Fe3O4@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon: An Excellent Catalyst in the Reduction of Nitroarenes and Suzuki–Miyaura Cross-Coupling

Article abstract of DOI:10.1007/s10562-016-1792-8

Abstract: Magnetic core double-shelled carbon with Fe₃O₄ nanoparticles as the core, reduced graphene oxide (RGO) as the inner shell and carbon (C) layer as the outer shell, have been successfully designed and prepared. This tailor-ma

Full text of DOI:10.1007/s10562-016-1792-8

Catal Lett
DOI 10.1007/s10562-016-1792-8
Fe O @RGO@Au@C Composite with Magnetic Core and Au
3
4
Enwrapped in Double-Shelled Carbon: An Excellent Catalyst
in the Reduction of Nitroarenes and Suzuki–Miyaura
Cross-Coupling
1
1
1
Minoo Dabiri
•
Noushin Farajinia Lehi
•
Siyavash Kazemi Movahed
Received: 6 March 2016 / Accepted: 12 June 2016
Ó Springer Science+Business Media New York 2016
Abstract Magnetic core double-shelled carbon with
Fe O nanoparticles as the core, reduced graphene oxide
extremely high catalytic performance on two different
kinds of organic reactions (1) reduction of nitroarenes,
and (2) Suzuki–Miyaura cross coupling of phenyl boronic
acid with aryl halides. Moreover, the synthesized catalyst
can be easily recovered and reused for at least ten cycles
due to its magnetically separable feature and good
stability.
3
4
(
RGO) as the inner shell and carbon (C) layer as the outer
shell, have been successfully designed and prepared. This
tailor-making structure acts as an excellent capsule for
encapsulating Au nanoparticles (Au NPs), which could
effectively prevent Au NPs from aggregation and leach-
ing. Because of its structural features, magnetic core-
double-shell Fe O @RGO@Au@C architecture exhibits
Graphical Abstract
3
4
Keywords Heterogeneous catalysis Á Suzuki reaction Á
Nanostructure Á Reduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1792-8) contains supplementary
material, which is available to authorized users.
&
Minoo Dabiri
m-dabiri@sbu.ac.ir
1
Faculty of Chemistry, Shahid Beheshti University,
Tehran 1983969411, Islamic Republic of Iran
123

M. Dabiri et al.
1
Introduction
polycyclic aromatic molecule is a potential candidate as
both support and stabilizer of Au NPs for chemical trans-
formations. For instance, Li et al. synthesized Au/graphene
hydrogel under hydrothermal conditions through the self-
assembly process. Exhibited excellent catalytic perfor-
mance towards the reduction of 4-Nitrophenol (4-NP) to
4-Aminophenol (4-AP), which is arising from the syner-
gistic effect of graphene with Au NPs [19]. Additionally,
In recent years, the design of magnetic nanoparticles
MNPs) has become important because of fundamental
(
scientific interest in MNPs and in their various cutting-edge
technological applications, including their use as magnetic
fluids, magnetic storage media, biomedicine, magnetic
recording devices, biosensors, targeted drug delivery, sep-
aration, contrast enhancement agents for magnetic reso-
nance imaging (MRI), bioprobes, and catalysis [1, 2].
Among these, the application of magnetic NPs as a catalyst
support has received increasing interest in recent decades
because they can be easily prepared from inexpensive
precursors, give the excellent dispersion in the reaction
mediums owing to their nanosizes, and can be simply
separated from the reaction mixture by employing an
external magnetic field. As a result, the magnetic NP-based
catalysts can potentially provide a unique, environmentally
acceptable catalytic route for organic transformations by
combining high activity with easy recyclability [3].
Wang and co-workers synthesized rGO/Fe
O /Au
3 4
nanocomposite with highly dispersed Au NPs and Fe
O
3 4
particles by a facile hydrothermal method. This graphene/
Au nanocomposite display good stability against agglom-
eration and show excellent catalytic activity in the reduc-
tion of 4-NP into 4-AP [20].
Recently, Zhang et al. [21] have reported new double-
shelled hollow carbon spheres with reduced graphene oxide
(RGO) as inner shell and carbon (C) layer as outer shell.
This tailor-making structure acts as an excellent capsule for
encapsulating with ultrafine Pd NPs, which could effec-
tively prevent Pd NPs from aggregation and leaching.
(Scheme 1a). The as-obtained RGO@Pd@C nanohybrid
exhibits superior and stable catalytic performance on the
reduction reaction of 4-NP to 4-AP.
Recently, much attention has been paid on the synthesis
of Fe O NPs/graphene as a new kind of hybrid material,
3
4
owing to wide-ranging applications such as immobilizing
bioactive substances, energy storage and environmental
Herein, we report for the first time the design and syn-
thesis of magnetic core/double-shelled reduced graphene
remediation [4–6]. The unique properties of Fe O4
3
NPs/graphene hybrids, combining characteristics of gra-
phene as a polycyclic aromatic molecule, which has high
conductivity, low price, high chemical inertness, and large
oxide@gold@carbon (Fe O @RGO@Au@C) with the
3 4
RGO as the inner and amorphous C as the outer shells.
2
Graphene is a two-dimensional sheet of sp bonded carbon
specific surface area [7–9], and Fe O4 NPs, with high
3
atoms, which can be viewed as an extra-large polycyclic
aromatic molecule. Recently, graphene has been used as
the support for metals and metal oxides, mainly because of
its large surface area, excellent electrical and thermal
conductivity, low price, high chemical inertness, ease of
modification and strong interactions with metal clusters
[22–24]. Au NPs grow well on the surface of inner shell by
spontaneous redox reaction between graphene oxide (GO)
magnetism, low-cost, and environmentally benign nature
[
10–14], open a new window for fabricating most
stable multifunctional nanomaterials using these hybrids as
support materials. In addition, Fe O has already been
3
4
introduced as a suitable support for preparing highly active
metal catalysts, and immobilizing noble metal nanocata-
lysts on magnetic Fe O support prevents agglomeration of
3
4
the catalyst particles during recovery and can be increasing
catalyst durability [15, 16]. Therefore, a combination of
Fe O NPs and graphene may optimize both dispersion and
and HAuCl [25]. Moreover, the outer shell combined with
4
the inner shell, confines Au NPs in itself, effectively pre-
vents the aggregation and leaching of Au NPs and
increases their catalytic active area, therefore, enhancing
their stability and catalytic.
3
4
catalytic activity of metal NPs.
There have been many efforts toward synthesizing
highly dispersed supported Au NPs. The catalytic perfor-
mance of Au NPs-support strongly depends on the size and
shape of Au NPs, the nature of the support, and the Au
NPs-support interface interaction [17]. The p-interaction of
aromatic rings of the supports with gold nanoparticles leads
to nanoparticle stabiliztion and improve the catalyst per-
formance in a variety of gold catalyzed reactions [18].
Graphene is an ideal candidate because of its a two-di-
2 Experimental
2.1 Characterization
Diffraction data were collected on a STOE STADI P with
scintillation detector, secondary monochromator and Cu-
2
˚
mensional sheet of sp bonded carbon atoms, which can be
Ka1 radiation (k = 1. 5406 A). XPS analysis was per-
formed using a Gammadata-scienta ESCA 200 hemi-
viewed as an extra-large polycyclic aromatic molecule and
large specific surface area [18]. Therefore graphene as a
spherical analyzer equipped with an Al Ka (1486.6 eV)
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
3 4
Scheme 1 Schematic diagram illustrating the synthesis of a RGO@Pd@C hollow sphere b magnetic core/double-shell Fe O @RGO@Au@C
CDSNs architectures
X-ray source. Scanning electron microscope of nanocom-
posites were performed using an electron microscope
Philips XL-30 ESEM. Transmission Electron Microscopy
characterization of nanocomposites were performed using
a transmission microscope Philips CM-30 with an accel-
erating voltage of 150 kV, Zeiss EM10C transmission
electron microscope with an accelerating voltage of 80 kV
and JEOL JEM-2100 transmission electron microscope
with an accelerating voltage of 200 kV. The concentration
of gold was estimated using Shimadzu AA-680 flame
atomic absorption spectrophotometer and inductively cou-
pled plasma optical emission spectrometer (ICP-OES)
Varian Vista PRO Radial. The thermal stability of the
Fe O @RGO@Au@C YSNs was determined using a
properties of the prepared nanocomposites were measured
using a homemade vibrating sample magnetometer
(Meghnatis Daghigh Kavir Company, Iran) at room tem-
perature from -8000 to ?8000 Oe. The nitrogen adsorp-
tion–desorption isotherm of Fe O @RGO@Au@C YSNs
3
4
was collected by using
a
Micrometrics PHS-
2828(PHSCHINA) surface area analyzer with N2 at
77.3 K. UV/Vis spectra were recorded employing an
Analytik Jena Specord S600 Diode Array spectrometer.
Gas chromatography was performed on a Trace GC ultra
from the Thermo Company equipped with FID detector
Ò
1
13
and Rtx -1 capillary column. H-NMR and C-NMR
spectra were recorded on BRUKERDRX-
a
300AVANCEspectrometer at 300.13 and 75.03 MHz,
1
respectively. H-NMR spectra were obtained in DMSO-d
3
4
thermogravimetric analyzer (TGA/DTA BAHR: STA 503)
-
6
1
under air and a heating rate of 10 °C min . The magnetic
using TMS as internal standard. Melting points of products
123

M. Dabiri et al.
were measured on an Elecrtothermal 9100 apparatus and
are uncorrected.
collected by centrifugation, washed with DI water for
several times, and then dried at 60 °C overnight.
3.4 Synthesis of Fe O @SiO @GO@Au
3 4 2
3
Materials
Nanocompiste
3
.1 Synthesis of Fe O Microsphere
3
150 mg of as-synthesized Fe O @SiO @GO core–shell
3
4
4
2
nanoparticle were dispersed in 60 mL of DI water, then
The magnetic particles were synthesized through a
solvothermal reaction according to the method reported by
Zhao et al. [26] with some modification. In a typical pro-
cedure, 1.08 g of FeCl Á6H O was first dissolved in 20 mL
3 mL of 20 mM HAuCl aqueous solution was added and
4
the mixture was kept in a vial under vigorous stirring for
3 h in an ice bath (0 °C). The products were centrifuged
and washed with DI water to remove the remaining
reagents followed by drying at 60 °C overnight.
3
2
of ethylene glycol under magnetic stirring until the solution
became clear. Then 2.99 g of sodium acetate.3H O was
2
added to this solution and stirred for another 1 h. After-
3.5 Synthesis of Fe O @SiO @RGO@Au@C
3
4
2
wards, 0.29 g trisodium citrate.2H O was added. When the
2
Nanocompiste
mixed solution was stirred for 5 h to form a homogeneous
dispersion, the resulting solution was transferred into a
Teflon-lined stainless-steel autoclave with a capacity of
150 mg of as-prepared F O @SiO @GO@Au nanocom-
2
e3
4
piste were dispersed in 16 mL water/ethanol (volume
ratio = 3/1) mixture by ultrasonication, then 4 mL of
0.5 M aqueous glucose solution was added under vigorous
stirring for 30 min. After that, the suspension was trans-
ferred to a 25 mL Teflon-lined autoclave, and heated in an
oven at 180 °C for 16 h. The dark gray products were
collected by a magnet and washed with ethanol and DI
water for six times, respectively. After drying at 60 °C
overnight, the resulting dark brown powder was carbonized
5
0 mL. The autoclave was sealed and heated at 200 Æ C for
1
2 h and naturally cooled to 25 °C. The black particles
were collected with the help of a magnet, followed by
washing with ethanol and deionized water several times,
and then dried under vacuum at 60 °C overnight [27].
3
.2 Synthesis of Fe O @SiO Core–Shell
3 4 2
Nanoparticle
at 500 °C for 4 h under N atmosphere.
2
Firstly, Fe O microspheres (500 mg) were added to a
3
4
mixture of de-ionized (DI) water (150 mL), NH .H O
3
3.6 Synthesis of Fe O @RGO@Au@C Core–Shell
3
2
4
(
50 mL) and ethanol (1500 mL), and sonicated for 4 h at
5 °C. Secondly, tetraethylorthosilicate (TEOS) (0.75 mL)
was dissolved in ethanol (250 mL). Thirdly, TEOS/ethanol
Nanoparticle
2
150 mg of as-prepared Fe O @SiO @RGO@Au@C
3
4
2
mixture (50 mL) was injected into Fe O suspension at every
3
nanocompiste were dispersed in 500 mL of 0.5 M NaOH
by ultrasonication and stirred for 24 h at 25 °C. Finally, the
products were collected by a magnet and washed with DI
water for several times, and then dried at 60 °C overnight.
Additionally, the loading level of the immobilized gold
4
1
0 min interval under sonication, and the same procedures
repeated for five times. After that, the mixture was further
sonicated for 70 min. The obtained products were separated
by a magnet and washed several times with ethanol [28].
-
1
was measured to be 0.092 mmol g by inductively cou-
pled plasma-optical emission spectrometry (ICP-OES).
3
.3 Synthesis of Fe O @SiO @GO Core–Shell
3 4 2
Nanoparticle
3.7 Preparation of GO
In a typical synthesis, 0.2 g of Fe O @SiO core–shell
3
4
2
nanoparticle were firstly dispersed in 100 mL ethanol by
sonication for 20 min. Next, 1 mL of 3-aminopropy-
ltrimethoxysilane was added and refluxed for 5 h to get
amine-functionalized Fe O @SiO core–shell nanoparti-
The graphite powder (2.5 g) was first treated with a mix-
ture of 12.5 mL of concentrated H SO with 2.5 g K S O
2 2 8
2
4
and 2.5 g P O . The mixture was kept at 80 °C for 6 h.
2
5
3
4
2
Subsequently, the mixture was cooled to 25 °C and diluted
with 500 mL DI water and left overnight. The mixture was
then filtered and washed with DI water to remove the
residual acid. The product was dried under ambient con-
ditions overnight. The pre-oxidized graphite was then
subjected to oxidation by Hummers’s method. The
cle. Then the products were separated by a magnet and
rinsed with ethanol to wash away the unreacted 3-amino-
propyltrimethoxysilane. After that, the 30 mL of 0.2 mg/
mL GO aqueous solution was added and the mixture was
stirred vigorously for 1 h. Finally, the products were
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
pretreated graphite powder was put into cold (0 °C) con-
4 Results and Discussion
centrated H SO (125 mL). Then KMnO4 (15 g) was
2
4
added gradually under stirring, and the temperature of the
mixture was kept below 20 °C by cooling. The mixture was
then stirred at 35 °C for 4 h and then diluted with DI water
The synthetic procedure of Fe O @RGO@Au@C CDSNs
4
3
is illustrated in scheme 1b. The magnetite particles were
synthesized via a modified solvothermal reaction of FeCl3
in the presence of sodium acetate and trisodium citrate
[27]. Then, magnetite nanoparticles were coated with silica
through classical Stober method using tetraethyl orthosili-
cate (TEOS) as a precursor [28]. The Fe O @SiO core–
(
250 mL). Because adding water to concentrated sulfuric
acid medium releases a large amount of heat, the dilution
was carried out in an ice bath to keep the temperature
below 50 °C. After adding all of the 250 mL DI water, the
mixture was stirred for 2 h, and then an additional 750 mL
DI water was added. Shortly thereafter, 20 ml 30 % H O
3
4
2
shell nanoparticles were modified by 3-aminopropy-
ltrimethoxysilane (APTMS) in order to introduce amine
groups on their surface. Subsequently, the amino-func-
tionalized Fe O @SiO is wrapped by the GO layer
2
2
was added to the mixture and the color of the mixture
changed into brilliant yellow and began bubbling. The
mixture was filtered and washed with 0.5 M HCl to remove
metal ions, followed by 500 mL DI water to remove the
acid, and then was dialyzed against DI water. The resulting
GO solid was dried in air [29, 30].
3
4
2
through the electrostatic reaction and hydrogen bonds
between the amino group and the oxygen-containing
groups on GO sheets. Next, the Au NPs were deposited on
Fe O @SiO @GO nanocomposite by a facile and green
3
4
2
method via a spontaneous redox reaction between HAuCl4
and GO. Then, the C precursor layers were coated on the
surface of the Fe O @SiO @GO@Au nanocomposite by
3
.8 General Procedure for the Reduction of 4-NP
3
4
2
The reduction of 4-NP by NaBH was chosen as a model
4
the pyrolysis of glucose under hydrothermal conditions
[21]. The as-obtained product is then dried and heated at
500 °C under inert atmosphere to carbonize the C precur-
sor shell. During this process, the GO layer is partially
converted to the reduced graphene oxide by thermal
reaction to investigate the catalytic performance of the
Fe O @SiO @GO@Au
3
Fe O @SiO @RGO@Au@C
3 4 2
4
2
and Fe O @RGO@Au@C nanostructures. In short 30 mL
4
3
of 4-NP (0.12 mM) were mixed with 30 mL of a freshly
prepared aqueous NaBH4 solution (0.17 M). Then
nanocomposite (2 mol% of Au) was added to the resulting
solution and the reaction was allowed to proceed until the
solution became colorless. The reaction conversion was
determined by ultraviolet visible spectroscopy (UV–Vis).
After completion of the reaction the heterogeneous mix-
ture was cooled to room temperature and the catalyst was
separated. Then the reaction mixture was extracted by
ethylacetate (15 9 3 ml) and dried over anhydrous
Na SO .
reduction [21, 31]. Finally, the SiO layers were etched by
2
NaOH solution and the magnetic core/double shelled
Fe O @RGO@Au@C CDSNs were obtained.
3
4
The morphologies of the intermediate and final products
were characterized by the transmission electron micro-
scope (TEM). From Fig. 1a, b, it is seen that Fe O @SiO
2
3
4
core–shell nanoparticles are tightly coated with the GO
sheet. Figure 1c, d shows TEM micrographs of Fe O
3
4
4
@SiO @GO@Au nanocomposite. The surfaces of Fe O
3
2
2
4
@SiO @GO nanocomposite are covered with good dis-
2
persion of Au NPs. The mechanism of the spontaneous
reductive deposition process that generates Au NPs on the
GO sheets likely involves a galvanic displacement and
redox reaction because of the relative potential difference
3
.9 General Procedure for Suzuki–Miyaura Cross-
Coupling
-
1
A mixture of nanocomposite (2 mol% of Au) K PO
3
between the reduction potential of AuCl4 (0.76 V vs.
SCE) and the oxidation potential of GO (0.48 V vs. SCE)
[25]. After the pyrolysis of glucose under hydrothermal
conditions and following calcination, the C shell covered
around Fe O @SiO @GO@Au nanocomposite (Fig. 1e,
4
(
(
3 mmol) aryl halide (1.0 mmol) phenyl boronic acid
1.3 mmol) and H O (3 mL) under air was stirred for 12 h
2
at 100 °C. The reaction progress was monitored by gas
chromatography (GC). After completion of the reaction
the heterogeneous mixture was cooled to 25 °C and the
catalyst was separated from the reaction medium by using
an external magnet. Then the reaction mixture was con-
centrated and then the residue was purified by thin layer
3
4
2
f). The size of Fe O @SiO @GO@Au nanocomposites are
2
3
4
about 120–140 nm. Additionally, the thickness of carbon
layer is about 4–5 nm.
After the removal of the sacrificial silica layer by NaOH
solution, Fe O @RGO@Au@C CDSNs were. The high res-
chromatography (SiO n-Hexane) to yield pure product.
2
3 4
The catalysts were recovered by using an external magnet
and washed extensively with acetone and deionized water
and drying in the air.
olution-transmission electron microscope (HR-TEM) micro-
graph Fe O @RGO@Au@C CDSNs is shown in Fig. 2c.
3
4
The chemical composition of the Fe O @RGO@Au@C
3
4
123

M. Dabiri et al.
3 4 2 3 4 2 3 4 2
Fig. 1 TEM micrographs of a, b Fe O @SiO @GO, c, d Fe O @SiO @GO@Au, e, f Fe O @SiO @RGO@Au@C nanostructures
CDSNs is determined using energy dispersive spectroscopy
EDS) analysis. We predict that the final nanostructure is the
isotherms based on the Brunauer–Emmett–Teller (BET)
analysis. It is found that the isotherm of Fe O @
(
3
4
yolk-double shell structure, and the estimated nanostructure
size will be about 120–140 nm. But the size of the final
structures is smaller than the predicted size that is 70–90 nm.
The Fe O core is wrapped by RGO layer due to the
RGO@Au@C CDSNs is the type IV according to the
IUPAC classification with a distinct hysteresis loop of the
H3 type (Fig. 4a). The distinct H3 hysteresis loop indicates
that the pores in the carbon shell directly open into the
hollow interior of double shell, supporting the idea that a
guest molecule could quickly diffuse into the hollow space
without any obstacle [35]. The BET total surface area of
3
4
decreasing size of the final structures [32–34]. The EDS
analysisinFig. 2eclearlyshowsthe sampleconsistsmainlyof
Fe and the presence of C and Au in the CDSNs.
2
-1
Additionally, the morphologies of the intermediate and
final products were characterized by the scanning electron
microscope (SEM) and shown in Fig. 3. From Fig. 3a, it is
seen that Fe O @SiO core–shell nanoparticles are wrap-
Fe O @RGO@Au@C CDSNs is found to be 221 m g .
3 4
The average pore size diameter of Fe O @RGO@Au@C
3
4
CDSNs is calculated to be 2.57 nm using Barrett–Joyner–
Halenda (BJH) analysis (Fig. 4b).
3
4
2
ped with the GO sheets.
As the magnetic Fe O core is residing inside the dou-
4
3
The porous nature of Fe O @RGO@Au@C CDSNs is
3
ble-shell RGO and C CDSNs, the magnetic property of the
obtained CDSNs is characterized (Fig. 5). The saturation
magnetization values were measured to be 20.39 and
4
evaluated by nitrogen physisorption measurements. The
specific surface area is calculated from the adsorption
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
Fig. 2 TEM micrographs of a,
b Fe @RGO@Au@C
CDSNs, c HR-TEM
3 4
O
micrographs of
3 4
Fe O @RGO@Au@C CDSNs,
d SAED pattern and e EDS
spectrum of
3 4
Fe O @RGO@Au@C CDSNs
-
6.25 emu g for Fe O @SiO @RGO@Au@C and Fe
1
5
710.52 eV, are assigned to Fe 2p1/2 and Fe 2p3/2 for Fe O ,
3 4
3
4
2
3-
O @RGO@Au@C nanostructures, respectively. The
4
respectively. Additionally, the absence of Si in XPS anal-
ysis of Fe O @RGO@Au@C CDSNs corroborates the
obvious increase in the Ms value of the Fe O @
3
4
3 4
RGO@Au@C CDSNs is attributed to the removal of the
removal of SiO layer by NaOH.
2
SiO template [36].
2
X-ray diffraction (XRD) patterns of Fe O , Fe O @
3
4
3 4
Thermogravimetric analysis (TGA) is further used to
study the thermal behaviour and stability of the Fe O @
SiO , Fe O @SiO @GO, Fe O @SiO @GO@Au, Fe O @
2 3 4 2 3 4 2 3 4
SiO @GO@Au@C, and Fe O @RGO@Au@C nanos-
2 3 4
3
4
RGO@Au@C CDSNs. This CDSNs showed high thermal
stability (Fig. 6). The total weight lost for Fe O @
tructures are illustrated in Fig. S1. XRD pattern of Fe3
O @RGO@Au@C CDSNs, the diffraction peak positions
4
3
4
RGO@Au@C CDSNs is only 9.86 % at temperatures
at 2h = 30.11, 35.64, 43.35, 53.77, 57.33, 62.95, and 74.39
can be attributed to the (2 2 0), (3 1 1), (4 0 0), (4 2 2),
(5 1 1), and (5 3 3) planes of Fe O , respectively. Addi-
6
00 °C.
The electronic properties of Fe O @RGO@Au@C
3
4
3 4
CDSNs is probed by XPS analysis. As shown in Fig. 7a,
the peaks corresponding to Au 4d and 4f, C 1 s, Fe 2p &
tionally, the diffraction peak positions at 2h = 38.25,
44.48, 64.62, and 77.75, can be attributed to (1 1 1), (2 0 0),
(2 2 0), and (3 1 1) planes of Au, respectively.
2
s, and O 1 s, are clearly observed in the XPS full spec-
trum. The XPS spectrum of Au 4f core for Fe O @
4
After careful investigation of the Fe O @RGO@Au@C
3 4
3
RGO@Au@C CDSNs level displays main peaks at 82.02
and 86.50 eV which correspond to the binding energy of
CDSNs prepared, it is tested for catalyzing two different
kinds of organic reactions (i) reduction of nitroarenes, and
(ii) Suzuki cross coupling of phenyl boronic acid with aryl
halides.
0
Au 4f and Au 4f5/2, respectively (Fig. 7b). From the Fe
0
7
/2
2
p XPS scan shown in Fig. 7c, the two peaks at 724.38 and
123

M. Dabiri et al.
3 4 2 3 4 2 3 4 2 3 4
Fig. 3 SEM micrographs of a Fe O @SiO @GO, b Fe O @SiO @GO@Au, c Fe O @SiO @RGO@Au@C and d, e Fe O @RGO@Au@C
nanostructure
As shown in Fig. 8a, the pure of 4-NP solution
exhibited a distinct absorption maximum at 317 nm,
which shifts to 400 nm in the presence of an alkali
because of the formation of 4-nitrophenolate ion. It is
found that the intensity of the characteristic absorption
peak of 4-nitrophenolate ion at 400 nm quickly decreases,
and the characteristic absorption of 4-AP at around
@RGO@Au@C catalysts, respectively (Table 1). In case
of Fe O @SiO @GO@Au catalyst, during the reaction
3
4
2
time GO reduced to RGO with NaBH [37] so the actual
4
catalyst is Fe O @SiO @RGO@Au. Therefore, the
3
4
2
increase in the rate constant of Fe O @SiO @RGO@
3
4
2
Au@C rather than Fe O @SiO @GO@Au (in actual state
3
4
2
Fe O @SiO @RGO@Au) is related to addition of the
3
4
2
3
00 nm also appears rapidly (Fig. 8b–d). The reaction
outer carbon shell. Additionally, Ji et al. reported the car-
bon species have no influence on the structure of catalyst
but enhance the stability and the activity of Au catalysts
and also increase the organic reactants adsorptive ability
[38]. Furthermore, the increase in the rate constant of
Fe O @RGO@Au@C rather than Fe O @SiO @
kinetics could be analyzed and confirmed from the time-
dependent absorption spectra, which showed the gradually
decrease of 4-nitrophenolate ion. Linear relationships
between ln(C /C ) and reaction time is obtained in the
t
0
reduction reaction catalyzed by Fe O @SiO @GO@Au,
3
4
2
3
4
3
4
2
Fe O @SiO @RGO@Au@C, and Fe O @RGO@Au@C
3 4
RGO@Au@C can be related to the nanorattle structure
characteristics, such as the large free reaction voids inside
the CDSNs [39] and the catalytic activity of iron species.
To prove the latter case, we have synthesized
RGO@Au@C hollow spheres [40] and used for the
reduction of 4-NP. The rate constant k is calculated to be
3
4
2
catalysts, which match well with the first-order reaction
kinetics (Fig. 8e).
The rate constant k is calculated to be 0.033, 0.170
-
and 0.496 min for the reactions catalyzed by Fe O @
1
3
4
SiO @GO@Au, Fe O @SiO @RGO@Au@C, and Fe O
3
2
3
4
2
4
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
Au@C CDSNs. This enhancement is similar to that
reported by Lin et al. [41] using Au-Fe O heterostructures.
3
4
The recyclability of the Fe O @RGO@Au@C CDSNs is
3
4
also examined by the reduction of 4-nitrophenol. It is found
that the recovery can be successfully achieved in twenty
successive reaction runs (Fig. 8f). ICP-OES result of the
used Fe O @RGO@Au@C CDSNs catalyst indicates the
3
4
leaching of 0.5 % of gold in the reduction of 4-NP after
twenty cycles.
We have further investigated the catalytic activity of
Fe O @RGO@Au@C CDSNs for the reduction of a series
3
4
of nitroarenes with structurally divergent functional groups
Table 2). Nitrobenzene yielded the desired aniline product
in 120 min in 79 % yield (Table 2, entry1). 2-, 3- and
-nitrophenols gave excellent yields of the corresponding
anilines in a very short span of time (Table 2, entries 2–4).
-NP is found to be the most reactive among all the three
(
4
3
nitrophenols. One can conclude that as the reaction pro-
ceeds through the formation of nitrophenolate ion, the
4-nitrophenolate ion will be the most stable ion due to the
delocalization of the oxygen’s negative charge throughout
the benzene ring making the system resonance stabilized.
2-NP is somewhat less stable than 4-NP because of less
effective resonance coupled with the certain degree of
steric effect. On the other hand, in 3-NP, the resonance
effect is entirely absent other than through conjugation. So
it is the least stable and the most reactive among all the
three nitrophenols [39, 42]. Nitroarenes possessing elec-
tron-donating groups such as p-toluidine and p-anisidine
also afforded excellent yield of the corresponding product
Fig. 4 a Nitrogen adsorption–desorption isotherm and b the corre-
sponding pore size distribution curve of Fe
CDSNs
3 4
O @RGO@Au@C
(
Table 2, entries 5–6).
-
.412 min for the reactions catalyzed by RGO@Au@C
1
0
In order to evaluate the catalytic results, we use the
hollow spheres that show the magnetic core lead to
the increase in the rate constant in Fe O @RGO@
turnover frequency (TOF) to determine the efficiency of
our structure catalyst for reduction of 4-NP and compared
3
4
Fig. 5 The VSM curves of
Fe @SiO @RGO@Au@C
and Fe @RGO@Au@C
nanostructures
3
O
4
2
3 4
O
123

M. Dabiri et al.
Fig. 6 TGA plot of
Fe @RGO@Au@C CDSNs
The thermogram is obtained at
3 4
O
(
-
1
a scan rate of 10 °C min
under air)
Fig. 7 a Full range XPS spectrum of Fe
3
O
4
@RGO@Au@C CDSNs, b Au 4f and c Fe 2p, core level regions XPS spectra of
3 4
Fe O @RGO@Au@C CDSNs, respectively
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
Fig. 8 UV–Vis spectra of a 4-nitrophenol and 4-nitrophenolate, the
reduction of 4-NP to 4-AP over b Fe @SiO @GO@Au, c Fe3-
@SiO @RGO@Au@C and d Fe @RGO@Au@C; e plot of
ln(C /C ) against the reaction time of the reduction of 4-NP over
Fe
@RGO@Au@C;
RGO@Au@C CDSNs
3
O
4
@SiO
2
@GO@Au, Fe
3 4 2 3 4
O @SiO @RGO@Au@C, and Fe O
3
O
4
2
f
3 4
the catalytic stability tests of Fe O @
O
4
2
3 4
O
t
0
Table 1 The rate constant k the reduction of 4-NP over Fe
RGO@Au@C
3 4
O @SiO
2
@GO@Au, Fe
3 4
O @SiO
2 3 4
@RGO@Au@C, Fe O @RGO@Au@C and
Nanostrucutre
Fe
3
O
4
@SiO
2
@GO@Au
Fe
3
O
4
@SiO
2
@RGO@Au@C
Fe
3
O
4
@RGO@Au@C
RGO@Au@C
0.412
-1
)
Rate constant k (min
0.033
0.170
0.496
with previously reported gold based heterogeneous cata-
lysts. The TOF of Fe O @RGO@Au@C CDSNs catalyst
reaction conditions. Table 3 compares efficiency of Fe3-
O @RGO@Au@C CDSNs (TOF and mol% of catalysts)
4
3
4
-
1
is 3.77 min , calculated by the moles of 4-NP reduced per
mole of gold complex per consumed time under the present
with efficiency of other reported gold based catalysts in
reduction of 4-NP.
123

M. Dabiri et al.
Inspired by the high activity and stability of Fe O @-
3
The heterogeneous nature of the catalysis is proved
using a hot filtration test and atomic absorption spec-
troscopy (AAS) analysis. To determine whether the cata-
lyst is actually functioning in a heterogeneous manner or
whether it is merely a reservoir for more active soluble
gold species, we performed a hot filtration test in the
Suzuki cross coupling reaction of phenyl boronic acid with
phenyl iodide after *50 % of the coupling reaction is
completed. The hot filtrates were then transferred to
another flask containing K PO (3 equiv.) in H O (3 mL) at
4
RGO@Au@C CDSNs the Suzuki coupling reaction is
further employed as another model reaction to test further
the performance of Fe O @RGO@Au@C nanocatalyst.
3
4
We chose the Suzuki coupling reaction of phenyl boronic
acid with phenyl iodide as an optimum reaction in H O as
2
solvent at 100 °C in the presence of K PO as base and
3
4
with a catalyst loading of 2 mol% of Au for 12 h (Table 4,
entry 4). Under this condition, we found that the cross
coupling reaction proceeds well, affording the excellent
yield (97 %) of the corresponding biphenyl. Additionally,
Fe O @SiO @GO@Au and Fe O @SiO @RGO@Au@C
3
4
2
100 °C. Upon the further heating of catalyst-free solution
for 24 h, no considerable progress (*1 % by GC analysis)
is observed. Moreover, using AAS of the same reaction
solution at the midpoint of completion indicated that no
significant quantities of gold were lost to the reaction
liquors during the process. The reusability of the Fe3-
3
4
2
3
4
2
were tested in the model reaction and yields of biphenyl in
both cases were remarkably lower (Table 4, entries 5 and
6
).
We next managed to examine the scope and limitation
of Suzuki–Miyaura reaction with various types of aryl
haides derivatives and phenyl boronic acid. (Table 5). It
can be seen from Table 5 that the Suzuki–Miyaura cross-
coupling reaction with most substrates preceded in good
yields. The hindered substrate such as 2-iodotoluene con-
verted into the corresponding products with a moderate
yield (Table 5, entry 4).
O @RGO@Au@C CDSNs is examined in the Suzuki–
4
Miyaura cross-coupling reaction of phenylboronic acid
with phenyl iodide. It is found that the recovery can be
successfully achieved in six successive reaction runs
(Table 5, entry 1).
Table 2 Fe
ious nitroarene
3
O
4
@RGO@Au@C CDSNs catalysed Reduction of var-
Table 4 Screening of the Suzuki–Miyaura cross-coupling reaction
conditions
a
a
Entry
Substrate
Time (min)
Yield (%)
Entry Catalyst
Base
Time (h) Yield
1
2
3
4
5
6
Nitrobenzene
120
7
79
99
99
98
79
74
1
2
3
4
5
6
Fe O @RGO@Au@C
3
K CO
2
12
49 %
66 %
78 %
97 %
71 %
86 %
4
3
2-nitrophenol
Fe O @RGO@Au@C
3
NaOH 12
4
3-nitrophenol
4
Fe O @RGO@Au@C
3
KOH
12
12
12
12
4
4-nitrophenol
13
140
150
Fe O @RGO@Au@C
3
K PO
3
4
4
4
4
1-methyl-4-nitrobenzene
1-methoxy-4-nitrobenzene
Fe O @SiO @GO@Au
3
K PO
3
4
2
Fe O @SiO @RGO@Au@C K PO
2
3
4
3
-
4
0 mL of 1.20 9 10 M nitroarene, 30 mL of 0.17 M NaBH
3
Fe @RGO@Au@C CDSNs (2 mol% with respect to the gold
4
and
Phenyl iodide (1.0 mmol), phenyl boronic acid (1.3 mmol), Base
a
3
O
4
(3.0 mmol), catalyst (2 mol% of Au), 100 °C, and H O (3 mL). GC
2
a
concentration) Isolated yields after column chromatography
yield, n-dodecane is used as an internal standard
Table 3 Comparison of
catalytic activity by gold based
catalysts for the reduction of
-1
)
Entry
Catalyst
TOF (min
Catalysts (mol%)
Ref.
1
2
3
4
5
6
7
8
9
Fe
HAuCl
Au-PMMA
3 4
O @RGO@Au@C
3.77
0.11
1.23
0.73
1.6
2
This work
4
-NP
4
.3H
2
O
46
7
43
44
45
46
47
48
19
20
49
Fe
Fe
3
O
4
@SiO
2
–Au@mSiO
2
9
O
3 4
@P(EGDMA-co-MAA)/Au
2.5
7
Au@SiO
2
0.45
0.77
0.19
11.93
8.06
Au NPs/SNTs
28
43
Au/graphene hydrogel
rGO/Fe
GO-Fe
3
O
4
/Au
1
0
3
O
4
-Au NPs(G).
7.3
1
23

3
Fe O
4
@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon…
9. Yao J, Sun Y, Yang M, Duan Y (2012) J Mater Chem 22:14313
0. Latham AH, Williams ME (2008) Acc Chem Res 41:411
Table 5 Fe
cross-coupling reaction
3 4
O @RGO@Au@C CDSNs catalyzed Suzuki–Miyaura
1
1
1. Frey NA, Peng S, Cheng K, Sun SH (2009) Chem Soc Rev
3
8:2532
1
2. Roca AG, Costo R, Rebolledo AF, Veintemillas-Verdaguer S,
Tartaj P, Gonz a´ lez-Carre n˜ o T, Morales MP, Serna CJ (2009) J
Phys D Appl Phys 42:224002
a
Entry
Ar
X
Time (h)
Yield
1
14. Kumar CSSR, Mohammad F (2011) Adv Drug Deliv Rev 63:789
3. Gijs MAM, Lacharme F, Lehmann U (2010) Chem Rev 110:1518
b
1
2
3
4
5
6
7
Ph
I
12
12
12
12
18
18
18
97 %, 95 %
99 %
1
1
1
1
5. Guo S, Dong S, Wang E (2009) Chem Eur J 15:2416
6. Guo S, Dong S, Wang E (2008) J Phys Chem C 112:2389
7. Guo S, Li J, Wang E (2008) Chem Asian J 3:1544
8. Corma A, Garcia H (2008) Chem Soc Rev 37:2096
4-NO
2
-C
6
H
4
I
4-MeCO-C
6
H
4
I
97 %
2-Me-C
Ph
6
H
4
I
82 %
Br
Br
Br
88 %
19. Li J, Liu CY, Liu Y (2012) J Mater Chem 22:8426
2
0. Wang Y, Li H, Zhang J, Yan X, Chen Z (2016) Phys Chem Chem
Phys 18:615
1. Zhang Z, Xiao F, Xi J, Sun T, Xiao S, Wang H, Wang S, Liu Y
4-Me-C
6
H
4
82 %
4-NO
2
-C
H
6 4
93 %
2
(
2013) Sci Rep 4:4053
22. Pumera M (2010) Chem Soc Rev 39:4146
Aryl halide (1 mmol), phenyl boronic acid (1.2 mmol), Fe
a
3
O
4
@-
RGO@Au@C (2 mol% of Au), K
b
yield. Yield after sixth cycle
3
PO
4
(3 mmol), 100 °C. Isolated
23. Huang X, Qi X, Boey F, Zhang H (2012) Chem Soc Rev 41:666
2
2
2
2
2
4. Movahed SK, Fakharian M, Dabiri M, Bazgir A (2014) RSC Adv
:5243
5. Zhang N, Qiu H, Liu Y, Wang W, Li Y, Wang X, Gao JF (2011) J
Mater Chem 21:11080
6. Liu J, Sun ZK, Deng YH, Zou Y, Li CY, Guo XH, Xiong LQ,
Gao Y, Li FY, Zhao DY (2009) Angew Chem Int Ed 48:5875
7. Yuan Q, Li N, Chi Y, Geng W, Yan W, Zhao Y, Li X, Dong B
(2013) J Hazard Mater 254–255:157
4
5
Conclusion
In this study, a novel magnetic core double-shelled carbon
with Fe O nanoparticles as core, reduced graphene oxide
3
4
8. Zhang X, Jiang W, Zhou Y, Xuan S, Peng C, Zong L, Gong X
(
(
RGO) as the inner shell and carbon (C) layer as the outer
2011) Nanotechnology 22:375701
shell have been successfully designed and prepared. This
tailor-making structure acts as an excellent capsule for
encapsulating Au nanoparticles (Au NPs), which could
effectively prevent Au NPs from aggregation and leach-
ing.The catalyst could be easily recovered by applying an
external magnetic field, and reused for next catalytic run.
The Fe O @RGO@Au@C nanocatalyst showed excellent
2
3
9. Hummers WS, Offeman RE (1958) J Am Chem Soc 80:1339
0. Kovtyukhova NI, Olliver PJ, Martin BR, Mallouk TE, Chizhik
SA, Buzaneva EV, Gorchinsky AD (1999) Chem Mater 11:771
1. Akhavan O (2010) Carbon 48:509
2. Xiao M, Huang M, Zeng S, Han D, Wang S, Sun L, Meng Y
(2013) RSC Adv 3:4914
3. Bai S, Chen S, Shen X, Zhu G, Wang G (2012) RSC Adv 2:10977
3
3
3
34. Wang Z, Lv X, Chen Y, Liu D, Xu X, Palmore GTR, Hurt RH
2015) Nanoscale 7:10267
3
4
(
catalytic activity for the reduction of nitrophenols and the
Suzuki–Miyaura cross-coupling reaction. The Fe O @
3
3
3
5. Zou H, Wang R, Li X, Wang X, Zeng S, Ding S, Li L, Zhang Z,
Qiu S (2014) J Mater Chem A 2:12403
6. Hu W, Liu B, Wang Q, Liu Y, Liu Y, Jing P, Yu S, Liu L, Zhang
J (2013) Chem Commun 49:7596
7. Choi Y, Bae HS, Seo E, Jang S, Park KH, Kim B-S (2011) J
Mater Chem 21:15431
8. Ji T, Li L, Wang M, Yang Z, Lu X (2014) RSC Adv 4:29591
9. Liu R, Qu F, Guo Y, Yao N, Priestley RD (2014) Chem Commun
3
4
RGO@Au@C nanocatalyst acts as a relatively green cat-
alyst with superparamagnetism, eco-friendly nature and
convenient recovery, and is a promising candidate for Au
NPs based catalytic applications in industrial synthesis.
3
3
Acknowledgments We gratefully acknowledge financial support
from the Research Council of Shahid Beheshti University.
5
0:478
4
0. The RGO@Au@C hollow sphere is synthesized with similar
method in ref. 18
4
4
1. F-h Lin, R-a Doong (2014) Appl Catal A General 486:32
2. Layek K, Kantam ML, Shirai M, Nishio-Hamane D, Sasaki T,
Maheswaran H (2012) Green Chem 14:3164
References
4
3. Pachfule P, Kandambeth S, Diaz DD, Banerjee R (2014) Chem
Commun 50:3169
4. Kuroda K, Ishida T, Haruta M (2009) J Mol Catal A Chem 298:7
5. Deng Y, Cai Y, Sun Z, Liu J, Liu C, Wei J, Li W, Liu C, Wang Y,
Zhao D (2010) J Am Chem Soc 132:8466
6. Woo H, Park KH (2014) Catal Commun 46:133
7. Wang Z, Fu H, Han D, Gu F (2014) J Mater Chem A 2:20374
8. Zhang Z, Shao C, Zou P, Zhang P, Zhang M, Mu J, Guo Z, Li X,
Wang C, Liu Y (2011) Chem Commun 47:3906
9. Hua J, Dong Y-L, Chen X-J, Zhang H-J, Zheng J-M, Wang Q,
Chen X-G (2014) Chem Eng J 236:1
1
2
. Reddy LH, Arias JL, Nicolas J, Couvreur P (2012) Chem Rev
12:5818
. Polshettiwar V, Luque R, Fihri A, Zhu H, Bouhrara M, Basset JM
2011) Chem Rev 111:3036
. Karimi B, Mansouri F, Vali H (2015) ChemPlusChem 80:1750
. Zeng T, Zhang X, Ma Y, Niu H, Cai Y (2012) J Mater Chem
1
4
4
(
3
4
4
4
4
2
2:18658
. Bai S, Shen X (2012) RSC Adv 2:64
5
6
. Dabiri M, Shariatipour M, Movahed SK, Bashiribod S (2014)
RSC Adv 4:39428
. Pumera M (2010) Chem Soc Rev 39:4146
. Huang X, Qi X, Boey F, Zhang H (2012) Chem Soc Rev 41:666
4
7
8
123