Binary copper and iron oxides immobilized on silica-layered magnetite as a new reusable heterogeneous nanostructure catalyst for the Knoevenagel condensation in water

Article abstract of DOI:10.1007/s11164-018-3475-0

Abstract: In this study, a novel heterogeneous and reusable nanostructure catalyst was synthesized through the immobilization of bimetallic Cu–Fe mixed oxides on silica-layered magnetite. The prepared nanomagnetic Fe₃O₄@SiO₂

Full text of DOI:10.1007/s11164-018-3475-0

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3475-0
Binary copper and iron oxides immobilized on silica-
layered magnetite as a new reusable heterogeneous
nanostructure catalyst for the Knoevenagel
condensation in water
Masumeh Gilanizadeh1
Behzad Zeynizadeh1
•
Received: 7 February 2018 / Accepted: 11 May 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract In this study, a novel heterogeneous and reusable nanostructure catalyst was
synthesized through the immobilization of bimetallic Cu–Fe mixed oxides on silica-
layered magnetite. The prepared nanomagnetic Fe3O4@SiO2@CuO–Fe2O3 was char-
acterized using Fourier-transform infrared spectroscopy, scanning electron microscopy,
energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, Brunauer–Emmett–
Teller analysis, thermogravimetric analysis, differential thermal gravity, a vibration
sample magnetometer, transmission electron microscopy and inductively coupled
plasma optical emission spectroscopy. The catalytic activity of this mesoporous
nanocomposite was studied in the Knoevenagel condensation of aromatic aldehydes and
malononitrile in water to afford benzylidenemalononitriles in high to excellent yields.
The nanocatalyst was able to be recycled five times without a significant loss in catalytic
activity. This nanostructure catalyst allows for mild reaction conditions and accept-
able reaction times, while delivering the desired products in high purity and yield
without the use of dangerous organic solvents.
Keywords Benzylidenemalononitriles Á Fe3O4@SiO2@CuO–Fe2O3 Á Knoevenagel
condensation Á Malononitrile Á Nanocatalyst
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3475-0) contains supplementary material, which is available to authorized users.
&
Masumeh Gilanizadeh
masumehgilanizadeh@gmail.com
1
Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran
123

M. Gilanizadeh, B. Zeynizadeh
Introduction
Heterogeneous catalysis is utilized extensively today for facilitating a wide variety
of organic reactions in both academic and industrial settings [1–12]. Numerous
papers and documents show the importance of this type of catalysis [13–21]. Among
the many heterogeneous catalysts, metal oxides exhibit a high level of activity, and
they can be readily used as either active phases or solid supports for the
immobilization of other promoters [22]. In this context, metal oxides containing
transition metals are the subject of increasing interest because of their inexpensive
preparation, ease of regeneration and selectivity. These materials are generally
classified by their crystalline systems and they are prepared in the form of a powder
or as single crystals. In addition, they are widely used in electronics, nuclear
research and ceramics [23–25].
Mixed metal oxides have two or more types of metal cations. According to the
number of diverse metal cations, they can be categorized as binary, ternary and
quaternary oxides. Hydrothermal methods [26, 27], mechanochemical synthesis
[28, 29], sol–gel [30–33], co-precipitation [34, 35], wet impregnation [36, 37] and
microwave irradiation [38] are commonly used for the preparation of mixed metal
oxides.
Recently, systems combining magnetic nanoparticles (MNPs) and mixed metal
oxides have been developed for application in numerous processes, due to the vast
surface area of the nanoparticles as well as the presence of acidic/basic sites on the
metal oxides which improve the promoter activity and selectivity of the mixed
composite systems. Moreover, they are easily separated by an external magnetic
field at the end of reaction [39–49]. In this context, a number of manuscripts
highlight the usefulness of mixed metal oxides as catalysts in several synthetic
transformations [50–58].
The Knoevenagel condensation is an important reaction used to install C=C
bonds in organic compounds. The reaction occurs via nucleophilic attack of an
active methylene group to an aldehyde followed by dehydration [59]. This method
is suitable for the preparation of structurally diverse alkene compounds which can
be utilized as intermediates for numerous reactions [60]. Generally, benzylidene-
malononitriles (BMNs) are synthesized by the Knoevenagel condensation of
aromatic aldehydes and malononitrile. BMN derivatives have been widely used in
biological and pharmaceutical studies. They exhibit various properties including
anti-inflammatory, anticonvulsant, antioxidant and anticancer activity [61, 62].
Several useful procedures have been reported for synthesis of BMN derivatives
[63–80]. Although most of the reported methods have their own merits, however,
they generally suffer from disadvantages such as the use of expensive organic
solvents or catalysts, harsh reaction conditions, prolonged reaction times, undesir-
able yields and tedious work-up procedures. Therefore, further efforts are needed
towards the development and introduction of easy protocols which use effective
catalysts under mild and green reaction conditions is still demanded.
In this study, we wish to introduce Fe3O4@SiO2@CuO–Fe2O3, a new type of
magnetic mixed metal oxide that can be successfully utilized for the Knoevenagel
123

Binary copper and iron oxides immobilized on silica…
condensation of diverse aromatic aldehydes with malononitrile to afford benzyli-
denemalononitrile products in high to excellent yields. All reactions were carried
out in refluxing H2O (Scheme 1).
Results and discussion
Synthesis and characterizations of the nanocatalyst
Magnetic nanoparticles of Fe3O4@SiO2@CuO–Fe2O3 were synthesized through a
three-step procedure: (1) the preparation of magnetite nanoparticles by a chemical
co-precipitation of FeCl2Á4H2O and FeCl3Á6H2O in an aqueous solution of
ammonia, (2) coating of SiO2 on the surface of magnetite-cores by tetraethyl
orthosilicate (TEOS) at room temperature, and (3) the use of an in situ growth
method to immobilize Cu2?and Fe3?salts on the core of silica-layered magnetite
followed by calcinations at 150 °C to prepare magnetic nanoparticles of Fe3O4@
SiO2@CuO–Fe2O3 MNPs (Scheme 2).
Nanocatalyst characterization
Fourier-transform infrared spectroscopy (FTIR)
FTIR spectroscopy is a useful technique for the structural elucidation of compounds.
In this context, the FTIR spectrum of nano Fe3O4 (Fig. 1a) exhibits a strong
absorption peak at 575 cm-1 corresponding to vibration of Fe–O bonds. The
absorption peaks at 3400 and 1625 cm-1 are attributed to O–H stretching and
deforming vibrations of adsorbed water, respectively. FTIR spectrum of Fe3O4@
SiO2 MNPs is also illustrated in Fig. 1b. The spectrum shows additional peaks at
796 and 1094 cm-1 that are assigned to the symmetrical and asymmetrical Si–O–Si
stretching vibrations. These results confirm the successful layering of SiO2 on the
cores–surface of magnetite. The FTIR spectrum of Fe3O4@SiO2@CuO–Fe2O3
MNPs (Fig. 1c) exhibits
a
wide and strong absorption band around
3200–3600 cm-1 that corresponds to superimposed hydroxyl stretching bands
arising from the O–H bond of water within the layers. An additional absorption band
around 1600 cm-1 can be attributed to the deforming mode of water molecules. In
addition, the absorption peaks around 400–600 cm-1 are attributed to the vibration
modes of Fe–O and Cu–O bonds, which confirms the formation of mixed CuO–
Fe2O3 on the cores–surface of Fe3O4@SiO2.
CHO
CN
Fe3O4@SiO2@CuO-Fe2O3 MNPs
H2O, Reflux
R
R
+
NC
R = H, Me, OMe, NO2, OH, Cl, CHO
Scheme 1 Synthesis of benzylidenemalononitriles by Fe3O4@SiO2@CuO–Fe2O3 MNPs
CN
CN
123

M. Gilanizadeh, B. Zeynizadeh
Scheme 2 Synthesis of Fe3O4@SiO2@CuO–Fe2O3 MNPs
Fig. 1 FTIR spectrum of
a Fe3O4, b Fe3O4@SiO2 and
c Fe3O4@SiO2@CuO–Fe2O3
MNPs
Scanning electron microscopy (SEM)
SEM is commonly used to determine the size distribution and morphology of the
synthesized particles. SEM images of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@
CuO–Fe2O3 MNPs are illustrated in Fig. 2. The images indicate that the
immobilized CuO–Fe2O3 on silica-layered magnetite was constructed from roughly
spherical and granule particles. In addition, particles of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2@CuO–Fe2O3 MNPs are distributed in the range of 23–43 nm
(Fig. 2a), 22–30 nm (Fig. 2b) and 27–29 nm (Fig. 2c–f), respectively. The meso-
porous structure of Fe3O4@SiO2@CuO–Fe2O3 MNPs is determined based on the
size of the nanoparticles.
Energy-dispersive X-ray spectroscopy (EDX)
The elemental composition of a material can be determined by electron dispersive
X-ray spectroscopy (EDX–SEM). Figure 3 shows the elemental analysis and EDX
spectrum of Fe3O4@SiO2@CuO–Fe2O3 MNPs. The analysis shows that Fe, Cu, Si
and O are present in the nanocomposite. Therefore, the copper–iron oxide layer was
successfully coated on the cores–surface of Fe3O4@SiO2 MNPs.
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Binary copper and iron oxides immobilized on silica…
Fig. 2 FE-SEM image of a Fe3O4, b Fe3O4@SiO2 and c–f Fe3O4@SiO2@CuO–Fe2O3 MNPs
CuL
4500
4000
3500
3000
2500
2000
1500
1000
500
O K
FeL
CuK
FeK
SiK
FeK
CuK
keV
0
0
5
10
15
Fig. 3 EDX spectrum of Fe3O4@SiO2@CuO–Fe2O3 MNPs
X-ray diffraction (XRD)
The crystalline structure of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@CuO–Fe2O3
MNPs was also analyzed by X-ray diffraction (XRD). Figure 4a shows the
diffraction peaks at 2h = 30.2°, 35.5°, 43.3°, 53.7°, 57.2° and 62.9° corresponding
to (220), (311), (400), (422), (511) and (440) crystal planes of nano Fe3O4. Based on
123

M. Gilanizadeh, B. Zeynizadeh
Fig. 4 XRD pattern of a Fe3O4,
b Fe3O4@SiO2 and
c Fe3O4@SiO2@CuO–Fe2O3
MNPs
this pattern, the prepared laboratory sample of magnetite has a crystalline cubic
spinel structure analogous to the standard structure of Fe3O4 (JCPDS 65-3107)
[81, 82]. The XRD pattern of Fe3O4@SiO2 MNPs is illustrated in Fig. 4b. Analysis
of this spectrum shows that the pattern is identical to that of Fe3O4, while the
intensity of the peaks decreased to some extent. This is attributed to crystalline
phase-intact of Fe3O4 through layering of SiO2 on the cores of Fe3O4. In the XRD
pattern of Fe3O4@SiO2@CuO–Fe2O3 MNPs, all characteristic peaks of Fe3O4 are
also observable. Furthermore, the peaks at 2h = 32.5°, 35.5°, 38.7°, 48.7°, 58.3°,
61.5°, 66.2°, 68.1° and 75.2° corresponded to (110), (-111), (111), (-202), (202),
(-113), (-311), (220) and (-222) crystal planes, which proves the monoclinic
crystalline structure of Fe3O4@SiO2@CuO–Fe2O3 MNPs. It is in agreement with
the documented-crystalline structure of copper oxide in JCPDS 80-1916 [83].
Through the Debye–Scherrer equation (D = kk/bcosh), the mean particle size of
Fe3O4@SiO2@CuO–Fe2O3 MNPs was calculated to be 9.67 nm. In this equation, b
is the full width at half maximum intensity (FWHM) and is equal to 0.91°
(0.016 rad) at h = 19.50°.
Brunauer–Emmett–Teller (BET)
The nitrogen adsorption and desorption isotherms of the synthesized Fe3O4@
SiO2@CuO–Fe2O3 MNPs is illustrated in Fig. 5. The surface area and pore size
distribution of the nanocatalysts were examined by BET and BJH methods. The
calculated BET specific surface area (SBET) is 128.03 m2 g-1 and the pore volume
(Vp) is 0.279 cm3 g-1. The obtained results suggest a high specific sur-
face area to volume ratio for the nanocatalyst, leading to a dramatic increase in
its catalytic activity. Through the Barrett–Joyner–Halenda (BJH) method, the
123

Binary copper and iron oxides immobilized on silica…
Fig. 5 Nitrogen adsorption–
desorption isotherm of
Fe3O4@SiO2@CuO–Fe2O3
MNPs
average pore size of the nanocomposite was determined to be 8.716 nm, confirming
the mesoporous structure of Fe3O4@SiO2@CuO–Fe2O3 MNPs.
Thermogravimetric analysis (TGA)
The thermal behavior, possible thermal stability and degradation processes of the
synthesized MNPs were examined by thermogravimetric analysis (TGA). The
located contents on the surface of MNPs can be generally determined by TGA
analysis. Figure 6a shows TGA-thermograph of Fe3O4, which demonstrates the high
thermal stability of magnetite at elevated temperature. Figures 6b and 7a represent
TGA and DTG thermographs of Fe3O4@SiO2 MNPs with two thermal degradation
steps. The 2.18% loss of mass in the range of 30–158 °C (first decomposition step)
Fig. 6 TGA thermogram of a Fe3O4, b Fe3O4@SiO2 and c Fe3O4@SiO2@CuO–Fe2O3 MNPs
123

M. Gilanizadeh, B. Zeynizadeh
Fig. 7 TGA and DTG of a Fe3O4@SiO2 and b Fe3O4@SiO2@CuO–Fe2O3 MNPs
corresponds to the evaporation of adsorbed solvent or water. The second
degradation step (loss of 3.28% mass) is observed at 474–616 °C and it is
attributed to the degradation of the SiO2 layer. Figures 6c and 7b illustrate TGA and
DTG thermographs of Fe3O4@SiO2@CuO–Fe2O3 MNPs with two thermal
degradation steps. The first loss of mass is identified in the range of 26–127 °C
(loss of 3.62% mass) and is attributed to the elimination of adsorbed water at the
surface. The second loss of mass in the range of 193–384 °C (loss of 5.66% mass)
corresponds to the degradation of the CuO–Fe2O3 or SiO2 layers.
Vibration sample magnetometer (VSM)
Magnetic characterization of the prepared nanoparticles by vibrating sample
magnetometer analysis is illustrated in Fig. 8. The curves represent the super
paramagnetic behavior of MNPs appearing in reversible and nonlinear platforms.
The saturation magnetization (Ms) values of Fe3O4 (Fig. 8a), Fe3O4@SiO2 (Fig. 8b)
and Fe3O4@SiO2@CuO–Fe2O3 (Fig. 8c) MNPs were found to be 70, 30 and
4 emu g-1, respectively. The graphs depict a decrease in the saturation
123

Binary copper and iron oxides immobilized on silica…
Fig. 8 Hysteresis loop of
a Fe3O4, b Fe3O4@SiO2 and
c Fe3O4@SiO2@CuO–Fe2O3
MNPs
magnetization (Ms) of Fe3O4-cores caused by encapsulation with SiO2 or CuO–
Fe2O3 layers.
Transmission electron microscopy (TEM)
The obtained transmission electron microscope (TEM) images of Fe3O4@SiO2@
CuO–Fe2O3 MNPs (Fig. 9) show that the nanocatalyst has the core–shell
nanostructure platform.
Inductively coupled plasma optical emission spectroscopy (ICP-OES)
The ICP-OES technique is generally utilized to determine the exact elemental
composition of a compound. Through this analysis, the quantities of Fe and Cu in
Fe3O4@SiO2@CuO–Fe2O3 MNPs were determined to be 28.38, and 45.61%,
respectively.
Fig. 9 TEM images of Fe3O4@SiO2@CuO–Fe2O3 MNPs
123

M. Gilanizadeh, B. Zeynizadeh
Synthesis of benzylidenemalononitrile derivatives
After the successful synthesis of Fe3O4@SiO2@CuO–Fe2O3 MNPs, the catalytic
activity of the heterogeneous nanocatalyst towards the Knoevenagel condensation
of aromatic aldehydes with malononitrile in H2O as a green and eco-friendly solvent
was studied. The reaction conditions were optimized by performing the conden-
sation reaction of benzaldehyde and malononitrile in the presence and absence of
the nanocatalyst as well varying the amount of catalyst, temperature and solvent
employed in the reaction (Table 1). The use of Fe3O4@SiO2@CuO–Fe2O3 MNPs
was found to be crucial for reaction efficiency. Moreover, the influence of
temperature is noteworthy: when the model reaction is performed in H2O at ambient
temperature, low conversion is observed after 40 min. However, running the
reaction at reflux dramatically influences the progress of the model reaction after
4 min. Entry 11 shows that conducting the reaction of benzaldehyde (1 mmol) and
malononitrile (1.1 mmol) in the presence of Fe3O4@SiO2@CuO–Fe2O3 MNPs
(30 mg) in refluxing H2O provided satisfactory results.
Next, to pinpoint the main catalytic center of Fe3O4@SiO2@CuO–Fe2O3, the
activity of SiO2, Fe3O4, Fe3O4@SiO2, CuO–Fe2O3 and SiO2@CuO–Fe2O3 NPs in
the Knoevenagel condensation of benzaldehyde with malononitrile was investigated
under the optimized reaction conditions (Table 2). Among the examined NPs, the
immobilized CuO–Fe2O3 on silica-layered magnetite exhibited extraordinary
Table 1 Optimization experiments for the Knoevenagel condensation of benzaldehyde and malononi-
trile using Fe3O4@SiO2@CuO–Fe2O3MNPs
CHO
CN
Fe3O4@SiO2@CuO-Fe2O3 MNPs
NC
CN
+
CN
Entry
Fe3O4@SiO2@CuO–Fe2O3 (g)
Solvent
T (°C)
Time (min)
Conversion (%)
1
–
Solvent-free
H2O
80
60
60
40
40
40
40
40
40
40
40
4
Trace
Trace
90
2
–
Reflux
80
3
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.04
0.02
Solvent-free
Solvent-free
H2O
4
r.t.
60
5
r.t.
50
6
H2O
70
60
7
EtOH/H2O
EtOH
70
70
8
70
20
9
MeOH
THF
70
70
10
11
12
13
70
20
H2O
Reflux
Reflux
Reflux
100
100
90
H2O
3
H2O
15
All reactions were carried out with 1 mmol of benzaldehyde and 1.1 mmol of malononitrile in 2 mL of
solvent
123

Binary copper and iron oxides immobilized on silica…
Table 2 Comparison of the influence of Fe, Si and Cu oxides on the Knoevenagel condensation of
benzaldehyde with malononitrile
Entry
Catalyst
Time (min)
Conversion (%)
1
2
3
4
5
6
SiO2
30
30
30
15
15
4
45
80
Fe3O4
Fe3O4@SiO2
CuO–Fe2O3
50
95
SiO2@CuO–Fe2O3
Fe3O4@SiO2@CuO–Fe2O3
98
100
All reactions were carried out with 1 mmol of benzaldehyde, 1.1 mmol of malononitrile and 0.03 g of
catalyst in H2O (2 mL) at reflux
activity in comparison to the singular species, due to the synergistic effect of all
compartments (Table 2, entry 6).
The utility of Fe3O4@SiO2@CuO–Fe2O3 MNPs in the Knoevenagel condensa-
tion of structurally diverse aromatic aldehydes with malononitrile was further
studied under the optimized reaction conditions. The results of this investigation are
summarized in Table 3. All reactions were carried out successfully in refluxing H2O
using the aldehyde (1 mmol), malononitrile (1.1 mmol) and Fe3O4@SiO2@CuO–
Fe2O3 MNPs (30 mg). The corresponding benzylidenemalononitriles were obtained
in high to excellent yields within 2–70 min. In the case of terephthalaldehyde and
isophthalaldehyde, which possess two formyl groups, the condensation reaction
required additional malononitrile (2.2 mmol) and afforded bis-substituted benzyli-
denemalononitriles in 91–93% yields (Table 3, entries 12 and 13). The calculation
shows that 0.03 g of the nanocatalyst contains 0.0171 g CuO (0.00022 mol).
Therefore, on the basis of CuO being a main component of the nanocatalyst, TON
and TOF values were calculated and the indexed data is presented in Table 3 [84].
The suitability of this synthetic protocol was highlighted by comparison of the
Knoevenagel condensation of benzaldehyde and malononitrile with Fe3O4@
SiO2@CuO–Fe2O3 MNPs and other reported reagents (Table 4). The current
protocol includes the advantageous in terms of its cost (0.09 USD per 30 mg of the
nanocatalyst) and reusability, as well as acceptable yields in shorter reaction times.
A plausible mechanism for the Knoevenagel condensation of aromatic aldehydes
and malononitrile catalyzed by Fe3O4@SiO2@CuO–Fe2O3 MNPs is shown in
Scheme 3. Activation of the aromatic aldehyde by the nanocatalyst triggers
nucleophilic attack of the methylene group of malononitrile to the activated
aldehyde, leading to C–C bond formation. Finally, dehydration of the intermediate
gives rise to the benzylidenemalononitrile product.
Recycling of Fe3O4@SiO2@CuO–Fe2O3 MNPs
The recoverability of Fe3O4@SiO2@CuO–Fe2O3 MNPs following the Knoevenagel
condensation of benzaldehyde and malononitrile under the optimized reaction
123

M. Gilanizadeh, B. Zeynizadeh
Table 3 The Knoevenagel condensation of aromatic aldehydes and malononitrile by Fe3O4@SiO2@
CuO–Fe2O3 MNPs
Mp (°C)
Time Yield
Entry
1
Substrate
CHO
Product
TONb,d
4091
TOFc,d
61364
Found
Reported
[Ref]
(min)
(%)a
CN
CN
81-83
82-84 [64]
4
90
CN
OMe
OMe
CHO
77-79
80 [68]
4227
16909
2
15
93
CN
CHO
CN
113-115
4318
4136
4091
12955
24818
49091
3
4
5
20
10
5
95
91
90
CN
112-114 [67]
MeO
Me
MeO
Me
CHO
CN
137-139
137-138 [68]
CN
Cl
Cl
CHO
CN
89-91
93-94 [78]
CN
CN
CHO
160-162
4136
4318
4227
35455
5182
6341
6
7
8
7
91
95
93
CN
161-162 [78]
Cl
Cl
O2N
CN
O2N
CHO
102-104
103-105 [78]
50
40
CN
CN
CHO
155-157
157-160 [67]
CN
O2N
O2N
O2N
CN
O2N
CHO
137-139
–
4364
4091
3740
9
70
5
96
90
CN
Cl
Cl
Cl
Cl
CHO
CHO
CN
141-143
–
49091
10
CN
Cl
Cl
MeO
CN
MeO
135-137
134-136 [71]
4409
4227
4136
17636
50727
11
12
13
15
5
97
93
91
CN
HO
HO
NC
CN
CN
OHC
CHO
CHO
175-177
–
CN
CN
CN
CN
260-262
295-297 [63]
124091
2
OHC
NC
All reactions were carried out with the reaction of aromatic aldehyde (1 mmol), malononitrile (1.1 mmol)
and Fe3O4@SiO2@CuO–Fe2O3 (30 mg) in refluxing H2O (2 mL). In entries 12 and 13: malononitrile
(2.2 mmol) was used
aYields refer to isolated pure products
bTON (turnover number): mmol of product per mmol of catalyst
cTOF (turnover frequency): mmol of product per mmol of catalyst per hour
dTON and TOF values were calculated on the basis of CuO (30 mg of the nanocatalyst contain 0.00022 mol CuO)
123

Binary copper and iron oxides immobilized on silica…
Table 4 Comparison of the promoter activity of Fe3O4@SiO2@CuO–Fe2O3 MNPs with other reported
reagents
CN
CN
CHO
Catalyst
NC
CN
+
Entry Catalyst
Condition/solvent Time
(min)
Yield
(%)
Reusability
(times)
Refs.
–
1
Fe3O4@SiO2@CuO–
Fe2O3 (30 mg)
reflux/H2O
4
90
5
2
3
4
Taurine (25 mg)
PANTTF (81 mg)
reflux/H2O
20 °C/H2O
r.t./H2O
14
90
86
99
94
6
[63]
[66]
[67]
21
5
CSC-Star-Glu-IL2
(200 mg)
120
5
6
7
[C4dabco][BF4] (19 mg)
MP(DNP) (14 mg)
ZnO (100 mg)
r.t./H2O
1
3
100
96
7
5
–
[74]
[76]
[69]
r.t./EtOH
r.t./solvent-free
80
92
Fe3O4@SiO2@CuO-Fe2O3 MNPs
CN
Ar
O
CN
Ar
H
H2O
O
H
H
H
OH
H
NC
CN
Ar
CN
Ar
CN
Scheme 3 A plausible mechanism for the Knoevenagel condensation catalyzed by Fe3O4@SiO2@CuO–
Fe2O3 MNPs
conditions was also studied. After completion of the reaction, the nanocatalyst was
separated from the reaction mixture by an external magnetic field, washed with
EtOH, and then dried in an oven for subsequent use. The magnetic mixed metal
oxide catalyst was able to be reused for five consecutive cycles without significant
loss of catalytic activity. The results of this investigation are summarized in Fig. 10.
123

M. Gilanizadeh, B. Zeynizadeh
Fig. 10 Recoverability of
Fe3O4@SiO2@CuO–Fe2O3
MNPs in the Knoevenagel
condensation of benzaldehyde
and malononitrile
100
80
60
40
20
0
90
90
89
89
89
1
2
3
4
5
Run number
Experimental
General
All chemicals were purchased from Merck Chemical Company and used without
1
further purification. H, 13C NMR and FTIR spectra were recorded on a Bruker
Avance spectrometer (300 MHz) and a Thermo Nicolet Nexus 670, respectively.
Melting points were obtained in open capillary tubes with a melting point apparatus
(Electrothermal) and were uncorrected. Thin-layer chromatography (TLC) on silica
gel 60 F254 aluminum sheets was used to determine the purity of the substrates and
products and to monitor reactions. Powder XRD was obtained by a PANalytical
X’Pert Pro (Netherlands) diffractometer at 40 kV and 30 mA with CuKa radiation
˚
(k = 1.5418 A), and the diffraction patterns were recorded in the 2h range (5–80°).
The morphology of the nanoparticles was examined by measuring SEM Images
using FESEM-TESCAN. The chemical composition of the nanocatalyst was
determined by EDX analysis. The N2 adsorption–desorption isotherms were
analyzed on a BELSORP-mini (BET Japan). The specific surface area of the sample
was measured by the Brunauer–Emmett–Teller (BET) technique. The pore volume
and pore size distribution were derived from the desorption profiles of the isotherms
using the Barrett–Joyner–Halenda (BJH) method. The magnetic properties of the
samples were obtained using a vibration sample magnetometer VSM (Meghnatis
Daghigh Kavir Co., Iran) under magnetic fields of up to 20 kOe. Thermogravimetric
analyses (TGA) were recorded on a simultaneous thermal analyzer (STA;
Rheometric Scientific Inc.). Transmission electron microscope (TEM) images were
obtained using an accelerating voltage of 100 kV on a Zeiss EM10C transmission
electron microscope. Inductively coupled plasma optical emission spectrometry
(ICP-OES) was utilized for the detection of chemical elements.
Preparation of magnetic Fe3O4 NPs
Nanoparticles of Fe3O4 were prepared by a chemical co-precipitation of chloride
salts of Fe2? and Fe3? [85]. In general, a solution of FeCl2Á4H2O (2.147 g,
0.0108 mol) and FeCl3Á6H2O (5.838 g, 0.0216 mol) in deionized H2O (100 mL)
123

Binary copper and iron oxides immobilized on silica…
was prepared and then the solution was stirred for 10 min at 85 °C under an N2
atmosphere. Upon addition of ammonia (25 wt%, 10 mL), the black nanoparticles
of Fe3O4 precipitated. The resulting mixture was again stirred at 85 °C for 30 min
under an N2 atmosphere. The mixture was cooled to room temperature, and the
magnetic nanoparticles of Fe3O4 were separated by an external magnetic field.
Washing the prepared nanoparticles twice with an aqueous solution of NaCl
(0.02 M) and deionized H2O afforded the pure Fe3O4 NPs, which were dried under
an air atmosphere.
Preparation of Fe3O4@SiO2 NPs
Nanoparticles of Fe3O4 were coated by a silica layer according to the reported
procedure [86]. A suspension of Fe3O4 MNPs (1.5 g) in deionized H2O (20 mL)
was prepared. Next, 2-propanol (200 mL) was added and the resulting mixture was
irradiated by ultrasound for 30 min. While the mixture was stirred, PEG (5.36 g),
deionized H2O (20 mL), ammonia (28 wt%, 10 ml) and TEOS (2 mL) were added
sequentially. The reaction mixture was then stirred for 28 h at room temperature.
Finally, the magnetic nanoparticles of Fe3O4@SiO2 were separated by an external
magnetic field and washed twice with deionized H2O and EtOH.
Preparation of Fe3O4@SiO2@CuO–Fe2O3 MNPs
Individually in three beakers (200 mL), a suspension of Fe3O4@SiO2 (0.1 g) MNPs
in deionized H2O (50 mL), a solution of Na2CO3 (1.589 g, 0.015 mol) and NaOH
(0.200 g, 0.005 mol) in deionized H2O (50 mL), and a solution of FeCl3Á6H2O
(1.352 g, 0.005 mol) and Cu(NO3)2Á3H2O (3.624 g, 0.015 mol) in deionized H2O
(50 mL) was prepared. The resulting suspension and solutions were irradiated under
ultrasound for 30 min. The prepared solutions of FeCl3Á6H2O/Cu(NO3)2Á3H2O and
Na2CO3/NaOH were then simultaneously added dropwise to the suspension of
Fe3O4@SiO2, and the resulting mixture was stirred vigorously. During the course of
the reaction, the pH was kept at 10–11 by the addition of an appropriate volume of
aqueous NaOH and HCl. The resulting slurry was left for 24 h at 80 °C without
stirring. The resulting mixture was cooled to room temperature and washed with
deionized H2O and EtOH. Calcination at 150 °C for 2 h afforded magnetic
nanoparticles of Fe3O4@SiO2@CuO–Fe2O3 (total weight: 2.091 g; Fe3O4@SiO2:
0.1 g, 4.78%; CuO: 1.193 g, 57.05% and Fe2O3: 0.798 g, 38.16%).
General procedure for the Knoevenagel condensation of benzaldehyde
and malononitrile
In a round-bottom flask (10 mL) equipped with a magnetic stirrer, a mixture of
benzaldehyde (0.106 g, 1 mmol), malononitrile (0.073 g, 1.1 mmol) and H2O
(2 mL) was well mixed at room temperature. Fe3O4@SiO2@CuO–Fe2O3 (30 mg)
was then added and the resulting mixture was stirred for 4 min at reflux. The
progress of the reaction was monitored by TLC (eluent: EtOAc/n-hexane: 2/4).
After completion of the reaction, the catalyst was separated by an external magnet
123

M. Gilanizadeh, B. Zeynizadeh
and the reaction mixture was extracted with EtOAc (2 9 5 mL). The organic
solution was then dried over anhydrous Na2SO4. Evaporation of the solvent afforded
the pure benzylidenemalononitrile in 90% yield (0.139 g, Table 3, entry 1).
Conclusions
In this study, magnetic nanoparticles of immobilized CuO–Fe2O3 on silica-layered
magnetite were synthesized. The magnetite mixed metal oxide was then charac-
terized using FTIR, SEM, EDX, XRD, BET, TGA, DTG, VSM, TEM and ICP-OES
analyses. The prepared Fe3O4@SiO2@CuO–Fe2O3 MNPs were successfully
utilized in the Knoevenagel condensation of structurally diverse aromatic aldehydes
and malononitrile in refluxing H2O. The corresponding benzylidenemalononitriles
were obtained in high to excellent yields within 2–70 min. This method has several
advantages, including high yields, short reaction times, mild reaction conditions, a
simple separation and work-up procedure, and the use of H2O as a green and
economical solvent. The catalyst can be reused for at least five consecutive cycles
without significant loss of catalytic activity.
Acknowledgements The authors gratefully acknowledged the financial support of this work by the
research council of Urmia University.
References
1. B. Aday, Y. Yildiz, R. Ulus, S. Eris, F. Sen, M. Kaya, New J. Chem. 40, 748 (2016)
2. H. Goksu, Y. Yildiz, B. Celik, M. Yazici, B. Kilbas, F. Sen, Catal. Sci. Technol. 6, 2318 (2016)
3. F. Sen, G. Gokagac, S. Sen, J. Nanopart. Res. 15, 1979 (2013)
4. B. Aday, H. Pamuk, M. Kaya, F. Sen, J. Nanosci. Nanotechnol. 16, 6498 (2016)
5. Y. Yildiz, E. Erken, H. Pamuk, H. Sert, F. Sen, J. Nanosci. Nanotechnol. 16, 5951 (2016)
6. O. Karatepe, Y. Yildiz, H. Pamuk, S. Eris, Z. Dasdelen, F. Sen, RSC Adv. 6, 50851 (2016)
7. Y. Yildiz, S. Kuzu, B. Sen, A. Savk, S. Akocak, F. Sen, Int. J. Hydrogen Energy 42, 13061 (2017)
8. E. Erken, Y. Yildiz, B. Kilbas, F. Sen, J. Nanosci. Nanotechnol. 16, 5944 (2016)
9. Y. Yildiz, T. Onal Okyay, B. Sen, B. Gezer, S. Kuzu, A. Savk, E. Demir, Z. Dasdelen, H. Sert, F.
Sen, ChemistrySelect 2, 697 (2017)
10. S. Akocak, B. Sen, N. Lolak, A. Savk, M. Koca, S. Kuzu, F. Sen, Nano Struct. Nano Objects 11, 25
(2017)
11. H. Goksu, B. Celik, Y. Yildiz, F. Sen, B. Kilbas, ChemistrySelect 1, 2366 (2016)
12. B. Sen, S. Kuzu, E. Demir, T.O. Okyay, F. Sen, Int. J. Hydrogen Energy 42, 23299 (2017)
13. Z. Dasdelen, Y. Yildiz, S. Eris, F. Sen, Appl. Catal. B Environ. 219, 511 (2017)
14. B. Sena, E. Hazal Akdere, A. Savk, E. Gultekin, O. Parali, H. Goksu, F. Sen, Appl. Catal. B Environ.
225, 148 (2018)
15. I. Esirden, E. Erken, M. Kaya, F. Sen, Catal. Sci. Technol. 5, 4452 (2015)
16. B. Celik, Y. Yildiz, H. Sert, E. Erken, Y. Koskun, F. Sen, RSC Adv. 6, 24097 (2016)
17. B. Celik, E. Erken, S. Eris, Y. Yildiz, B. Sahin, H. Pamuk, F. Sen, Catal. Sci. Technol. 6, 1685 (2016)
18. E. Erken, I. Esirden, M. Kaya, F. Sen, RSC Adv. 5, 68558 (2015)
19. Y. Yildiz, H. Pamuk, O. Karatepe, Z. Dasdelen, F. Sen, RSC Adv. 6, 32858 (2016)
20. H. Goksu, Y. Yildiz, B. Celik, M. Yazici, B. Kilbas, F. Sen, ChemistrySelect 1, 953 (2016)
21. M. Gilanizadeh, B. Zeynizadeh, New J. Chem. (2018). https://doi.org/10.1039/C8NJ00788H
22. S.U. Sonavane, M.B. Gawande, S.S. Deshpande, A. Venkataraman, R.V. Jayaram, Catal. Commun.
8, 1803 (2007)
123

Binary copper and iron oxides immobilized on silica…
23. Y. Izumi, N. Natsume, H. Takamine, I. Tamaoki, K. Urabe, Bull. Chem. Soc. Jpn. 62, 2159 (1989)
24. K. Tanabe, W.F. Holderich, Appl. Catal. A 181, 399 (1999)
25. B.M. Reddy, A. Khan, Catal. Rev. Sci. Eng. 47, 257 (2005)
26. S. Ajaikumar, A. Pandurangan, Appl. Catal. A 357, 184 (2009)
27. W.C. Sheets, E.S. Stampler, H. Kabbour, M.I. Bertoni, L. Cario, T.O. Mason, T.J. Marks, K.R.
Poeppelmeier, Inorg. Chem. 46, 10741 (2007)
28. A. Tang, H. Yang, X. Zhang, Int. J. Phys. Sci. 1, 102 (2006)
29. V.V. Zyryanov, Inorg. Mater. 39, 1163 (2003)
30. H. Cui, M. Zayat, D. Levy, J. Sol-Gel Sci. Technol. 35, 175 (2005)
31. A. Elia, P.M. Aispuro, N. Quaranta, J.M. Martın-Martınez, P. Vazquez, Macromol. Symp. 301, 136
(2011)
32. Y.J. Kim, S.B. Rawal, S.D. Sung, W.I. Lee, Bull. Korean Chem. Soc. 32, 141 (2011)
33. P.F. Fulvio, S. Pikus, M. Jaroniec, A.C.S. Appl. Mater. Interfaces 2, 134 (2010)
34. D. Jiang, L. Su, L. Ma, N. Yao, X. Xu, H. Tang, X. Li, Appl. Surf. Sci. 256, 3216 (2010)
35. B.M. Reddy, I. Ganesh, J. Mol. Catal. A Chem. 169, 207 (2001)
36. B.M. Reddy, B. Chowdhury, P.G. Smirniotis, Appl. Catal. A 211, 19 (2001)
37. G. Sankar, C.N.R. Rao, T. Rayment, J. Mater. Chem. 1, 299 (1991)
38. A.S. Kulkarni, R.V. Jayaram, J. Mol. Catal. A Chem. 223, 107 (2004)
39. Y.C. Chang, S.W. Chang, D.H. Chen, React. Funct. Polym. 66, 335 (2006)
40. V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J.M. Basset, Chem. Rev. 111, 3036 (2011)
41. R. Abu-Reziq, H. Alper, D. Wang, M.L. Post, J. Am. Chem. Soc. 128, 5279 (2006)
42. M. Shokouhimehr, Y. Piao, J. Kim, Y. Jang, T. Hyeon, Angew. Chem. Int. Ed. 46, 7039 (2007)
43. D.H. Zhang, G.D. Li, J.X. Li, J.S. Chen, Chem. Commun. 3414 (2008)
44. A.H. Lu, E.L. Salabas, F. Schuth, Angew. Chem. Int. Ed. 46, 1222 (2007)
45. M.B. Gawande, P.S. Branco, R.S. Varma, Chem. Soc. Rev. 42, 3371 (2013)
46. S. Shylesh, V. Schu¨nemann, W.R. Thiel, Angew. Chem. Int. Ed. 49, 3428 (2010)
47. S.M. Baghbanian, M. Farhang, Synth. Commun. 44, 697 (2014)
48. A.P. Amrute, A. Bordoloi, N. Lucas, K. Palraj, S.B. Halligudi, Catal. Lett. 126, 286 (2008)
49. S.J. Singh, R.V. Jayaram, Tetrahedron Lett. 49, 4249 (2008)
50. Q. Shi, R. Lu, L. Lu, X. Fu, D. Zhao, Adv. Synth. Catal. 349, 1877 (2007)
51. M. Kang, E.D. Park, J.M. Kim, J.E. Yie, Catal. Today 111, 236 (2006)
52. N. Li, C. Descorme, M. Besson, Appl. Catal. B 76, 92 (2007)
53. S.S. Deshpande, R.V. Jayaram, Catal. Commun. 9, 186 (2008)
54. Q. Zhuang, J.M. Miller, Appl. Catal. A 209, L1 (2001)
55. M. Crivello, C. Peꢀrez, E. Herrero, G. Ghione, S. Casuscelli, E. Rodrıguez-Castellon, Catal. Today
107–108, 215 (2005)
56. A.K. Singh, S.D. Fernando, Energy Fuels 23, 5160 (2009)
57. G. Centi, S. Perathoner, Catal. Rev. Sci. Eng. 40, 175 (1998)
58. M.A. Carreon, V.V. Guliants, Eur. J. Inorg. Chem. 2005, 27 (2005)
59. L.F. Tietze, U. Beifuss, Comprehensive Organic Synthesis, vol. 2 (Pergamon Press, Oxford, 1991),
p. 341
60. F. Freeman, Chem. Rev. 69, 591 (1969)
61. R.K.G. Panicker, S. Krishnapillai, Tetrahedron Lett. 55, 2352 (2014)
62. M. Almasi, V. Zelenak, M. Opanasenko, J. Cejka, Dalton Trans. 43, 3730 (2014)
63. F. Shirini, N. Daneshvar, RSC Adv. 6, 110190 (2016)
64. S. Wang, Z. Ren, W. Cao, W. Tong, Synth. Commun. 31, 673 (2001)
65. J. Zhang, T. Jiang, B. Han, A. Zhu, X. Ma, Synth. Commun. 36, 3305 (2006)
66. G. Li, J. Xiao, W. Zhang, Green Chem. 14, 2234 (2012)
67. P. Gupta, M. Kour, S. Paul, J.H. Clark, RSC Adv. 4, 7461 (2014)
68. M.M. Heravi, K. Bakhtiari, S. Taheri, H.A. Oskooi, J. Chin. Chem. Soc. 54, 1557 (2007)
69. M. Basude, P. Sunkara, V.S. Puppala, J. Chem. Pharm. Res. 5, 46 (2013)
70. M.A. Pasha, K. Manjula, V.P. Jayashankara, Indian J. Chem. 49, 1428 (2010)
71. R. Pal, Int. J. Adv. Chem. 2, 27 (2014)
72. R. Gupta, M. Gupta, S. Paul, R. Gupta, Bull. Korean Chem. Soc. 30, 2419 (2009)
73. W.X. Zuo, R. Hua, X. Qiu, Synth. Commun. 34, 3219 (2004)
74. D.Z. Xu, Y. Liu, S. Shi, Y. Wang, Green Chem. 12, 514 (2010)
75. A. Rostami, B. Atashkar, H. Gholami, Catal. Commun. 37, 69 (2013)
76. S.K. Panja, N. Dwivedi, S. Saha, RSC Adv. 5, 65526 (2015)
123

M. Gilanizadeh, B. Zeynizadeh
77. R. Vaid, M. Gupta, Monatshefte Chem. 146, 645 (2015)
78. S.L. Khillare, A.O. Dhokte, M.K. Lande, B.R. Arbad, Int. J. Chem. Pharm. Sci. 5, 96 (2014)
79. M. Gupta, R. Gupta, M. Anand, Beilstein J. Org. Chem. 5, 68 (2009)
80. C. Zhuo, D. Xian, W. Jian-wei, X. Hui, ISRN Org. Chem. 676789 (2011)
81. G.Y. Li, Y.R. Jiang, K.L. Huang, P. Ding, L.L. Yao, Colloids Surf. A Physicochem. Eng. Asp. 320,
11 (2008)
´
82. J.A. Lopez, F. Gonzalez, F.A. Bonilla, G. Zambrano, M.E. Gomez, Rev. LatinAm. Metal. Mater. 30,
´
60 (2010)
83. A. Azam, A.S. Ahmed, M. Oves, M.S. Khan, S.S. Habib, A. Memic, Int. J. Nanomed. 7, 6003 (2012)
84. J.J. Boruah, S.P. Das, S.R. Ankireddy, S.R. Gogoi, N.S. Islam, Green Chem. 15, 2944 (2013)
85. X. Liu, Z. Ma, J. Xing, H. Liu, J. Magn. Magn. Mater. 270, 1 (2004)
86. Y. Zhang, G.M. Zeng, L. Tang, D.L. Huang, X.Y. Jiang, Y.N. Chen, Biosens. Bioelectron. 22, 2121
(2007)
123