu-
◦
tion, thoroughly rinsed with distilled water and dried with nitrogen. Three samples
a peak at 2ꢂ = 37.65 that can be assigned to hexagonal NiO2
(
2
indicated by A, B, and C) have been modified using the repeated seeding cycles (1,
and 3 cycles), respectively by using the same process as described above. Two
nickel oxide (0 0 6) plane (JCPDS data No. 85-1977). In the case
of Ni-NPs prepared in EG, the peaks are less pronounced due
to the large thickness of organic films deposited on the ITO
substrate.
Chemical composition of Ni-NPs/ITO was analyzed using the
X-ray energy dispersive spectrometry order to confirm the pres-
ence of Ni (Fig. 2B). Peaks of Si and Ca are originated from the glass
substrate on which ITO and Ni were successively deposited. While
peaks of In and Sn are due to ITO films.
It is known that the wavelength of surface plasmon resonance
ꢁSPR is sensitive to various parameters like particle size and shape,
environment and inter-particle interactions nature of substrate,
where the resonance band becomes broader as its refractive index
increases [20]. The absorbance spectra of Ni-NP grown on ITO
others samples (indicated by D and E) were immersed during 12 and 24 h, respec-
tively without disturbance. During growth process, the temperature was fixed at
◦
2
8
C and we have observed that the Ni precursor complex solution color turned
from colorless to black upon reduction.
2.2. Growth of nickel nanoparticles by NaBH4 in EG
In this case, an appropriate amount of nickel nitrate (0.01 M) hexahydrate was
dissolved in 20 ml of capped bottle EG with constant magnetic stirring and heat-
ing. Then, an appropriate amount of 0.055 g of poly(N-vinilpyrrolidone) (PVP) and
◦
1
1
.0 M NaOH solution (100 ␮l) were added in sequence. At a temperature of 60 C,
ml of fresh ice-cold 0.1 M NaBH4 aqueous solution was added into the Ni precursor
complex solution and then after 30 s, the heated system turned off. And the solu-
tion cooled to room temperature and kept it for 1 h. The ITO substrate was then
immersed in this precursor solution for different growth times (1 h, 2 h, 6 h, 12 h
and 24 h). In this case we have observed the attachment only after 24 h growth
(150 ꢀ/sq) under various seeding cycles are reported in Fig. 3.
(
sample F).
The size and morphology of the Ni-NP grown on ITO surface were moni-
All the spectra present an absorption edge within 374–422 nm
spectral range, depending on the sample, which corresponds to
the surface plasmon resonance (SPR) of Ni. This is in a good
agreement with work of Amekura et al. [21], who reported the
convening experimental observation and theoretical analysis of
SPR in Ni nanoparticles deposited on silica glass. For nickel (1
cycle, curve A), the SPR energy is quite lower on energy than the
other samples, but it is quite higher than the results observed
by Yeshchenko on Ni/SiO2 [14]. In Table 1, we report a compar-
ison between our ꢁSPR values and the literature. We also notice
that the absorbance increases with increasing seeding cycle’s
number, which can be explained by the increase of the den-
sity and the size of the attached Ni-NPs on ITO surface. This is
caused by inter-particle interactions which determine the effec-
tive masses of electrons and corresponding plasmons. The observed
broadening of SPR bands is due to the large damping of free
electrons motion in nickel compared to electron motion in noble
metals.
tored with field emission scanning electron microscopy (FE-SEM, JSM-7400F; JEOL).
The optical spectrophotometer, U4100 Hitachi Ltd. with spectral resolution about
0
.1 nm, was used to observe the absorption spectra of the Ni-NPs/ITO.
The Grazing X-ray diffraction pattern of Ni-NPs attached ITO was analyzed
by Rigaku D/max-2400 diffractometer using CuK˛-1 radiation ꢁ = 0.15406 nm in
Bragg–Brentano geometry. The background was eliminated in the intensity deter-
mination. Silicon powder with a purity of 99.9999% was used as an external standard
material to calibrate the peak positions and intensities.
So for the first time we realized in situ attaching Ni-NPs on ITO substrate. We
reported the results obtained with two different ways, from solution reduction pro-
cess by using NaBH4 as reducing agent in the presence of PVP as protective and
stabilizing agents and by polyol process under ethylene glycol EG as a solvent.
This difference may be caused by different polarizabilities of the particle in the
solvants.
3
. Results and discussion
Fig. 1A–C shows the FE-SEM images of the Ni-NPs grown on
the ITO surfaces, which were prepared using the repeated seeding

5
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K. Nouneh et al. / Journal of Alloys and Compounds 509 (2011) 5882–5886
Fig. 1. (A–E) The FE-SEM images of the Ni-NPs grown on the ITO surfaces in aqueous solution, which were prepared using the repeated growth cycles of 1 h (A), 2× 1 h (B)
and 3× 1 h (C). (D–E) Ni-films on ITO under 12 h and 24 h, respectively. (F) Ni-NPs on ITO under 24 h growths, prepared in ethylene glycol.
To demonstrate the dynamics of the nanoparticle’s growth and
absorption on the different stages of the nanocrystallite growth the
corresponding data are presented in Figs. 4 and 5. Following these
data one can clearly see that the increasing time of the sample’s
treatment leads to the shift of the average size distribution towards
the higher values. And the corresponding absorption spectra do not
show any evidence of the maxima typical for the Ni-NP deposited
on the surfaces (compare Fig. 3). So the intermolecular interactions
within the colloids do not give sufficient contribution to the SPR for
the Ni-NP samples.
At the same time due to interaction of the SPR excitations
with the lattice phonons of the substrate we have some con-
Table 1
ꢁSPR wavelength values as reported by other authors and in the present study.
Sample
Average Ni-NPs size (nm)
ꢁSPR (nm)
Reference
Ni/SiO2
Ni/SiO2
Ni EG
1.5
20
8
376
358–382
355
[21]
[14]
[15]
This work
Fig. 2. (A) X-ray diffraction spectra of Ni/ITO prepared in aqueous solution (sample
C) and in ethylene glycol (sample F). (B) X-ray energy dispersive spectrometry of
the sample Ni/ITO (sample C).
Ni/ITO
10–40
374–422

K. Nouneh et al. / Journal of Alloys and Compounds 509 (2011) 5882–5886
5885
Fig. 5. UV–visible of the Ni-NPs in aqueous solution, at different growth times 1 h,
h, 3 h, 12 h and 24 h.
2
Fig. 3. UV–visible of the Ni-NPs grown on the ITO surfaces in aqueous solution,
which were prepared using the repeated growth cycles of 1 h (A), 2 ×1 h (B) and
3
×1 h (C). Curves D and E represent the absorbance for a continuous growth time
of 12 h and 24 h, respectively. Curve F represents the case of Ni-NPs produced by
NaBH4 in ethylene glycol under 24 h growth.
tral maximum of the SPR in the spectral wavelengths. One can
expect that the proposed materials may be very sensitive to the
polarization of the environment and after appropriate referenc-
ing they may determine the external polarizabilities. The latter
may be promising for nonlinear optical and spintronics applica-
tions [22,23]. It is also important that additional broadening is the
SPR spectra was observed in the Ag NP [2], which confirm the
same origin of the broadening and possible attraction to the ITO
substrate.
tribution to the broadening originating from electron–phonon
interactions and in particularly of the anharmonic ones [22]. The
relatively large sheet resistance of the ITO creates an effective
carrier for the carriers forming the SPR excitations. As a con-
sequence the border between the ITO and Ni-NP is partially
polarized forming an effective potential which shift the spec-
Fig. 4. Nickel nanoparticles size distribution in aqueous solution, at different growth times 1 h, 2 h, 3 h, 12 h and 24 h.

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K. Nouneh et al. / Journal of Alloys and Compounds 509 (2011) 5882–5886
4
. Conclusion
been also done in the framework of the Morocco-Hispano Univer-
sity collaboration by the AECI Project No. A/027536/09. The authors
thank also the Hassan II Academy of Science and Technology.
Spherical nickel nanoparticles deposited on ITO surface were
successfully fabricated using a wet chemical solution method. For
the first time we realized in situ attaching Ni-NPs on ITO substrate.
We report the results obtained with two different ways, from solu-
tion reduction process by using NaBH4 as reducing agent in the
presence of poly(N-vinilpyrrolidone) as protective and stabilizing
agents and by polyol process under ethylene glycol as a solvent.
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