Binary roles of schiff bases as capping agent and precursor for synthesis of metallic nickel ultrafine nanoparticles

Article abstract of DOI:10.1080/15533174.2013.862824

This study focused on the synthesis and characterization of nickel nanoparticles by simple precipitation method. The various Schiff bases such as ethylenediamine (acacen), 1,3-propylenediamine (acacpn), and butane-1,4-diamine (acacbn) acetyl acetonate were prepared and were used for preparing of nickel-Schiff base complexes and then, these complexes as precursor were reduced in the presence of KBH₄, for the first time. In addition, the anti-aggregation effect of prepared Schiff bases was compared with common surfactants and results demonstrated that the huge ligands can be considered as novel surfactants. The obtained nickel nanoparticles were characterized by XRD, TEM, HRTEM, FT-IR, SEM, and EDS.

Full text of DOI:10.1080/15533174.2013.862824

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Binary Roles of Schiff-bases as Capping Agent and Precursor for Synthesis of Metallic Nickel
Ultrafine Nanoparticles
F. Motahari a, M.-R. Mozdianfard a, F. Soofivand b and M. Salavati-Niasari *,b
a Department of Chemical Engineering, Faculty of Engineering, University of Kashan, Kashan, P. O. Box.
87317-51167, I. R. Iran.
b Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box.87317-51167,
I. R. Iran.
* Corresponding author. E-mail: salavati@kashanu.ac.ir (M. Salavati-Niasari)
This study focused on the synthesis and characterization of nickel nanoparticles by simple
precipitation method. The various Schiff-bases such as: ethylenediamine (acacen), 1,3-
propylenediamine (acacpn), and butane-1,4-diamine (acacbn) acetyl acetonate were prepared and
were used for preparing of nickel-Schiff base complexes and then, these complexes as precursor
were reduced in the presence of KBH4, for the first time. In addition, the anti-aggregation effect of
prepared Schiff bases was compared with common surfactants and results demonstrated that the
huge ligands can be considered as novel surfactants. The obtained nickel nanoparticles were
characterized by XRD, TEM, HRTEM, FT-IR, SEM and EDS.
Keywords Schiff-base, nickel, nanoparticles, precipitation method, anti-aggregation
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INTRODUCTION
In the past two decades metallic nanostructures have received more interest for possible applications in
the field of catalysis, microelectronics, biology and material science [1-4]. Synthesis of some metals such as
nickel, copper, and iron in the zero valence state are relatively difficult because they are easily oxidized.
Among various routs developed for the production of metallic nanoparticles, chemical reduction is an
economical technique because it is much faster, cleaner and it does not need special equipments. Various
reducing agents such as hydrazine, alcohols, KBH4 and many other reductants have been used to provide
nanosized nickel particles [1-4]
.
Using of the novel compound can lead to nanomaterials with controlled size, shape and particle size
distribution. Tetradentate Schiff base complexes of transition metal ions have attracted much attention in
the field of coordination chemistry [5-9]. Schiff bases—the condensation proceeds of an amine and ketone
or aldehyde with general formula of R2C=NR are well-known organic repressors [10, 11]. The –N=CH–
(imine) group is indicator of Schiff bases which is significant in explaning the mechanism of
transamination and racemisation reactions in biological systems [12, 13]
.
There is a great interest in our group for novel precursors to control size and morphology of prepared
nanoparticles [14-21]. The Ni nanoparticles were synthesized with using of nickel-Schiff base complexes as
new precursors in the presence of KBH4, also synthesized Schiff bases were utilized as anti-aggregation,
and this is the first report on the synthesis of metallic nickel nanoparticles by reducing of complexes
[Ni(acacen)],
acacen
=
bis(acetylacetonato)ethylenediimine;
[Ni(acacpn)],
acacpn
=
bis(acetylacetonato)propylene-1,3-diimine; [Ni(acacbn)], acacbn = bis(acetylacetonato)buthylene-1,4-
diimine, in the presence of KBH4. The operation of Schiff bases were compared with common surfactants
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and results demonstrated that the huge ligands can be considered as novel surfactant. The products were
characterized by XRD, TEM, HRTEM, SEM, FT-IR spectroscopy and EDAX.
EXPERIMENTAL
Acetyl acetonate, (acac), butane-1, 4-diamine(bn), 1,3-propylenediamine(pn), ethylenediamine(en),
toluene, hexane, different kinds of nickel salt, (KBH4), methanol and ethanol were purchased from Aldrich
and used as received. Fourier transform infrared spectroscopy spectra were recorded on Magna-IR,
spectrometer 550 Nicolet in KBr pellets in the range of 400–4000 cm-1. Powder X-ray diffraction was
carried out on a Philips diffractometer of X’pert company with mono chromatized Cu Kα radiation (k =
1.5406 Å). Microscopic morphology of products was visualized by scaning electron (LEO 1455VP) and
transmission electron microscope images were obtained on a JEM-2100 with an accelerating voltage of
60-200 kV in 50 V steps. Nuclear magnetic resonance spectrum of Schiff base precursors, were recorded
by BRUKER (400 MHz) in acetone-d6.
Synthesis of Schiff base ethylenediamine (H2acacen), 1, 3-propylenediamine (H2acacpn), butane-1, 4-
diamine (H2acacbn) acetyl acetonate
Various alkyl Schiff bases were synthesized by the condensation reaction of amines, namely: ethylene,
propylene and buthelyne diamine. 5 ml of acetylacetonate dissolved in 20 ml methanol and was added to a
stoichiometric amount of desired amine solution dissolved in 20 ml methanol. The reaction mixture was
heated under reflux for 4 h. The brown precipitate was collected and then washed with ethanol and dried
O
in vacuum oven in 50 C. The chemical structures of the prepared Schiff bases were confirmed by using
1
different analysis, (FT-IR and H-NMR spectra). The prepared Schiff-bases NMR spectra (Fig. 1) have
1
good agreement with the spectra which are consistent in references [22-24]. H-NMR spectra of the
produced ligands are presented in Fig 1, which conforms to the bonding structure of these compounds as
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follows: Fig. 1a-c are related to ethylenediamine, 1,3-propylenediamine, butane-1, 4-diamine acetyl
acetonate, respectively. In this Figure (δ (ppm)): 10.9 (s, 2H, OH); 4.956 (s, 2H, -CH-); 3.496-3.510 (t,
4H, -CH2-); 1.939 (s, 6H, -CH3); 1.868 (s, 6H, -CH3) is related to ethylenediamine acetyl acetonate and δ
(ppm): 10.9 (s, 2H, OH); 4.963 (s, 2H, -CH-); 3.367-3.416 (m, 4H, -CH2-), 2.055 (s, 6H, -CH3); 1.951-
1.969 (d, 6H, -CH3); 1.837-1.887 (m, 2H, -CH2-) and (δ (ppm)): 10.9 (s, 2H, OH); 4.956 (s, 2H, -CH-);
3.496-3.510 (t, 4H, -CH2-); 1.939 (s, 6H, -CH3); 1.868 (s, 6H, -CH3) are related to acetyl acetonate 1, 3-
propylenediamine and acetyl acetonate butane-1, 4-diamine, respectively. In Fig. 1b The FT-IR spectra of
three Schiff-base acetyl acetonate ethylenediamine (H2acacen), acetyl acetonate 1, 3-propylenediamine
(H2acacpn), and acetyl acetonate butane-1, 4-diamine (H2acacbn) are shown in Fig. 2a, b and c,
respectively. Their successful synthesis was confirmed by two index and important peaks at around 1610
cm-1 and 1570 cm-1 in every spectrum, which are related to stretching mode of C=O and C=N,
respectively. These two peaks shifted due to intramolecular hydrogenic bonds. Although, the peaks at
around 1510 cm-1 and 3000 cm-1 in each spectrum are indicating vibrations of C-N group in residual
amine used for synthesis of Schiff-base.
Synthesis of Nickel-Schiff base complexes and Ni nanoparticles
For synthesis of nickel nanoparticles, 1 mmol of nickel salt was dissolved in 20 ml of distilled water and
50 ml solution of 0.02 M of synthesized Schiff-base (in methanol) was then added into the Ni solution
under magnetic stirring at the room temperature for preparation of nickel-Schiff base complex. Then 90
ml of KBH4 aqueous solution (0.2 M) was added drop-wise to the produced Ni-Schiff base complex
solution. After a few minutes the color of solution changed slowly from emerald green to black. The black
solution was centrifuged and then washed with distilled water and ethanol. These products could easily be
dispersed in non-polar organic solvents, such as hexane or toluene.
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RESULTS
The effects of metal-to-ligand ratio, different metallic salts and Schiff-bases on the particle size and
morphology of products were investigated. All of the preparation conditions were illustrated in Table1
with more details.
FT-IR spectroscopy
Infrared vibrational spectroscopy was used for confirming purity of the products. Fig. 2 shows the FT-IR
spectra in the range 400–4000 cm-1. Fig. 2d is related to the obtained Ni under explained condition for
sample F. Presence of ligand group on the synthesized Ni nanoparticles is indicated by the peak of the C–
N stretching at 1020 cm−1 and a peak at 674.50 representing the CH2 bending modes of the acetyl
acetonate butane-1, 4-diamine (H2acacbn) ligand capping the Ni nanoparticles. The peak at 1397.04 and
1587.62 cm−1 are associated with the C–N bending mode and C=N group vibrations, respectively. The
weak peak at 3435 cm−1 can be assigned to the ethanol used in the separation step.
X-ray diffraction (XRD) patterns
XRD analysis was employed to investigate the prepared sample. Fig. 3a shows XRD pattern of the
obtained Ni nanoparticles without calcination. A solid with fractional crystallization was formed as
illustrated by the low intensity of diffraction peaks in the pattern. Fig. 3b depicted pattern of the obtained
O
nickel nanoparticles that calcinated in 800 C for 30 min under N2 atmosphere. Increasing temperature
from 25 to 800 OC led to arising of the crystalline phase. All diffraction peaks can be indexed to cubic Ni.
Three characteristic peaks at 44.3, 52.1, 76.6 for cubic nickel (JCPDS, no. 87-0712) were observed. Some
other minor peaks exist that may be obtained from oxidation of Ni nanoparticles. The average crystallite
diameter of the as-synthesized nickel, Dc, was calculated from the major diffraction peaks using the
Scherer equation: Dc = Kλ/βcosθ; where K is a constant (ca. 0.9) [25], λ is the X-ray wavelength used in
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XRD (1.5418 Å), θ is the Bragg angle and β is the pure diffraction broadening of a peak at half-height
which is enlargement due to the crystallite dimensions. The average crystallite diameter calculated by the
Scherer equation is 8 nm.
SEM and TEM
The surface morphological study of the nickel nanoparticles was carried out by using scanning electron
microscope. Since presence of surfactant is an important parameter on the shape and particle size of the
products, therefore much attention has been paid to the study of such supramolecular structures.
[26-
Surfactants played an important role as both template and micro-reactor for producing nanomaterials
28]. Schiff bases of acetyl acetonate ethylene diamine (acacen), acetyl acetonate 1, 3-propylenediamine
(acacpn) and acetyl acetonate butane-1,4-diamine (acacbn) as ligand and stabilizing agent have been used
to make the stable nanoparticles and to prevent their agglomeration. Schiff-bases provided great steric
hindrance thus this agent can decrease ripening process and create smaller particles. Scheme 1 steric
hindrance effect of ligand investigated. Comparison to different surfactant sodium dodecyl sulfate(SDS),
sodium dodecyl benzene sulfonate (SDBS) and cetyl trimethyl ammonium bromide(CTAB) are illustrated
in Fig. 4a-c, respectively. Fig. 4a shows that the produced nanoparticles have average diameter of 70 nm,
while by using SDBS the products with larger diameter were achieved (Fig. 4b). In the presence of CTAB
the smallest nanoparticles have been synthesized while it seems nickel nanoparticles are agglomerated
(Fig. 4c).
The effects of various ligands acetyl acetonate ethylenediamine (H2acacen), acetyl acetonate 1, 3-
propylenediamine (H2acacpn) and acetyl acetonate butane-1,4-diamine (H2acacbn) are shown in Fig. 4d-f,
respectively. The results proved using ligands with higher steric hindrance led to particles with lower size.
So nanoparticles that have been synthesized by using acetyl acetonate butane-1,4-diamine (H2acacbn)
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(Fig. 4f) are the smallest ones, and the produced particles with acetyl acetonate 1, 3-propylenediamine
(H2acacpn) (Fig. 4e) are smaller than those prepared by acetyl acetonate ethylenediamine (H2acacen) (Fig.
4d) complexes. Ultimately, the huge ligands can operate instead of common stabilizers.
The influence of utilized salt to prepare precursor on size of obtained Ni nanoparticles was investigated
and outcome SEM images are depicted in Fig. 5. When Ni(NO3)2.6H2O was used, nanoparticles of Ni
with particle size of about 15 nm were attained (Fig. 5a). Fig. 5b, c are related to NiCl2.6H2O and
Ni(ClO)4.6H2O, respectively, which led to nanoparticles of Ni with diameter of about 20 nm. Also, the
type of salt played an important role in produced particle size. Nickel Chloride and nickel per chlorate led
to larger particles while synthesized Ni nanoparticles by using nitrate salt were smaller. As shown in Fig.
6, structures of Ni with nanometer dimensions were investigated by different molar ratios of ligand to
nitrate salt. According to SEM images when the molar ratio is 1:2, the average size of produced particles
is 180 nm (Fig. 6a) and with increasing of the ratio to 1:1 (Fig. 6b), the size of nanoparticles reaching 15
nm while increasing of the ratio to 2:1 (Fig. 6c) larger particles are produced that their size is about 30-40
nm.
The TEM images of sample F are presented in Fig. 7a. It was observed that the particles were spherical
shape with average size of 5 nm and the ligand covered nickel nanosphere. Fig. 7b showed high-resolution
TEM (HRTEM) image of the nanoparticles, the crystalline nature of the nanoparticles is obvious. The
lattice fringes clearly observed and the spacing of the two neighboring plane is about 0.1 nm.
Energy dispersive X-ray spectroscopy (EDAX)
To further confirmation the chemical composition of the as-prepared Ni, EDAX spectrum was recorded
for sample F. In the EDAX spectrum of related sample (Fig. 8), Ni and O elements are detected. Synthesis
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of nickel in the zero valence states not easy because they are easily oxidized, thus the sampling oxidized
and the oxygen are recognizable.
CONCLUSION
Nickel nanoparticles have been prepared via a simple and facile precipitation method at the room
temperature in water. Nanoparticles were prepared by using nickel–Schiff base complexes [Ni(acacen)],
acacen = bis(acetylacetonato)ethylenediimine; [Ni(acacpn)], acacpn = bis(acetylacetonato)propylene-1,3-
diimine; [Ni(acacbn)], acacbn = bis(acetylacetonato)buthylene-1,4-diimine, as new precursors. The effects
of metal-to-ligand ratio, different salts and Schiff-bases on the particle size and morphology of products
were investigated. In addition, the anti-aggregation effect of Schiff bases was compared with common
surfactants and results demonstrated that the huge ligands can be considered as novel surfactants. FT-IR,
EDAX, XRD, SEM and TEM analyses confirmed the successful synthesis of Ni nanostructures by this
method.
ACKNOWLEDGEMENTS
Authors are grateful to Council of University of Kashan for providing financial support to undertake this
work by Grant No (159271/95).
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Figure captions:
Fig. 1 1H-NMR of Schiff-base; (a): H2acacen (b): H2acacpn (c): H2acacbn
Fig. 2 FT-IR spectra of Schiff-base; (a) H2acacen, (b) H2acacpn, (c) H2acacbn, and (d) sample F.
Fig. 3 XRD pattern of sample F; (a) without calcination, and (b) calcination in 800 OC for 30 min
Fig. 4 SEM images of Ni nanoparticles obtained from samples: (a) A, (b) B, (c) C, (d) D, (e) E,
and (f) F.
Fig. 5 SEM images of Ni nanoparticles obtained from samples: (a) F, (b) G, and (c) H.
Fig. 6 SEM images of Ni nanoparticles obtained from samples: (a) I, (b) F, and (c) J.
Fig. 7 Images of Ni obtained from sample F; (a) TEM, (b) HRTEM.
Fig. 8 EDAX spectrum, Ni nanoparticles obtained from sample F.
Scheme.1 Pattern illustration of the Schiff-base effect on the morphology of Ni nanoparticles.
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Table 1. Preparation conditions of samples A to J.
Sample
Surfactant type
Precursor type
Molar ratio of surfactant to precursor
A
B
C
D
E
F
G
H
I
SDS
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
NiCl2.6H2O
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:2
2:1
SDBS
CTAB
H2acacen
H2acacpn
H2acacbn
H2acacbn
H2acacbn
H2acacbn
H2acacbn
Ni(ClO4)2.6H2O
Ni(NO3)2.6H2O
Ni(NO3)2.6H2O
J
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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Fig. 8
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Scheme 1.
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