Facile one-pot strategy to prepare Ag/Fe2O3 decorated reduced graphene oxide nanocomposite and its catalytic application in chemoselective reduction of nitroarenes

Article abstract of DOI:10.1016/j.jallcom.2016.04.229

The present work reports about one-pot hydrothermal synthesis of a composite of Ag/Fe₂O₃ anchored on reduced graphene oxide (rGO) via homogeneous chemical precipitation of Fe(OH)₃ and simultaneous reduction of Ag(I). The p

Full text of DOI:10.1016/j.jallcom.2016.04.229

Accepted Manuscript
Facile one-pot strategy to prepare Ag/Fe O decorated reduced graphene oxide
2 3
nanocomposite and its catalytic application in chemoselective reduction of nitroarenes
Bappi Paul, Debraj Dhar Purkayastha, Siddhartha Sankar Dhar, Subhankar Das,
Sudipta Haldar
PII:
S0925-8388(16)31207-5
10.1016/j.jallcom.2016.04.229
JALCOM 37427
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 23 February 2016
Revised Date: 6 April 2016
Accepted Date: 22 April 2016
Please cite this article as: B. Paul, D.D. Purkayastha, S.S. Dhar, S. Das, S. Haldar, Facile one-pot
strategy to prepare Ag/Fe O decorated reduced graphene oxide nanocomposite and its catalytic
2 3
application in chemoselective reduction of nitroarenes, Journal of Alloys and Compounds (2016), doi:
10.1016/j.jallcom.2016.04.229.
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Graphical abstract
One pot in-situ synthesis of Ag/Fe2O3 anchored rGO assisted by urea and PEG 4000 is described. The
novel nanohybrid material (Ag/Fe2O3-rGO) is used as highly efficient magnetically separable
heterogeneous catalyst for chemoselective reduction of nitroarenes to corresponding amines.

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Facile one-pot strategy to prepare Ag/Fe2O3 decorated reduced graphene oxide
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nanocomposite and its catalytic application in chemoselective reduction of nitroarenes
Bappi Paula, Debraj Dhar Purkayasthaa, Siddhartha Sankar Dhara*, Subhankar Dasb, Sudipta Haldarb
aDepartment of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam, India
bDepartment of Mechanical Engineering, National Institute of Technology Silchar, Silchar-788010,
Assam, India
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*Corresponding authors. Tel: +91-03842-242915; fax: +91-03842-224797
Email:ssd_iitg@hotmail.com (S.S. Dhar)
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Abstract
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The present work reports about one-pot hydrothermal synthesis of a composite of Ag/Fe2O3
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anchored on reduced graphene oxide (rGO) via homogeneous chemical precipitation of
Fe(OH)3.and simultaneous reduction of Ag(I).The pristine aqueous suspension of graphene
oxide (GO) synthesized by Hummers method is mixed with Fe(NO3)3.9H2O, AgNO3, urea and
polyethylene glycol (PEG 4000).The mixture under hydrothermal conditions transforms into
Ag/α-Fe2O3-rGO nanohybrid. Here PEG 4000plays dual role of surfactant as well as reducing
agent for Ag(I). The synthesized Ag/Fe2O3-rGO nanocomposite was used as magnetically
recoverable catalyst for room-temperature chemoselective reduction of aromatic nitro groups to
the corresponding amines.
Keywords: Reduced graphene oxide; Magnetic catalyst; Nitroarenes; Chemoselective.
1. Introduction
Selective reduction of aromatic nitro compounds to amines is one of the highly useful organic
transformations[1]. Functionalized aromatic amines are important feedstock for the synthesis of
agrochemicals, dyes, pharmaceuticals, polymers, and various other industrially important fine
chemicals[2-4]. In industry, the reduction of nitroaromatics is carried out in the gas phase using a
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nickel, copper or iron catalyst in the presence of various hydrogen sources[5,6]. The most
commonly used method for the production of aromatic amines is the reduction of corresponding
nitro substrates, using stoichiometric amounts of reducing agents. However, these traditional
noncatalytic processes are environmentally non-sustainable because of generation of the large
amount of waste[6-8]. Homogenous catalysts generally dissolve in reaction media, thus
providing more readily-accessible active catalytic sites, which results in mild reaction conditions
and good selectivity. These catalysts, however, have limited usages due to problems in
separating the products contaminated with unstable residuesas well asrecycling of the expensive
catalysts[9].Whereas the catalytic reductions of nitro groups in the presence of metal complexes,
metal sulfides or metal powder have various practical drawbacks, such as toxic by-products and
inefficient reusability[4,10-12]. Magnetic nanoparticles (NPs) can play a dual role in serving
both as catalysts as well as magnetic carriers of catalysts. Noble metal NPs possess fascinating
physicochemical properties and their catalytic activities have been extensively explored in recent
times. However, these NPs tend to aggregate due to their high surface energy during reaction
which eventually diminish their catalytic activity[13]. Industrial applications of these NPs are
also limited due to their high cost and poor recoverabilityfrom the reaction medium. These
problems are usually overcome by immobilizing noble metal NPs of specific shapes and sizes on
various solid supports[14-16]. Among the solid supports, magnetic NPs and porous carbon
materials have received great attention in recent past[17-18]. Magnetic nanoparticles are easy to
separate from the reaction medium by use of external magnet while carbon materials possess
high specific surface area. The combination of these types of materials may significantly can
further improve activity and dispersibility of noble metal NPs[19-22]. Recently, heterodimeric
nanocrystals with noble metals and iron oxides have been synthesized and used as magnetic
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reusable catalyst. Park and co-workers synthesized Au-Fe3O4 heterodimer nanocatalysts and
applied them for the chemoselective reduction of nitro compounds[23]. Jang et al. reported a
simple and one pot synthesis of Rh-Fe3O4 heterodimer nanocatalyst and demonstrated their
application as magnetically recoverable catalyst for efficient and selective reduction of
nitroarenes[24]. A core-shell magnetic Fe@Au NPs anchored graphene oxide have been recently
reported for chemoselective and regioselective reduction of aromatic nitro group[19].
Recently,copper nanoparticles loaded on Fe3O4@SiO2have been designed and catalytic
performance was investigated in the reduction of aromatic nitro compounds[25]. Although above
cited noble metal supported on iron oxide magnetic nanocatalysts have various advantages, such
as easy recovery and good efficiency, however their activity and selectivity are affected by steric
and diffusion factors[6]. Therefore, such heterodimeric nanocatalysts if supported on porous
carbon material, the surface area is substantially increased and nanocatalyst can be evenly
dispersed in the pores[26]. Graphene oxide has been proven to be one of the most important
porous carbon supports for anchoring metal nanoparticles[27-31].Graphene oxide possesses very
large specific surface area (up to 400 to 1500 m2 g-1) and also exhibits high utilization of its
surface area because both sides of its nanosheets are accessible[28,32].Therefore, there exists a
great possibility of high synergistic effect between noble metals and GO, which can greatly
enhance the performance of the material. Ag NPs supported on various metal and metal oxides
nanoparticles including magnetically recoverable nanoparticles have been the subject of
considerable interest for past several years[33]. To the best of our knowledge, Ag supported
Fe2O3 embedded on rGO has not been reported.As a part of our ongoing research on synthesis
and application of nanocatalysts[34-37], herein, we report development of one-pot hydrothermal
synthesis of Ag/Fe2O3 embedded rGO and studies of its catalytic activity for room-temperature
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chemoselective reduction of aromatic nitro groups. The morphology, structure and composition
of as-prepared catalyst were characterized by various analytical techniques. The catalyst showed
superior performance and good selectivity for reduction of nitroarenesto amines by hydrazine
hydrate.
2. Experimental
2.1 Materials and physical measurements
Graphite powder, ferric nitrate and silver nitrate were purchased from Sigma Aldrich. Urea and
PEG 4000 were purchased from Merck India Ltd. Double distilled water was used throughout
the experiment. FT-IR spectrum was recorded on KBr matrix with Bruker 3000 Hyperion
Microscope with Vertex 80 FT-IR system. Thermogravimetric analysis (TGA) was performed in
air on a Netzsch STA449F3 thermal analyzer maintaining flow rate of 20 mL/min and heating
rate of 10°C/min. XRD measurements were carried out on a Bruker AXS D8-Advance powder
X-ray diffractometer with Cu-Kα radiation (λ=1.5418Å) with a scan speed of 2°/min.
Transmission electron microscopy images were obtained on a JEOL, JEM2100 equipment. The
sample powders were dispersed in ethanol under sonication and TEM grids were prepared using
a few drops of the dispersion followed by drying in air. Nitrogen adsorption-desorption
isotherms were obtained with a Micromeritics ASAP 2010 surface area and porosity analyzer.
Magnetism of the material was studied using a Lakeshore VSM 7410 at 300 K.
2.2 Synthesis of Graphene Oxide
Graphite powder (GP) was oxidized by modified Hummers method[38,39].In detail,
concentrated H3PO4 and concentrated H2SO4 were mixed in a 250 mL round bottomed flask
(RB), followed by addition of graphite powder. The RB was put in a preheated 50°C water bath
under magnetic stirring, followed by slow addition of KMnO4 and the stirring was continued for
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another 6 h.This was followed by addition of diluted H2O2 into the solution without interruption
until no bubbles were produced,while the color of the solution changed from black to purple and
finally became bright yellow. The mixture was stirred for another 3 h. The solid product thus
obtained was cooled to room temperature and separated by centrifuge. Product was then washed
with HCl (5%), alcohol, and deionized water to obtain the graphene oxide. The collected
sediment was dispersed in alcohol and treated ultrasonically. Subsequently, the concentration of
the graphene oxide suspension was calculated by weighing the mass of the sample after drying at
90°C for 24 h.
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2.3 Synthesis of Ag/α-Fe2O3-rGO nanocomposite
An amount of 0.80 g of Fe(NO3)3.9H2O (2 mmol) and 0.084 g of AgNO3 (0.5 mmol) were added
to 20 mL of a 1.8 mg mL-1 GO aqueoussolution while stirring.To this 1.08 g of urea(0.0018 M)
and 2 g of PEG 4000 (0.5 mmol) were added and the above mixture was sonicated for 15 min at
25°C. After sonication for 15 min about 80 mL deionized water was added to the resulting
solution and transferred into a 100 mL Teflon-lined stainless steel autoclave, and heated at 180
°C in an electric oven for 8 h. The resulting black product was cooled to room temperature,
washed withdeionized water and ethanol several times. Finally, the productwas dried at 50°C in a
vacuum oven for 3 h. For comparison, bare nano Ag/α-Fe2O3 material without GO was also
prepared under the similar condition.
2.4General procedure for the room temperature reduction of nitroarenes
In a typical procedure, 1.0 mmol of aromatic nitro compound was slowly added to the stirred
aqueous suspension of 50 mg of freshly prepared nanoparticles catalysts (Ag/α-Fe2O3-rGO)and
the contents was stirredat room temperature for about 5 min. A total of 0.2 mL of hydrazine
monohydrate was then added to the mixture and the reaction contents was further stirred. Stirring
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was continued for required time (Table 2) till complete conversion was achieved. Progress of the
reaction was monitored by thinlayer chromatography. After completion of the reaction, the
catalyst was separated magnetically from the reaction mixture and the product was extracted by
ethyl acetate (3×5 mL).The organic layer was dried over anhydrous Na2SO4 and filtered off, and
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the solvent was evaporated at reduced pressure. All of the products were characterized by H
NMR (400 MHz with TMS as the standard).
3. Results and Discussion
Synthesis of a composite of Ag/Fe2O3 anchored on rGO has been successfully achieved by
hydrothermal heating of a ferric hydroxide (Fe(OH)3) precursor obtained by a homogeneous
chemical precipitation and simultaneous reduction of Ag(I) (Scheme 1). Here, urea was used for
hydroxylation. Urea decomposes at the experimental temperature to NH3 and CO2. NH3
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combines with water to produce ammonium (NH4 ) and hydroxide (OH-) ions. Here, hydroxide
anions are produced by hydration of urea, which cause a uniform rise in pH of the solution till
the solubility limit. The free OH- ions then combines with Fe3+ ions forming Fe(OH)3. It is
pertinent to mention here that polyethylene glycol (PEG) with uniform and ordered chain
structure can act as a very useful surfactant to control size and morphology of the nanomaterials.
Normally for reduction of GO to rGO, a reducing agent such as sodium borohydride, aluminium
hydride, hydrohalic acid, hydrazine etc. is required, but the main advantage of using urea lies in
the fact that no extra reducing agent is required. In the present synthesis, hydroxylating agent
urea also served as reducing agent for GO. Here, PEG 4000 also plays dual role assurfactant in
order to control the particle size, size distribution of the nanoparticles and as well as reducing
agent for AgNO3.The Ag/α-Fe2O3 nanoparticles are grown on the surfaces of the reduced
grapheme oxide nanosheets through in situ reduction of the pristine GO under a hydrothermal
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treatment at 180°C for 8 h. The main advantage in this process is that uniform rise in pH
prevents the occurrence of high local supersaturation, allowing nucleation to occur
homogeneously throughout the solution.
<Scheme 1.>
3.1 Catalyst characterization
XRD analysis of the catalyst
<Fig.1.>
The powder XRD pattern was recorded for identification of phases exhibited by the synthesized
material. Fig.1 shows the powder XRD pattern of the synthesized Ag/α-Fe2O3-rGO
nanocomposite. The diffraction peaks matches well with the reported data of α-Fe2O3 (JCPDS
File no. 87-1166). α-Fe2O3 possess a rhombohedrally centered hexagonal structure of the
corundum type with a close-packed oxygen lattice in which two thirds of the octahedral sites are
occupied by Fe(III) ions[40]. In addition, two diffraction peaks at 2θ values 38.19° and 44.46°
corresponds to (111), and (200) planes of face-centered cubic Ag (JCPDS File no. 87-0720).
This indicates formation of pure Ag/α-Fe2O3 nanoparticles. The Ag/α-Fe2O3-rGO nanocomposite
also showed an additional diffraction peak at 25.5° which can be attributed to (002) plane of
rGO. The average crystallite size of the synthesized Ag/α-Fe2O3-rGO nanocomposite was
estimated by the Debye-Scherrer equation [34], d=kλ/βCosθ, where‘d’ is the average crystallite
size, ‘λ’ is the wavelength of Cu-Kα radiation, ‘β’ is the full width at half maximum (FWHM) of
the highest intensity diffraction peak, ‘θ’ is the Bragg diffraction angle and ‘k’ is the shape
factor, whose value is about 0.9. The average crystallite size of the synthesized Ag/α-Fe2O3-rGO
nanocomposite was found to be 25.1 nm.
TEM and EDSanalysis of the catalyst
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<Fig.2.>
The TEM image of the synthesized Ag/α-Fe2O3-rGO nanocompositeis shown in Fig.2. From the
TEM image it can be seen that the α-Fe2O3 and Ag nanoparticles are distributed homogeneously
in the rGO sheets. Fig.2b shows irregularly shaped particles of α-Fe2O3 with diameter 10-35 nm
and Ag NPs of size 2-5 nm. It can be seen from Fig.S1 in ESI Ag nanoparticles are in close
contact with α-Fe2O3 nanoparticles.The spacing of the lattice fringes werefound to be separated
by 0.251 and 0.234 nm, possibly due to (110) plane of α-Fe2O3 and (111) plane of metallic Ag
respectively.The ED pattern indicated polycrystalline nature of the material. The EDS pattern
(Fig.3) showed Fe, C, Ag and O, which confirms the formation of Ag/α-Fe2O3-rGO
nanocomposite.
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<Fig.3.>
Raman spectra of the catalyst
<Fig.4.>
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Fig.4 shows the SERS signal of GO and Ag/α-Fe2O3-rGO nanocomposite in the range of 1000-
1800 cm-1.The materials showed two prominent peaks at 1352 and 1590 cm-1, which correspond
to D-band (defect (D) peak) and G-band (graphite (G) peak), respectively. The values are
consistent with literature reports [41]. The D-band/G-band intensity ratio (ID/IG) of these peaks
provide the disorder levels of the materials. The ID/IG of GO and Ag/α-Fe2O3-rGO
nanocomposite were determined to be 0.826 and 1.001, respectively. The increase in the ratio of
ID/IG of Ag/α-Fe2O3-rGO was recognized due to the reduction of GO to rGO in the process of
synthesis of Ag/α-Fe2O3-rGO.
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TGA of the catalyst
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<Fig.5.>
The TGA curves of GO and Ag/α-Fe2O3-rGO nanocomposite are shown in (Fig.5 (a,b)). The
mass loss of 5 % at around 100-170°C which may be attributed to the removal of water molecule
trapped inside the GO and a maximum weight loss of 65 %in the temperature range of 170-
525°C may be ascribed to the pyrolysis of the labile oxygen-containing groups in the forms of
CO, CO2 and steam. Ag/α-Fe2O3-rGO exhibits overall weight loss of only 17% when the sample
was heated up to 800°C at the heating rate of 10°C per minute. This weight loss corresponds to
loss of residual oxygen-containing groups of rGO from Ag/α-Fe2O3-rGO.
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N2adsorption-desorption isotherm analysis of the catalyst
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<Fig.6.>
TheN2 adsorption-desorption isothermof Ag/α-Fe2O3-rGO nanocomposite (Fig.6) follows the
characteristics of a type IV isotherm with a type H3 hysteresis loop associated with aggregates of
plate-like particles forming slit-like pores [42]. The material showed high BET specific surface
area and pore volume of 772.65(m2/g) and 1.47(cm3/g), respectively. The Barrett Joyner Halenda
(BJH) pore size distribution indicates that most of the pores range from 5 to 20 nm as shown in
inset of Fig.6.
VSM analysis of the catalyst
<Fig.7.>
The magnetic hysteresis measurement Fig.7 of Ag/α-Fe2O3-rGO nanocomposite was carried out
at 300 K with the applied magnetic field sweeping from -20000 to +20000 G. The magnetic
hysteresis loops showed a ferromagnetic behavior with a remnant magnetization (Mr) of 15.13
emu g-1 and coercivity (Hc) of 572.03 G. The saturation magnetization of Ag/α-Fe2O3–rGO
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catalyst is 57.2 emu g-1. The nature of the hysteresis loop and value of saturation magnetization
clearly indicate strong ferromagnetic property of the nanocomposite.
3.2 Catalytic activity of Ag/α-Fe2O3–rGO nanocomposite for reduction of nitroarenes using
hydrazine monohydrate at room temperature.
After successful synthesis and full characterization of Ag/α-Fe2O3-rGO nanocomposite, we
examined its catalytic activity for reduction of nitroarenes to aromatic amines by hydrazine
hydrate. In order to get best results, the reaction variables such as solvent, and amount of catalyst
were optimized. For this purpose, nitrobenzene was chosen as a model substrate. The experiment
was conducted under different solvents viz. acetonitrile, dichloromethane, toluene and water. It is
evident from the optimization studies that water is the best solvent for the present catalytic
system. The reaction was also studied at different mole ratios of substrate, reducing agents and
catalyst (Table 1). A blank run in absence of the catalyst gives a very poor yield of the product
after a long reaction time.
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<Table 1.>
Best results were obtained when catalyst amount is 50 mg and ratio of substrate to reducing
agent is 1:4. Increasing the amount of reducing agent beyond four equivalents did not improve
the yield significantly. To demonstrate the scope of the catalyst, a range of aromatic nitro
compounds were reduced to corresponding amines employing optimized reaction conditions and
the results are summarized in Table 2. Expectedly nitroarenes with both electron withdrawing as
well as electron donating functional groups, afforded good to excellent yields. All the products
were characterized by IR spectroscopy and melting point determination.To ascertain the role of
the catalyst, we have prepared Ag NPs and α-Fe2O3 NPs separately using our reported
methods[34,35] and used them separately as catalyst for reduction of nitroarenes to aromatic
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amines and observed that independently they also show catalytic activity but efficiency is
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significantly less compared to the nanocomposite. We then mixed these NPs (Ag NPs and α-
Fe2O3 NPs) at room temperature and used this mixture as catalysts for reduction of nitroarenes
but we have not seen any improvement of the yield of the product. The Ag/α-Fe2O3 (Ag
supported α-Fe2O3) was also synthesized and used as catalysts but some improvement in the
catalytic performance was observed butstill no way comparable to the performance of the Ag/ α-
Fe2O3-rGOnanocomposite. This clearly indicates Ag NPs and α-Fe2O3 NRs in isolation, a simple
random mixture of these components as well as Ag/α-Fe2O3 have significantly lowercatalytic
effect on reduction of nitroarenes. Therefore it can be concluded that role of rGO as a support in
Ag/α-Fe2O3-rGO is very important in enhancing the performance of the composite catalyst.A
comparison between the present catalyst and some of the previously reported catalytic methods
for reduction of nitroarenes to aromatic amines is summarized in Table 3.The comparison reveals
thatcatalytic reaction presented hereinis better than to the some of the most efficient catalytic
reductions of aromatic nitroarenes to amines. The added advantage of the present catalyst is its
easy recovery and recyclability.
<Table 2.>
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<Table 3.>
3.3. Recyclability of the catalyst
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After completion of the reaction, the solid catalyst was separated magnetically from the reaction
mixture and washed thoroughly with acetone and reused for multiple cycles to check the
efficiency of the recycled catalyst. The catalytic reduction of nitroarenes to aromatic amines was
carried out with the reused catalyst under the same reaction condition. The activity of the
recovered catalyst after 5 consecutive runs did not show any significant decline (Fig.8). The
TEM image of the spent catalyst showed an almost similar size and shape to that of the fresh
catalyst (Fig.S2 in ESI).Leaching test has been carried out by procedure reported[41]. To
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confirm that there is no leaching of Ag particles during the reaction, we have removed the
catalystmagnetically after 15min of the reaction. The yield of the product obtained at 15
minuteswas noted. The reaction was further continued without the catalyst for another 15
minutes but we did not observe any increase in the yield. Since Ag is one of the catalytically
active components of the composite, so if there had been leaching of Ag NPs, we would have
observed some rise in yield. Therefore it can be stated that there is no leaching of Ag NPs from
the Ag/α-Fe2O3-rGO catalyst during the reaction.
<Fig.8.>
4. Conclusion
In summary Ag/α-Fe2O3-rGO nanocomposite has been successfully synthesized by the one-pot
hydrothermal method. The role of urea as hydroxylating agent and PEG 4000 as surfactant as
well as reducing agent are important features of the synthesis method. This novel
nanocomposite, Ag/α-Fe2O3-rGO, is used as recyclable catalyst in reduction of range of aromatic
nitroarenes to amines. To the best our knowledge, such rGO embedded nanocomposite has not
been previously used for conversion of nitroarenes to amines. This catalytic protocol has various
advantages such as high yields, elimination of homogeneous catalysts, simple work-up and easy
separation and recycling of the catalyst. The catalyst also shows true heterogeneity as its
efficiency remains almost same after five cycles of reuse.
Acknowledgement
The authors thank SAIF, IIT Madras, SAIF, IIT Bombay and SAIF, North Eastern Hill
University for analysis. The Director NIT Silchar is acknowledged for financial support.
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Scheme caption
Scheme 1. Synthesis of Ag/α-Fe2O3-rGOnanocomposite.
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Figure captions
Fig.1. Powder XRD pattern of Ag/α-Fe2O3-rGOnanocomposite.
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Fig.2. (a, b) TEM images (c) HRTEM image and (d)ED pattern of Ag/α-Fe2O3-rGO
nanocomposite.
Fig 3. EDS pattern of Ag/α-Fe2O3-rGOnanocomposite.
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Fig.4. Raman spectra of GO and Ag/α-Fe2O3-rGOnanocomposite.
Fig.5. TGA curve of (a) GO and (b) Ag/α-Fe2O3-rGOnanocomposite.
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Fig.6. (a, b)N2adsorption-desorption isotherms of Ag/α-Fe2O3-rGOnanocomposite.
Fig.7. Room temperaturemagnetization hysteresis loop of Ag/α-Fe2O3-rGOnanocomposite.
Fig.8. Catalytic activity of Ag/α-Fe2O3-rGO nanocompositeagainst number of cycles.
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Table captions
Table 1. Optimization of reductionof nitroarenes.
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Table2. Reductionof nitroarenesin presence of Ag/α-Fe2O3-rGO catalyst.
Table 3. Comparison of the literature reported catalyst with the present catalyst.
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<Scheme 1.>
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<Fig.1.>
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<Fig.2.>
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<Fig.3.>
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<Fig.4.>
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<Fig.5.>
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<Fig.6.>
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<Fig.7.>
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<Fig.8.>
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Table 1.
Entry
Substrate Catalyst Reducing agent Time(min) Temperature Yield(%)
(equiv)
(mg)
100
50
(equiv)
(°C)
27
1
2
3
4
5
6
1
1
1
2
1
1
4
8
4
4
4
4
60
60
15
60
60
60
95
96
98
76
92
76
27
50
27
50
27
30
70
50
80
383
384
385
386
387
388
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Table2.
Entry
1
Substrate
Product
Time (min)
Yield (%) Selectivity(%)
NH2
NO2
98
98
>99
>99
30
NO2
NH2
25
2
3
Br
NO2
Br
NH2
97
95
>99
>99
45
30
Cl
Cl
NO2
NH2
4
5
I
I
NO2
NH2
>99
98
95
99
20
F
F
NH2
NO2
6
>99
>99
60
30
CH3
NO2
CH3
NH2
7
8
NH2
NH2
NH2
NO2
Br
Br
>99
>99
45
40
92
95
NH2
NH2
NO2
CH3
NH2
CH3
9
NO2
NH2
92
>99
90
10
390
391
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Table 3.
Entry
Catalyst
Solvent
Temp Time Yield/conversion Ref
°C
rt
(min) (%)
1
2
3
4
5
6
7
Ni NPs
Co NPs
Water
Water
EtOH
Glycerol
EtOH
EtOH
EtOH
75
99 conversion
4
rt
300 50 conversion
180 99 conversion
180 94 yield
4
Au/TiO2
Ni-Fe3O4
Au-Fe3O4
Rh-Fe3O4
Pd-Fe3O4
rt
43
44
23
24
45
25
46
80
rt
10
60
60
15
GC yield 99
99 yield
80
rt
90 yield
8
9
Fe3O4@SiO2/EP.EN.EG@Cu Water
rt
85 yield
Reduced graphene oxide
N2H4.H2O 30
/H2O
2880 97 yield
10
Ag/α-Fe2O3–rGO
Water
rt
30
98 yield
Present
Work
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394
395
396
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398
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Highlights
ꢀ One pot in-situ synthesis of Ag/Fe2O3 anchored rGO.
ꢀ PEG 4000 as surfactant and reducing agent for Ag(I).
ꢀ Formation of Ag/Fe2O3-rGO is confirmed by TEM, XRD, EDS and Raman
spectroscopy.
ꢀ As-synthesized novel material exhibits pronounced activity as magnetic
catalyst.
ꢀ The catalyst used for chemoselective reduction of aromatic nitro groups.