Rice husk-SiO2supported bimetallic Fe-Ni nanoparticles: as a new, powerful magnetic nanocomposite for the aqueous reduction of nitro compounds to amines

Article abstract of DOI:10.1039/d0ra05381c

This paper reports a novel green procedure for immobilization of bimetallic Fe/Ni on amorphous silica nanoparticles extracted from rice husk (RH-SiO₂). The heterogeneous nanocomposite (Fe/Ni?RH-SiO₂) was identified using SEM, EDX, TEM, BET, H₂-TPR, TGA, XRD, VSM, ICP-OES, and FT-IR analyses. The Fe/Ni?RH-SiO₂nanocomposite was applied as a powerful catalyst for the reduction of structurally diverse nitro compounds with sodium borohydride (NaBH₄) in green conditions. This procedure suggests some benefits such as green chemistry-based properties, short reaction times, non-explosive materials, easy to handle, fast separation and simple work-up method. The catalyst was separated by an external magnet from the reaction mixture and was reused for 9 successive cycles with no detectable changes of its catalytic efficiency.

Full text of DOI:10.1039/d0ra05381c

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PAPER
Rice husk-SiO supported bimetallic Fe–Ni
2
nanoparticles: as a new, powerful magnetic
Cite this: RSC Adv., 2020, 10, 33389
nanocomposite for the aqueous reduction of nitro
compounds to amines
Mohammad Ghadermazi, * Setareh Moradi and Roya Mozafari
This paper reports a novel green procedure for immobilization of bimetallic Fe/Ni on amorphous silica
nanoparticles extracted from rice husk (RH-SiO
was identified using SEM, EDX, TEM, BET, H -TPR, TGA, XRD, VSM, ICP-OES, and FT-IR analyses. The Fe/
Ni@RH-SiO nanocomposite was applied as a powerful catalyst for the reduction of structurally diverse
nitro compounds with sodium borohydride (NaBH ) in green conditions. This procedure suggests some
2 2
). The heterogeneous nanocomposite (Fe/Ni@RH-SiO )
2
2
4
Received 19th June 2020
Accepted 31st August 2020
benefits such as green chemistry-based properties, short reaction times, non-explosive materials, easy to
handle, fast separation and simple work-up method. The catalyst was separated by an external magnet
from the reaction mixture and was reused for 9 successive cycles with no detectable changes of its
catalytic efficiency.
DOI: 10.1039/d0ra05381c
rsc.li/rsc-advances
more interested due to its remarkable capacity in catalytic
processes.
Besides, nickel catalysis has made tremendous advances in
1
. Introduction
14,15
Agricultural wastes are dened as the residues from the growing
and processing of raw agricultural products such as fruits, organic synthesis, especially the synthesis of heterocycle
vegetables, and crops. Utilization of agricultural processing compounds, which have been widely used among a variety of
wastes in the production of high value-added products has pharmaceutical compounds due to their relative insensitivity to
1
6–20
increased the protability of the food processing industry by air, low toxicity and price.
1–3
reducing the cost of disposal of these wastes. Rice husk is one
The design and preparation of green catalysts have attracted
of the most valuable agricultural wastes in the world. As it much attention in both academic area and pharmaceutical
contains over 70% silica and can be an economically viable raw industry. For this mean, heterogenization of the catalysts to
material for the preparation of several silicon compounds, solid supports is one of the interesting choices to prevent
wasting the catalyst. Besides, the supports usually have a great
pure silicon and zeolite. The inorganic silica possesses effect on the activity of the catalyst.
considerable advantages such as abundant availability, catalysts to solid bases can provide opportunities for the easy
4
21
5
6
7
including sodium silicate, silicon nitride, silicon carbide,
8
22,23
The heterogeneity of
24–26
adequate surface functionalization, hydrophilic nature, separation of the catalysts from reaction mixtures.
Also,
sustainable and almost free of cost, unique biocompatibility of current literature reveals that the catalytic activity of Ni nano-
9
silanol (Si–OH) and silicate skeletons (Si–O–Si). The amor- particles is high but their small nano-sized particles cannot be
27–29
phous silica with high surface area can be extracted from the separated by conventional methods such as ltration.
RH by chemical treatment with acid followed by process of Therefore, nickel is loaded on the surface or inside the pores of
ꢀ
10
burning at 700 C.
The rice husk can be modied by changing of the graed which could be useful way to x the mentioned shortcom-
solid supports such as zeolite, cellulose, silica and polymer,
30,31
species. Transition metals incorporated onto the surface of RH- ings.
SiO
act as an efficient catalyst in several reactions, such as metal catalysts such as CoFe
oxidation, acylation, benzylation, etc. Therefore, several 41, Cu–Ni/Ti-MCM-41, Fe
supported metal catalysts have been recently prepared and their and SBA-15@ABA-M (M ¼ Cu, Ni and Pd).
applications have been developed in the organic reactions.
Aromatic nitro compounds are highly toxic and are intro-
Especially, metal-containing organosilica nanocomposite is duced to the environment through the wastewaters of dyes,
A great deal of attention has been recently devoted to
32
O @GO–K 22$Ni, Ni/Mg@MCM-
2 4
O @PMDA/Pd, NiCu/SBA15
3 4
2
11
12
13
33
34
35
36
37
38–43
agrochemicals, synthetic resins and plastics etc.
On the
other hand, the nitroarenes reduced to arylamines are consid-
ered as important starting materials and intermediates in
Department of Chemistry, University of Kurdistan, P.O. Box 66135-416, Sanandaj,
Iran. E-mail: mghadermazi@yahoo.com; Fax: +98 87 3324133; Tel: +98 87 33624133
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44–47
pharmaceutical, antioxidants and agricultural industries.
expensive catalysts and long reaction times, which ultimately
Therefore, the catalytic reduction of nitro compounds to amines lead to the production of large amount of toxic waste. With the
in sustainable method with green solvent has attracted a great purpose of developing more convenient or selective catalysts or
deal of attention. Some catalytic systems have been reported reagents, reducing the number of separate reaction steps, higher
4
8
49
such as g-Fe
2
O
3
@HAp-CD$Ag, Fe
3
O
4
@TA/Ag, NiFe
2
3
O
O
4
@- efficiency and minimal by-products, herein, for the rst time
@- a novel magnetically retrievable nanocomposites of RH-SiO and
50
51
52
53
Cu, Co
Cu(OH)
reviews on heterogeneous catalytic reduction, see ref. 57–62.
In spite of their merits, the most commonly reported methods amines with NaBH
3
O
4
-NGr/C, Fe
3
O
4
@SiO
4
,
Pd-NPs@G.Tea, Fe
4
2
5
4
55
56
x
/NaBH
4
,
RGO@Pt/H
2
,
CuFe
2
O
4
/NaBH
4
.
For further Fe/Ni is prepared, characterized and its catalytic system appli-
cation for reduction of various nitro groups to the corresponding
as reducing agent in H O is investigated. The
4
2
suffer from the use of hazardous reagents, unsatisfactory yields, synthesized nanocatalyst with a combination of the catalytic
environmental pollution, large amounts, poor recovery of activity of Ni nanoparticles and the magnetic properties of Fe is
Scheme 1 The schematic pathway for preparing Fe/Ni@RH-SiO
2
nanocomposite and its application in the reduction of nitro compounds to
amines.
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shown to have an excellent catalytic activity, as well as the
recoverability and reusability in the synthesis of amines.
2. Experimental
2.1 Characterization methods
The instruments used for the characterization of Fe/Ni@RH-SiO2
include FTIR, TGA, FESEM, EDX, TEM, XRD, V SM, ICP-OES, BET,
H -TPR. The models of the apparatus are as following: the particle
2
morphology and size were examined by measuring scanning
electron microscopy (SEM) using SEM-TESCAN MIRA3. Energy-
dispersive X-ray spectroscopy (EDX) analysis was obtained by
MIRA3TESCANXMU instrument. Thermogravimetric analysis
(TGA) was determined by Shimadzu DTG-60 instrument. The X-ray
powder diffraction (XRD) data were collected by Co Ka radiation (l
˚
¼
n1.78897 A) operating at n40 keV. Vibrating sample magne-
2
Fig. 2 TGA curve of Fe/Ni@RH-SiO nanocomposite.
tometer (VSM) measurement was recorded by a Vibrating Sample
Magnetometer MDKFD. The content of cobalt and vanadium in
the nanocomposite were measured by inductively coupled plasma-
optical emission spectrometry (ICP-OES). H
grammed Reduction (H -TPR) experiment were carried out using
a NanoSORD NS91 (made by Sensiran Co., Iran) apparatus. Fourier
transforms infrared (FT-IR) spectra were investigated by KBr disc
using a VRTEX 70 model BRUKER FT-IR spectrophotometer. The
size of the as-synthesized nanoparticle was determined by trans-
pore size distribution of nitrogen uptake pores at 77.4 K on a Bel-
sorp18, were calculated using the Brunauer–Emmett–Teller
method and the Barrett–Joyner–Halenda model, respectively. NMR
spectra were taken using a BRUKER Advance 400 MHz NMR
spectrometer and deuterated DMSO.
2
-Temperature Pro-
2
2.2 Production of silica from residual rice husk
mission electron microscopy (TEM) techniques using Zeiss- First, 30 g of residual rice husk with 1.0 M nitric acid was stirred
EM10C Transmission electron. The specic surface area and the in a 250 mL ask at room temperature for approximately 24 h. It
2 2 2
Fig. 1 FT-IR spectra of RH-SiO (a), Fe@RH-SiO (b), and Fe/Ni@RH-SiO (c).
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white. To extract silica from rice husk, 5 g of ash was stirred in
250 mL of 1.0 M sodium hydroxide solution at room tempera-
ture for 24 h. Then the combination was ltered and titrated
with 3.0 M nitric acid. Titration (the drop in HNO was
3
1
ꢁ
controlled by a dropper with a drop of 1 mL min ) and
continued until the pH of the solution reached 5.0. Next,
smooth silica gel was washed with distilled water, and dried at
ꢀ
1
00 C for 24 hours in the oven.
2
2.3 Preparation of Fe@RH-SiO nanocomposite
In a 250 mL 3-necked, round-bottomed ask, 1 g of nanosilica
extracted from rice husk) was ultrasonicated in 50 mL of
distilled water for 30 minutes. A solution of iron(II) chloride
1.78 g in distilled water 25 mL) was added to the suspension
(
(
Fig. 3 XRD patterns of RH-SiO
2
(a) and Fe/Ni@RH-SiO
2
(b).
of nanosilica and was ultrasonicated for 30 minutes and the
mixture was stirred for 30 minutes in the N2 atmosphere.
Aerwards, a solution of sodium borohydride (1.35 g in
distilled water 50 mL) was added dropwise with constant
stirring under inert atmosphere, the black Fe nanoparticles
was rinsed thoroughly with distilled water until the pH of the
solution is xed, then it was dried at 80 C in the oven, and was
incinerated in the muffle oven for 6 h at 600–800 C to turn
ꢀ
ꢀ
2 2
Fig. 4 SEM images of Fe/Ni@RH-SiO (a and b), and TEM image of Fe/Ni@RH-SiO (c).
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ꢀ
were immobilized on RH-SiO
2
nanospheres. Ultimately, the the ask and the mixture was stirred vigorously at 50 C. Aer

nal product was isolated by an external magnet and washed completion of the reaction as indicated by TLC [using ethyl
ꢀ
twice with distilled water/ethanol and dried in oven at 70 C acetate/n-hexane as eluent: 1/5], the insoluble supported
for 12 h.
nanocatalyst was isolated with the aid of an external magnetic
and the product was extracted from liquid with diethyl ether.
The products were puried by column chromatography.
Products 1–11 are known compounds, and their NMR spectra
2
.4 Preparation of Fe/Ni@RH-SiO
Briey, in a 250 mL 3-necked, round-bottomed ask, Fe@RH-
SiO (1 g), was sonicated in 30 mL of deionized water for 20 min.
Then a solution of NiCl $2H O (0.8 g, 6 mmol) in deionized
water (30 mL) was added to the suspension of Fe@RH-SiO and
the mixture was again sonicated for 20 min. Subsequently,
.27 g of sodium borohydride was dissolved in 30 mL of H O
2
nanocomposite
63–68
are in accordance with those reported in the literature.
2
Aniline (1). Yellow oil. Evaporation of the solvent under
2
2
reduced pressure affords a crude product that is puried by
2
1
column chromatography. H NMR (400 MHz, CDCl ) d (ppm) ¼
3
7
.16 (m, 2H, ArH), 6.77 (m, 1H, ArH), 6.69 (m, 2H, ArH), 3.35
0
2
2
(br. s, 2H, NH ).
and then was added dropwise into the above reactant mixtures
and was stirred for 1 h at room temperature. In the next step,
the composite was separated by an external magnet and washed
with ethanol/deionized water several times. Black solid of Fe/
Ni@RH-SiO
temperature before use.
Benzene-1,4-diamine (2). Light brown solid, mp ¼ 141–
ꢀ
1
43 C. Evaporation of the solvent under reduced pressure
affords a crude product that is puried by recystallization from
1
EtOH to yield 2. H-NMR (400 MHz, CDCl
H), 6.36 (s, 4H).
3
) d (ppm) ¼ 4.18 (s,
2
nanocomposite was dried overnight at room
4
ꢀ
4
-Aminophenol (3). Brown solid, mp ¼ 188–190 C. Evapo-
ration of the solvent under reduced pressure affords a crude
product that is puried by recystallization from EtOH to yield 3.
2.5 A general procedure for reduction of nitro compounds
with NaBH in the presence of Fe/Ni@RH-SiO
nanocomposite
1
4
2
H NMR (400 MHz, DMSO) d (ppm) ¼ 6.45 (d, J ¼ 8.56 Hz, 2H,
ArH), 6.38 (d, J ¼ 8.56 Hz, 2H, ArH), 4.35 (br. s, 2H, NH
2
).
ꢀ
In a 50 mL round bottom ask equipped with a magnetic stirrer,
nitro compound (1 mmol), H O (3 mL) and Fe/Ni@RH-SiO
Benzen-1,2-diamine (4). Light brown solid, mp ¼ 105–108 C.
1
The product was puried by column chromatography. H NMR
2
2
(
0.03 g) were added and the mixture was stirred for 1 min at (400 MHz, CDCl
room temperature. Then, NaBH (4 mmol, 0.151 g) was added to
) d (ppm) ¼ 6.73–6.69 (m, 4H), 3.29 (s, 4H).
3
4
2
Fig. 5 EDX spectrum and X-ray atomic map of Fe/Ni@RH-SiO nanocomposite.
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-Chloroaniline (5). Pale yellow oil. The product was puried
Paper
4
1
by column chromatography. H NMR (400 MHz, CDCl
7.13–7.06 (m, 1H), 6.64–6.56 (m, 1H), 3.65 (s, 1H).
3
) d (ppm)
¼
ꢀ
4
-(Aminophenyl)methanol (6). Pale yellow solid, mp ¼ 82 C.
1
The product was puried by column chromatography. H NMR
400 MHz, CDCl ) d (ppm) ¼ 7.03 (d, J ¼ 8.1 Hz, 2H, Ar), 6.61 (d, J
(
¼
3
8.4 Hz, 2H, Ar), 4.42 (s, 2H, CH ), 2.94 (bs, 3H, NH and OH).
2 2
p-Toluidine (7). Yellow oil. The product was puried by
1
column chromatography. H NMR (400 MHz, CDCl
.97 (d, J ¼ 7.0 Hz, 2H), 6.61 (d, J ¼ 3.2 Hz, 1H), 6.59 (s, 1H), 3.51
s, 2H), 2.24 (d, J ¼ 6.2 Hz, 3H).
-(1-Hydroxyethyl)aniline (8). Yellow solid, mp ¼ 93–95 C.
3
) d (ppm) ¼
6
(
ꢀ
4
1
The product was puried by column chromatography. H NMR
400 MHz, CDCl ) d (ppm) ¼ 7.89–7.76 (m, 2H), 6.64 (d, J ¼
(
8
3
.5 Hz, 2H), 4.16 (s, 2H), 2.77 (bs, 1H) 1.51 (s, 3H).
4
-Aminobenzoicacid (9). Light pink solid, mp ¼ 181 ꢀC.
Evaporation of the solvent under reduced pressure affords
a crude product that is puried by recystallization from EtOH to
1
yield 9. H NMR (400 MHz, CDCl
7
3
) d (ppm) ¼ 7.92 (t, J ¼ 2.2 Hz),
.9–7.89 (m), 6.68–6.63 (m), 4.12 (s).
Butan-1-amine (10). Yellow oil. The product was puried by
1
column chromatography. H NMR (400 MHz, CDCl ) d (ppm) ¼
3
2
.56 (t, J ¼ 6.9 Hz, 2H), 1.75 (s, 2H), 1.37–1.15 (m, 4H), 0.79 (t, J
¼
7.1 Hz, 3H).
Propan-1-amine (11). Pale yellow oil. The product was puri-
ed by column chromatography. H NMR (400 MHz, CDCl
1

3
)
d (ppm) ¼ 2.60 (t, J ¼ 6.2 Hz, 2H), 1.50 (m, 2H), 1.25 (s, 2H), 0.95
(t, J ¼ 7.0 Hz, 3H).
Fig. 7 Nitrogen adsorption/desorption isotherm (top) and pore size
distributions curve (bottom) of Fe/Ni@RH-SiO
2
2.6 A general procedure for the recovery of the Fe/Ni@RH-
SiO nanocomposite
2
The reusability of the catalyst was evaluated by the reaction of
nitrobenzene, H O and NaBH using catalyst Fe/Ni@RH-SiO2
2
4
under optimized conditions (Table 2, entry 6). The catalytic activity
of the recovered catalyst in the same reaction under optimized
conditions shows that the magnetically separated nanocatalyst is
reusable for nine consecutive runs without any signicant loss in
catalytic activity (Fig. 8).
2 2
Table 1 Textural properties of the RH-SiO and the Fe/Ni@RH-SiO
BET surface
area [m g
Pore volume
2
ꢁ1
3
ꢁ1
Samples
]
[cm g
]
RH-SiO
Fe@RH-SiO
Fe/Ni@RH-SiO2
2
347
190.7
129.42
10.4
7.33
3.84
2
Fig. 6 Magnetization curves of Fe@RH-SiO
2 2
(A), and Fe/Ni@RH-SiO
(
B).
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the anchoring Fe nanoparticles on RH-SiO
2
. At the third step,
deposition of Ni nanoparticles on Fe@RH-SiO2 afforded the
nanocomposite of Fe/Ni@RH-SiO . Aer that, the performance
2
of the synthesized nanocomposite was assessed by applying it in
the reduction of nitro compounds to corresponding amines in
the presence of NaBH
water as green solvent at 50 C (Scheme 1).
4
. All reduction reactions were carried in
ꢀ
Characteristics of the nanocomposite, and the immobiliza-
tion of bimetallic Fe/Ni on the pore surface of amorphous
nanosilica was comrmed using TEM and SEM images, XRD,
TGA, ICP-OES, EDX, BET, FT-IR, VSM, and then reaction
conditions were optimized.
3
.1 Catalyst characterization
Fig. 8 Temperature programmed reduction of Fe/Ni@RH-SiO
2
The FT-IR techniques are able to characterize and conrm the
preparation of the catalyst. Fig. 1 demonstrates the FT-IR
spectra of RH-SiO
2
(a), Fe@RH-SiO
2 2
(b), and Fe/Ni@RH-SiO
3
. Results and discussions
(
c). Spectrum of the RH-SiO
2
(Fig. 1a) clearly exhibits absorp-
ꢁ1
The organic-inorganic Fe/Ni@RH-SiO2 nanocomposite was
prepared with a three-step procedure (Scheme 1). For this goal,
nano-silica was easily extracted from rice husk and the reaction
was carried out by chemical reduction of Fe and Ni ions by
NaBH to bimetallic Fe/Ni nanoparticles on the surface or
inside the pores of RH-SiO . For this propose, the supported
Fe(0) on nano-silica (Fe@RH-SiO ) was primarily synthesized by
tion band at around 3434 cm which is characteristic of the
presence of stretching band of Si–OH bond and hydroxyl
functional group (O–H) of water molecules adsorbed on the
silicon oxide surface. The adsorption band at 1636 cm can
be attributed to the stretching of water molecules bound to the
2
+
2+
ꢁ
1
4
ꢁ
1
2
silica matrix. The peak at 1080 cm is due to asymmetric
stretching vibration of the structural Si–O–Si bond. The
5
2
2
2
Table 2 Optimization experiments for the reduction of nitrobenzene, using Fe/Ni@RH-SiO nanocomposite
Temp.
( C)
ꢀ
a
Entry
Catalyst amount (mg)
Reducing agent
Solvent
CH CN
n-Hexane
Toluene
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
30
30
30
30
30
30
30
—
30
30
30
30
30
20
30
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
—
4
4
4
4
4
4
4
4
4
4
4
4
(4 mmol)
(4 mmol)
(4 mmol)
(4 mmol)
(4 mmol)
(4 mmol)
(4 mmol)
(4 mmol)
(4.5 mmol)
(3 mmol)
(2 mmol)
(1 mmol)
50
50
50
50
50
50
50
50
50
50
50
50
50
50
r.t.
50
100
60
100
3
120
140
100
100
100
10
45
100
10
45
45
45
100
45
—
—
—
—
40
97
77
—
97
85
79
68
—
89
35
70
37
51
60
CH
2 2
Cl
EtOAc
H O
2
EtOH
H
H
H
H
H
H
H
H
H
H
H
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
10
11
12
13
14
15
16
17
18
19
NaBH
NaBH
NaBH
4
4
4
(4 mmol)
(4 mmol)
(4 mmol)
120
90
180
30
Fe@RH-SiO
2
30
30
30
H
2
(1 atom)
HCOOH
i
PrOH
—
480
a
Isolated yield.
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ꢁ
1
ꢁ1
bands at 798 cm and 467 cm can be attributed to the Table 3 Reduction of nitro compounds by NaBH
4
in the presence of
O at 50 C as green condition
ꢀ
Fe/Ni@RH-SiO
2
catalyst in H
2
deformation of Si–O.
The stretching of the Fe–O and Ni–O bands were observed at
a
Entry Nitro compound Product
Time (min) Yield (%)
ꢁ1
around 400–800 cm which overlap with Si–O bonds. Addi-
tionally, the spectral analysis shows that a, b and c are the same,
however, immobilization of bimetallic Fe/Ni on nanosilica
1
10
10
97
95
(
Fig. 1b and c) makes the peaks overlap and reduce their
intensity.
The thermal stability of Fe/Ni@RH-SiO
2
was investigated by
thermo-gravimetric analysis (TGA) in the temperature range of
ꢀ
2
5–800 C (Fig. 2). One step of weight loss in the combined TGA
2
curve shows that the magnetic nanocomposite has a reasonable
ꢀ
stability up to 330 C. Above this temperature, weight loss is
serious but it could also indicate the parsing of RH-SiO
structure.
2
These analyses entirely displayed that the heterogeneous
system could be utilized successfully around mentioned
temperature.
3
4
5
12
10
15
93
90
91
Fig. 3 shows the XRD patterns of RH-SiO (a) and Fe/Ni@RH-
2
SiO (b). In XRD pattern of the amorphous silica only one peak
2
appeared at 2q ¼ 21.7 (Fig. 3a). The two reections peaks at 2q ¼
ꢀ ꢀ
4.4 and 53.7 , which are related to (111) and (200) planes of
4
metallic nickel with a face centered cubic structure. In addition,
ꢀ
ꢀ
two peaks appeared at 2q ¼ 45.03 and 65.37 are assigned to
ꢀ
Fe(0) (JCPDS 851410) (Fig. 3b). The absence of peaks at 35.6
ꢀ
and 38.5 , corresponding to Fe O , and Fe O , suggests that
2
3
3 4
69
iron oxides were not formed.
In XRD pattern of the amorphous silica only one peak
appeared at 2q ¼ 21.7 (Fig. 3a). Retaining the characteristic
2
peaks of RH-SiO aer the anchoring of Fe/Ni reveals that the
2
well-ordered structure of RH-SiO has not been destroyed, but
ꢀ
ꢀ
two peaks appeared at 2q ¼ 45.03 and 65.37 are assigned to
Fe(0) (JCPDS 851410) (Fig. 3b).
6
8
95
SEM images of the Fe/Ni@RH-SiO catalyst are displayed in
2
Fig. 4a and b. The amorphous hump aer the thermal treat-
ment shows that the rice husk is composed mostly of amor-
phous silica, but still contains quartz as crystalline form of SiO2.
Transmission electron-microscopy (TEM) studies of the Fe/
7
8
9
10
94
92
90
Ni@RH-SiO
particles were successfully incorporated into RH-SiO
Fig. 4c). In addition, the particles are distributed in range of
3–24 nm for Fe/Ni@RH-SiO nanocomposite.
2
nanocomposite conrm that the Fe/Ni nano-
2
support
(
1
2
The EDX pattern (Fig. 5) of the Fe/Ni@RH-SiO shows the
2
existence of Si, O, Fe and Ni in nanocomposite. Also, the
elemental mapping further conrmed a homogeneous distri-
7
bution of the elements in the RH-SiO
exact amount of Fe and Ni load on the RH-SiO
analysis was performed and they were found to be 0.44 and
2
. In order to determine the
2
, the ICP-OES
ꢁ1
0
.49 mmol g respectively.
12
The magnetic properties of the Fe@RH-SiO2 (A) and Fe/
Ni@RH-SiO2 (B) nanomaterials were analyzed using sample
magnetometer analysis (Fig. 6). It should be mentioned that the
1
1
0
1
10
8
93
95
saturation magnetization value (M
s
) of the bare Fe@RH-SiO
0.10 emu g while aer coating of Ni nanoparticles, M value
is 40.91 emu g . However, this magnetic
is still enough to ensure that the
2
is
ꢁ1
6
s
ꢁ1
of Fe/Ni@RH-SiO
2
property of Fe/Ni@RH-SiO
2
a
Isolated yield.
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Table 4 Comparison of catalytic activity of Fe/Ni@RH-SiO catalyst with the some recently reported procedures
Entry
Catalyst
Time (min)
Reaction conditions
Yield (%)
Ref.
ꢀ
1
2
3
4
5
6
7
8
Fe/Ni@RH-SiO
Pd-NPs@Oak gum
Pt/CoFe-LDH
2
10
60
60
40–45
30
8
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
4
4
4
4
4
4
4
4
, H
, EtOH:H
2
O, 50 C (30 mg)
97
96
97
99
99
99
98
93
This work
ꢀ
2
O, 50 C (6.0 mg)
71
72
73
74
75
48
66
ꢀ
, isopropanol, 70 C (10 mg)
, toluene, 115 C (200 mg)
ꢀ
Cu/Al
Fe
Zinc phthalocyanine in PEG-400
g-Fe @HAp-CD$Ag
Fe–Cu@MCC
2
O
3
ꢀ
2
O
3
/Ag
, H
2
O, 100 C, (1 mg)
ꢀ
, EtOH, 100 C, (1 mmol)
ꢀ
2
O
3
30
8
, H
/H
2
O, 80 C, catalyst (0.05 g)
ꢀ
2
O, 70 C, (0.03 g)
catalyst can easily be recovered from the solution using an different reaction conditions such as the solvent, reducing
external magnet force.
agents, amount of catalyst and temperature were studied (Table
The surface area, the pore volume and the distribution of 2).
pore size of Fe/Ni@RH-SiO
2
was also determined using BET
To investigate the best reaction temperature, this procedure
ꢀ
adsorption isotherm and Barrett–Joyner–Halenda (BJH) tech- was studied at various temperatures and the best one was 50 C
niques (Fig. 7). The catalyst had type IV isotherm, indicating (Table 2, entry 6). This procedure was studied in different
2 2 2
that the mesostructure remained intact. According to the solvents such as EtOH, H O, CH Cl , n-hexane, toluene and
results in Table 1 surface area, pore volume and pore size of Fe/ EtOAc and it was found that H O is a suitable solvent for this
2
2
ꢁ1
3
ꢁ1
Ni@RH-SiO2 (129.42 m
g
, 3.84 cm
g
and 14.33 nm, reaction and with the nonpolar solvent under the same condi-
respectively), decreased compared with Fe@RH-SiO and RH- tion no reaction to proceeded (Table 2, entries 1–4). Then, the
2
70
i
SiO
2
,
indicating the Fe/Ni nanoparticles are successfully different reducing agents HCOOH, PrOH and H
2
were studied
loaded onto the silica matrix.
(Table 2, entries 17–19). These hydrogen sources showed lower
To show the oxidation state of the available Ni and Fe in the activity compared to that of NaBH
4
. Table also shows that the
and gave
(Table 2, entries 10–13).
RH-SiO
2 2 4
support, we have analyzed the (H -TPR) graph. As reaction did not perform in the absence of NaBH
shown in Fig. 8, there are small picks visible in the positive a low yield in a low amount of NaBH
4
region of the graph with small percentage which indicate that The reduction NO group did not performed in the absence of
2
small percentages of Fe(II) and Ni(II) have remained on the RH- catalyst and the reaction yields were decreased in the low
SiO which have not been reduced. Also, a pick is visible on the amounts of catalyst (Table 2, entries 8 and 14). Furthermore, the
2
ꢀ
negative region of the graph in the (400 C) area which is an reaction was performed in the presence Fe@RH-SiO
2
as catalyst,
indication of H
concluded that the metals have been reduced on the RH-SiO
with NaBH
2
release/expulsion. Therefore, it can be but it did not proceed aer a long time (Table 2, entry 16). This
2
result conrms that optimum reaction conditions to afford
4
.
aniline as a sole product in high yield was the molar ratio of 1 : 4
for nitrobenzene and NaBH
RH@Fe/Ni catalyst.
Aer nding to improve the reaction conditions, we
employed different substituted nitroarenes for the synthesis of
arylamines. The results indicated that both electron releasing,
4
in the presence of 0.03 g of
3
.2 Catalytic activity
Initially, we proceeded to optimize the catalytic conditions by
studying the reduction of nitrobenzene. The effect of several
2
Fig. 9 Recyclability of Fe/Ni@RH-SiO nanocomposite in the reduction of nitrobenzene to aniline.
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Fig. 10 FT-IR spectrum (a) and SEM image (b) of recovered Fe/Ni@RH-SiO catalyst.
and electron withdrawing groups have good to excellent yields truly heterogeneous in nature or whether Ni is leaching out
in short time without the formation of any byproducts (Table 3). from the solid catalyst to the solution. In this experiment, aer
Molecules with the complexity of aldehyde and nitro groups did continuing the reaction under optimized conditions, we found
not display any selectivity and both of mentioned functional the yield of product in a half time of the reaction to be 68%.
groups were reduced with the same reactivity (Table 3, entries 6 Then the reaction was repeated and in a half time of the reac-
and 8). Also, Primary aliphatic nitro compounds were rapidly tion, the catalyst was removed from the reaction mixture, using
reduced to their corresponding amines in excellent yields (Table a magnet. The yield of reaction in this stage was 71% that
3, entries 10 and 11).
conrmed the reaction proceeds heterogeneously with stability
In comparison with several previously reported methods in of the catalyst and no signicant leaking of effective Ni metal.
the literature, it has been demonstrated that the amorphous
silica nanoparticles catalyst provided a high activity and green
catalytic protocol for the reduction of nitrobenzene (Table 4).
These results clearly show that the catalyst is equally or more
efficient to other catalysts reported in terms of easy catalyst
isolation and suitable recyclability, high yields, the amount of
used catalyst, the reaction temperature and reaction time.
4
. Conclusions
In the present work, magnetic nanoparticles of bimetallic Fe/Ni
were immobilized on amorphous RH-SiO extracted from rice
husk. The TEM, X-ray atomic map and XRD analyses success-
2
fully conrmed well immobilization and high stability of Fe and
2
Ni moieties onto RH-SiO framework. The magnetic property of
3
.3 Recycling of Fe/Ni@RH-SiO catalyst
the nanocomposite was investigated by VSM analysis. The
catalytic status of nanocomposite was obtained as a green
system for the reduction of nitro compounds to corresponding
amines in water by using NaBH as the source of hydrogen.
4
The key features of this method are high yields, simple
operations, time, environmental compatibility, availability and
2
For studying the recyclability of Fe/Ni@RH-SiO , the catalyst
can be recovered from the reaction mixture by an external
magnet and washed with Et O and then dried under air atmo-
2
sphere. The catalyst was recycled and used more than 9
successive runs without considerable decrease in activity
2
2
reusability of the catalyst. The reaction conditions (H O as
(Fig. 9).
green solvent) coupled with activity and stability of the nano-
composite make the described heterogeneous catalyst highly
desirable from the green chemistry point of view. We expect that
this feature will enable this protocol to nd extensive applica-
tions in the eld of academic area and pharmaceutical industry.
The FT-IR and SEM analyses of the recovered catalyst were
carried out following the ninth cycle, and the results are dis-
played below (Fig. 10). These analyses demonstrated that the
chemical structure of the catalyst was remained unchanged.
Final investigation of the recycled catalyst was carried out by
measuring the content of the loaded Fe and Ni atoms by ICP-
OES technique. It was found that the amounts of Fe and Ni in
fresh catalyst and the recycled one aer 9 times are 0.46–
Conflicts of interest
ꢁ
1
ꢁ1
There are no conicts to declare.
0
.38 mmol g , and 0.42–0.36 mmol g respectively, which
there by indicating the minimal amounts Fe and Ni leaching in
the catalytic process and affirming the stability and efficiency of
the catalyst. Also, the reduction of 4-methylnitrobenzene in the
Acknowledgements
2
presence of Fe/Ni@RH-SiO has been investigated by carrying The authors are deeply grateful to University of Kurdistan for
out a hot ltration test in order to nd whether the catalyst is nancial support of this research project.
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4 Y. Yang, G. Ren, W. Li, D. Gu, Z. Liang, Y. Liu and Q. Pan,
Polyhedron, 2020, DOI: 10.1016/j.poly.2020.114599.
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