Enhanced reduction of nitrobenzene derivatives: Effective strategy executed by Fe3O4/PVA-10%Ag as a versatile hybrid nanocatalyst

Article abstract of DOI:10.1016/j.catcom.2019.105850

Herein, we present an organic–inorganic hybrid nanocomposite constructed of polyvinyl alcohol (PVA), iron oxide (Fe₃O₄), and 10% of silver nanoparticles (Ag NPs). First, a convenient in situ method is introduced for the preparation of this efficient catalytic system (Fe₃O₄/PVA-10%Ag). Further, we study the high catalytic performance for the reduction of nitrobenzene (NB) derivatives as a hazardous species of chemicals and the significant biological activity (antibacterial effects) of the nanocomposite. However, high reaction yields (99%) have been obtained in short reaction times (~15 min). A plausible mechanism is suggested, and all the required characterizations of the presented nanocatalyst are investigated in this study.

Full text of DOI:10.1016/j.catcom.2019.105850

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Enhanced reduction of nitrobenzene derivatives: Effective
strategy executed by Fe3O4/PVA-10%Ag as a versatile hybrid
nanocatalyst
Jamal Rahimi, Reza Taheri-Ledari, Maryam Niksefat, Ali Maleki
PII:
S1566-7367(19)30311-5
DOI:
https://doi.org/10.1016/j.catcom.2019.105850
CATCOM 105850
Reference:
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
20 July 2019
14 October 2019
15 October 2019
Please cite this article as: J. Rahimi, R. Taheri-Ledari, M. Niksefat, et al., Enhanced
reduction of nitrobenzene derivatives: Effective strategy executed by Fe3O4/PVA-10%Ag
as a versatile hybrid nanocatalyst, Catalysis Communications (2018), https://doi.org/
10.1016/j.catcom.2019.105850
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Enhanced reduction of nitrobenzene derivatives: Effective strategy executed by
Fe3O4/PVA-10%Ag as a versatile hybrid nanocatalyst
Jamal Rahimi, Reza Taheri-Ledari, Maryam Niksefat, Ali Maleki*
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of
Science and Technology, Tehran 16846-13114, Iran
*Corresponding author. Tel.: +98 21 73228313; fax: +98 21 73021584. E-mail address:
maleki@iust.ac.ir (A. Maleki).
Abstract
Herein, we present an organic–inorganic hybrid nanocomposite constructed of polyvinyl alcohol
(PVA), iron oxide (Fe3O4), and 10% of silver nanoparticles (Ag NPs). First, a convenient in situ
method is introduced for the preparation of this efficient catalytic system (Fe3O4/PVA-10%Ag).
Further, we study the high catalytic performance for the reduction of nitrobenzene (NB) derivatives as
a hazardous species of chemicals and the significant biological activity (antibacterial effects) of the
nanocomposite. However, high reaction yields (99%) have been obtained in short reaction times (~15
min). A plausible mechanism is suggested, and all the required characterizations of the presented
nanocatalyst are investigated in this study.
Keywords: Hybrid magnetic nanocomposite; Hazardous materials; Effective electronic interactions;
Nitrobenzene derivatives; Polyvinyl alcohol.
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1. Introduction
In the field of environmental studies, removal of contaminants from the natural resources has become
a serious concern and attracted much attention [1]. Proportional to increasing industrial activities and
discharge of the waste into the water resources, this concern has become more intense in the last
decade [2]. Among various hazardous species of the aqueous pollutants, nitrobenzene (NB), which
results from industrial sources such as pharmaceuticals, agrochemicals, and dyes, is noted for its
toxicity, carcinogenicity, and persistence [3-5]. One of the most convenient methods to deal with NB
is the reduction of NB derivatives to anilines as nonhazardous compounds [6─10]. In this regard,
several methods and tools have been reported by researchers to facilitate the reduction reaction of NB
derivatives [3─11]. Among numerous efficient nanocatalysts, iron oxide (Fe3O4) nanoparticles (NPs)
have attracted increasing attention owing to their magnetic property, extreme surface area, surface-
functionalization ability, notable thermal resistance, nontoxicity, and therapeutic properties [12─16].
Our research group has reported several works on these magnetic catalytic systems. Moreover,
Mallakpour et al. have also reported an LDH-supported Fe3O4/PVA magnetic nanocomposite for the
removal of methyl orange from aqueous solution [17]. As a continuation of our previous research, herein,
Fe3O4 NPs coated with PVA (Fe3O4/PVA) are decorated with silver nanoparticles (Ag NPs) and
employed for the reduction of NB derivatives to anilines in the presence of hydrazine hydrate
(N2H4.H2O) [18─21]. Reduction of NB derivatives using N2H4.H2O in the presence of a nanoscale
facilitator has been introduced as an efficient strategy. For example, this method has recently been
implemented with CeO2 NPs, by Anbu et al. [22]. Noble metal-supported Fe3O4 nanostructured
materials have shown better activity owing to the synergistic effect between metal and metal oxides
[23,24]. Nevertheless, PVA is typically used to modify the surface of Fe3O4 NPs and increase hydroxyl
groups onto the surface of the NPs. Through this method, more ratios of Ag NPs could be loaded onto
the surface of PVA-coated NPs, and as a result, more active sites are obtained.
Herein, we present PVA-coated Fe3O4 NPs decorated with Ag NPs with 9.94% weight ratio
(Fe3O4/PVA-10%Ag) as an effective nanocatalyst for the reduction of the NB derivatives to anilines.
A convenient separation process was carried out using an external magnet, through the magnetic
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property of Fe3O4/PVA-10%Ag. The NB reduction reactions were precisely screened in the presence
of N2H4.H2O and under mild conditions, and acceptable reaction yields were obtained during the short
reaction times. Additionally, the catalyst reusability was monitored after recycling and using the
catalyst several times. As the second application, the biological activity of Fe3O4/PVA-10%Ag was
precisely investigated through the implementation of the antimicrobial tests.
2. Results and discussion
2.1. Preparation
PVA-coated Fe3O4 NPs were prepared by an in situ co-deposition process in which PVA strands
o
(72000) were well dissolved in deionized water at 80 C until a homogeneous mixture was obtained.
Then, NH3 was added into the flask until pH~12 was attained. Afterward, the atmosphere of the
reaction was neutralized using N2 gas, and a clear yellow solution of FeCl2.4H2O and FeCl3.6H2O in
deionized water was added drop wise into the flask. After conversion of the mixture to dark particles,
o
stirring was continued for additional 2 h at 80 C (reflux condition), and then, they were magnetically
separated and washed several times with acetone and deionized water. The washed particles were
o
dried at 60 C in an oven, and powdered as fine particles by the ball milling process. At the second
stage, the synthesized Fe3O4/PVA magnetic NPs were well dispersed in deionized water by
ultrasonication (15 min), and then, silver nitrate was added, and the mixture was stirred for 4 h at room
temperature. Ultimately, the produced dark brown particles were magnetically isolated from the
mixture and washed several times with deionized water and dried at 60 oC in the oven (Scheme 1).
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Scheme 1. Synthetic pathway of the Fe3O4/PVA-10%Ag nanocomposite.
2.2. Characterization
For structural characterization studies of the fabricated Fe3O4/PVA-10%Ag nanocomposite, both
Fourier-transform infrared (FT-IR) spectroscopy and energy dispersive X-ray (EDX) spectroscopy
were performed and the spectra were precisely investigated, as shown in Figure S1 in the
Supplementary Information (SI) section. Elemental analysis on the desired product proved that all
essential elements such as iron, carbon, oxygen, and silver were present in the structure of the
Fe3O4/PVA-10%Ag nanocomposite, and the quantitative ratio of each element is reported in Table S1
in the SI section. As shown in the table, the weight ratio of Ag NPs with a near approximation is
considered 10%. The presence of the Ag NPs was also approved by X-ray photoelectron spectroscopy
(XPS) (Figure S7). Figure S1b shows the FT-IR spectra of PVA-coated Fe3O4 NPs and the
Fe3O4/PVA-10%Ag nanocomposite. The comprehensive interpretation of the peaks that appeared in
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the FT-IR spectra has also been given in the SI section, which proves the well surface-
functionalization of the magnetic NPs. To obtain more confirmation about the structure of the
Fe3O4/PVA-10%Ag nanocomposite, X-ray diffraction (XRD) pattern of the desired product was
obtained and compared with the reference patterns of Fe3O4 NPs and Ag NPs (Figure 1). The XRD
patterns of Fe3O4 MNPs and Ag NPs have been reported according to the database of JCPDS
(PDF#99-0073) and (PDF#87-0597), respectively. As shown in the figure, the peaks that appeared at
2= ~30.7o, 36.2o, 43.8o, 57.7o, and 63.4o are related to the diffraction pattern of Fe3O4 NPs (pattern
a). They are highlighted as blue circles in the XRD pattern of the desired product (pattern c). They are
also marked by their Miller indices (2 2 0), (3 1 1), (4 0 0), (5 1 1), and (4 4 0), respectively (pattern
a). In addition, the peaks that appeared at 2= ~38.0o, 44.2o, 64.3o, and 77.2o corresponded to the Ag
NP diffraction pattern (pattern b). They are highlighted as red squares in the XRD pattern of the
desired product. Additionally, they are marked by their Miller indices (1 1 1), (2 0 0), (2 2 0), and (3 1
1) (pattern b). As compared with two reference patterns (a,b), a new peak appeared at ~32.7o, which
has been marked as a star, was observed in the spectrum of the Fe3O4/PVA-10%Ag nanocomposite.
This new peak is attributed to the PVA strands that coated the magnetic core. The mean size of the
Fe3O4/PVA-10%Ag nanocomposite was also calculated as ~21 nm using HighScore Plus software and
Debye-Scherrer formula.
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Figure 1. XRD patterns of (a) Fe3O4 NPs; (b) Ag NPs; and (c) Fe3O4/PVA-10%Ag nanocomposite;
(⁎): new peak, (●): peak related to Fe3O4 NPs, and (): peak related to Ag NPs.
Microscopic images of the desired product were also captured using a scanning electron microscope
(SEM), and the results of the morphology and size of the NPs were precisely investigated. As shown
in Figure 2, the uniform spherical NPs collectively were fabricated during the in situ process.
However, agglomeration was also observed in some places of the sample, which probably occurred
because of the swelling and shrinkage property of the PVA polymeric network and the
superparamagnetic behavior of the nanocomposite. The SEM images of the Fe3O4/PVA-10%Ag
nanocomposite revealed the particle size. The statistical data of particle sizes (for 30 particles)
revealed that the mean size is 20±15 nm, and this value completely corresponded to the obtained
value from the XRD study. Moreover, some of the brilliant spots in the image (a) were most likely
related to the Ag NPs onto the surface of Fe3O4 NPs. The TEM images are illustrated in Figure S8 (SI
section), and they show well distribution of the Ag NPs onto and between the PVA textures.
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Figure 2. SEM images of the Fe3O4/PVA-10%Ag nanocomposite.
The thermal behavior of the fabricated Fe3O4/PVA-10%Ag nanocomposite in a thermal range of 50-
o
700 C under air atmosphere and its magnetic trait were investigated by thermogravimetric analysis
(TGA) and vibrating sample magnetometry (VSM), respectively (Figures S2 and S3, in the SI
section). As shown in the TGA curve, proportional to temperature increase, the first shoulder (ca. 10%
o
weight loss) was observed until ca. 280 C, probably due to the removal of the PVA polymeric
network. Then, a gradual weight loss trend was observed until ca. 480 oC, attributed to the dehydration
of –OH groups in the PVA strand structure. The fabricated Fe3O4/PVA-10%Ag nanocomposite
exhibited a typical superparamagnetic behavior, as presented in Figure S3. By having this property,
the separation process of the nanocatalyst is achieved with high convenience. The magnetic property
of the magnetic core is typically reduced proportional to more core coating and new layer creation
[25−27]. Accordingly, the M-H curves show that the composition of the PVA polymeric network and
Ag NPs causes a reduction in the magnetic property of Fe3O4 NPs. More comprehensive discussion on
the TGA and VSM curves is given in the SI section. Brunauer–Emmett–Teller (BET) results are
shown in Figures S9-11.
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2.3. Application
2.3.1. Catalytic activity
To investigate the catalytic efficiency of the produced Fe3O4/PVA-10%Ag nanocomposite, first, the
reaction condition was precisely optimized with various solvents, catalytic ratios, and hydrazine
amounts in the reduction reaction of NB (Table 1, entry 1). Detailed information of the optimization
process has been reported in Tables S2 and S3, in the SI section. Then, the catalytic activity of the
prepared Fe3O4/PVA-10%Ag nanocomposite was carefully screened using different derivatives of NB,
as reported in Table 1. As shown in the table, high reaction yields were obtained when using the
Fe3O4/PVA-10%Ag nanocomposite for short times. However, these results strongly prove the high
catalytic performance of the Fe3O4/PVA-10%Ag nanocomposite when compared with that of other
reported catalysts (see Table S4, in the SI section). These values have revealed that Fe3O4/PVA-
10%Ag could be considered as a substantial catalyst for NB reduction reactions. To investigate the
effectiveness of the composited Fe3O4 NPs in terms of catalytic performance, PVA-10%Ag was also
applied under the same conditions. According to the Table S2 (entry 11), there was a partial decrease
in the obtained yield after removing the Fe3O4 NPs.
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Table 1. Obtained yields after the reduction of NB derivatives to aniline derivatives using the
Fe3O4/PVA-10%Ag nanocomposite (30.0 mg), NB (1.0 mmol), N2H4.H2O (5.0 mol%), and ethanol
(2.0 mL), at 70℃.
MP (oC)
Ref.
Entry
1
NB structure
Time (min)
Yieldb (%)
Products
Found/Reported
Liquid sample*
[28]
[29]
5
99
143-145/144-146
2
3
15
7
99
92
135-140/136.2-138.1
[30]
170-175/171-173
187-189/186-188
[29]
[28]
4
5
10
9
94
93
187-189/185-187
64-66/65-66
[32]
[33]
6
7
15
10
89
96
50-53/52-53
[31]
8
14
90
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41-44/42-43
69-71/70-72
[32]
[29]
9
5
97
97
10
8
209-212/208-210
[34]
11
16
89
*Liquid sample was identified with boiling point screening and thin-layer chromatography (TLC) (bp ca.184
oC)
b: The yields refer to the isolated products.
2.3.2. Suggested mechanism
The catalytic role of Ag NPs in the reduction reaction of NB derivatives in the presence of N2H4.H2O
and a plausible mechanism are illustrated in Figure 3. According to the figure, based on the observed
results in the present work and knowledge from earlier precedents, it is believed that effective
electronic interactions between Ag and heteroatoms can create an appropriate substrate for this type of
reaction [35]. These close electronic interactions of heteroatoms with dissociated hydrogen atoms
from hydrazine hydrate, onto the surface of the Ag NPs cause NB derivatives to be adsorbed and
converted to anilines during successive dehydration processes. In fact, hydrazine hydrate is considered
as a substantial H-supporter for the reduction process and can effectively interact with Ag NPs
surfaces from its nitrogen sites.
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Figure 3. A plausible mechanism for the reduction of NB derivatives to anilines using the
Fe3O4/PVA-10%Ag nanocomposite in the presence of hydrazine hydrate.
2.3.3. Recyclability
To monitor the recyclability of the produced Fe3O4/PVA-10%Ag hybrid nanocomposite, it was
separated from the reaction mixture using an external magnet after completion of the reaction of NB
reduction. Then, the particles were washed well several times with ethanol and deionized water, dried,
and used again in further reactions. Afterward, they were dispersed well in deionized water by
ultrasonication and washed again with ethanol. Finally, they were dried well at 60 oC. After recycling
and reusing five times, reduction in the reaction yields was observed, probably due to the separation of
Ag NPs during the catalytic process (Figure S4, in the SI section).
2.3.4. Biological activity
The presented product Fe3O4/PVA-10%Ag hybrid nanocomposite could be used for biological
applications. This property was achieved through the composition of Ag NPs with Fe3O4 NPs.
Accordingly, we evaluated the antibacterial activity of our desired product by carrying out the in vitro
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biological tests. The antibacterial properties of the samples toward gram-positive Staphylococcus
aureus (S. aureus, ATCC 12600) and gram-negative Escherichia coli (E. coli, ATCC 9637) bacteria
were evaluated according to the disc diffusion antibiotic sensitivity test. The samples were poured
onto the nutrient agar plates cultured with bacterial cells, and then the plates were incubated at 37 °C
for 24 h. The antibacterial effects of the Fe3O4/PVA-10%Ag hybrid nanocomposite were investigated
with execution of the zone of the inhibition (ZOI) on E. coli and S. aureus cells, which show the
inhibitory property of microbial growth around the discs (Figure S5 a,b – in the SI section). The
antibiotic gentamicin was employed as the positive control in this study. Colony-forming unit (CFU)
test was also carried out to monitor the antibacterial activity of Fe3O4/PVA-10%Ag using E. coli and
S. aureus. As shown in Figure S5 c─f, a large number colonies of E. coli and S. aureus (images c and
d) were reduced by our nanoscale composite product after 24 h (images e and f). The results obtained
from the plate count technique are reported in Table 2.
Table 2. Results obtained from disk diffusion and CFU tests using the Fe3O4/PVA-10%Ag
nanocomposite.
Sample
ZOI E. coli (mm)
6 ± 0.7
ZOI S. aureus (mm)
7.5 ± 0.8
P.C (E. coli)
768 ± 71
P.C (S. aureus)
644 ± 59
Gentamicin
Fe3O4/PVA-10%Ag
2.22 ± 0.24
3.09 ± 0.22
185 ± 24
48 ± 32
mm: clear area in millimeters, P.C: plate count.
3. Experimental
3.1. Materials and devices
All the chemicals and equipment used in this study are reported in the SI section.
3.2. Practical methods
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Preparation of the PVA-coated Fe3O4 NPs
In a three-necked round-bottom flask (250 mL), polyvinyl alcohol (PVA; 2.0 g, PVA 72000) was
dissolved well in 40.0 mL deionized water into an oil bath at 80 oC until a homogeneous mixture was
obtained. Then, under N2 atmosphere, ammonia solution (12.0 mL) was added into the flask and pH
was carefully checked with a pH paper (pH~12). Next, a homogeneous yellow solution of FeCl2.4H2O
(1.0 g, 7.9 mmol) and FeCl3.6H2O (2.5 g, 9.2 mmol) in deionized water (10.0 mL) was added
dropwise. After completion of the addition, the solution was stirred continuously for additional 2 h
under the same conditions. Afterward, the produced dark magnetic NPs were magnetically collected
and washed several times with deionized water and ethanol. Finally, the dark magnetic NPs were dried
at 60 °C.
Preparation of the Fe3O4/PVA-10%Ag hybrid nanocomposite
The prepared Fe3O4/PVA NPs (0.5 g) were initially dispersed well in deionized water (15.0 mL) using
an ultrasonic bath. Then, AgNO3 (1.0 g, 5.9 mmol) was added into the flask and stirred for 4 h at room
temperature. Ultimately, the magnetic NPs were collected using an external magnet and washed
several times with ethanol and deionized water. The dark brown NPs were dried at 60 °C.
3.3. Spectral data for selected compounds
1
4-Aminophenol (Table 3, Entry 6): white solid, H NMR (500 MHz, DMSO): δ (ppm)ꢀ=ꢀ4.38 (2H, s,
NH2), 6.42–6.44 (2H, d, J=10 Hz, H–Ar), 6.48–6.50 (2H, d, J=10 Hz, H–Ar), 8.37 (1H, s, OH).
4. Conclusions
Among various species of hazardous chemical compounds, NB derivatives are compounds that have
to be removed or converted to nontoxic aniline derivatives through convenient strategies. In this
regard, one of the most convenient methods is the use of magnetic nanocatalysts, as they have
distinguished properties such as magnetic property, extreme surface area, surface-functionalization
ability, notable thermal resistance, and nontoxicity. Herein, we introduced an efficient organic–
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inorganic hybrid nanocomposite made of iron oxide nanoparticles, PVA strands, and Ag NPs
(Fe3O4/PVA-10%Ag) for the reduction of the NB derivatives to their aniline forms. According to the
suggested mechanism, Ag NPs, which were loaded onto the surface of PVA-coated iron oxide
nanoparticles, are responsible for the catalytic activity of this nanocomposite through their electronic
effects with heteroatoms. Additionally, they have added the biological effect to the presented
nanocomposite through their antibacterial property. All structural characterization studies such as FT-
IR, EDX, XRD, and TGA were performed, and the results obtained were precisely interpreted in the
context. Moreover, the magnetic property of the presented nanocatalyst was investigated by VSM
analysis, and super-paramagnetic treatment was observed. The morphology, uniformity, and size of
the particles were investigated by SEM imaging.
Acknowledgments
The authors gratefully acknowledge the partial support from the Research Council of the Iran
University of Science and Technology and the Iran National Science Foundation (INSF).
Disclosure statement
The authors declare no potential conflict of interest.
Supplementary data
Supplementary data can be found in the online version of this article.
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Competing interests statement
The authors whose names are listed in this article have no competing interests in this paper.
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Highlights
 Fe3O4/PVA-10%Ag is presented a novel, efficient and recyclable magnetic nanocomposite.
 Uniform and spherical shape nanoparticles in the mean size 21 nm have been prepared.
 Versatile nanocomposite with high catalytic and biological activities is introduced.
 Reduction of nitrobenzenes have been done in short reaction times.
 Synergistic magnetic effect between Ag and Fe3O4 nanoparticles has been investigated.
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Figure 3