Bentonite clay as an efficient substrate for the synthesis of the super stable and recoverable magnetic nanocomposite of palladium (Fe3O4/Bentonite-Pd)

Article abstract of DOI:10.1016/j.poly.2019.01.054

Bentonite has a potential for the catalytic carrier because their surface and special structure are very suitable for supporting transition metals. This clay as a nontoxic, inexpensive, freely available and abundant natural mineral was used to synthesize magnetic nanocomposite of palladium as a super stable and recoverable green catalyst (Fe₃O₄/Bentonite-Pd). The catalytic activity of this system was evaluated in the Suzuki cross-coupling reaction. Determination of novel nanoparticles structure was performed using FT‐IR, XRD, VSM, TGA, and SEM–EDX spectral data.

Full text of DOI:10.1016/j.poly.2019.01.054

Accepted Manuscript
Bentonite clay as an efficient substrate for the synthesis of the super stable and
recoverable magnetic nanocomposite of palladium (Fe3O4/Bentonite-Pd)
Behjat Bananezhad, Mohammad Reza Islami, Ehsan Ghonchepour, Hamid
Mostafavi, Ahmad Momeni Tikdari, Hamid Reza Rafiei
PII:
S0277-5387(19)30076-2
https://doi.org/10.1016/j.poly.2019.01.054
POLY 13727
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 November 2018
15 January 2019
23 January 2019
Please cite this article as: B. Bananezhad, M.R. Islami, E. Ghonchepour, H. Mostafavi, A.M. Tikdari, H.R. Rafiei,
Bentonite clay as an efficient substrate for the synthesis of the super stable and recoverable magnetic nanocomposite
of palladium (Fe3O4/Bentonite-Pd), Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.01.054
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Bentonite clay as an efficient substrate for the synthesis of the super
stable and recoverable magnetic nanocomposite of palladium
(Fe3O4/Bentonite-Pd)
Behjat Bananezhad1, Mohammad Reza Islami*1, Ehsan Ghonchepour1, Hamid Mostafavi2, Ahmad
Momeni Tikdari1, and Hamid Reza Rafiei3
1Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Avenue, 76169 Kerman, Iran
2Kerman Agricultural and Natural Resource Research and Education Center, (AREEO), Kerman, Iran
3Department of Soil Science, Shahid Bahonar University of Kerman, 22 Bahman Avenue, 76169 Kerman, Iran
*Corresponding author: mrislami@uk.ac.ir
Keywords:
Magnetic nanoparticles, Palladium, Bentonite clay, C-C coupling, Heterogenization, Green catalyst, Suzuki reaction
Abstract
Bentonite has a potential for the catalytic carrier because their surface and special structure are
very suitable for supporting transition metals. This clay as a nontoxic, inexpensive, freely available
and abundant natural mineral was used to synthesize magnetic nanocomposite of palladium as a
super stable and recoverable green catalyst (Fe3O4/Bentonite-Pd). The catalytic activity of this
system was evaluated in the Suzuki cross-coupling reaction. Determination of novel nanoparticles
structure was performed using FT‐ IR, XRD, VSM, TGA, and SEM–EDX spectral data.
Introduction
Since the beginning of history, soils play an effective rule in humane life. They are useful materials
for many purposes such as constructing shelters, producing consumable goods, industrial and
pharmaceutical applications [1-3]. There are different kinds of soil in nature, each having unique
structure and characteristics such as texture, color, contents. Clays are the most important category
of soils which are a class of inorganic layered compounds. Clay particles have a diameter of less
than 0.002 mm.Among the minerals in clay, bentonite is one of the most important natural material
that has many usages in industries such as bonding, plasticizing, and suspending.
1

The large surface area, mechanical properties, high thermal stability, and other unique properties
have caused that bentonite widely applied in adsorbents and composites.[4] Bentonite consists of
two silica tetrahedral sheets and one central alumina octahedral sheet. The structural formula of
Bentonite is defined as Rx(H2O)4{(Al2-x,Mgx)2[(Si,Al)4O10](OH)2} that R is the exchangeable
cations of alkali and alkali-earth metals between the layers.[5] It has a cation-exchange capacity
of about 70 to 110 meq/100 g of clay.[6] Schema of bentonite structure shown in Fig. 1.
Fig 1. Schema of bentonite structure with exchangeable cations.
Literature mining revealed that bentonite can absorb heavy metals such as Cd(II), Ni, Pb(II), and
Co(II) from aqueous solution and wastes.[3, 7-9] Also Buxing and co-works showed that bentonite
has very great potential in green chemical processes to absorbed palladium in the surface and make
a stable composite.[10]
The main challenge in the industry is the design of efficient catalysts that are environmentally
friendly and consistent with the principles of green chemistry.[11-13] According to the principles
of green chemistry, a catalyst should not pollute the environment and have no degradation effects,
therefore the use of heterogeneous catalysts that are easier to separate from the reaction media is
more important than homogeneous catalysts. The toxicity of homogeneous catalysts, difficult
2

separation, and not using them more than once are problems of these catalysts.[14] Recently, to
avoid these problems, a heterogeneous catalytic system has been extensively used in industrial and
various synthetic reactions. The use of heterogeneous systems in reactions has been many
advantages such as mild reaction conditions, the reusability of catalysts, straightforward
experimental procedures, and minimal waste disposal.[15]
Today, many methods and system are used to prepare such catalysts. Among them, the use of a
surface containing magnetic nanoparticles is a useful method, in which the catalyst can be
separated by using an external magnetic field. The advantages of these catalysts can be
summarized in minimizing changes in the activity, selectivity and, longer lifetimes than
homogeneous catalysts.[16, 17] The magnetic nanoparticles surface may be synthesized using
different methods, such as (a) covering the surface with oxides, carbon, polymer, or metallic layers;
(b) the non-covalent approach with polymers or surfactants; or (c) the covalent approach between
hydroxyl groups of the nanoparticles surface and anchoring agents such as carboxylic acid,
phosphoric acid, and dopamine derivatives.[17, 18]
The carbon-carbon cross-coupling reactions are an important class of reactions which accepted in
the synthesis of natural products, agrochemical, pharmaceuticals and bioinorganic materials. This
method is also utilized to the selective construction of biaryls.[19] The usefulness of the Suzuki
reaction is attributed to the non-toxicity boron compounds, the convenient replacement of boron
by other groups and the ability to use it in environmentally friendly solvents.[20-23] In recent
years, many improvements have been made in this field and known as the Suzuki-Miyaura cross-
coupling reaction.[24, 25] Palladium is an expensive metal that is not economically useful as a
homogeneous catalyst because some of it is wasted in the separation step. To resolve this problem,
the use of heterogeneous palladium catalysts such as palladium complexes immobilized on
polymer, carbon, silica, alumina, metal oxides and other inorganic supports have been
recommended.[26-37] In spite of the successful processes in this area, there are still some requests
for development of new protocols in this field for C-C coupling which complies with the following
conditions: a low quantity of catalyst, highly efficient in terms of reactivity and selectivity, ease
separation of catalyst, reuse of it without reducing its activity and high efficiency of products.
According to the above-mentioned points, we decided to synthesize an efficient palladium
magnetic composite by using bentonite clay. In this system, we used bentonite as a ligand for the
3

heterogenization of palladium chloride on Fe3O4 nanoparticles surface as a novel, inexpensive,
recoverable, high temperature stable, and green catalyst (Fe3O4/bentonite-Pd). The TGA analysis
of this catalyst shows that it has great stability, keeping its nature at temperatures over 600 °C.
Also, it exhibited an excellent catalytic activity in the Suzuki cross-coupling reactions. The
structure of catalyst was characterized systematically by different techniques such as FT-IR, ICP,
SEM-EDX, XRD, VSM, and TGA.
Scheme 1. Synthesis pathway of Fe3O4/Bentonite- Pd
Experimental section
Material
All solvents and reagents were directly used in analytical grade purity without further purification.
All experiments were performed using deionized water.
4

Characterization
FT-IR spectra were recorded on a commercial spectrophotometer (Bruker Tensor 27 FT -IR). 1H
and 13C NMR spectra were recorded on a Bruker 400 Ultrashield NMR Magnet (400 MHz for 1H
NMR) with TMS as the internal standard. Powder X-ray diffraction (XRD) spectra were recorded
at room temperature with a Philips X-Pert 1710 diffractometer using Co Kα(λ=1.78897 Å) at a
voltage of 40 Kv and a current of 40 mA and data were collected from 10° to 90° (2θ) with a scan
speed of 0.02° s. The morphology of the catalyst was studied using scanning electron microscopy
(SEM; Philips XL 30 and S-4160) with coated gold equipped with dispersive X-ray spectroscopy
capability. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were
performed using a thermal analyzer with a heating rate of 20°C min in a temperature range of 25–
1100°C under flowing compressed nitrogen. The magnetic property of the catalyst was measured
with a vibrating sample magnetometer (VSM).
Synthesis of Fe3O4/Bentonite
Bentonite (1 g) was dispersed in 50 ml of deionized water via adequate ultrasonic. The solution
was then stirred for 1h and then the solution was added to 50 ml of distilled water containing
FeCl2·4H2O (0.8457 g) and FeCl3·6H2O (2.2992 g). The mixture was stirred under N2 atmosphere
at 80°C for 0.5 h. Then, 25 ml of 25% (W/W) NH3·H2O was rapidly injected into the reaction
mixture and stirred under N2 for another 1h. The obtained magnetic composite was washed three
times with hot water and separated by an external magnet and was dried under vacuum at 70°C.
Synthesis of Fe3O4/Bentonite-Pd
0.5 g of Fe3O4/bentonite composite (which was previously prepared) was added to a mixture of
105 mg of palladium (II) chloride and 50 mL solvent (H2O/MeOH 1:1). The mixture was
continuously stirred for 24 h at room temperature. The composite material was separated by an
o
external magnet and washed thoroughly with distilled water and was dried under vacuum at 70
C for 5 h to give the catalyst Fe3O4/Bentonite-Pd.
General procedure for the Suzuki–Miyaura coupling reactions
5

Catalyst (10 mg), arylhalide (1.0 mmol, 1 equiv.), phenylboronic acid (0.14 g, 1.2 mmol, 1.2
equiv.), potassium carbonate (0.26 g, 2.0 mmol) and a solution of 10 mL of EtOH/H2O (v/v = 1/1)
were mixed in a round bottom flask. The mixture was vigorously stirred at 80 °C for 20 min
(Scheme 2). The reaction was monitored through Thin Layer Chromatography (TLC). When the
reaction completed, the catalyst was recovered with an external magnet and product was extracted
with dichloromethane (2 × 30 ml). Then the organic layers were dried over anhydrous Na2SO4,
and the solvent was removed under reduced pressure. The products were purified using a short
column of silica gel with eluted (silica gel, n-hexane).
2-Methoxy-biphenyl (Table 2, entry 4). Yield 65%. A colorless oil. 1H NMR (400 MHz, CDCl3)
δ 7.65 (d, 2H, J=7.39 Hz), 7.52 (t, 2H, J=7.39 Hz), 7.44-7.41 (m, 3H), 7.14 (t, 1H, J=7.3 Hz), 7.08
(d, 1H, J=8.2 Hz), 3.9 (s, 3H, OCH3). 13C NMR (100 MHz, CDCl3) δ: 55.64, 111.35, 120.98,
127.07, 128.14, 128.78, 129.71, 130.84, 131.04, 138.70, 156.59.
4-Methoxy-biphenyl (Table 2, entry 5). Yield 90%. Mp 85-88 ℃. 1H NMR (400 MHz, CDCl3) δ
7.62-7.55 (m, 4H), 7.46 (t, 2H, J=7.7 Hz), 7.35 (t, 1H, J=7.3 Hz), 7.02 (d, 2H, J=8.5 Hz), 3.91 (s,
3H, OCH3). 13C NMR (100 MHz, CDCl3) δ: 55.37, 114.24, 126.70, 126.78, 128.19, 128.77,
133.79, 140.86, and 159.18.
1-Phenyl naphthalene (Table 2, entry 7). Yield 75%. A colorless oil. 1H NMR (400 MHz, CDCl3)
δ 7.83 (d, 2H, J= 8. 8 Hz), 7.78 (d, 1H, J=9.0, 1.6 Hz), 7.47-7.39 (m, 6H), 7.37-7.33 (m, 3H). 13C
NMR (100 MHz, CDCl3) δ: 125.58, 125.96, 126.22, 127.13, 127.42, 127.83, 128.45, 128.47,
129.05, 130.26, 131.80, 133.99, 140.43, 140.94.
1
2'-fluoro-1,1':4',1''-terphenyl (Table 2, entry 8). Yield, 60%. Mp 152-154 ℃. H NMR (400
MHz, CDCl3) δ 7.69-7.65 (m, 4H), 7.59-7.41 (m, 9H).
4-Acetylbiphenyl (Table 2, entry 9). Yield 90%. Mp 116-119 ℃. 1H NMR (400 MHz, CDCl3) δ
8.06 (d, 2H, J= 8.5 Hz), 7.71 (d, 2H, J=8.01 Hz), 7.65 (d, 2H, J=6.7 Hz), 7.50 (t, 2H, J=7.6 Hz),
7.43 (t, 1H, J=7.3 Hz), 2.67 (s, 3H, CH3).
4-Methyl-biphenyl (Table 2, entry 10). Yield 95%. Mp 46-47 ℃. 1H NMR (400 MHz, CDCl3) δ
7.63 (dd, 2H, J= 8.0, 0.8 Hz), 7.56 (dd, 2H, J=8.0, 1.6 Hz), 7.48 (t, 2H, J=7.8 Hz), 7.38 (t, 1H,
J=7.4 Hz), 7.31 (d, 2H, J=7.9 Hz), 2.45 (s, 3H, CH3).
6

4-Nitro-biphenyl (Table 2, entry 11). Yield 78%. Mp 111-113 ℃. 1H NMR (400 MHz, CDCl3) δ
8.32 (d, 2H, J= 8.7 Hz), 7.76 (d, 2H, J=8.7 Hz), 7.65 (d, 2H, J=7.45 Hz), 7.55-7.46 (m, 3H)
4-Cyano-biphenyl (Table 2, entry 13). Yield 79%. Mp 84-86 ℃. 1H NMR (400 MHz, CDCl3) δ
7.73 (m, 4H, J= 18.0 Hz), 7.62 (d, 2H, J=8.0, 7.11 Hz), 7.52 (t, 2H, J=6.8 Hz), 7.46 (d, 1H, J=7.1
Hz).
Results and Discussion
FT-IR Spectra
Figure 2 shows the FT-IR spectra of (a) bentonite, (b) Fe3O4/bentonite, and (c) Fe3O4/bentonite-
Pd composite. The FT-IR spectrum of bentonite exhibits stretching bands at 3627 and 3440 cm−1
for O–H and hydrogen binding of H2O molecules. Absorption bands of H–O–H deformation
appear at 1668 and 1644 cm−1. Absorption band of Si–O–Si appears at 1038 cm−1. Absorption
band of 796 cm−1 is attributed to the Si–O stretching of quartz and silica and the band at 522 cm−1
is due to the Al–O–Si deformation. In the FT-IR of Fe3O4/bentonite, (Fig. 2b) the absorption band
at 566 cm−1 is related to the Fe–O stretching vibration of the bare magnetic nanoparticles.[38] Fig.
2(c) exhibits the IR spectrum of the final catalyst indicating the presence of Pd on Fe3O4/bentonite.
As you can see, all absorbing bands have shifted to lower frequencies, and this confirms that
palladium metal was placed on the magnetic composite. For example, the stretching frequency of
hydroxyl group shifted to a lower frequency at 3417 cm-1. This shift approves that the OH group
was coordinated to the palladium ion.
7

Fig 2. FT-IR spectra of (a) bentonite, (b) Fe3O4/bentonite, and (c) Fe3O4/bentonite-Pd composite.
SEM-EDX Analyze
The surface morphology of Fe3O4/bentonite-Pd composite was analyzed using SEM and TEM
technique (Fig 3). According to the images obtained from the catalyst levels, spherical
nanoparticles of Pd and Fe3O4 have successfully been deposited on surfaces of bentonite. Also,
these images indicate that nanoparticles size is between 30-50 nm. Transmission electron
microscopy (TEM) confirmed the formation of single-phase Fe3O4 nanoparticles on the surface of
bentonite with spherical morphology (Fig 3b).
8

Fig 3. SEM image of Fe3O4/Bentonite-Pd (a), and TEM image of Fe3O4/Bentonite-Pd (b).
9

Fig 4. EDX analyze of Fe3O4/Bentonite-Pd.
EDX is a qualitative technique used to prove the presence of elements in a catalyst. EDX spectrum
of Fe3O4/bentonite-Pd composite is shown in Fig.4. This spectrum confirms that several elements
such as Fe, Pd, Si, Al, O, and Mg are present in the catalyst. The analyses also confirm that Pd was
coated in the catalyst structure.
Vibrating Sample Magnetometry analyze
The magnetic property of the catalyst was determined using a vibrating sample magnetometer
(Lake Shore VSM7410) from −8000 Oe to +8000 Oe at room temperature. Bare nanocrystals of
Fe3O4 have a high saturation magnetization of 73.7 emu.gr-1 which decreases to 32 emu.g-1 for
Fe3O4/bentonite-Pd (Fig 5).[16] This magnitude of magnetization indicates that this nanocatalyst
still has a high magnetic permeability and can be separated from the reaction mixture by an external
magnet.
10

Fig 5. VSM curve of Fe3O4/bentonite-Pd composite.
XRD pattern analyze
The XRD patterns of Fe3O4/bentonite similar diffraction peaks at around 2θ = 30.06°, 36°, 44.01°,
54.70°, 58.30°, 64.28°, and 74.05° which relate to the seven crystal faces (111), (220), (311), (400),
(422), (511) and (440) respectively. These peaks are completely compatible with the standard
pattern for crystalline magnetite (Fe3O4) with inverse spherical structure.[39] The six peaks of
Fe3O4/bentonite can also be seen in the XRD pattern of the synthesized Fe3O4/bentonite-Pd. This
comparison shows that the final structure of catalyst does not have two different phases, and the
prepared Fe3O4 nanoparticles at this stage are pure and have a spinel structure. Also, the observed
diffraction peaks in Fe3O4/bentonite-Pd at 2θ = 40, 46.5 and 68 are related to two faces (111),
(200) and (220) respectively. These peaks are well suited to Pd0, which has been achieved by the
reduction of Pd2+ cations in methanol as solvent.[40, 41]
11

Fig 6. The XRD patterns of Fe3O4/bentonite (a) and Fe3O4/bentonite-Pd (b).
The thermogravimetric analysis (TGA) technique was used for measuring the sustainability of
Fe3O4/bentonite-Pd, and was recorded by heating the sample at a rate of 10 °C min-1. As shown in
Fig. 7, the endothermic peak at lower temperatures (lower than 110 °C) can be attributed to
desorption of physically absorbed water on the surface of bentonite and Fe3O4. This analysis
indicates that the 0.86% weight loss in the range of 400-600 °C can be attributed to the removal of
water.[42] Therefore, this composite is stable at 600 °C, and according to this analysis, the Fe3O4/
bentonite-Pd is a high-temperature-stable catalyst. The amount of palladium metal deposited onto
the Fe3O4/bentonite was measured by induced coupled plasma (ICP) analysis, and the amount of
Pd metal per gram of catalyst was determined to be 0.014 g (0.14 mmol g-1). Also, the ICP of the
reused catalyst and hot filtration test were investigated and the results showed no change in the
amount of palladium loaded on the catalyst surface after the reaction. These results confirm the
true heterogeneity of nanocatalyst.
12

Fig 7. The TGA spectra of Fe3O4/bentonite-Pd
Catalytic activity
The catalytic activity of Fe3O4/bentonite-Pd was appraised in the C–C coupling reaction of aryl
halides with phenylboronic acid. The coupling reaction of phenylboronic acid and iodobenzene
was used to optimize conditions and the results are summarized in Table 1. Our observations
showed that the reaction was not carried out in the absence of catalyst in the following conditions:
phenylboronic acid (1 mmol, 0.122 g), iodobenzene (1 mmol, 0.204 g) and 2 mmol (0.276 g)
potassium carbonate as base in EtOH/H2O (8 mL, 1:1) at 50 °C under an air atmosphere for 20
min (Table 1, entry 1). This result confirmed that the catalyst plays a vital role in this reaction
(Table 1, entry 2). Then we examined the effect of temperature on the reaction. The best yields
were obtained at 70 ° C (Table 1, entry 3). Several solvent systems were also examined and the
best reaction efficiency (98% yield) was obtained in EtOH/H2O (1:1). (Table 1, entries 3-6).
Several bases such as KOH, K2CO3, Na2CO3, and CaCO3 were used in the reaction and K2CO3 had
the best performance (Table 1, entries 3 and 9). In the next section, the reaction was performed in
the presence of various amounts of catalyst 5, 7 and 10 mg, which the best yield was obtained
when 10 mg of catalyst was used (Table 1, entries10-12). When the reaction was carried out in the
presence of bentonite, Fe3O4, and Fe3O4/bentonite as catalysts, the yield of product was 0, 8 and
5% respectively (Table 1, entries 13-15).
13

Table 1. Investigation of the optimal condition of Suzuki reaction in the presence of different
catalyst and condition.a
Catalyst
(mg)
Base
(eq)
Temp Yieldb
Entry
Catalyst
Solvent
(°C)
%
EtOH/H2O
1:1
EtOH/H2O
1:1
1
2
-
-
K2CO3
K2CO3
50
0
Fe3O4/bentonite-Pd
10
50
84
EtOH/H2O
1:1
3
4
5
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
10
10
10
K2CO3
K2CO3
K2CO3
70
70
70
98
10
98
H2O
EtOH/H2O
2:1
EtOH/H2O
1:2
Acetone/H2O
1:1
EtOH/H2O
1:1
EtOH/H2O
1:1
EtOH/H2O
1:1
EtOH/H2O
1:1
EtOH/H2O
1:1
EtOH/H2O
1:1
6
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
Fe3O4/bentonite-Pd
bentonite
10
10
10
10
10
5
K2CO3
K2CO3
KOH
70
70
70
70
70
70
70
70
70
70
56
0
7
8
45
90
10
20
52
0
9
Na2CO3
Ca2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
10
11
12
13
14
15
7
10
10
10
EtOH/H2O
1:1
EtOH/H2O
1:1
Fe3o4
8
Fe3o4- bentonite
5
a Reaction condition: Iodobenzene 1 mmol, phenylboronic acid 1 mmol, base 2 mmol, catalyst, solvent (8 mL), and
under air atmosphere for 20 min. b Isolated yield.
Capability and efficiency of Fe3O4/bentonite-Pd were investigated in Suzuki reaction by using
different aryl halides under optimized conditions. A variety of aryl halides were subjected to
optimal conditions, and the results are shown in Table 2.
Scheme 2. Optimize condition for C-C coupling of various aryl halides
14

Table 2. C-Coupling of various aryl halides in the presence of Fe3O4/bentonite-Pd under optimal
condition.a
Entry
1
Ar-X
Product
Yieldb %
98
2
3
90
43
4
65
5
6
90
85
7
8
75
60
90
95
78
9
10
11
12
13
0
79
a Reaction condition: 1 mmol of aryl halide, 1 mmol phenylboronic acid, 2 mmol K2CO3 in 8 ml solvent (EtOH/H2O
1:1), and in the presence of 10 mg Fe3O4/bentonite-Pd at 70 °C for 20 min. b Isolated yield.
15

All products were known and characterized by melting point (mp), 1H and 13C NMR spectral data.
These data are consistent with what is reported in the literature for these compounds.[43-49]
The difference of this catalyst with some catalysts used previously for the reaction of iodobenzene
with phenylboronic acid is shown in Table 3. Also, all of the catalysts compared base on the
turnover number (TON) and Turnover frequency (TOF) factors, that results show high TON and
TOF factor for Fe3O4/bentonite-Pd with comparing to other catalysts. Efficient reusability, easy
separation and short reaction time are advantages of the new catalyst.
Table 3. A comparison between the Fe3O4/bentonite-Pd and a number of catalysts which were
previously used in the Suzuki reaction.
mol%
Catalyst
0.40
Catalyst
Temp. (°C)
60
Time
24 h
Yield (%)a
99
TONb
TOF (h-1)c
1031
[Ref]
[50]
NHC‐ PdCl2 species
24750
Fe3O4@EDTA-Pd2+
PdNPs/P. a. kurdicagum
MNP@PAMPS‐ Pd(II)
Fe3O4/bentonite-Pd
80
60
80
70
3 h
94
95
99
95
16785
95000
14143
67857
5595
380000
28286
[16]
[51]
[52]
0.56
0.10
0.7
15 min
30 min
20 min
Present
work
0.14
203571
a Isolated yield; average of two runs.
b Turnover number: moles of aryl halide converted per mole of Pd.
c Turnover frequency.
To study the longevity and activity of the catalyst, it was separated from the reaction medium by
an external magnet and used up to 5 times in the Suzuki reaction, and it was found that it still
maintains its efficiency and can respond well (Fig. 8).
16

Fig 8. Reusability of Fe3O4/bentonite-Pd in the model reaction, (a) Reaction environment before catalyst isolation,
(b) Catalyst adsorbed with an external magnet after completion of the reaction.
Pd leaching during the reaction process was scanned by ICP of recycled catalyst. The results didn’t
show any change in Pd amount in the structure of catalyst after recovering from the reaction
mixture. The XRD patterns of the recycled catalyst after Suzuki model reaction is shown in Fig 9.
These XRD patterns exhibit that the catalyst structure has not changed after the reaction.
Fig 9. XRD patterns of nanocatalyst after using in the reaction mixture
Conclusions
In conclusion, in this study bentonite was used as a new and efficient substrate for heterogenization
of palladium on the surface of magnetic nanoparticles. It is a super-stable composite in high
temperature that can be used in the C-C coupling reactions. The catalytic activity of this
nanocomposite was tested in the Suzuki cross-coupling reaction. The advantages of this catalyst
include the use of a nanocomposite that meets the principles of green chemistry and avoids the use
of environmental pollutants
Acknowledgments
17

The authors express appreciation to the Shahid Bahonar University of Kerman Faculty Research
committee funds for its support of this investigation.
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22

Bentonite clay as an efficient substrate for the synthesis of super
stable and recoverable magnetic nanocomposite of palladium
(Fe3O4/Bentonite-Pd)
Behjat Bananezhad1, Mohammad Reza Islami*1, Ehsan Ghonchepour1, Hamid Mostafavi2, Ahmad
Momeni Tikdari1, and Hamid Reza Rafiei3
1Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Avenue, 76169 Kerman, Iran
2Kerman Agricultural and Natural Resource Research and Education Center, (AREEO), Kerman, Iran
3Department of Soil Science, Shahid Bahonar University of Kerman, 22 Bahman Avenue, 76169 Kerman, Iran
*Corresponding author: mrislami@uk.ac.ir
Bentonite as a nontoxic, inexpensive, free available and abundant natural clay was used to
synthesize magnetic nanocomposite of palladium as a super stable and recoverable green catalyst
(Fe3O4/Bentonite-Pd).
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