Copper ferrite-graphene hybrid: A highly efficient magnetic catalyst for chemoselective reduction of nitroarenes

Article abstract of DOI:10.1039/c4ra05059b

In this paper, a superparamagnetic copper ferrite-graphene hybrid nanocomposite (CuFe₂O₄-G) was synthesized by a hydrothermal method and used as an efficient catalyst for the reduction of nitroarenes for the first time. The method ha

Full text of DOI:10.1039/c4ra05059b

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Copper ferrite–graphene hybrid: a highly efficient
magnetic catalyst for chemoselective reduction of
nitroarenes†
Cite this: RSC Adv., 2014, 4, 31328
Received 28th May 2014
Accepted 4th July 2014
*
Haiyan Zhang, Shutao Gao, Ningzhao Shang, Chun Wang and Zhi Wang
DOI: 10.1039/c4ra05059b
www.rsc.org/advances
In this paper, a superparamagnetic copper ferrite–graphene hybrid explored the catalytic application of CuFe2O4 nanoparticles for
nanocomposite (CuFe2O4–G) was synthesized by a hydrothermal the Friedel–Cras acylation. Feng et al.6 investigated the catalytic
method and used as an efficient catalyst for the reduction of nitro- activity of CuFe2O4 nanoparticles for the reduction of 4-nitro-
arenes for the first time. The method has been applied to a broad phenol to 4-aminophenol with excess amount of NaBH4.
range of compounds with different properties. The CuFe2O4–G
catalyst can be readily recovered and reused for at least five consec- has enjoyed tremendous research interest in a wide range of
Graphene(G), discovered in 2004 by Geim and co-workers,12
utive cycles without significant loss of its catalytic activity.
elds over the past decades. Graphene-related nanomaterials
exhibit a great application potential in catalysis13 thanks to their
large specic surface area, easy modication, remarkable elec-
trical conductivity, excellent adsorptivity, ultrathin thickness,
superior structural exibility, and high chemical and thermal
stability. To date, various kinds of catalysts, including TiO2,14
SnO2,15 ZnO,16 Pt,17,18 Pt–Ru,19 Pt–Pd,20 Pd21 and so on, have been
supported on graphene-based templates for catalyzing different
chemical transformations, energy conversion and photo-
catalytic reactions. Recently, superparamagnetic graphene–
Fe3O4 nanocomposite (G–Fe3O4) was fabricated and used as an
efficient catalyst for the reduction of nitroarenes with hydrazine
hydrate as reductant, which is a toxic reagent.22 Copper ferrite–
graphene hybrid was developed as an effective photocatalyst for
the degradation of methylene blue under visible light irradia-
tion, which also showed excellent electrochemical behaviors for
use as the anode in lithium-ion batteries.23 However, to our best
knowledge, there has been no report yet about the use of copper
ferrite–graphene (CuFe2O4–G) magnetic nanocomposite as
catalyst for organic synthesis.
Introduction
Development of new catalytic transformations with easy separa-
tion and recyclability of the catalyst is an essential task in
chemical synthesis. Aromatic amines are important starting
materials and intermediates for the manufacture of a great
variety of chemicals such as dyes, pesticides, herbicides, and
agrochemicals.1–3 They are generally synthesized by the chemical
reduction of nitroarenes. Iron-compound,4 mixed metal
compounds,5 transition metals (Cu, Ni)6 and noble metals (Pt, Pd,
Au)7–9 are commonly employed as the catalyst for the reduction
reaction. However, some of the methods employed have draw-
backs, for example using expensive reagents, prolonged reaction
time, using toxic and volatile solvent, unsatisfactory yield, etc.
Hence, the development of an inexpensive, facile and effective
method for the synthesis of aromatic amines is of high demand.
The copper ferrite, CuFe2O4 with a spinel structure, is one of
the most important ferrites in powder form, has been widely
applied in sensors, electronics and catalysts owing to its advan-
tages of environmentally compatible, moisture insensitive, high
dispersion, high reactivity and easy separation at an external
magnet in recent years. Amini et al.10 investigated the low
temperature CO oxidation over mesoporous CuFe2O4 nano-
powders synthesized by a novel sol–gel method. Parella et al.11
In the present work, the catalytic activity of magnetic
CuFe2O4–G nanocomposite for the chemoselective reduction of
nitroarenes was investigated using sodium borohydride as a
hydrogen donor. The results demonstrate that the combination
of CuFe2O4 with graphene results in a dramatic enhancement of
the catalytic activity of CuFe2O4.
Results and discussions
Material characterizations
College of Science, Agricultural University of Hebei, Baoding 071001, Hebei, China.
E-mail: chunwang69@126.com; Fax: +86-312-7528292; Tel: +86-312-7528291
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra05059b
X-ray powder diffraction analysis was used to identify the crystal
structure of the CuFe2O4–G (0.25) and CuFe2O4. As shown in
31328 | RSC Adv., 2014, 4, 31328–31332
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Fig. 1, except some Cu impurity peaks at 43.0ꢀ and 50.6ꢀ, all
peaks were indexed to be CuFe2O4 (JCPDS 77-0010), in detail,
the peaks at 30.5ꢀ, 35.2ꢀ, 57.0ꢀ, 62.8ꢀ and 74.1ꢀ are attributed to
(220), (311), (511), (440) and (533) crystal planes of CuFe2O4.
While no typical diffraction peak of reduced graphene oxide was
observed. It is speculated that the GO in the CuFe2O4–G(0.25)
heteroarchitecture was fully exfoliated due to the crystal growth
of CuFe2O4 nanoparticles between the interlayer of GO sheets,
which result in the low diffraction intensity of GO. The forma-
tion of copper was identied based on the reported data (JCPDS
85-1326) at 43.0ꢀ and 50.6ꢀ. The reason of existence of metallic
copper was that some of Cu2+ was reduced to copper metal in
the formation process of CuFe2O4 due to the strong reducing
capability of ethylene glycol.6
Fig. 2 SEM image of CuFe2O4–G(0.25).
Fig. 2 shows the SEM image of CuFe2O4–G (0.25). It can be
seen that CuFe2O4–G(0.25) were composed of quasi-sphere
particle with particle sizes of about 100 nm.
The FTIR spectra were recorded to further testify the hybrid
material. As shown in Fig. 3, the spectrum of GO is in good
agreement with previous work.24 The broad, intense band at
3250 cmꢁ1 is assigned to the stretching of O–H. The peak at
1728 cmꢁ1 corresponds to the stretching of the –C]O and
–COOH groups on GO sheets. The peak at 1616 cmꢁ1 (aromatic
C]C) can be ascribed to the skeletal vibrations of unoxidized
graphene domains. The C–O bond is associated with the band
at 1047 cmꢁ1. From the FTIR spectrum of GO and CuFe2O4–G
(0.25) samples, it is can be clearly seen that the graphene oxide
exhibits an obvious characteristic absorption peak at about
1728 cmꢁ1 corresponds to the stretching of the –C]O and
–COOH groups. However, it is can not be seen from the FTIR
spectrum of CuFe2O4–G (0.25). It turned out that graphene
oxide was reduced to graphene due to the strong reducing
capability of ethylene glycol. From the FTIR spectrum of
CuFe2O4 and CuFe2O4–G (0.25) samples, the spectra show two
main absorption corresponding to the stretching vibration of
Fig. 3 FT-IR spectra of the GO, CuFe2O4–G(0.25) and CuFe2O4.
spectrum referred to the vibration of remainder H2O in the
sample.6
the tetrahedral and octahedral sites around 586 and 400 cmꢁ1
respectively. The observed values illustrate that the frequency
,
Catalytic activity CuFe2O4–G
bands appearing at 586 and 400 cmꢁ1 are responsible for the To obtain the optimal reaction conditions, the effect of type of
formation of CuFe2O4. The absorption band at 1596 cmꢁ1 on catalyst and catalyst dosage on the reduction of p-nitrophenol
were initially investigated (Table 1). As shown in Table 1, no
product was obtained in the absence of the catalyst (Table 1,
entry 1), indicating that the catalyst was necessary for the
reaction. Only low yields of the product were obtained with
either graphene, Fe3O4 or Fe3O4–graphene (with 25 wt% gra-
phene) as catalyst (Table 1, entries 2–4). While CuFe2O4 could
catalyze the reduction of p-nitrophenol efficiently, 99% yield
was obtained when the reaction was performed at 343 K for 16
min (Table 1, entry 5). The combination of CuFe2O4 with
appropriate amount of graphene results in
a dramatic
enhancement of the catalytic activity of CuFe2O4. The reaction
time required to complete the reaction decreased with
increasing the loading amount of graphene in CuFe2O4–G until
25 wt% (Table 1, entries 7–9). Compare with CuFe2O4 catalyst,
the reaction time could lower down to 9 min from 16 min with
CuFe2O4–G (0.25) as the catalyst, which can be attributed to its
unique heteroarchitechture, which provides the remarkable
synergistic effect between the CuFe2O4 and the graphene sheets.
Fig. 1 XRD pattern of as-prepared CuFe2O4–G(0.25) and CuFe2O4.
Symbols (O) represent peaks of Cu.
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Table 1 Screening and control experiments for hydrogenation of p-
nitrophenola
Entry
Catalyst
Catalyst (mg)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
—
G
20
20
20
20
20
20
20
20
20
10
30
50
20
500
500
60
60
16
35
9
12
14
12
4
—
Trace
26
39
99
99
99
99
99
99
99
99
99
Fe3O4
Fe3O4–G(0.25)
CuFe2O4
CuFe2O4–G(0.35)
CuFe2O4–G(0.25)
CuFe2O4–G(0.15)
CuFe2O4–G(0.1)
CuFe2O4–G(0.25)
CuFe2O4–G(0.25)
CuFe2O4–G(0.25)
CuFe2O4–G(0.25)
Fig. 4 Successive UV-vis absorption spectra of the reduction of p-
nitroaniline with NaBH4 in the presence of CuFe2O4–G (0.25).
9
10
11
12
13
3
40b
molecule such as 1-nitronaphthalene with high yield (Table 2,
entry 7).
a
Reaction condition: p-nitrophenol (1 mmol), solvent (10 mL,
1 : 1), NaBH4 (5 mmol), temperature (343 K).
Temperature (333 K).
EtOH : water
¼
The reusability and recycling of CuFe2O4–G(0.25) was also
investigated. The catalyst was separated from the reaction
mixture using an external magnet, washed with ethanol for
three times, dried at 60 ꢀC in a vacuum oven for 2 h and reused
in another reaction. The catalytic activity of CuFe2O4–G(0.25)
did not show any signicant decrease even aer ve runs.
b
The presence of graphene could enhance the adsorption of
reactant molecules onto the catalytic sites of the CuFe2O4–G
through the p–p stacking and/or electrostatic interaction.
However, the catalytic activity of CuFe2O4–G decreased when Experimental
the content of graphene was increased to 35% (Table 1, entry 6).
Materials and instrumentation
The large amount of graphene in CuFe2O4–G might decrease
the number of the catalytic sites, which resulted in the
decreasing of the catalytic activity of CuFe2O4–G (0.35). The
above results also indicating that there is the most synergistic
effect between CuFe2O4 and the graphene sheets. The reaction
time could be further reduced with increasing the dosage of
CuFe2O4–G (0.25) (Table 1, entries 11 and 12). But a longer
reaction time was required to complete the reaction with
decreasing the reaction temperature from 343 K to 333 K (Table
1, entry 13).
Fig. 4 showed the UV-vis absorption spectra of the reduction
of p-nitroaniline by NaBH4 at various reaction times in the
presence of CuFe2O4–G (0.25). The observed peak at 385 nm for
the p-nitroaniline shows a gradual decrease in intensity with
time and a new peak appeared at 295 nm indicating the
formation of p-phenylene diamine. The results indicated that
CuFe2O4–G (0.25) exhibited considerably high activity for the
reduction of nitroarenes with sodium borohydride as the
hydrogen donor.
To show the generality of this model reaction, the reduction
of a series of nitro aromatics was studied under the optimized
reaction conditions. As shown in Table 2, aromatic nitro
compounds containing various electrons donating (Table 2,
entries 1–6) or electron-withdrawing groups (Table 2, entries 8)
were converted to the corresponding amino aromatics in good
yields and all the reactions could proceed smoothly. Moreover,
the reduction was also successfully carried out on bulkier
Ferric trichloride hexahydrate (FeCl3$6H2O), copper sulfate
pentahydrate (CuSO4$5H2O), sodium borohydride (NaBH4),
glycol, sodium hydroxide (NaOH), ethanol were all obtained
from Chengxin Chemical Reagents Company (Baoding, China).
Nitroaromatics were purchased from Aladdin Reagent Limited
Company. The water used throughout the work was double-
distilled on a SZ-93 automatic double-distiller from Shanghai
Yarong Biochemistry Instrumental Factory (Shanghai, China).
IR spectra (cmꢁ1) were measured with a WQF-510 spec-
trometer. UV-vis absorption spectra were measured with a UV-
vis spectrometer (UV-3600, Shimadzu). The size and
morphology of the catalyst were observed by scanning electron
microscopy (SEM) using a Hitachi S4800 eld emission electron
microscope operated at 30 kV. The XRD patterns of the samples
were recorded with a Rigaku D/max 2500 X-ray diffractometer
using Cu Ka radiation (40 kV, 150 mA) in the range 2q ¼ 10ꢀ–
1
80ꢀ. H NMR (400 MHz) spectra were obtained with a Brucker
AVANCE 400 spectrometer (DMSO-d6) using TMS as an internal
standard.
Synthesis of CuFe2O4–graphene heteroarchitecture
Graphite oxide (GO) was prepared according to the procedure
reported by us.25,26 CuFe2O4–graphene heteroarchitectures with
differing graphene content (10, 15, 25, 35 wt%) were synthe-
sized by a modied hydrothermal method reported in the
literature.
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Table 2 Chemoselective reduction of nitro compounds into amines by sodium borohydride catalyzed by CuFe2O4–G(25%)a
Entry
1
Carbonyl compound
Product
NaBH4 (mmol)
5
Time (min)
9
Yieldb (%)
99
2
5
4
99
3
4
5
5
10
30
96
95
5
6
5
5
45
10
92
99
7
8
5
20
91
6
5
30
30
93
92
9
a
b
Reaction condition: nitro compounds (1 mmol), solvent (10 mL, EtOH : water ¼ 1 : 1), catalyst (20 mg), temperature (343 K). Isolated yields.
A typical experiment procedure for the synthesis of CuFe2O4– Upon completion of the reaction (monitored by TLC), the
graphene heteroarchitecture with 25 wt% graphene content is mixture was cooled to room temperature and the catalyst was
as follows: 40 mg of GO was dispersed into 30 mL of ethylene separated by a magnet for recycling tests. The reaction mixture
glycol with sonication for 12 h. 0.1675 g (0.67 mmol) of was extracted with ether (3 ꢂ 10 mL). The organic phase were
CuSO4$5H2O and 0.3618 g (1.34 mmol) of FeCl3 were added to combined together and dried over anhydrous MgSO4. The
10 mL of ethylene glycol and sonicated for 1 h. The above two solvent was evaporated under vacuum. The pure products were
solutions were then mixed together and stirred for 30 min. Aer obtained by silica-gel column chromatography using petroleum
that, the mixture was adjusted to pH of 8 with 6 mol Lꢁ1 NaOH ether : ethylacetate (4 : 1) as the eluent. The products were
1
aqueous solution and stirred for 30 min, yielding a stable bot- identied by IR and H NMR.
tlegreen homogeneous emulsion. The resulting mixture was
transferred into a 70 mL Teon-lined stainless steel autoclave
and heated to 180 ꢀC for 24 h under autogenous pressure. Aer
Conclusions
In conclusion, an inexpensive and magnetically recyclable
catalyst, CuFe2O4–G (0.25), was synthesized by a hydrothermal
method. CuFe2O4–G (0.25) was used as an efficient catalyst for
the reduction of nitroarenes. The results demonstrate that the
combination of CuFe2O4 with graphene results in a dramatic
enhancement of the catalytic activity of CuFe2O4, which can be
attributed to the remarkable synergistic effect between the
CuFe2O4 and the graphene sheets. The CuFe2O4–G (0.25) cata-
lyst can be readily isolated from the reaction mixture using an
the reaction mixture was cooled down to room temperature, the
precipitate was ltered, washed with distilled water and
ethanol, and dried in a vacuum oven at 30 ꢀC for 12 h. The
product was labeled as CuFe2O4–G (0.25). For comparison, the
same method was used to synthesize CuFe2O4 without
adding GO.
Reduction reactions of nitroarenes
In a 25 mL round bottom ask, nitroarenes (1.0 mmol, 1 eq.) external magnet due to its superparamagnetism and it can be
was dissolved in a mixture of 10 mL H2O–EtOH (1 : 1, v/v). Then, reused at least ve consecutive cycles without signicant loss of
sodium borohydride (5.0 mmol, 5 eq.) and CuFe2O4–G (0.25) its catalytic activity. We believe that this method is important
(20 mg) were added. The mixture was stirred at 70 ꢀC for an addition to known procedures for reduction of aromatic nitro
appropriate time depending upon the nature of the substrate. compounds either on a lab as well as on larger scale.
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This work was nancially supported by the National Natural
Science Foundation of China (no. 31171698), the Innovation
Research Program of Department of Education of Hebei for
Hebei Provincial Universities (LJRC009) and Natural Science
Foundation of Hebei Province (B2011204051).
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