Nickel-substituted cobalt ferrite nanoparticles supported on arginine-modified graphene oxide nanosheets: Synthesis and catalytic activity

Article abstract of DOI:10.1002/aoc.3859

The amino acid arginine was used to modify the surface of graphene oxide nanosheets and then nickel-substituted cobalt ferrite nanoparticles were supported on those arginine-grafted graphene oxide nanosheets (Ni_0.5Co_0.5Fe₂O₄@Arg–GO). The prepared Ni_0.5Co_0.5Fe₂O₄@Arg–GO was characterized using flame atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The application of Ni_0.5Co_0.5Fe₂O₄@Arg–GO as a catalyst was examined in a one-pot tandem oxidative cyclization of primary alcohols with o-phenylenediamine to benzimidazoles under aerobic oxidation conditions. The results showed that 2-phenylbenzimidazole derivatives were successfully achieved using Ni_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite catalyst via the one-pot tandem oxidative cyclization strategy.

Full text of DOI:10.1002/aoc.3859

Received: 2 February 2017
DOI: 10.1002/aoc.3859
Revised: 20 March 2017
Accepted: 28 March 2017
F U L L PA P E R
Nickel‐substituted cobalt ferrite nanoparticles supported on
arginine‐modified graphene oxide nanosheets: Synthesis and
catalytic activity
Rahim Ghadari1
| Hassan Namazi1 | Mohammad Aghazadeh2
1 Department of Organic and Biochemistry,
Faculty of Chemistry, University of Tabriz,
5166616471 Tabriz, Iran
2 Microbiology Department, Faculty of
Medicine, Tabriz University of Medical
Sciences, Tabriz, Iran
The amino acid arginine was used to modify the surface of graphene oxide nano-
sheets and then nickel‐substituted cobalt ferrite nanoparticles were supported on
those arginine‐grafted graphene oxide nanosheets (Ni0.5Co0.5Fe2O4@Arg–GO).
The prepared Ni0.5Co0.5Fe2O4@Arg–GO was characterized using flame atomic
absorption spectroscopy, inductively coupled plasma optical emission spectrometry,
energy‐dispersive spectroscopy, Fourier transform infrared spectroscopy, ultravio-
let–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric
analysis, scanning electron microscopy and transmission electron microscopy. The
application of Ni0.5Co0.5Fe2O4@Arg–GO as a catalyst was examined in a one‐pot
tandem oxidative cyclization of primary alcohols with o‐phenylenediamine to
benzimidazoles under aerobic oxidation conditions. The results showed that 2‐
Correspondence
Rahim Ghadari, Department of Organic and
Biochemistry, Faculty of Chemistry,
University of Tabriz, 5166616471 Tabriz,
Iran.
Email: r‐ghadari@tabrizu.ac.ir
Funding information
Iran National Science Foundation (INSF),
Grant/Award Number: 94011834
phenylbenzimidazole
derivatives
were
successfully
achieved
using
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite catalyst via the one‐pot tandem oxida-
tive cyclization strategy.
KEYWORDS
arginine, graphene oxide, nickel‐substituted cobalt ferrite nanoparticles
1 | INTRODUCTION
low mass, high water dispersibility, easy surface modification
and oxygen‐carrying functionalities are employed to immobi-
Graphene is an atomically thin two‐dimensional carbona-
ceous material with exceptional electronic, electrical and
mechanical properties which has attracted tremendous atten-
tion in the scientific community.[1] Due to the exceptional
properties of graphene, this two‐dimensional material has
lize catalytically active metal or metal oxide nanoparticles
with high loadings and high dispersion by keeping the size
of the nanoparticles as small as possible.
Due to the good coordinative interaction of amino acids
and metal ions or metal/metal oxide nanoparticles on the
one hand and the green nature of them on the other hand,
preparation of amino acid‐grafted GO as a support to immo-
bilize catalytic active metal or metal oxide nanoparticles can
be introduced as a good protocol to improve the catalytic
performance of active sites.[5] The appropriate functional
groups on the amino acids which are selected to modify
the surface of GO can well control the morphology,
distribution and loading of catalytically active sites on the
support. Therefore, an enhanced catalytic performance was
achieved for catalytically active sites supported on modified
attracted increasing attention as
a
promising new
nanomaterial for a variety of unique applications.[2–4]
Graphene oxide (GO) as heavily oxygenated graphene can
readily exfoliate in water. Exfoliation of GO in water yields
stable dispersions of single‐layer sheets, this property making
GO a potential material for green applications. Due to the
unique and fascinating behaviour of GO as a support in cata-
lytic applications, this carbonaceous material can be used
beneficially where supports with high surface area, high
mechanical strength and electrical conductivity, intrinsic
Appl Organometal Chem. 2017;e3859.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3859

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GHADARI ET AL.
GO compared to the unmodified GO support.[5] The struc-
tures of some α‐amino acids have free ─NH2 functional
groups which can accelerate base‐assisted reactions; by
using these α‐amino acids as modifiers for the preparation
of a support to immobilize catalytically active sites, high
performance can be achieved for designed reactions which
need both basic and catalytic systems. Also the presence
of side‐chain groups on amino acids helps them to bind
the GO surface. Among the common α‐amino acids, argi-
nine has a unique structure which contains guanidine func-
tional groups on its side chain. Due to the presence of
─NH2 and guanidine functional groups in arginine, this
amino acid is capable of binding to various compounds
chemically by using nucleophilic substitution reactions and
it can be used as an organic base.
In order to develop a new heterogeneous catalyst for
organic transformations, the synthesis of nickel‐substituted
cobalt ferrite nanoparticles supported on arginine‐grafted
GO nanosheets (Ni0.5Co0.5Fe2O4@Arg–GO) was studied.
Reduction and oxidation reactions are among the most
important transformations in synthetic chemistry, such redox
reactions providing key methodologies to introduce and mod-
ify functional groups.[12–14] Therefore the catalytic activity of
the synthesized Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite
was investigated in the one‐pot tandem oxidative synthesis
of 2‐phenylbenzimidazole derivatives. The obtained novel
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite has both arginine
and Ni0.5Co0.5Fe2O4 moieties which can be used not only in
organic base catalysis but also applied in oxidation reactions.
Spinel ferrites, especially cobalt ferrite (CoFe2O4) and
nickel ferrite (NiFe2O4) nanoparticles, have been intensively
studied because of their unique magnetic and catalytic prop-
erties as well as their considerable chemical and mechanical
stability.[6] Due to the unique chemical features of nanosized
cobalt ferrite (as the most technologically important ferrite),
CoFe2O4 nanoparticles can be used as an attractive candidate
for a wide range of advanced catalytic applications. Also,
NiFe2O4 as an important magnetic ferrite has extensive uses
in diverse areas such as catalysis, sensing, photomagnetic
materials, drug delivery, magnetic resonance imaging, etc.[6]
Synthesis of mixed metal ferrites is a common approach
for increasing and improving the catalytic properties of the
mentioned materials[7–9] because of the synergy effect
between metals in the structure of spinel ferrite. Substitution
of metal ferrite by another appropriate transition metal can
optimize the catalytic activity and provide both an active
and selective catalyst. Therefore, in order to modify the cata-
lytic properties of CoFe2O4 nanoparticles, substitution of
nanosized cobalt ferrite by nickel was selected as preferred
transition metal due to considerable catalytic properties of
nickel ferrite.[10]
Nanosized particles have unique chemical and physical
properties compared to their bulk counterparts due to their
nanodimension.[11] Agglomeration and aggregation of nano-
particles is one of the main constraints in the synthesis of
nanosized ferrite[11] because the transfer rate of reactants to
the nanosized ferrite within the solvent in the reaction
medium is inversely proportional to the size of the nanoparti-
cles. To overcome this drawback, modified GO nanosheets
with high surface area and suitable functional groups as sup-
port can be used to isolate the nanoparticles. On the other
hand, a hybrid combining GO and nanosized metal oxide par-
ticles could have the properties and features of both GO (as a
fascinating paper‐shape material) and metal oxide nanoparti-
cles, so the use of GO as a nanoscale substrate for the forma-
tion of nanocomposites with metal oxides is technically
considerable.
2 | EXPERIMENTAL
Since GO has inertness for immobilization of ferrite nanopar-
ticles, arginine was used to modify the GO surface. The
selection of the arginine for modification of the surface of
GO nanosheets was made because of good coordination
interaction between ─NH2 group of arginine and ferrite nano-
particles. Also, use of arginine for the synthesis of the cata-
lyst gave a double nature to the prepared catalyst (oxidation
capability of ferrite moiety and basic property of arginine
moiety of Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite) which
made it possible for us to use the same catalyst in the oxida-
tion and synthetic parts of the one‐pot tandem oxidative
synthesis of 2‐phenylbenzimidazole derivatives. The
Ni0.5Co0.5Fe2O4@Arg–GO nanocatalyst was prepared as
shown in Figure 1.
2.1 | Synthesis of arginine‐grafted GO
Nanosheets (Arg–GO)
The synthesis of GO was done using a modified Hummers
method.[15,16] Graphite powder (1.0 g) was added to a
round‐bottom flask containing the mixture of K2S2O8
(1.0 g) and P2O5 (1.0 g) in concentrated H2SO4 and the
resulting mixture was stirred with a magnetic bar at 80 °C.
After 6 h, the reaction medium was cooled to room tempera-
ture and diluted by addition of 200 ml of deionized (DI)
water. The stirring of the reaction medium was continued
overnight while keeping at room temperature. Finally, the
preoxidized graphite was obtained by filtration of the reaction
mixture and washing the residue using DI water. The
preoxidized graphite was dried at room temperature. The
obtained powder was added to a round‐bottom flask contain-
ing concentrated H2SO4 (50 ml) at 0 °C. Under vigorous stir-
ring, KMnO4 (6.0 g) was added slowly and the resulting
mixture was stirred for 4 h while the temperature was kept
below 25 °C. Then, the reaction vessel was kept in an ice bath

GHADARI ET AL.
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FIGURE 1 Preparation of Ni0.5Co0.5Fe2O4@Arg–GO nanocatalyst
and DI water in two steps (at first 100 ml and, after 2 h,
300 ml) was added slowly to the reaction mixture and the
solution was stirred for 30 min. Next, hydrogen peroxide
(30%) was added dropwise to the mixture until the colour
changed from black to golden yellow. The resulting precipi-
tate was centrifuged and washed repeatedly with HCl
(0.1 M, 300 ml) and DI water and dried in air at room temper-
ature. The GO was obtained as a brown powder.
For the grafting reaction of arginine and GO nanosheets,
GO (0.3 g), SOCl2 (20 ml) and dimethylformamide (DMF;
0.5 ml) were added to a round‐bottom flask and the reaction
medium was stirred at 70 °C for 24 h under nitrogen atmo-
sphere. Then, the excess solvent was evaporated at 100 °C.
The residue was washed with dry tetrahydrofuran for at least
five times. To the obtained acylated product in a round‐bot-
tom flask, dry DMF (20 ml) and arginine (2.0 mmol, 0.1 g)
were added. The reaction mixture was stirred at 90 °C for
12 h. Then, the reaction mixture was subjected to centrifuga-
tion and thorough washing with DI water and ethanol
successively, followed by drying at 50 °C under vacuum.
The Arg–GO product was obtained as a black powder.
(0.4 mmol) and NiCl2⋅6H2O (0.4 mmol) were added. The
prepared mixture was sonicated at room temperature for
1 h. After that, the temperature of the reaction mixture was
raised to 80 °C. Magnetic stirring of the mixture was done
continuously for 30 min while keeping the temperature at
80 °C. By dropwise addition of NaOH solution (0.1 M) to
the reaction medium during 20 min, the pH was raised to
10. After stirring of the obtained mixture for 30 min, the tem-
perature was decreased to room temperature and stirring con-
tinued for 6 h. Finally, the Ni0.5Co0.5Fe2O4@Arg–GO
nanocomposite was separated (by centrifuging), washed
(with DI water and EtOH) and dried (at room temperature).
2.3 | General procedure for catalytic reactions
In a two‐necked flask containing a solution of diamine
(1.0 mmol) and alcohol (1.2 mmol) in CH3CN (7.0 ml),
Ni0.5Co0.5Fe2O4@Arg–GO (0.06 g) was added. The reaction
mixture was stirred magnetically under air blowing (air was
bubbled into the reaction mixture at a rate of 5 ml min−1
)
and reflux conditions (at 80 °C). The progress of the reaction
was monitored by GC and TLC. After reaction completion,
filtration of reaction mixture was done to separate the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite and the separated
catalyst was washed with EtOH. Finally, the organic solvents
were removed and the crude product was separated on a silica
gel column to afford 2‐phenylbenzimidazole derivatives.
(The final products were identified using 1H NMR
2.2 | Synthesis of Ni0.5Co0.5Fe2O4@Arg–GO
For the synthesis of Ni0.5Co0.5Fe2O4@Arg–GO, a mixture of
Arg–GO (1.0 g) in DI water (200 ml) was dispersed by
ultrasonication for 30 min. To the as‐prepared dispersed
Arg–GO mixture, FeCl3⋅6H2O (1.6 mmol), CoCl2⋅6H2O

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GHADARI ET AL.
1
spectroscopy and quantified by isolated yield; selected H
NMR spectra are included in the supporting information.)
investigate the structure of graphite, GO and
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite (Figure 3). The
spacing between two layers gives structural information of
parent graphite and GO nanosheets. The parent graphite
shows a characteristic diffraction peak at 26.7° related to an
interlayer spacing of 0.33 nm (Bragg equation). The XRD
pattern of GO nanosheets shows a diffraction peak at
2θ = 11.3° that indicates an interlayer spacing of 0.78 nm.
The increased interlayer spacing is mainly due to a large
amount of oxygen‐containing functional groups produced
during oxidation of graphite. The appearance of the GO peak
at 11.3° and the disappearance of the graphite peak at 26.7°
confirmed that the prepared GO nanosheets were completely
oxidized. The XRD pattern of Ni0.5Co0.5Fe2O4@Arg–GO
indicates characteristic diffraction peaks at 2θ values of
30.2°, 32.7°, 35.6°, 43.3°, 57.3° and 62.9° which agree with
those reported in the literature for Ni0.5Co0.5Fe2O4.[7,10,17]
These reflection peaks, which demonstrate the formation of
Ni0.5Co0.5Fe2O4, correspond to the characteristic inter‐planar
spacing between (220), (222), (311), (400), (511) and (440)
planes of spinel ferrite with cubic symmetry.[7,10,17] In the
XRD pattern of Ni0.5Co0.5Fe2O4@Arg–GO, the characteris-
tic diffraction peaks of Arg–GO were not observed because
the diffraction peaks of the ferrite moiety are stronger than
the diffraction peaks of Arg–GO. The mentioned characteris-
tic peaks related to Ni0.5Co0.5Fe2O4 confirm the successful
preparation of the Ni0.5Co0.5Fe2O4@Arg–GO catalytic
system.
3 | RESULTS AND DISCUSSION
The characterization of the prepared Ni0.5Co0.5Fe2O4@Arg–
GO nanocomposite was done using flame atomic absorption
spectroscopy (FAAS), inductively coupled plasma optical
emission spectrometry (ICP‐OES), energy dispersive spec-
troscopy (EDS), Fourier transform infrared (FT‐IR) spectros-
copy, UV–visible spectroscopy, Raman spectroscopy, X‐ray
diffraction (XRD), thermogravimetric analysis (TGA), scan-
ning electron microscopy (SEM) and transmission electron
microscopy (TEM). The amounts of nickel, cobalt and iron
of the Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite were cal-
culated using FAAS. The Ni0.5Co0.5Fe2O4 content in the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite was determined
as 9.04 wt%. ICP‐OES analysis was also used to determine
the amounts of nickel, cobalt and iron in the prepared
nanocomposite, the obtained result corroborating the deter-
mined nickel, cobalt and iron content in the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite. The obtained
results from FAAS and ICP‐OES analyses showed that the
composition of the prepared specimen is corroborated within
the composition of predicted Ni0.5Co0.5Fe2O4@Arg–GO
nanocomposite. Also, determination of the chemical compo-
sition of Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite was
done using EDS analysis. As is clear from Figure 2, the
EDS analysis confirmed the presence of carbon, nitrogen,
Raman spectroscopy is used to investigate the electronic
and phonon structure of graphene‐based materials. So,
Raman spectroscopy as a useful tool was applied to study
the prepared Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite
(Figure 4). The Raman spectrum of GO indicates two prom-
inent peaks at 1584 cm−1 (G‐band) and 1317 cm−1 (D‐band).
G‐band is the result of the first‐order E2g mode from sp2 car-
bon domains and D‐band is characteristic of a breathing
mode for k‐point. For the Ni0.5Co0.5Fe2O4@Arg–GO nano-
composite, the characteristic D‐band and G‐band are observ-
able at around 1313 and 1588 cm−1, respectively, which
show the Raman lines of GO.
oxygen,
nickel,
cobalt
and
iron
in
the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite.
XRD analysis as an effective method for characterizing
the interlayer change and degree of crystallinity of
graphene‐based materials and was employed to further
FIGURE
2
SEM‐EDS result for Ni0.5Co0.5Fe2O4@Arg–GO
FIGURE
3
XRD patterns of graphite (I), GO (II) and
nanocomposite
Ni0.5Co0.5Fe2O4@Arg–GO (III)

GHADARI ET AL.
5 of 9
FIGURE 4 Raman spectra of GO (I) and Ni0.5Co0.5Fe2O4@Arg–GO
(II)
The UV–visible spectral analysis of GO, Arg–GO and
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite is presented in
Figure 5. These spectra were obtained with GO, Arg–GO
and Ni0.5Co0.5Fe2O4@Arg–GO dissolved in concentrated
HCl and diluted with DI water.
Chemical attachment of arginine to the GO nanosheets
and immobilization Ni0.5Co0.5Fe2O4 on Arg–GO were con-
firmed using FT‐IR spectroscopy (Figure 6). The successful
synthesis of GO nanosheets was corroborated from the FT‐
IR spectrum of GO which reveals characteristic bands at
3408 (─OH), 1713 (carboxyl ─C═O), 1600 (aromatic
─C═C─), 1391 (carboxyl ─C─O), 1229 (epoxy ─C─O)
and 1093 cm−1 (alkoxy ─C─O).[18] The new bands at
1624 cm−1 (─C═N stretch) and 1408 cm−1 (─C─N stretch)
are associated with the presence of arginine moiety in Arg–
GO.[5] The amount of arginine amino acid grafted to GO
nanosheets was 12 wt% according to elemental analysis. In
the case of Ni0.5Co0.5Fe2O4@Arg–GO, the characteristic
bands at 617 and 436 cm−1 can be attributed to metal─O
stretching vibrations.[19] The presence of characteristic bands
of Arg–GO and Ni0.5Co0.5Fe2O4 nanoparticles in the FT‐IR
spectrum of Ni0.5Co0.5Fe2O4@Arg–GO indicates the suc-
cessful preparation of the nanohybrid.
FIGURE
Ni0.5Co0.5Fe2O4@Arg–GO
6
FT‐IR
spectra
of
GO,
Arg–GO
and
The SEM image of Arg–GO (Figure 7b) indicated that argi-
nine was grafted on GO nanosheet surface without a large
change in the morphology of GO. The presence and good
dispersion of Ni0.5Co0.5Fe2O4 nanoparticles on the Arg–GO
nanosheet surface are observable in Figure 7(c,d).
TEM images of GO (Figure 8a), Arg–GO (Figure 8b) and
Ni0.5Co0.5Fe2O4@Arg–GO nanoparticles (Figure 8c) con-
firm the uniform dispersion and the size distribution of the
Ni0.5Co0.5Fe2O4 nanoparticles supported on the Arg–GO
surface.
The relatively high thermal stability of the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite in air was con-
firmed using TGA. The thermograms of GO and
Ni0.5Co0.5Fe2O4@Arg–GO are shown in Figure 9. TGA
curve of the Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite indi-
cated three stages: the low‐temperature range (up to 156 °C,
related to the removal of adsorbed water on the surface of
the nanocomposite) and 156–503 and 503–710 °C ranges
(attributed to the decomposition of GO and arginine).
In order to develop a suitable catalytic system using the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite, optimization
studies were conducted with o‐phenylenediamine (1a) and
benzyl alcohol (2a) as model substrates using various
amounts of catalyst, solvents and temperatures (Table 1).
SEM analysis was used to characterize the morphology of
the obtained GO, Arg–GO and Ni0.5Co0.5Fe2O4@Arg–GO.
FIGURE
5
UV–visible spectra of GO, Arg–GO and
Ni0.5Co0.5Fe2O4@Arg–GO in H2O–HCl (10:1)
Initially,
the
effect
of
various
amounts
of

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GHADARI ET AL.
FIGURE
8
TEM images of GO (a), Arg–GO (b) and
Ni0.5Co0.5Fe2O4@Arg–GO (c)
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite was investigated.
The obtained results confirmed that, in the absence of cata-
lyst, the formation of 3a was not observed (entry 1). The
use of Arg–GO as catalyst failed to give 2‐
phenylbenzimidazole product, which excluded the contribu-
tion of Arg–GO itself as a catalyst (entry 2). Subsequent
screening of various amounts of Ni0.5Co0.5Fe2O4@Arg–GO
nanocomposite revealed that 0.06 g of catalyst exhibited the
FIGURE
Ni0.5Co0.5Fe2O4@Arg–GO (c, d)
7
SEM images of GO (a), Arg–GO (b) and

GHADARI ET AL.
7 of 9
took place to give product 3a in 47% yield when the sub-
strates were stirred in acetonitrile at 60 °C for 6 h (entry
10). The use of a reaction temperature of 40 °C led to a
decrease in product yield to 20% (entry 11). The reaction at
room temperature gave an inferior result (entry 12). To show
the role of Arg–GO nanosheets as support in the oxidative
synthesis of 2‐phenylbenzimidazole product, the reaction
was
accomplished
using
Ni0.5Co0.5Fe2O4
and
Ni0.5Co0.5Fe2O4@Arg–GO under the same reaction condi-
tions. The obtained results (Table 1, entries 3 and 4) con-
firmed that Ni0.5Co0.5Fe2O4@Arg–GO has higher catalytic
activity than unsupported Ni0.5Co0.5Fe2O4. The adsorption
of aromatic reactants on the surface of the
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite because of the
π–π interaction between graphene support and benzene skel-
eton of the reactants seems to enhance the efficiency of
Ni0.5Co0.5Fe2O4@Arg–GO compared to unsupported
Ni0.5Co0.5Fe2O4.[20,21] To examine the role of arginine in
the synthesis of product 3a, Ni0.5Co0.5Fe2O4@Arg–GO and
Ni0.5Co0.5Fe2O4@GO (nickel‐substituted cobalt ferrite nano-
particles supported on graphene oxide nanosheets without
FIGURE 9 TGA curves of GO (I) and Ni0.5Co0.5Fe2O4@Arg–GO
(II) in air
best result, leading to 3a in 79% yield, while lowering the
amount of catalyst afforded the target product in less than
55% yield (entries 4–6). The obtained results related to the
effect of solvent indicated that the use of acetonitrile as a sol-
vent led to an increase the 2‐phenylbenzimidazole product
yield to 79%, whereas solvents such as o‐xylene, DMF and
toluene gave inferior results (entries 4, 7–9). The reaction
TABLE 1 Optimization of reaction conditions for oxidative synthesis of 2‐phenylbenzimidazole derivatives catalysed by Ni0.5Co0.5Fe2O4@Arg–
GO nanocompositea
Entry
Catalyst
Amount of catalyst (g)
Solvent
Time (h)
Temperature (°C)
Yield (%)b
1
—
—
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
o‐Xylene
DMF
24
24
6
80
80
80
80
80
80
80
80
80
60
40
r.t.
80
80
80
80
Trace
Trace
26
2
Arg–GO
0.06
0.01
0.06
0.05
0.04
0.06
0.06
0.06
0.06
0.06
0.06
0.06
0.06
0.01
0.01
3
Ni0.5Co0.5Fe2O4
4
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@Arg–GO
Ni0.5Co0.5Fe2O4@GO
Ni0.5Co0.5Fe2O4@Arg–GO
NiFe2O4
6
79
5
6
52
6
6
41
7
6
74
8
6
38
9
Toluene
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
6
60
10
11
12
13
14c
15
16
6
47
6
20
6
11
6
49
6
Trace
7
6
CoFe2O4
6
12
aReaction conditions: o‐phenylenediamine (1.0 mmol), benzyl alcohol (1.2 mmol), solvent (7.0 ml), air as oxidant.
bIsolated yield.
cIn the absence of air oxidant.

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GHADARI ET AL.
use of arginine) were applied in the reaction. The obtained
results showed that arginine amino acid enhances the cata-
lytic activity of the prepared system for the synthesis of prod-
uct 3a. In fact, use of arginine for the synthesis of
Ni0.5Co0.5Fe2O4@Arg–GO nanocomposite gave a basic
property to the prepared catalytic system by which it can
catalyse the synthetic part of the one‐pot tandem oxidative
synthesis of 2‐phenylbenzimidazole. From the data presented
in Table 1 (entries 2, 4 and 13), it could be concluded that the
double nature of Ni0.5Co0.5Fe2O4@Arg–GO led to the pro-
motion of the catalytic activity of prepared nanocomposite
in the oxidation and synthetic parts of the one‐pot tandem
oxidative synthesis of product 3a due to the oxidation capa-
bility of ferrite moiety and basic property of arginine moiety
of Ni0.5Co0.5Fe2O4@Arg–GO. The successful carrying out
of the one‐pot tandem oxidative synthesis of product 3a con-
firmed the utility of the synthesized Ni0.5Co0.5Fe2O4@Arg–
GO nanocomposite for both aerobic oxidation and base
catalysis, as it had been designed. It is important to note that
the synthesis of 2‐phenylbenzimidazole product did not
proceed without air blowing (entry 14). A comparison
was done of the catalytic activities of NiFe2O4, CoFe2O4,
Having the optimal conditions in hand, the scope of the
protocol was investigated for the synthesis of 2‐
phenylbenzimidazole derivatives using the reaction of a
series of substituted benzyl alcohols with diamines
(Table 2). As is clear from Table 2, electron‐donating and
electron‐withdrawing substituents on benzyl alcohols readily
promote the reaction.
The
recyclability
of
the
synthesized
Ni0.5Co0.5Fe2O4@Arg–GO catalyst was examined in the oxi-
dative synthesis of 2‐phenylbenzimidazole compound. After
completion of the reaction, the catalyst was recovered from
the reaction medium by centrifuging and was washed with
EtOH. The recovered Ni0.5Co0.5Fe2O4@Arg–GO catalyst
was dried and then reused for five repeat cycles of the reac-
tion (Figure 10). The obtained results indicated that the
Ni0.5Co0.5Fe2O4,
Ni0.5Co0.5Fe2O4@GO
and
Ni0.5Co0.5Fe2O4@Arg–GO catalysts (entries 3, 4, 13, 15
and 16). The obtained results show that the substitution of
cobalt ferrite nanoparticles by nickel transition metal and
use of arginine amino acid give a more active catalytic
system.
FIGURE 10 Successive use of Ni0.5Co0.5Fe2O4@Arg–GO catalyst
for oxidative synthesis of 2‐phenylbenzimidazole
TABLE 2 Oxidative synthesis of 2‐phenylbenzimidazole derivatives catalysed by Ni0.5Co0.5Fe2O4@Arg–GO nanocompositea
Melting point (°C)
Yield
(%)b
Entry
Diamine
Alcohol
Product
Found
Reported
1
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
o‐Phenylenediamine
4‐Methyl‐o‐phenylenediamine
4‐Methyl‐o‐phenylenediamine
Benzyl alcohol
3a
3b
3c
3d
3e
3f
79
81
89
90
88
91
87
90
93
85
81
293–295
222–224
272–273
257–259
159–160
218–220
288–289
230–231
256–258
241–242
105–106
292–293[22]
223–224[22]
275–276[22]
260–261[22]
156–158[23]
218–219[22]
287–289[24]
232–235[25]
255–256[22]
243–245[24]
106–108[26]
2
2‐Methylbenzyl alcohol
4‐Methylbenzyl alcohol
4‐Bromobenzyl alcohol
2‐Methoxybenzyl alcohol
4‐Methoxybenzyl alcohol
4‐Chlorobenzyl alcohol
2‐Nitrobenzyl alcohol
4‐Nitrobenzyl alcohol
Benzyl alcohol
3
4
5
6
7
3g
3h
3i
8
9
10
11
3j
2‐Chlorobenzyl alcohol
3k
aReaction conditions: diamine (1.0 mmol), alcohol (1.2 mmol), Ni0.5Co0.5Fe2O4@Arg–GO (0.06 g), CH3CN (7.0 ml), air as oxidant, 80 °C.
bIsolated yield.

GHADARI ET AL.
9 of 9
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posite is not altered by a considerable amount during succes-
sive uses.
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Modification of the surface of GO nanosheets was done using
the amino acid arginine to produce arginine‐grafted GO
nanosheets as a support for immobilization of nickel‐
substituted cobalt ferrite nanoparticles. Functionalization of
GO with arginine led to a catalytic system with uniform dis-
persion of Ni0.5Co0.5Fe2O4 nanoparticles which has both oxi-
dation capability of ferrite moiety and basic property of
arginine moiety. The one‐pot tandem oxidative reaction of
readily available alcohols with o‐phenylenediamines
proceeds smoothly in the presence of the prepared
Ni0.5Co0.5Fe2O4@Arg–GO catalyst to afford substituted 2‐
phenylbenzimidazole derivatives. The use of arginine‐grafted
GO nanosheets to immobilize nickel‐substituted cobalt ferrite
nanoparticles enhances the catalytic activity of the prepared
system. The use of a green and inexpensive catalytic system,
air as green oxidant and readily available starting materials
are significant practical advantages of the presented protocol.
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ACKNOWLEDGEMENTS
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Financial support from the Iran National Science Foundation
(INSF), project number 94011834, is gratefully acknowl-
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University of Tabriz is gratefully acknowledged.
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How to cite this article: Ghadari R, Namazi H,
Aghazadeh M. Nickel‐substituted cobalt ferrite
nanoparticles supported on arginine‐modified
graphene oxide nanosheets: Synthesis and catalytic
activity. Appl Organometal Chem. 2017;e3859. https://
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