Synthesis and characterization of a magnetic graphene oxide/Zn-Ni-Fe layered double hydroxide nanocomposite: An efficient mesoporous catalyst for the green preparation of biscoumarins

Article abstract of DOI:10.1039/c9nj04718b

In this study, a nanocomposite of Fe₃O₄@GO@Zn-Ni-Fe-layered double hydroxide was synthesized as a novel and efficient mesoporous magnetic nanocatalyst. The synthesis was carried out via the immobilization of Fe₃O₄

Full text of DOI:10.1039/c9nj04718b

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Synthesis and characterization of a magnetic
graphene oxide/Zn–Ni–Fe layered double
hydroxide nanocomposite: an efficient mesoporous
catalyst for the green preparation of biscoumarins†
Cite this: New J. Chem., 2019,
43, 18794
Behzad Zeynizadeh * and Masumeh Gilanizadeh
In this study, a nanocomposite of Fe3O4@GO@Zn–Ni–Fe-layered double hydroxide was synthesized as a
novel and efficient mesoporous magnetic nanocatalyst. The synthesis was carried out via the immobilization
of Fe3O4 MNPs (magnetic nanoparticles) on graphene oxide and then the layering of Zn–Ni–Fe-layered
double hydroxide moieties on the constituents of Fe3O4@GO. The magnetic graphene oxide/layered double
hydroxide system was then characterized using SEM, EDX, FTIR, XRD, TEM and VSM analyses. The catalytic
activity of the prepared composite system was further studied towards one-pot Knoevenagel–Michael
reaction of aromatic aldehydes with 4-hydroxycoumarin in water. All reactions were carried out under
reflux conditions giving biscoumarin materials in 87–95% yields within 3–40 min. This method has
noteworthy advantages in terms of mild reaction conditions, short reaction times, utilizing water as an
environmental friendly solvent and applying a magnetically separable catalyst system.
Received 14th September 2019,
Accepted 4th November 2019
DOI: 10.1039/c9nj04718b
rsc.li/njc
Fe3O4@GO is prepared. This composite system prevents the
aggregation of magnetic nuclei effectively. A literature survey
Introduction
Nowadays, there is an intense focus on using heterogeneous shows that graphene oxide, because of its unique characteristics,
catalysts for the promotion of various chemical transformations.1,2 has been widely used in the fields of sensors, nanofiltration, solar
In addition, heterogeneous catalysis is a very interesting tool cells, electrodialysis, electronics and nanocatalysts for chemical
that facilitates many organic reactions.3–9 In this context, the transformations.18–25 In addition, the presence of carboxylic acids
application of heterogeneous nanocatalysts with particular and epoxy functionalities in the basal planes of graphene oxide
activities has also attracted the attention of numerous scientists. boosts its propagation in water. Moreover, they can operate as
After the synthesis and application of heterogeneous nano- active sites for the functionalization and hybridization of graphene
catalysts, their recovery and reusability as one of the essential oxide with other nanomaterials.26,27 On the other hand, layered
aspects of green chemistry are more important. A literature double hydroxides (LDHs) have a two-dimensional structure and
review shows that a combination system of heterogeneous belong to the category of anionic clay minerals.28 They are defined
nanocatalysts with various magnetic materials could be a prominent as environmentally friendly materials and exhibit attractive
choice for the above mentioned strategy. The magnetic nano- chemical and physical properties.29,30 LDHs are naturally occur-
catalysts are easily separated from the reaction mixture using an ring and therefore can be easily prepared by routine procedures.
external magnetic field and facilitate the recovery of the examined Based on the unique characteristics of graphene oxide and LDH
catalyst systems.10–12 In spite of this, however, due to high surface materials, nowadays, the focus on the combination systems of GO
energy and attraction of magnetic cores, nanoparticles of magnetic and LDHs has gained considerable interest.
materials have a high tendency for aggregation.13–15
Coumarin and biscoumarin derivatives are heterocyclic com-
Graphene oxide (GO) as a multi-functional carbon material ponents of various synthetic and natural organic compounds.
and possessing huge surface area is commonly used for protecting Coumarins show several applications in fragrance and pharma-
magnetic nanoparticles (MNPs), particularly Fe3O4.16,17 By the ceutical industries.31 In addition, biscoumarin materials represent
in situ immobilization of Fe3O4 MNPs on the surface or inter- a wide range of biological activities including antibiotics, anti-
lamellar spaces of graphene oxide, the nanocomposite of cancer, anticoagulants, insecticidal, antifungal and HIV protease
inhibition.32–34 Because of these great potentialities, the synthesis
of biscoumarin materials was carried out using Pechmann,
Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran.
Reformatsky, Perkin, Wittig and Knoevenagel reactions. Among
these, application of the Knoevenagel condensation reaction
E-mail: bzeynizadeh@gmail.com; Fax: +98-44-32755294; Tel: +98-44-32755294
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c9nj04718b
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using different catalyst/promoter systems is more investigated.35–40
Although most of the reported methods have their own merits,
they generally suffer from some limitations. Therefore, the
development of simple synthetic procedures utilizing recyclable
green catalyst systems41–45 is still demanded for the preparation
of biscoumarin materials. In line with the outlined strategies,
herein, we wish to report the synthesis of nanostructured
Fe3O4@GO@Zn–Ni–Fe-LDH composite system as a novel hetero-
geneous and highly efficient mesoporous catalyst towards the
Knoevenagel–Michael reaction of 4-hydroxycoumarin with aro-
matic aldehydes in refluxing H2O to afford biscoumarin materials
in high yields.
Results and discussion
Synthesis and characterization of the
Fe3O4@GO@Zn–Ni–Fe-LDH system
The study was started by the synthesis of a nanostructured
Fe3O4@GO@Zn–Ni–Fe-LDH composite system via a four step
procedure (Fig. 1). Primarily, the synthetic process was carried
out with the transformation of graphite to graphene oxide.
Next, the magnetic nanoparticles of Fe3O4 were immobilized on
the surface or interlamellar spaces of graphene oxide via a
chemical co-precipitation method. Zn–Ni–Fe-layered double
hydroxide was then prepared and after that it was immobilized
on the surface of the Fe3O4@GO constituents. Structural elucidation
of the prepared nanocomposite system was then carried out using
SEM, EDX, FTIR, XRD, TEM and VSM analyses.
Fig. 2 Scanning electron microscopy images of the Fe3O4@GO@Zn–Ni–
Fe-LDH system.
The scanning electron microscopy technique as a primary tool the formation of small segments with the size distribution
was utilized to determine the size distribution of the nanoparticles ranging from 25 to 39 nm.
as well as the surface-morphology of the Fe3O4@GO@Zn–Ni–Fe-
Next, the elemental composition of the composite system
LDH composite system. The illustrated SEM images (Fig. 2) show was determined using the energy-dispersive X-ray spectroscopy
that the surface of the composite system is extremely porous and technique. Fig. 3 represents the elemental contents and EDX
constructed from rough/irregular nanoparticles. The images spectrum of the nanostructured Fe3O4@GO@Zn–Ni–Fe-LDH
also represent that the agglomeration of nanoparticles led to system. The analysis clearly shows that the elements of Fe,
Fig. 1 Synthesis of the Fe3O4@GO@Zn–Ni–Fe-LDH system.
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Fig. 3 EDX spectrum of the Fe3O4@GO@Zn–Ni–Fe-LDH system.
O, C, Zn and Ni exist in the structure of the nanocomposite
system.
The existence of functional groups in graphene oxide, Fe3O4,
Fe3O4@GO, Zn–Ni–Fe-LDH and Fe3O4@GO@Zn–Ni–Fe-LDH
was also elucidated using Fourier transformed infrared spectro-
scopy (Fig. 4). The FTIR spectrum of graphene oxide shows a
strong absorption peak at 3416 cmꢀ1 corresponding to the
stretching vibration of O–H bonds. This absorption clearly
verifies the existence of OH or COOH groups in the structure
of graphene oxide. In addition, the symmetric and asymmetric
stretching vibrations of C–H bonds (2927 and 2962 cmꢀ1), the
stretching vibration of CQO bonds (1724 cmꢀ1) and CQC from
the unoxidized graphitic domain (1627 cmꢀ1), deformation of
O–H bonds (1373 cmꢀ1), and stretching vibration of C–O bonds
in the epoxy groups (1221 cmꢀ1) and C–O bonds in the alkoxy
groups (1050 cmꢀ1) are also observable in the spectrum of
graphene oxide. In this context, the FTIR spectrum of Fe3O4
shows a strong absorption peak at 575 cmꢀ1 attributed to the
vibration of Fe–O bonds in iron oxide. The absorption peaks at
1625 and 3400 cmꢀ1 are also assigned to the O–H deformation
and stretching vibrations of OH groups on the surface or the
adsorbed water in Fe3O4, respectively. Consequently, the FTIR
spectrum of the Fe3O4@GO system represents that the spectrum
contains the characteristics peaks of Fe3O4 and GO constituents.
This verifies that the magnetic nanoparticles of Fe3O4 were
successfully immobilized on the surface and interlamellar
spaces of GO. In the cases of FTIR spectra of Zn–Ni–Fe-LDH
and Fe3O4@GO@Zn–Ni–Fe-LDH systems, the presence of a strong
absorption peak at 3435 cmꢀ1 is attributed to the stretching
vibrations of OH groups in metal–OH groups as well as hydrogen
bonding from the adsorbed water. Deformation of OH groups
Fig. 4 FTIR spectra of graphene oxide, Fe3O4, Fe3O4@GO, Zn–Ni–Fe-
LDH and Fe3O4@GO@Zn–Ni–Fe-LDH.
exhibits an additional absorption peak at 1630 cmꢀ1. In addition,
2ꢀ
asymmetric stretching of CO3 is observed around 1360 cmꢀ1
.
The lattice vibration modes of M–OH and M–O also exist between
1000 and 500 cmꢀ1
.
In continuation, the phase purity and crystalline character
of the Fe3O4 and Fe3O4@GO@Zn–Ni–Fe-LDH composite system
were studied using X-ray diffraction analysis (Fig. 5). The XRD
diffraction pattern of Fe3O4 (Fig. 5a) shows the reflection planes
at 2y = 30.21 (0 2 2), 35.51 (1 1 3), 43.31 (0 0 4), 53.71 (2 2 4), 57.21
Fig. 5 X-ray diffraction patterns of (a) Fe3O4 and (b) the Fe3O4@GO@Zn–
(1 1 5) and 62.91 (0 4 4) corresponding to the standard one of Ni–Fe-LDH system.
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the cubic spinel structure of Fe3O4 with a high phase purity and
crystallinity (JCPDS 65-3107).46,47 In the XRD pattern of the
Fe3O4@GO@Zn–Ni–Fe-LDH system, consequently, the corres-
ponding reflection planes at 2y = 11.41 (0 0 3), 23.01 (0 0 6),
34.61 (0 1 2), 39.01 (0 1 5), 46.31 (0 1 8), 60.21 (1 1 0) and 61.51
(1 1 3) represent the characteristic signals for the layered
double hydroxide moiety (Fig. 5b). The nanocomposite has a
rhombohedral crystalline structure and exhibits the ICSD
reference pattern of 01-089-7111 for nickel oxide hydroxide.
The reflection planes of (0 0 3), (0 0 6), (1 1 0) and (1 1 3) are the
particular characteristics of LDH-like materials.48 The literature
review shows that graphene oxide has the reflection planes at
2y = 10.61 (0 0 1), 22.51 (0 0 2), 43.21 (1 0 1) and 50.91 (1 0 2).49 In
the case of the XRD pattern of the Fe3O4@GO@Zn–Ni–Fe-LDH
system, the relevant peaks of graphene oxide were overlapped
or influenced by the reflection planes of LDH and Fe3O4
constituents.
Structural elucidation of the Fe3O4@GO@Zn–Ni–Fe-LDH
composite system was further investigated using the transmission
electron microscopy (TEM) technique. The depicted images in
Fig. 6 clearly represent that the nanocomposite was constructed
from the layering of LDH over Fe3O4@GO constituents. In
addition, the nanoparticles are agglomerated to some extent
to afford bigger segments.
The magnetic behavior and value of the Fe3O4 and Fe3O4@
GO@Zn–Ni–Fe-LDH system were also studied using vibrating
sample magnetometer (VSM) analysis. The depicted graphs in
Fig. 7 show the non-linear and reversible magnetic property for
Fe3O4 (curve a) and Fe3O4@GO@Zn–Ni–Fe-LDH (curve b). The
saturation magnetization (Ms) values of Fe3O4 and the Fe3O4@
GO@Zn–Ni–Fe-LDH system are respectively 70 emu gꢀ1 and
16 emu gꢀ1. It is clear that when a layer of non-magnetic LDH
surrounds the magnetic graphene oxide species, the saturation
magnetization value of Fe3O4 was intensively decreased. Never-
theless, the magnetization value is still enough for any magnetic
separation.
Preparation of biscoumarin materials
After the successful synthesis and characterization of the nano-
structured Fe3O4@GO@Zn–Ni–Fe-LDH system, in continuation,
it was prompted that the catalytic activity of the prepared
nanocomposite system was studied towards one-pot Knoevenagel–
Michael reaction of aromatic aldehydes with 4-hydroxycoumarin. In
this context, the condensation reaction of benzaldehyde with
4-hydroxycoumarin was selected as a model reaction and there-
fore the influence of the amount of nanocatalyst, temperature
Fig. 6 TEM images of the Fe3O4@GO@Zn–Ni–Fe-LDH system.
and solvent was studied therein. The results of this investigation condensation reaction within 3 min. Therefore, the conditions
are summarized in Table 1. Investigation of the results exhibited mentioned in entry 14 (Table 1) were selected as the require-
that the progress of the condensation reaction in the absence of ments to carry out the condensation reaction of benzaldehyde
the nanocatalyst led to poor to moderate yield of the product. By with 4-hydroxycoumarin efficiently.
examining the title reaction in DMF, CH3CN, EtOAc, MeOH,
The usefulness and catalytic activity of the Fe3O4@GO@Zn–
EtOH, H2O–EtOH and H2O with 20–40 mg of the Fe3O4@ Ni–Fe-LDH system was further studied toward one-pot Knoevenagel–
GO@Zn–Ni–Fe-LDH system, it was concluded that H2O as a Michael reaction of structurally diverse aromatic aldehydes
green solvent was the best solvent of choice and 30 mg of the with 4-hydroxycoumarin at the optimized reaction conditions
nanocatalyst was an adequate amount to promote the condensation (Table 2). Reviewing the results shows that all the condensation
reaction perfectly. Moreover, using reflux conditions completed the reactions were carried out successfully within 3–40 min to
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reusability of the nanocatalysts, the present work exhibited a more
outstanding result than the previous systems.
Although the exact mechanism of this synthetic protocol is
not known, the depicted mechanism in Fig. 8 exhibits the role of
Fe3O4@GO@Zn–Ni–Fe-LDH in the catalysis of the Knoevenagel–
Michael reaction of 4-hydroxycoumarin with aromatic aldehydes.
The figure shows that through the activation of aldehyde by the
nanocatalyst, the nucleophilic attack of 4-hydroxycoumarin took
place. Subsequently, the Michael reaction of another molecule of
4-hydroxycoumarin with the prepared intermediate of benzylidene-
coumarin affords the final biscoumarin material.
Reusability of the Fe3O4@GO@Zn–Ni–Fe-LDH system
The economic and green aspect of the Knoevenagel–Michael
reaction of benzaldehyde with 4-hydroxycoumarin in the
presence of the Fe3O4@GO@Zn–Ni–Fe-LDH system was further
studied by examining the reusability of the nanocomposite at
the optimized reaction conditions. In this context once the
Fig. 7 Magnetization curves of (a) Fe3O4 and (b) the Fe3O4@GO@Zn–Ni–
Fe-LDH system.
afford the corresponding biscoumarin materials in 87–95% condensation reaction was completed, the nanocatalyst was
yields. In addition, an examination for gram-scale synthesis of magnetically separated from the reaction mixture, washed with
biscoumarin materials with the present protocol represents EtOAc and then dried under air atmosphere. The reaction vessel
that the condensation reaction of 4-hydroxycoumarin (3 mmol) was again charged with fresh benzaldehyde, 4-hydroxycoumarin
and benzaldehyde (1.5 mmol) in the presence of Fe3O4@ and the recycled nanocatalyst to run the reaction for a second
GO@Zn–Ni–Fe-LDH (90 mg) was carried out successfully under time. Fig. 9 shows that the Fe3O4@GO@Zn–Ni–Fe-LDH system
reflux conditions to afford 3,30-benzylidenebis(4-hydroxycoumarin) can be reused for 5 consecutive cycles with a small loss in the
in 94% yield (1.16 g) within 10 min.
yield from 95% to 87%. In this context, the FTIR spectrum
Next, the suitability of this synthetic method was high- (Fig. S1, ESI†), SEM (Fig. S2, ESI†) and EDX analysis (Fig. S3,
lighted by the comparison of the obtained result for the Fe3O4@ ESI†) of the first recycling step of the Fe3O4@GO@Zn–Ni–Fe-
GO@Zn–Ni–Fe-LDH system with those reported for other protocols. LDH system represent that during the progress of the condensation
Table 3 represents that in terms of the yield, reaction time and reaction, the morphology and elemental composition of the
Table 1 Optimization experiments for the Knoevenagel–Michael reaction of benzaldehyde with 4-hydroxycoumarin catalyzed by the Fe3O4@GO@Zn–
Ni–Fe-LDH systema
Entry
Fe3O4@GO@Zn–Ni–Fe-LDH (mg)
Solvent (2 mL)
Temp. (1C)
Time (min)
Conversion (%)
1
2
3
4
5
6
7
8
—
—
—
30
30
30
30
30
30
30
30
30
30
30
20
40
H2O
H2O
Solvent-free
Solvent-free
H2O
H2O
H2O–EtOH (1 : 1)
EtOH
MeOH
EtOAc
CH3CN
DMF
r.t.
600
70
90
30
15
360
60
30
30
30
30
30
60
3
70
60
Trace
50
100
60
90
50
30
40
60
70
70
100
100
100
Reflux
100
70
70
r.t.
Reflux
70
70
70
70
70
r.t.
Reflux
Reflux
Reflux
9
10
11
12
13
14
15
16
H2O
H2O
H2O
H2O
15
1
a
All reactions were carried out with the molar ratio of 1 : 0.5 for 4-hydroxycoumarin and benzaldehyde in 2 mL of solvent. Conversions less than
100% were determined on the basis of the recovered 4-hydroxycoumarin.
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Table 2 Synthesis of biscoumarin materials by the Fe3O4@GO@Zn–Ni–Fe-LDH systema
M.p. (1C)
Entry
1
R
Product
Time (min)
Yieldb (%)
Found
Reportedref.
229–23136
H
3
95
230–232
267–269
2
4-Me
20
90
266–26936
3
4
5
6
4-OMe
2-OMe
4-Cl
20
25
10
5
91
89
91
89
249–251
190–193
257–259
200–202
250–25236
—
261–26336
2-Cl
201–20336
7
8
4-NO2
3-NO2
4
93
91
231–233
215–217
233–23536
10
214–21536
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Table 2 (continued)
M.p. (1C)
Entry
9
R
Product
Time (min)
Yieldb (%)
Found
Reportedref.
249–25230
4-Cl-3-NO2
15
93
251–253
200–202
10
2,4-Cl2
12
90
198–20040
11
12
13
4-OMe-3-OH
4-OH-3-OMe
4-CHO
40
30
3
91
93
89
243–245
201–203
181–183
—
—
—
14
4-CHO
7
87
263–265
—
a
All reactions were carried out with the molar ratio of 1 : 0.5 for 4-hydroxycoumarin and aromatic aldehydes in the presence of 30 mg of the
b
nanocatalyst under refluxing H2O (2 mL). In the case of entry (14), 4-hydroxycoumarin (2 mmol) was used. Yield refers to isolated pure product.
nanocatalyst remained intact. However after five recycling steps, active species and/or collapse of the mesopores on the surface or
yield-losing of the product could be attributed to the leaching of within the interlamellar spaces of the nanocomposite system.
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Table 3 Comparison of the synthesis of 3,30-benzylidenebis(4-hydroxycoumarin) with Fe3O4@GO@Zn–Ni–Fe-LDH and other reported systems
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Entry
Catalyst
Condition/solvent
Time (min)
Yield (%)
Reusability
Ref.
a
1
2
3
4
5
6
7
Fe3O4@GO@Zn–Ni–Fe-LDH
RuCl3ꢁnH2O
Reflux/H2O
80 1C/H2O
80 1C/solvent-free
80 1C/H2O
r.t./EtOH
Reflux/H2O
80 1C/EtOH
3
25
30
20
30
12
20
95
84
92
93
92
94
93
5
6
3
5
3
5
3
35
36
37
38
39
40
[MIM(CH2)4SO3H][HSO4]
Phosphotungstic acid
(H14[NaP5W30O110])/SiO2
CuO–CeO2
SiO2–OSO3H NPs
a
Present work.
Fig. 8 A proposed mechanism for the Knoevenagel–Michael reaction of aromatic aldehydes with 4-hydroxycoumarin catalyzed by the Fe3O4@
GO@Zn–Ni–Fe-LDH system.
then characterized using SEM, EDX, FTIR, XRD, TEM and VSM
Conclusions
analyses. Next, the catalytic activity of Fe3O4@GO@Zn–Ni–Fe-
In this study, through the combination system of magnetic LDH (30 mg) was further investigated towards the Knoevenagel–
graphene oxide and Zn–Ni–Fe-layered double hydroxide con- Michael reaction of 4-hydroxycoumarin (1 mmol) with structurally
stituents, the nanocomposite of Fe3O4@GO@Zn–Ni–Fe-LDH diverse aromatic aldehydes (0.5 mmol). All reactions were carried
was synthesized. The prepared magnetic GO–LDH system was out in refluxing H2O to afford biscoumarins in 87–95% yields
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drop-wise manner and the reaction mixture was stirred at 98 1C
for 15 min. Next, the addition of distilled water (100 mL) and
H2O2 (20 mL, 30%) to the reaction mixture was also carried out.
The solid residue was filtered and washed twice by an aqueous
solution of HCl (5%). The prepared graphene oxide was then
dried in an oven at 50 1C.
Synthesis of the magnetic graphene oxide composite system
The composite of magnetic graphene oxide was prepared by a
chemical co-precipitation method.52 Accordingly in a round-
bottom flask containing a solution of distilled water (100 mL)
and glacial acetic acid (3 mL), FeCl2ꢁ4H2O (1.29 g, 0.0065 mol)
and FeCl3ꢁ6H2O (3.51 g, 0.013 mol) were added under vigorous
stirring. In another vessel, a mixture of graphene oxide (50 mg)
in distilled water (15 mL) was sonicated for 2 h. After that, the
solution of iron chlorides and suspension of graphene oxide
were mixed together and the prepared mixture was stirred at
80 1C. Next, aqueous ammonia (20 mL, 25 wt%) was added
rapidly and the resulting mixture was stirred for 20 min. During
the addition of ammonia, nanoparticles of Fe3O4 were success-
fully immobilized on the surface or within the interlamellar
spaces of graphene oxide. Finally, the prepared composite of
Fe3O4@GO was magnetically separated and washed twice with
ethanol and distilled water and left to dry in an oven at 50 1C.
Fig. 9 Reusability of the Fe3O4@GO@Zn–Ni–Fe-LDH system in the
synthesis of 3,30-benzylidenebis(4-hydroxycoumarin) material.
within 3–40 min. Moreover, this synthetic protocol was success-
fully utilized for the gram-scale synthesis of 3,30-benzylidenebis(4-
hydroxycoumarin) material. The prepared nanocatalyst system was
reused for 5 consecutive cycles with a small decrease in the yield.
This synthetic method represents the advantages in terms of
preparing the novel magnetic graphene oxide-LDH composite
system, high yield of biscoumarin materials, short reaction times
and applying water as a green solvent as well as the magnetic
separation of the nanocatalyst system.
Synthesis of the Zn–Ni–Fe-LDH system
The layered double hydroxide system of Zn–Ni–Fe was prepared
by the in situ growth of Zn2+, Ni2+ and Fe3+ cations. In this
context, a solution of sodium carbonate (1.060 g, 0.01 mol) and
sodium hydroxide (0.160 g, 0.004 mol) in distilled water (30 mL)
was prepared. In another vessel, a solution of Zn(NO3)2ꢁ6H2O
(1.785 g, 0.006 mol), Ni(NO3)2ꢁ6H2O (2.617 g, 0.009 mol) and
FeCl3ꢁ6H2O (1.352 g, 0.005 mol) in distilled water (30 mL) was
also prepared. Both of the solutions were sonicated for 30 min
and at the same time were added to a vessel containing distilled
water (30 mL) under vigorous stirring. The pH of the reaction
mixture was adjusted at the value of 11. The prepared slurry was
stirred for 30 min at ambient temperature and then stored at
80 1C for 24 h. After cooling and filtration, finally, the prepared
Zn–Ni–Fe-LDH system was dried in an oven at 150 1C.
Experimental
Materials and methods
All materials and reagents were purchased from commercial
sources and they were used without further purifications. FT-IR
1
and H NMR spectra were recorded on Thermo Nicolet Nexus
670 and Bruker Avance 300 MHz spectrometers, respectively.
The obtained products were characterized using physical and
spectral data followed by a comparison with authentic data.
The purity of the chemicals and also the progress of the
reactions were monitored by TLC over silica gel 60 F254 aluminum
sheet. X-ray diffractions were recorded by an X’PertPro Panalytical
diffractometer at 40 kV (30 mA, CuKa radiation source, l = 1.5418 Å)
at 2y = 101–801. The size and morphology of the particles were
determined using SEM images from an FESEM ZEISS-Sigma VP
instrument. Magnetic properties of the nanocatalysts were measured
by vibrating sample magnetometer (Meghnatis Daghigh, Iran) under
magnetic fields up to 20 kOe. The irradiation of ultrasound was
carried out on SOLTEC SONICA 2400MH S3 (305 W).
Preparation of the Fe3O4@GO@Zn–Ni–Fe-LDH composite
system
The nanocomposite of the Fe3O4@GO@Zn–Ni–Fe-LDH system
was prepared through a solvothermal method. For this, in a round-
bottom flask containing distilled water (40 mL), Fe3O4@GO
(0.30 g) and Zn–Ni–Fe-LDH (0.8 g) were added and the resulting
mixture was sonicated for 20 min. After stirring the mixture for
Synthesis of graphene oxide
The synthesis of graphene oxide was carried out via the modified 2 h, the resulting slurry was stored at 90 1C for 24 h. The solid
Hummers procedure.50,51 In a round-bottom flask containing residue was then filtered and dried in an oven at 100 1C to afford
concentrated sulfuric acid (46 mL) and under vigorous stirring, the Fe3O4@GO@Zn–Ni–Fe-LDH composite system.
graphite (1.0 g) was added. After the addition of NaNO3 (1.0 g),
Typical procedure for the synthesis of biscoumarin materials
stirring of the reaction mixture was continued for 30 min. To the
prepared mixture, KMnO4 (6.0 g) was gradually added and the In a round-bottom flask, a mixture of benzaldehyde (0.053 g,
reaction mixture was stirred for 2 h at 0 1C and an additional 2 h 0.5 mmol) and 4-hydroxycoumarin (0.162 g, 1 mmol) in water
at 35 1C. In continuation, distilled water (46 mL) was added in a (2 mL) was prepared. Fe3O4@GO@Zn–Ni–Fe-LDH (30 mg) was
18802 | New J. Chem., 2019, 43, 18794--18804 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

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NJC
16 N. Ye, Y. Xie, P. Shi, T. Gao and J. Ma, Mater. Sci. Eng., C,
2014, 45, 8.
17 X. Huang, X. Qi, F. Boey and H. Zhang, Chem. Soc. Rev.,
2012, 41, 666.
18 S. Khodabakhshi, B. Karami, K. Eskandari, S. J. Hoseini and
A. Rashidi, RSC Adv., 2014, 4, 17891.
19 S. Khodabakhshi, F. Marahel, A. Rashidi and M. Khaleghi
Abbasabadi, J. Chin. Chem. Soc., 2015, 62, 389.
20 W. C. Hou and Y. S. Wang, ACS Sustainable Chem. Eng.,
2017, 5, 2994.
then added and the mixture was stirred for 3 min under reflux
conditions. Once the reaction was completed (monitored by
TLC, n-hexane/EtOAc: 4/2), the mixture was cooled to room
temperature. The nanocatalyst was magnetically separated from
the reaction mixture. EtOAc (5 mL) was then added and the
reaction mixture was stirred for an additional 10 min. The
organic layer was separated and then dried over anhydrous
Na2SO4. The evaporation of the solvent under reduced presssure
affords pure 3,30-benzylidenebis(4-hydroxycoumarin) in 95%
yield (Table 2, entry 1). FT-IR (KBr, n cmꢀ1) 3065, 2737, 1659,
1609, 1564, 1336, 1090, 755; 1H NMR (300 MHz, CDCl3) d (ppm)
6.12 (s, 1H, CH), 7.23–8.07 (m, 13H, ArH), 11.32 (s, 1H, OH),
11.55 (s, 1H, OH).
21 M. Singh, A. Sahu, S. Mahata, P. K. Singh, V. K. Rai and
A. Rai, New J. Chem., 2019, 43, 14972.
22 F. Fei, L. Cseri, G. Szekely and C. F. Blanford, ACS Appl.
Mater. Interfaces, 2018, 10, 16140.
23 M. V. Prabhagar, M. P. Kumar, C. Takahashi, S. Kundu,
T. N. Narayanan and D. K. Pattanayak, New J. Chem., 2019,
43, 14313.
24 L. Cseri, J. Baugh, A. Alabi, A. AlHajaj, L. Zou, R. A. W. Dryfe,
P. M. Budd and G. Szekely, J. Mater. Chem. A, 2018, 6, 24728.
25 N. Mitoma, Y. Yano, H. Ito, Y. Miyauchi and K. Itami, ACS
Appl. Nano Mater., 2019, 2, 4825.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors gratefully acknowledge the financial support of
this work by the research council of Urmia University.
26 X. Guo, B. Du, Q. Wei, J. Yang, L. Hu, L. Yan and W. Xu,
J. Hazard. Mater., 2014, 278, 211.
27 L. L. Li, L. L. Fan, M. Sun, H. M. Qiu, X. J. Li, H. M. Duan
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28 L. Xiao, W. Ma, M. Han and Z. Cheng, J. Hazard. Mater.,
2011, 186, 690.
29 X. Wu, X. Tan, S. Yang, T. Wen, H. Guo, X. Wang and A. Xu,
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18804 | New J. Chem., 2019, 43, 18794--18804 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019