Convenient conversion of hazardous nitrobenzene derivatives to aniline analogues by Ag nanoparticles, stabilized on a naturally magnetic pumice/chitosan substrate

Article abstract of DOI:10.1039/d0ra08376c

Herein, silver nanoparticles (Ag NPs), as an effective catalyst for the reduction process of nitrobenzene derivatives to non-hazardous and useful aniline derivatives, are conveniently synthesized on an inherently magnetic substrate. For this purpose, an efficient combination of volcanic pumice (VP), which is an extremely porous igneous rock, and a chitosan (CTS) polymeric network is prepared and suitably used for the stabilization of the Ag NPs. High magnetic properties of the fabricated Ag@VP/CTS composite, which have been confirmed via vibrating-sample magnetometer (VSM) analysis, are the first and foremost advantage of the introduced catalytic system since it gives us the opportunity to easily separate the particles and perform purification processes. Briefly, higher yields were obtained in the reduction reactions of nitrobenzenes (NBs) under very mild conditions in a short reaction time. Also, along with the natural biocompatible ingredients (VP and CTS) in the structure, excellent recyclability has been observed for the fabricated Ag@VP/CTS catalytic system, which convinces us to do scaling-up and suggests the presented system can be used for industrial applications. This journal is

Full text of DOI:10.1039/d0ra08376c

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PAPER
Convenient conversion of hazardous nitrobenzene
derivatives to aniline analogues by Ag
nanoparticles, stabilized on a naturally magnetic
pumice/chitosan substrate†
Cite this: RSC Adv., 2020, 10, 43670
Reza Taheri-Ledari, ‡a Seyedeh Shadi Mirmohammadi,‡a Kobra Valadi,a
a
bc
*
*
Ali Maleki
and Ahmed Esmail Shalan
Herein, silver nanoparticles (Ag NPs), as an effective catalyst for the reduction process of nitrobenzene
derivatives to non-hazardous and useful aniline derivatives, are conveniently synthesized on an
inherently magnetic substrate. For this purpose, an efficient combination of volcanic pumice (VP), which
is an extremely porous igneous rock, and a chitosan (CTS) polymeric network is prepared and suitably
used for the stabilization of the Ag NPs. High magnetic properties of the fabricated Ag@VP/CTS
composite, which have been confirmed via vibrating-sample magnetometer (VSM) analysis, are the first
and foremost advantage of the introduced catalytic system since it gives us the opportunity to easily
separate the particles and perform purification processes. Briefly, higher yields were obtained in the
reduction reactions of nitrobenzenes (NBs) under very mild conditions in a short reaction time. Also,
along with the natural biocompatible ingredients (VP and CTS) in the structure, excellent recyclability has
been observed for the fabricated Ag@VP/CTS catalytic system, which convinces us to do scaling-up and
suggests the presented system can be used for industrial applications.
Received 30th September 2020
Accepted 27th November 2020
DOI: 10.1039/d0ra08376c
rsc.li/rsc-advances
characteristic properties like magnetism, recyclability of the
heterogeneous catalyst will be signicantly facilitated.11 By only
1. Introduction
applying an external magnet from the outside part of the ask,
the catalyst could be conveniently separated and reused.
Previously, so many magnetic catalytic systems in which iron
oxide nanoparticles play the crucial role as the magnetic core of
the whole structure have been reported by our research
group.12–23 Also, we have used the mentioned particles as the
drug delivery systems with high efficiency,24,25 due to its non-
toxicity and biodegradability.26
Pumice is a volcanic stone that includes numerous voids in
its structure, and since it is fallen into the category of the light-
weight materials, it can be well dispersed/submerged in the
reaction mixture.27 The volcanic pumice (VP) consists of
internal particles, totally separated from outside, and external
particles linked to the surface resembling a sponge.28 Generally,
porous compounds such as metal–organic frameworks, pumice
particles, carbon nanotubes, and graphene oxide are promising
materials in the catalytic applications due to their broad surface
area, which increases the catalytic performance and effi-
ciency.29,30 In the case of the VP, the noticeable inherent
magnetic property makes it more distinguished from other
types of the porous materials applicable for the catalytic aims.31
As discussed above, inherent magnetic property of the VP
provides ultra-affluence in the separation as well as the puri-
cation processes. Hence, we decided to continue our previous
Recently, the design and development of heterogeneous cata-
lytic systems has attracted much attention because they have
a great potential advantage of recyclability over the homoge-
nous types.1 By immobilization of metallic particles into various
combinations of organic and inorganic materials like polymers
and clay resources, the scope of the heterogeneous catalytic
systems has been amazingly developed.2–4 Chitosan (CTS) as
a natural polysaccharide with alkaline substances is extracted
from chitin shells of crustaceans.5 So far, CTS has been widely
used for medicinal applications like controlled drug release
systems,6 skin substitutes,7 vaccine delivery,8 antibacterial
agents,9 and wound dressings.10 Also, it is a conventional
natural metal ion absorbent and is a great candidate for cata-
lytic applications.5 Through the addition of some other
aCatalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran
University of Science and Technology (IUST), Tehran 16846-13114, Iran. E-mail:
maleki@iust.ac.ir; Fax: +98-21-73021584; Tel: +98-21-77240640-50
bCentral Metallurgical Research and Development Institute (CMRDI), P.O. Box 87,
Helwan, Cairo 11421, Egypt. E-mail: a.shalan133@gmail.com
cBCMaterials, Basque Center for Materials, Applications and Nanostructures, Martina
Casiano, UPV/EHU Science Park, Barrio Sarriena s/n, Leioa 48940, Spain
† Electronic supplementary information (ESI) available: The NMR data of all of
the synthesized aniline derivatives can be found. See DOI: 10.1039/d0ra08376c
‡ Authors contributed equally.
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studies on the VP by using that as an appropriate substrate for reusability behaviors of the Ag@VP/CTS catalytic system are
metal ion stabilization and further catalytic purposes.32–35 In carefully monitored in the reduction reactions of the NB
this work, we intend to prepare another efficient catalytic derivatives. In summary, it was revealed that more than 95% of
system based on a completely natural matrix (including VP and the reaction yield is obtained during only 8 minutes reaction
CTS), and apply that for the reduction reaction of the nitro- time, at room temperature, through applying the Ag@VP/CTS
benzene (NB) derivatives. In addition, the NB derivatives are catalytic system. Besides, this is exhibited that the presented
widely used in the pharmaceutical processes or in producing catalytic system is reused for 12 successive runs (by magnetic
dyes.36 These derivatives are extremely hazardous compounds separation). Ultimately, a feasible mechanism aimed at the
toward humans and other environmental organisms, and they catalyzed reduction of the NB derivatives is suggested.
are barely degraded in the biological processes.37–39 So far, so
many various strategies have been designed and reported for
2. Result and discussion
2.1. Preparation of the Ag@VP/CTS catalyst
the reduction pathway of the NB derivatives to converted them
to their aniline analogues.40 To name a few, the electrochemical
approach,41 photocatalyst technique,42 and the catalytic systems
The preparation route of the Ag@VP/CTS catalyst is given in
based on the noble or transition metals43 are the most common
Fig. 1. Initially, the VP is well grinded and converted to a very
strategies. All of the mentioned strategies included few draw-
ne powder via ball-milling technique. For enhancing and
depleting the pumice pores from the unwanted llers, the
calcination process was applied using a furnace.51 Aerward,
backs that needed to be modied and improved. For instance,
in order to apply catalytic system based on transition metals for
reduction reactions, elevated pressure and temperature is
the uniformed pumice particles were washed with hydrochloric
required.44 Moreover, low current efficiency is the main disad-
acid, and dispersed in a solution of the concentrated CTS via
vantage of electrochemical approach.40
ultrasonication, under a mild condition. The mixture was
So far, it has been revealed that silver nanoparticles (Ag NPs)
washed for removing the excess CTS, and the silver nitrate salt
are among the best competent candidates in the catalytic
was added to the mixture, which was stirred at room tempera-
processes due to including impressive electronic and optical
ture. Finally, the obtained magnetic particles were collected
properties.45 Moreover, the Ag NPs have a considerably high
together and washed with distilled water for several times and then
surface to volume ratio that changes their chemical, biological
dried in the oven for 1 h. The synthesized composite is founded to
and physical properties.46 According to the literature and as our
be exceptionally stable as a result of the presence of numerous
previous experiences disclosed, the Ag NPs include high surface
–OH groups on both VP and CTS structures, resulting in the
powerful H-bindings. Previously, so many methods have been re-
ported in which the Ag ions were stabilized and reduced to the Ag
NPs by using of the different polymeric species such as polyvinyl
energy that leads them to be quickly aggregated.21,47 This
property makes the Ag NPs as a signicant reducing agent in the
catalytic applications. Additionally, the immobilization of the
Ag NPs on a polymeric substrate like CTS, enhances their
alcohol,52 polyethylene glycol,53 and polyvinyl chloride.54
agglomeration.48–50
Herein, a novel heterogeneous catalyst is prepared by using
of the VP particles and the CTS strands, as a natural-based
2.2. Characterization
substrate for the stabilization of the Ag ions, and conversion
to the pure metallic NPs. From the architecture aspect, this is
demonstrated that the Ag NPs are uniformly synthesized (equal
in size and morphology) and nely distributed onto the VP/CTS
substrate, via an in situ process. Then, the magnetic behavior
and other critical characteristic properties of the prepared
Ag@VP/CTS catalytic system such as average size, porosity,
chemical state of the present, metallic elements, and thermal
stability are carefully investigated by using different analytical
methods. Next, the catalytic performance as well as the
In order to perform the characterization stage, Fourier-
transform infrared (FT-IR) spectra of the neat VP, and Ag@VP/
CTS nanocomposite catalyst were provided. As Fig. 2a shows,
the peaks related to the stretching vibrations of Si–O–Si and
O–H bands at ca. 1100 and 3400 cmꢀ1, respectively, have been
appeared sharper aer the calcination process. It can be
attributed to the removal of the unwanted llers in the pores of
the VP.51 Aer combination of the CTS, a sharp peak appeared at
about 2900 cmꢀ1, which origins from the C–H bonds with
hybridization state sp3. This peak proves successful composition
Fig. 1 Schematic diagram of the synthetic route of the Ag@VP/CTS nanocomposite.
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Fig. 2 (a) FT-IR spectra, (b) EDX spectra, (c) TGA curves, and (d) VSM curves (at room temperature) of the individual VP nanoparticles (blue line),
VP/CTS (green line), and the prepared Ag@VP/CTS nanocomposite (red line).
of the CTS, as the organic component in the structure. Also, the composite was also measured via vibrating-sample magne-
peaks appeared at ca. 3400 cmꢀ1 and 1650 cmꢀ1 are belonging to tometer (VSM) machine. As is observed in Fig. 2d, the hysteresis
N–H and C]O bonds, respectively, which present in the CTS's curves of the Ag@VP/CTS nanocatalyst demonstrates about ca.
structure.55 The conrmation of the existence of all the essential 10.0 emu gꢀ1 decrease in the magnetic saturation, which is
elements was done by energy-dispersive X-ray (EDX) spectroscopy quite reasonable since all constitutes of the nanocatalyst don't
(Fig. 2b). Furthermore, in comparison to the individual VP, the have magnetic properties. As is observed in the magnetic–
synthesized VP/CTS and Ag@VP/CTS composites have shown hysteresis curves, the magnetic behavior of the VP/CTS
sharper peak for the carbon element that approving the successful composite has not been signicantly reduced aer addition of
addition of the CTS to the structure. Also, the EDX spectrum of the the Ag particles. Through this great magnetic property, the
Ag@VP/CTS nanocatalyst veries the presence of the Ag element in Ag@VP/CTS particles could be collected without difficulty
the nal composition structure.
through applying of a magnet, and reapplied for several times.
Microscopic images were checked by scanning electron
Moreover, the thermal stability of the Ag@VP/CTS nano-
catalyst was associated with the neat VP via thermogravimetric microscopy (SEM) and transmission electron microscopy (TEM)
analysis (TGA), under the air atmosphere in a thermal range of for exploring the morphology as well as the size of the synthe-
50 to 600 ꢁC (Fig. 2c). As the TGA curves demonstrate, in all sized Ag@VP/CTS composite (Fig. 3). Image (3a) is appointed to
ꢁ
three curves, between ca. 60 and 120 C, a gradual weight loss the VP powder and image (3b) is related to the VP NPs aer
has emerged that is attributed to the separation of the captured grinding via ball-milling. It was evident that the plates are
water molecules in the silica network of the VP, which perfor- detached and well-dispersed, while they are in agglomerated
mances as an excessive molecular sieve.56 In the range of 120 to form before grinding process. Image (3c) is related to the
500 ꢁC, an excellent weight loss has been appeared for the curve Ag@VP/CTS nanocomposite. As shown, the spherical Ag NPs
related to the VP/CTS and Ag@VP/CTS composites, which is and the combined CTS strands with VP particles are easily
accredited to the loss of the –OH groups present in the CTS identied. Finally, the TEM image illustrates the formation of
structure. According to the literature, at this range, the hydroxyl the Ag NPs appeared by dark spots in the image. Also, well
groups of the polymeric chains are removed as the hydrate distribution of these metallic particles on to the VP/CTS
molecules.23 Aerward, in the curve of Ag@VP/CTS, the Ag NPs surfaces is veried (images 3d–f). Generally, this is clearly
and then the VP start to decomposition. The inherent magnetic observed in the SEM and TEM images that the dominant phase
performance of the neat VP particles, VP/CTS, and Ag@VP/CTS onto the surfaces is formed by the Ag NPs.
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Fig. 3 SEM image of: (a) VP powder, (b) VP nanoparticles (prepared via ball-milling), and (c) Ag@VP/CTS nanocomposite, and TEM images of the
Ag@VP/CTS nanocomposite (d–f).
Hence, it is quite reasonable to expect that the X-ray 368 and 374 eV, respectively, indicating Ag0 state (metallic
diffraction (XRD) pattern of the Ag@VP/CTS nanocomposite nanoparticles).61
be similar to the individual Ag NPs. In this regard, the XRD
2.3. Application
pattern of the Ag@VP/CTS nanocomposite was prepared and
compared with the pattern of the individual Ag NPs, based on
the database of JCPDS (PDF#87–0597) (Fig. 4a).57 Accordingly,
the peaks emerged at 38.07, 44.26 are attributed to the Ag NPs
signing by their Miller indices of (1 1 1), and (2 0 0), respectively.
The broad peak appeared at ca. 25–30ꢁ is related to the amor-
phous structure of the silica network present in the VP's struc-
ture.12 Also, peaks are observed in the pattern at ca. 32ꢁ,43ꢁ, 51ꢁ,
53ꢁ, and 54ꢁ are assigning to the (Ca,Na)(Si,Al)4O3.58
For conrming the porosity of the synthesized composite via
adsorption/desorption of N2 gas Brunauer–Emmett–Teller
(BET) surface area analysis was detected in Fig. 4b and c. The
physisorption isotherms of the VP aer calcination and Ag@VP/
CTS composite is shown. The VP NPs curve Fig. 4b indicates
type IV isotherm of mesoporous materials. As shown in the
curves, although some internal pores are lled aer the addi-
tion of CTS and Ag, there are still large internal pores for
incorporating the catalytic reaction of the NB reduction. Based
on the curves, the pore size range has decreased from 40 nm for
pumice powder to 20 nm belonging to Ag@VP/CTS composite.
Moreover, the specic surface area also follows the same trend.
Results conrmed the occupation of some of the internal pores
aer composition with CTS and Ag nanoparticles.59,60 Also, X-ray
photoelectron spectroscopy (XPS) was employed to characterize
the valence state of the Ag element (Fig. 4d and e). As expected,
two peaks related to Ag (3d3/2) and Ag (3d5/2) were detected at ca.
2.3.1. Optimization of the catalytic system in the reduction
of NB derivatives. For reaching the optimized condition, the
catalytic performance of the prepared Ag@VP/CTS was
explored. For this purpose, different catalytic amounts of the
nanocomposite, and amount of the used hydrazine in the
reduction reaction of the nitrobenzene were precisely moni-
tored. The detailed information of this experiment is reported
in Table 1. As claimed by the table, to reveal the importance of
the VP porous structure in the catalyst, the sole Ag/CTS was also
applied under the same conditions during the reduction reac-
tion. As can be detected in Table 1 (entry 11), the obtained
reaction yield is reduced aer removing the VP particles from
the catalytic system. Moreover, since Ag is the main catalyst site
of this catalytic system it is estimated that by removing Ag from
the catalytic system, yield of the reaction would be signicantly
deducted (see Table 1 entry 2). From the table, it has been
revealed that the optimum conditions were provided by using
0.03 g of the Ag@VP/CTS catalyst during 5 min stirring, at room
temperature (Table 1, entry 5).
2.3.2. Catalyzed synthesis of the aniline derivatives. The
catalytic efficiency of the prepared Ag@VP/CTS composite was
also investigated by utilizing the various NB derivatives as founded
in Table 2. Surprisingly, in a brief period by using Ag@VP/CTS in
the reaction, high yield was obtained. Comparing the results to
other synthesized catalysts, the results reveal that the prepared
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Fig. 4 (a) XRD pattern of the Ag@VP/CTS nanocomposite, (b) BET curves, (c) the average pore volume of the individual VP nanoparticles and the
fabricated Ag@VP/CTS nanocomposite, via adsorption/desorption of N2, under ambient conditions, and (d and e) XPS spectra of the Ag@VP/CTS
nanocomposite.
Ag@VP/CTS is a great candidate for NB reduction reactions. hydrogen atoms of the hydrazine hydrate spontaneously attack
Additionally, the NMR data of all of the synthesized aniline nearby NB molecules and produce the reduced non-hazardous
derivatives are founded in Fig. S1–S10, in the ESI.†
form.71 In our previous report, a schematic of the plausible
2.3.3. Suggested mechanism. Based on the knowledge mechanism has been submitted that can properly justify the
from the current report, Ag NPs are the leading catalytic site of passing route by the Ag@VP/CTS catalytic system.21
the magnetic Ag@VP/CTS composite. They can facilitate the
2.3.4. Recyclability effect of the nanocomposite catalytic
reduction reaction in a short reaction time. The catalytic system. In order to explore reusability of the fabricated Ag@VP/
process is described through the electron transfer system. The CTS catalytic system, the particles were magnetically collected
foremost advantage of the Ag NPs is their signicant electronic from the reaction mixture, and prepared for further reactions.
interactions with the heteroatoms like oxygen. Hydrazine Aer separation of the particles, they were well washed with the
hydrate is an electron reducing agent with a signicant supply distilled water for several times and dried in an oven. The
of electron.70 Thus, the leading reason of the reduction of the fabricated Ag@VP/CTS was applied for the eight successive
NB derivatives is the dehydration process, which occurs because times in the model reaction, which is the reduction of nitro-
of the electron transfer between the hydrazine hydrate and the benzene. As depicted in Fig. 5a, monitoring the catalytic process
Ag NPs. Aer the electron transfer process occurred, the conrms that the reaction yield has not been signicantly
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Table 1 Reaction optimization by utilizing different amounts of nanocatalyst and N2H4$H2O, in ethanol and reflux conditions in reduction
reaction of NBs
Entry
Cat.
Cat. amount (mg)
N2H4 (mol%)
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
—
VP@CTS
—
30
10
20
30
40
50
30
30
30
30
5
5
5
5
5
5
5
4
2
1
5
15
5
5
5
5
5
5
5
5
5
5
Trace
20
85
91
95*
95
95
92
85
70
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag@VP/CTS
Ag/CTS
9
10
11
94
a
*Optimum condition using the Ag@VP/CTS nanocomposite (30.0 mg), nitrobenzene (1.0 mmol), N2H4$H2O (5.0 mol%), and ethanol (2.0 mL), at
70 ꢁC.
changed. Fig. 5b indicates the FT-IR spectrum of the recovered the previously reported systems that included Ag NPs and have
Ag@VP/CTS composite comparing with the spectrum of the been utilized for the conversion of the NBs to their aniline
fresh particles. As can be seen, emerging the sharp peak at analogues. As Table 3 demonstrates, there are several advantages
ꢂ1100 cmꢀ1 proves that the internal networks of the VP parti- for the prepared Ag@VP/CTS composite in comparison with the
cles (silica and alumina) have not been damaged during the other species: (1) generally, magnetic systems are highly preferred
recycling process. Only, the intensity of the peak appeared at due to their convenient separation process. As discussed in the
ꢂ1650 cmꢀ1 (belonging to C]O) has been a bit reduced that previous sections, VP component inherently includes the magnetic
may be due to separation of a part of CTS network. From the property due to the presence of the iron element in its structure. (2)
SEM imaging (Fig. 5c), it is gured out that particles agglomeration Signicant conversion (95%) of the NB derivatives has been
is occurred aer an 8-time recycling. As discussed, since the VP observed during a short contact time (5 min), whereas in the most
particles are inherently magnetic, they are prone to attract each cases (Table 3, entries 1, 2, 3, and 5) the reaction time exceeded 2
other and make bigger masses. This happening may be the main hours. (3) In the design and preparation stage, this is important to
contributor to the reduction of the catalytic performance during use the low cost materials with high degrees of biocompatibility
the eight times recycling. The EDX analysis shown in panel (d) of and biodegradability. In comparison with the system reported in
the Fig. 5 proved that all of the essential elements were present Table 3 (entry 4), although the obtained results by the reported
aer recycling. Also, the XRD pattern of the recovered Ag@VP/CTS catalytic system are great, but exploitation of the abundant natural
catalytic system was prepared (Fig. 5e) to investigate any possible materials (like VP rock) has always been preferred due to its
changes in the structural phases. As is observed, there was no economic advantage. In addition of the mentioned excellences, the
noticeable change in comparison with the fresh catalyst (Fig. 4a), use of the light-weight substrates with the porous structure causes
only the intensity of the appeared peaks has a bit changed. To the catalyst particles to be well dispersed in the reaction medium,
investigate the particle size of the combined Ag NPs aer the and as a result the total performance will be increased.
recycling process, the TEM image of the recovered Ag@VP/CTS was
prepared. As Fig. 5f illustrates, the spherical morphology of the Ag
particles with the mean size of ca. 17 nm has been maintained
3. Experimental section
during the recycling processes. In comparison with the fresh
particles (Fig. 3e), the number of the Ag NPs distributed on the VP/
CTS substrate seems to be reduced. It may be another reason for
the observed reduction in the catalytic performance aer an 8-time
recycling. To obtain more conrmation on this claim, the induc-
tively coupled plasma optical emission spectroscopy (ICP-OES) was
performed on a sample of the supernatant aer eighth time of the
particles usage, and it was revealed that 0.423 ppm of Ag element
exist in the sample. It means that the leaching of the Ag element
from the catalytic system is an inevitable event, but this partial
leaching does not have any signicant effects on the catalytic
performance.
3.1. Materials and physical characterizations
Altogether, the applied chemicals as well as the utilized appa-
ratuses in the current report are listed in the ESI† part.
3.2. Practical approaches
3.2.1. Synthesis of VP. First, 2.5 g of the obtained pumice
powder was grinded by ball-milling technique for 1 h in 50 Hz.
Aerwards, grinded pumice was added to the crucible and went
through the calcination procedure for 5 h at 400 ꢁC. Aer cooling
down to room temperature, 1.5 g of the obtained pumice was
moved to the round bottom ask (50 mL) and by utilizing an
ultrasonic bath, it was dispersed in prepared HCl solution at room
temperature (0.1 M, 20 mL). Under the same condition, the bottom
ask was stirred for another 12 h. Employing an external magnet,
2.3.5. Comparison of the prepared Ag@VP/CTS with other
catalytic systems. In this section, we intend to make a quick
comparison between our presented nanocatalyst and some of
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Table 2 Gained yields after the reduction of NB derivatives to aniline analogues under optimized condition
Mp (ꢁC)
Found
Entry
1
NB structure
Product
Time (min)
6
Yield (%)
95
Reported
Liquid sample62
2
8
96
136–137
136–138 (ref. 63)
3
4
12
14
88
98
64–66
65–66 (ref. 64)
145–146
144–146 (ref. 65)
5
3
99
172–174
171–173 (ref. 63)
6
7
5
9
96
95
186–189
184–186
186–188 (ref. 62)
185–187 (ref. 66)
8
10
94
209–212
208–210 (ref. 67)
9
10
6
84
97
52–54
41–44
52–53 (ref. 68)
42–43 (ref. 69)
10
VP was separated, and washed for a couple of times with distilled was dispersed in the ask via the ultrasonication process, and the
water. Finally, it was dried over oven heat (60 ꢁC) for 24 h.
reaction mixture was stirred continuously at room temperature for
3.2.2. Preparation of VP/CTS. VP/CTS was synthesized by an additional 5 h. VP/CTS was magnetically collected, washed with
0.01 g of CTS powder and 30 mL of deionized water to the round distilled water, and dried (at 60 ꢁC) for 24 h.
bottom ask (100 mL) and stirred at room temperature till a clear
3.2.3. Preparation of Ag@VP/CTS composite. Obtained VP/
bleached solution was gained. Aerward, 1.0 g of the prepared VP CTS (0.6 g) was dispersed in deionized water (20 mL) and transferred
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Fig. 5 (a) Recyclability diagram, (b) the FT-IR spectra of fresh and recovered catalyst, (c) SEM image (d) EDX spectrum, (e) XRD pattern, and (f)
TEM image of the recovered Ag@VP/CTS nanocatalyst.
Table 3 Previously reported nanoscale catalytic systems based on the Ag element, applied for the conversion of the NB derivatives to their
aniline analogues
Entry
Catalyst
Condition
Cat. amounta (mg)
Time (min)
Conversion (%)
Ref.
1
2
3
4
5
6
Ag–Ni core/shell NPs
Ag–rGOc composite
80 ꢁC, KOH, IPAb
Visible light irradiation
80 ꢁC, NaOH, under N2
NaBH4, r.t.
50
50
250
10
5
150
240
600
6
150
5
95
98
97
95
97
95
72
73
74
75
76
—
Ag–MPTA-1d composite
Ag–SBA-15e composite
Ag–mNCf composite
Ag–VP/CTSg composite
NaBH4, r.t.
N2H4$H2O, 70 ꢁ
C
30
a
Per 1.0 mmol of the NB compound. b Isopropyl alcohol (IPA). c Reduced graphene oxide. d Poly-triallylamine (MPTA-1). e SBA-15 is a mesoporous
silica. f Mesoporous melamine-N-doped carbon (mNC). g This work.
to a round bottom ask (50 mL). AgNO3 (1.0 g, 5.9 mmol) was hazardous NBs to nontoxic aniline derivatives. Overall, Ag NPs
dispersed in the ask via ultrasonic at room temperature. By were successfully stabilized on the surface of biocompatible
maintaining the same condition, it was stirred for 5 h. The magnetic ingredients. This catalytic system contains natural components,
composite was separated by an external magnet, washed with VP with inherently signicant magnetic property and CTS poly-
distilled water, and dried (as mentioned in the previous section).
meric strands. Ag NPs are the main catalyst sites. They can facili-
tate the reduction reaction of NB derivatives with signicant yield,
in short reaction time under mild condition. The foremost
advantage of magnetic catalysts is that they can be conveniently
isolate from the reaction mixture. VP has great magnetic property
along with structural stability, which results in signicant reus-
ability. This well-designed catalyst is based on green principles
since all the ingredients are from natural components.
3.3. Spectral information aimed at the selected composites
4-Aminophenol (Table 2, entry 7): white solid, 1H NMR (500 MHz,
DMSO): d (ppm) ¼ 4.38 (2H, s, NH2), 6.42–6.44 (2H, d, J ¼ 10 Hz,
H–Ar), 6.48–6.50 (2H, d, J ¼ 10 Hz, H–Ar), 8.37 (1H, s, OH).
4. Conclusions
Conflicts of interest
In this report, a heterogeneous organic–inorganic catalytic system
was introduced and applied successfully in the conversion of There are no conicts of interest.
This journal is © The Royal Society of Chemistry 2020
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palladium-catalyzed Diels–Alder approach, ChemistrySelect,
2018, 46, 13057–13062.
Acknowledgements
13 R. Taheri-Ledari, J. Rahimi and A. Maleki, Synergistic
catalytic effect between ultrasound waves and pyrimidine-
This work was nancially supported by the research council of
the Iran University of Science and Technology (IUST). Further-
more, AES thanks the National Research grants from MINECO
“Juan de la Cierva” [FJCI-2018-037717].
2,4-diamine-functionalized
applied for synthesis
magnetic
of 1,4-dihydropyridine
nanoparticles:
pharmaceutical derivatives, Ultrason. Sonochem., 2019, 59,
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K. O. Aghbash, The use of k-carrageenan/Fe3O4
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