Synthesis, characterization, structural, optical properties and catalytic activity of reduced graphene oxide/copper nanocomposites

Article abstract of DOI:10.1039/c4ra12552e

This paper reports on the synthesis and use of copper nanoparticles supported on reduced graphene oxide, as separable catalysts for N-arylation of phenylurea with aryl halides under ligand-free and microwave conditions. The catalyst can be recovered and reused several times without significant loss of its catalytic activity. Also, the structural and optical properties are studied. Experimental absorbance spectra are compared with results obtained from the Maxwell-Garnett theory (MGT).

Full text of DOI:10.1039/c4ra12552e

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: M.
nasrollahzadeh, F. babaei, P. Fakhri and B. Jaleh, RSC Adv., 2015, DOI: 10.1039/C4RA12552E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

View Article Online
DOI: 10.1039/C4RA12552E
Page 1 of 7
RSC Advances
CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 3.1) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS
Synthesis, characterization, structural, optical properties and catalytic
activity of reduced graphene oxide/copper nanocomposites
a
b
c
c
Mahmoud Nasrollahzadeh * Ferydon Babaei, Parisa Fakhri and Babak Jaleh
5
a
Department of Chemistry, Faculty of Science, University of Qom, PO Box 37185-359, Qom, Iran. E-mail: mahmoudnasr81@gmail.com; Fax: +98 25
3
2103595; Tel: +98 25 32850953
b
Department of Physics, Faculty of Science, University of Qom, Qom, Iran
c
Department of Physics, Bu-Ali Sina University, Postal Code 65174, Hamedan, Iran
1
0
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
First published on the web Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
1
5
This paper reports on the synthesis and use of copper
nanoparticles supported on reduced graphene oxide, as separable
catalysts for N-arylation of phenylurea with aryl halides under
ligand-free and microwave conditions. The catalyst can be
recovered and reused several times without significant loss of its
catalytic activity. Also, the structural and optical properties are
studied. Experimental absorbance spectra compared with results
that obtained from the Maxwell-Garnett theory (MGT).
graphene hybrids have been reported and fewer studies have
investigated their catalytic and optical properties.
1
7,18
2
0
Introduction
2
Graphene sheets are two dimensional sp -carbon bonds with
1
-3
2
3
3
4
4
5
5
5
0
5
0
5
0
5
thermodynamical stability and crystal shape such as graphite.
It may be a promising alternative to carbon nanotubes (CNT)
in polymer nanocomposites. The dispersion of metal
nanoparticles on graphene sheets potentially provides a new way
to develop catalytic materials. One of the significant
characteristics of graphene is its extensive surface originated
from planar structure which can strongly immobilize guest 65 those of bulk substances.19,20 Among various metal nanoparticles,
nanoparticles. Furthermore, the oxygen of graphene oxide (GO)
facilitate the nanoparticles immobilization. Then base on the
aforementioned properties, the surface of graphene sheets and
metal ions have ability for simultaneously reduction using
reducing agents such as chemical, heat treatment and UV-
irradiation. Also reduced grapheme oxide (RGO) loaded with
NPs is protected from the aggregation through the sheet
The combination of
grapheme/NPs show many applications and benefits in catalysis,
supercapacitors, sensors and hydrogen storage due to the
synergism effect between the inherent function of metal
nanoparticles and the merits of graphene, high electrical
conductivity, large surface area, excellent stability, exclusive
4
60
Figure 1. Proposed structure of graphene oxide (GO).
In recent years, noble metal nanoparticles have been used
widely due to their interesting electronic, optical, mechanical,
magnetic and chemical properties, which differ greatly from
5
copper nanoparticles (Cu NPs) have been widely used in many
fields due to their excellent physical and chemical properties,
6
2
1-25
easy preparation and the low synthetic cost.
The synthesis of
copper nanoparticles costs less than both silver and gold NPs.
They are able to catalyze a wide variety of chemical reactions
70
25
under homogeneous and heterogeneous conditions. Also, they
7
-9
are exploited in wound dressings and socks to give them biocidal
21,22
properties.
1
0
interaction after drying process.
Palladium-catalyzed C-N cross-coupling reactions have
evolved into a highly versatile and synthetically attractive
technique for targeting pharmaceutically useful intermediates
7
75
1
1
12
13
26
such as diarylureas. Generally, phosphine ligands such as
Xantphos in combination with palladium precursors provide
27
effective catalysts for the C-N bond-forming reaction. However,
1
-3
basal plan structure and low cost.
8
8
9
0
5
0
the toxicity of phosphine ligands and high cost of palladium
catalysts restrict their industrial uses.
Among the methods presented to synthesis the mono layer
graphene, converting graphene to graphene oxide using
physicochemical exfoliation of graphite oxide then reduction of
Among various copper catalysts for the coupling reactions,
homogeneous catalysts in combination with ligand have been
widely investigated, while less expensive heterogeneous catalysts
have received less attention. A disadvantage of homogeneous
catalysis is the difficulty in separating the catalyst from the
reaction mixture, and the impossibility to reuse it in subsequent
reactions. Therefore, the development of mild, highly efficient
and environmentally benign methods for ligand-free coupling
reactions remains an active research area.
7
,8,14,15
produced graphite oxide to graphene is of great interest.
Although the structure of GO is still subject to interest researches
in which the graphene lattice is interrupted by epoxide, hydroxyl,
1
6
carbonyl and carboxylic groups (Figure 1). Among the recently
reported methods for synthesis of graphene/NPs composites, the
most common utilizes the chemical reduction of GO in which
NPs simply attach its surface for presence OH or epoxide
functional groups. However, only a few metal nanoparticles-

View Article Online
DOI: 10.1039/C4RA12552E
RSC Advances
Page 2 of 7
In continue of our researches on the applications of
heterogeneous catalysts, graphene, metal nanoparticles and
The morphological study has been performed by scanning
electron microscopes (SEM) and transmission electron
microscopy (TEM). The TEM and SEM images of the RGO/Cu
NPs are shown in Figure 3 and 4, respectively, from which it is
clearly observed that the Cu grain pervaded between RGO sheets,
which display a good combination between RGO sheet and Cu
NPs. The TEM observations showed the diameter of the Cu NPs
was around 30 nm (Figure 4).
2
8-31
synthesis of N-aryl ureas,
herein we report a new protocol for
35
the preparation of copper nanoparticles supported on reduced
graphene oxide (RGO/Cu NPs). The catalyst was characterized
by SEM, XRD, BET, EDS and FT-IR. The optical absorption
properties were measured by UV-visible spectrophotometer.
Also, the catalytic properties of RGO/Cu NPs were measured in
the N-arylation of phenylurea with aryl halides.
5
1
1
2
2
0
5
0
5
Result and Discussion
RGO/Cu NPs was fabricated via a simple synthetic process
and characterized using powder XRD, BET, FT-IR, SEM, TEM,
EDS and Raman spectroscopy.
The phase and crystallinity of the catalyst were determined by
powder X-ray diffraction (XRD). The X-ray diffraction pattern of
GO and RGO/Cu NPs is shown in Figure 2, on which the peak at
2
θ = 11.1° is the characteristic peak of GO. The X-ray diffraction
pattern of synthesized RGO/Cu NPs shows the presence of
metallic copper and cuprous oxide phases. The Figure 2 shows
two broad peaks of 2θ values 43.5° and 50.4° which are assigned
to the (111) and (200) indices of face centered cubic (fcc) lattice
of metallic Cu. The presence of cuprous oxide is possible because
the effect of air oxidation on copper during drying. Peaks at 42.6°
and 62.6° could be attributed to cuprous oxide. RGO exhibits a
broad peak (002) around 2θ = 25°. Moreover, the characteristic
peak of GO at 10.7° (001) disappeared. This result clearly
demonstrates that the GO was reduced to RGO.
40
Figure 3. SEM image of RGO/Cu NPs.
3
2
2
Cu O
CuO
Cu
CuO
2
Cu O
rGO
GO
1
0
20
30
40
50
60
70
80
2θ (degree)
3
0
Figure 2. X-Ray diffraction pattern of GO and RGO/Cu NPs.
Figure 4. TEM image of RGO/Cu NPs.
45
Energy dispersion X-ray spectroscopy (EDS) is shown in
Figure 5. In the EDS spectrum of catalyst, peaks related to C, O
and Cu are observed.
50
Figure 5. EDS analysis of RGO/Cu NPs.

View Article Online
DOI: 10.1039/C4RA12552E
Page 3 of 7
RSC Advances
Figure 6 represents the FT-IR spectrum of RGO/Cu NPs. The
dielectric constant of composite medium (Cu-vacuum) is defined
3 f (1Cu
 Cu  f (1Cu
analysis of FT-IR bands of RGO/Cu NPs shows that most of the
oxygen-containing groups of GO, particularly carboxyl groups,
have been removed by the reducing reaction.
)
as
for Cu nanoparticles
eff 1
2
)
embedded in vacuum, where Cu are dielectric constant of
copper, while is the volume fraction of nanoparticles
dispersed. We have used the bulk experimental refractive indexes
f
35
C=O
3
6
Cu for homogenization. In our work, we extracted the refractive
index k and n of RGO from absorption coefficient and measured
O-H
37,38
transmittance k    / 4 , using Swanepoel model,
as shown
C-OH
C=C
in Figure 8. The optical constants of Quartz substrate adapted
3
6
40
from Handbook of Palik. Also, we have included the dispersion
3
9
and dissipation of dielectric function.
4
000
3500
3000
2500
2000
1500
1000
500
-1
Wavelenght(cm )
Figure 6. FT-IR spectra of RGO/Cu NPs.
The surface area of RGO/Cu NPs was obtained from nitrogen
5
0
2
-1
gas adsorption and the BET surface area was 29.96 m g . The
Barrett-Joyner-Halenda (BJH) analysis shows that the pore
1
1
2
-
2
-1
volume is 5.2×10 cc g .
For understanding interaction between Cu and RGO sheet, we
used the Raman spectroscopy. As shown in Figure 7, the Raman
spectra of GO and GO/Cu NPs show the presence of D and G
bands at 1340 and 1580, respectively. G band is corresponded to
the in-phase vibration of the graphene lattice, and D band is
5
3
3,34
related to the defects and disorder.
As shown in Figure 7 the
presence of nanoparticles on GO enhances the intensity of G and
D bands. This observation suggests a chemical interaction or
3
3,34
0
bond formation between Cu NPs and RGO sheet.
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
D-band
RGO
RGO/Cu NPs
%
62
G-band
Figure 8. (a) Measured transmittance of RGO; (b) Simulated refractive
index and extinction coefficient for RGO as a function of wavelength.
4
5
%
55
The calculated absorbance spectra as a function of wavelength
for RGO/Cu NPs are depicted in Figure 9a. In our calculation for
Figure 9, the structural parameters such as the thickness of
composite, RGO thin film and the volume fraction of Cu NPs, d1
50
=
10 nm, d = 0.4 nm and fCu = 0.00002 were fixed from the
2
experimental results, respectively. In Figure 9a it can be seen that
our optical modeling is consistent with experimental result. The
8
00
1000 1200 1400 1600 1800 2000
2
-1
plot of (h) vs. photon energy is shown in Figure 9b. The
Raman shift (cm )
55
absorption coefficient was calculated from the absorbance spectra
A
Figure 7. Raman spectra of RGO and RGO/Cu NPs.
using formula
, where A is absorbance and h is

 2.303
d
Optical results
photon energy. In order to obtain to the energy band gap, one can
2
5
It is well known that in order to obtain of the effective
dielectric constant for dispersed phase volume fractions smaller
than  / 6 and the size of features much smaller than the
wavelength of the incident electromagnetic wave in two
components composite medium, we can use the Maxwell-Garnett
2
depict(h) curve versus h .The direct transition of photon
energy is calculated from linear part of (h) . The energy E of
RGO/Cu NPs was determined Eg = 1.32 eV. The maximums
observed ultraviolet absorption are at λ = 220 nm and 360 nm
(that respectively are attributed to π-π* transitions of aromatic
2
g
60
3
5
3
0
theory (MGT). In this approximation method, the effective

View Article Online
DOI: 10.1039/C4RA12552E
RSC Advances
Page 4 of 7
C=C bonds and n-π* transitions of C=O bonds) that are
consistent with the literature.
Table 1. N-Arylation of phenylurea with aryl halides under microwave
4
0
irradiation.
a
Entry
Phenylurea
Aryl halide
Product
Yield %
b
1
87, 84
2
3
85
89
4
88
5
6
86
84
7
8
83
82
a
b
35
Yields refers to pure isolated product. Yield after the 4th cycle.
Catalyst recyclability
5
2
RGO/Cu NPs works under heterogeneous conditions. After the
completion of the reaction, the catalyst was separated from the
reaction mixture by filtration, washed with water and ethyl
acetate and dried. The catalyst can be reused four times with no
significant loss in its reactivity (Table 1, entry 1). In every
experiment, more than 98% of the catalyst was easily recovered
and reused for the next reaction.
To check the heterogeneity of this catalyst, which is an
important factor, the copper leaching was also studied by an ICP
technique. The catalyst showed very high stability against
leaching of the copper under the given reaction conditions. It was
shown that very low copper contamination was observed into
solution during the course of a reaction. Meanwhile, TEM
observation after the repeated catalytic tests was also carried out
to check the stability of the as-prepared catalyst (Figure 10).
These results further confirmed the high recyclability of the
catalyst.
Figure 9. Computed absorbance and (h) for RGO/Cu NPs (a)
2
absorbance vs. wavelength; (b)
vs. photon energy.
(h)
4
4
5
0
5
0
The influence of Cu O or CuO on the optical properties of
RGO/Cu NPs was also studied in Supporting Information.
2
1
1
2
0
5
0
Catalytic activity of RGO/Cu NPs in the N-arylation of
phenylurea with aryl halides
Due to the importance of ureas in synthetic organic chemistry
and in pharmaceutical and agrochemical industry,
turned our attention to applying RGO/Cu NPs to the synthesis of
symmetrical and unsymmetrical diarylureas via the N-arylation of
phenylurea with aryl halides under microwave irradiation
4
1,42
we next
(Scheme 1).
During this study, symmetrical and unsymmetrical diarylureas
were synthesized from N-arylation of phenylurea with aryl
halides containing both electron-donating and electron-
withdrawing groups in excellent yields under microwave
irradiation which the results were indicated in Table 1.
2
5
1
13
The products were confirmed by H NMR, C NMR, FT-IR
1
and melting points. The purity of the product was checked by H
1
3
0
NMR spectroscopy. The H NMR spectra of the products showed
1
3
two NH proton signals. The C NMR spectra of the products
showed one signal for the carbonyl carbon.

View Article Online
DOI: 10.1039/C4RA12552E
Page 5 of 7
RSC Advances
ice bath, and KMnO4 (300 g) were slowly added under
continuous stirring. After 2 h, the suspension was removed from
the ice bath and warmed to 40 °C and kept at 40 °C for 1 h. 500
mL de-ionized water was added to the mixture, causing an
increase in temperature to 100 °C. Subsequently, the excess
potassium permanganate was removed by treatment with 2.5 mL
hydrogen peroxide (30 wt. %). Then, the suspension was filtered
and washed with 1:10 HCl solution (200 mL) in order to remove
metal ions by filter paper and funnel and distilled water, and
centrifuged. The resulting product was then freeze-dried in the
freeze-dryer and stored in vacuum desiccators before use.
5
5
6
6
7
7
8
8
9
9
0
5
0
5
0
5
0
5
0
5
Preparation of Reduced Graphene Oxide (RGO)
Chemical reduction of graphene oxide to reduced graphene
oxide was done according to a new procedure. Suspension
aqueous colloids of GO were prepared from the dried graphene
oxide (GO) by mechanical stirring and heat treatment with a
circulator. In the experiment, 10 g of graphene oxide was stirred
into 1 L of distilled water. This dispersion was stirring using a
Fisher mechanical stirring until it became a clear solution with no
visible particulate material. After that, the pH of the solution was
increased to 10 by adding NaOH solution and 20 mL of the
hydrazine monohydrate was added and the reaction mixture was
Figure 10. TEM image of the catalyst after repeated catalytic tests.
Conclusion
In conclusion, we have developed a simple and efficient
methodology for the preparation of RGO/Cu NPs as
5
0
5
0
5
0
5
0
5
a
heterogeneous and reusable catalyst. The catalyst was
characterized by SEM, XRD, BET, EDS, UV-Vis, Raman and
FT-IR spectroscopy techniques. The optical properties of the
catalyst were also studied. This catalyst demonstrated high
catalytic activity in promoting N-arylation reactions between
phenylurea and aryl halides to synthesize symmetrical and
unsymmetrical diarylureas in high yields under microwave
irradiation. Further, the catalyst was reused for a new batch of
reactions without significant loss of their activity under the same
conditions. Further investigations on the application of this
catalyst on other catalytically synthetic reactions are in progress.
o
stirred at 95 C for 4 h. After completion of the reaction, the
reduced graphene oxide was filtered as a black powder. The
obtained product was then washed several times with distilled
water to until the pH is nearly 7 and until to remove the excess
hydrazine. The final product was dried in a vacuum oven at 100
1
1
2
2
3
3
4
4
o
C for 24 h.
Preparation of Cu NPs
After 20 min the color of the solution changed from yellow to
dark brown
2
00 mL NaOH (2 M) solution was added slowly to the 100
mL CuSO .5H O (2 M) solution and the reaction mixture was
4
2
Experimental
heated to 80 °C under constant severe stirring. Copper hydroxide
(Cu(OH) ) and copper oxide (CuO ) was obtained and deposited
All chemicals and solvents were obtained from commercial
x
x
1
sources and used without further purification. The H NMR and
as sediments. The sediments were filtered and then recovered. To
the obtained precipitate, distilled water and glucose was added
and agitated until the color of the solution changed into dark red.
Glycine (NH -CH -COOH) was then added to the above solution
1
3
C NMR spectra were recorded on a Bruker DRX spectrometer
using tetramethylsilane (TMS) as the internal standard. The FT-
IR spectra were run on a Perkin-Elmer 781 spectrometer. Raman
and UV-visible spectra were taken using a Micro-Raman
spectrometer system (inVia Reflex, Renishaw, UK) and a double‐
beam spectrophotometer (Hitachi, U‐2900), respectively. X-ray
diffraction (XRD) was used to characterize the crystalline
structure of RGO/Cu NPs on Philips PW 1373 using Cu Kα
radiation. Scanning electron microscopy (SEM) was recorded on
a Cam scan MV2300 instrument. Energy dispersive X-ray
spectroscopy (EDS) was used on the Oxford Instruments INCA.
Transmission electron microscopy (TEM) was recorded on a
Philips CM120. TLC was performed on Merck-precoated silica
gel 60-F254 plates. Specific surface area and the porosity of the
samples were measured with the BELSORP-max nitrogen
adsorption apparatus (Japan Inc.). The Brunauer-Emmett-Teller
2
2
and the mixture was ultrasonicated for the appropriate time. 100
mL NaBH4 (24 M) solution was then added dropwise to the
above solution. After the completion of reaction and allowing the
mixture to cool to room temperature, the reaction mixture was
filtered, washed with distilled water, after that dried it at 110 °C
in
a vacuum dryer. The molar ratio of the mixture
+2
45,46
Cu :NaOH:Glycine:NaBH are 1:2:1:12 respectively.
4
Preparation of RGO/Cu NPs
In a typical procedure, RGO powder and deionized (DI) water
1
00 were mixed in a 500 ml three-necked flask, and the mixture was
ultrasonicated for 45 min at room temperature. Cu nanoparticles
were then slowly added to the above solution while stirring at 110
°C for 12 h. The well shaked mixture was filtered and washed
with DI water in order to remove by-products. The resulting
05 product (RGO/Cu NPs) was then dried at 100 °C for 12 h under
vacuum.
(
BET) surface area and pore size distribution were obtained by N2
adsorption measurements carried out at 77 K on a Micromeritics
ASAP 2020 sorption analyzer.
1
Preparation of Graphene Oxide (GO)
Graphene oxide was prepared from purified natural graphite
by a modified Hummer’s method that involves a strong oxidation
of graphite powder with H SO /KMnO and exfoliation process
Optical modeling
Let us we consider a region 0  z  d1 as a composite of Cu
2
4
4
4
3,44
110 nanoparticles (Cu NPs) dispersed in vacuum and the region
in solution.
GO prepared by this way is widely used to
d1  z  d2 is considered a thin film of few layer of RGO, while
synthesize the reduced graphene oxide (RGO). Briefly, graphite
powder (10 g) was added to concentrated H SO (230 mL) in an
2
4

View Article Online
DOI: 10.1039/C4RA12552E
RSC Advances
Page 6 of 7
the region d2  z  d3 be occupied by a Quartz substrate
Figure 11). The regions z  0 and are
their spectroscopic data identical to that reported in the
5
0
literature.
(
1
z  (d  d  d )
1
2
3
1,3-Diphenylurea (Table 1, entries 1 and 2): H NMR (400
4
5
MHz, DMSO) δ = 8.60 (s, 2H), 7.43 (d, J = 8.5 Hz, 4H), 7.25 (t, J
considered vacuum. Assume a polarized plane wave from z  0
=
7.7 Hz, 4H), 6.95 (t, J = 7.2 Hz, 2H).
is axially incident on composite structure. The electric fields of
4
7,48
N-(4-Methoxyphenyl)-N'-phenylurea (Table 1, entries 3 and 4):
5
incident, reflected and transmitted are as:
1
i
K0
z
H NMR (300 MHz, DMSO) δ = 8.52 (s, 1H), 8.41 (s, 1H), 7.40

Einc (r)  [as u y  ap u x ] e
,
z  0
z  0
z  (d
(1)


(d, J = 8.5 Hz, 2H), 7.34 (d, J = 9.0 Hz, 2H), 7.25 (t, J = 7.7 Hz,
2H), 6.92 (t, J = 7.4 Hz, 1H), 6.83 (d, J = 9.0 Hz, 2H), 3.70 (s,
 i K0
z


E
E
ref (r)  [r
tr (r)  [t
s
u
y
 r
t
p
u
x
] e
,
50
i
K0 (z(d1 d2 d3 ) )


s
u
y
p
u
x
] e
,
 d  d )
1 2 3
3
H).
N-(2-Methylphenyl)-N'-phenylurea (Table 1, entry 5): H NMR
300 MHz, DMSO) δ = 8.97 (s, 1H), 7.89 (s, 1H), 7.81 (dd, J =
.0, 8.0 Hz, 1H), 7.43 (dt, J = 1.4, 8.5 Hz, 3H), 7.28-7.23 (m,
55 3H), 7.16-7.08 (m, J = 7.5, 15.0 Hz, 3H), 6.97-6.88 (m, 2H), 2.22
s, 3H).
1
The amplitudes of incident plane wave, and reflected and
transmitted waves for S- or P- polarizations are ( a ,a )
,
p
(
1
s
(
r ,r ) and (t ,t ), respectively K      2 / is
s
p
s
p
0
0
0
0
(
1
0
the free space wave number, 0 is the free space wavelength,
1
N-(4-Nitrophenyl)-N'-phenylurea (Table 1, entries 6 and 7): H
12
1
7
1
0
 8.85410 Fm
,
  4 10 Hm
are the
NMR (500 MHz, DMSO-d ) δ = 9.42 (s, 1H), 8.92 (s, 1H), 8.20
0
6
(d, J = 9.0 Hz, 2H), 7.70 (d, J = 9.0 Hz, 2H), 7.07 (d, J = 7.3 Hz,
permittivity and permeability of free space (vacuum) and ux,y,z
are the unit vectors in Cartesian coordinates system.
6
6
7
7
0
5
0
5
2H), 7.31 (t, J = 7.7 Hz, 2H), 7.04 (t, J = 7.5 Hz, 1H).
Acknowledgement
We gratefully acknowledge the Iranian Nano Council and the
University of Qom for the support of this work.
References
1
Y. W. Zhu, S. Murali, M. D. Stoller, K. J. Ganesh, W. W. Cai,
P. J. Ferreira, et al., Science, 2011, 332, 1537.
M. D. Stoller, S. Park, Y. Zhu, J. An, R. S. Ruoff, Nano Lett.,
2008, 8, 3498.
2
1
5
Figure 11. Schematic of the boundary-value problem for optical
modeling.
3
J. Yang, S. Y. Deng, J. P. Lei, H. X. Ju, S. Gunasekaran,
Biosensors and Bioelectronics, 2011, 29, 159.
4
T. Ramanathan, S. Stankovich, D. Dikin, A. H. Liu, H. Shen,
The amplitudes of the reflectance and transmittance in
conjunction with the continuity of the tangential components of
S. T. Nguyen, L. C. Brinson, Journal of Polymer Science Part B:
Polymer Physics, 2007, 45, 2097.
2
0
4
9
electrical and magnetic fields at interfaces can be calculated as:
5
R. Muszynski, R. B. Seger, P. V. Kamat, J. Phys. Chem. C,





t 
 a
s



2008, 112, 5263.
6 P. V. Kamat, J. Phys. Chem. Lett., 2010, 1, 520.
7 B. Seger, P. V. Kamat, J. Phys. Chem. C, 2008, 113, 7990.
80 8 Y. Zhu, M. D. Stoller, W. Cai, A. Velamakanni, R. D. Piner,
D. Chen, et al., ACS Nano, 2010, 4, 1227.
s


tp
ap
(2)
1




K

.

M

.

K

.


 r 
0
s





0 
 r


p

9
I. V. Lightcap, T. H. Kosel, P. V. Kamat, Nano Lett., 2010, 10,
The different terms and parameters of this equation are given
4
7
577.
in detail by Lakhtakia. Herein, the absorbance for natural light
1
0 S. Yongchao, T. S. Edward, Chem. Mat., 2008, 20, 6792.
TS T
P
2
5
is
determined
as
,
where
A  Log[
]
85 11 J. Yang, S. Gunasekaran, Carbon, 2013, 51, 36.
2
1
1
2 R. S. Dey, C. R. Raj, J. Phys. Chem. C, 2010, 114, 21427.
3 A. K. Singh, M. A. Ribas, B. I. Yakobson, ACS Nano, 2009, 3,
2
ti
.
Ti 
T ;T
i, j

;i, j  s, p
1657.
4 Z. B. Lei, L. Lu, X. S. Zhao, Energy & Environmentala

ji
aj
js, p
1
Typical experimental procedure for the N-arylation of 90 Science, 2012, 5, 6391.
phenylurea with aryl halides
15 Y. Chen, X. Zhang, D. Zhang, P. Yu, Y. Ma, Carbon, 2011,
A Smith process vial was charged with 18 mg RGO/Cu NPs
and K CO (1 mmol). After sealing the cap and twice purging
49, 573.
3
3
4
0
5
0
16 D. R. Dreyer, S. Park, C. W. Bielawski, R. S. Ruoff, Chem.
Soc. Rev., 2010, 39, 228.
2
3
with N , the vial was charged with 0.5 mL of DMF and stirred at
2
room temperature for 10 min. A solution of 0.6 mmol of aryl 95 17 J. Li, C.-Y. Liu, Eur. J. Inorg. Chem., 2010, 2010 (8), 1244.
halide and 0.5 mmol of phenylurea in 0.5 mL of DMF was
introduced via syringe and the mixture was vigorously stirred at
room temperature for 30 min and the vial was irradiated at 130 °C
for 1 h by microwave. The reaction mixture was cooled to room
18 L. Dong, R. R. S. Gari, Z. Li, M. M. Craig, S. Hou, Carbon,
2010, 48 (3), 781.
19 M. D. Malinsky, K. L. Kelly, G. C. Schatz, R. P. Van Duyne,
J. Am. Chem. Soc., 2001, 123, 1471.
temperature and filtered through a pad of Celite. The combined 100 20 M. C. Daniel, D. Astruc, Chem. Soc. Rev., 2004, 104, 293.
organic extracts were dried with anhydrous Na SO and
21 G. Borkow, J. Gabbay, R. Dardik, A. I. Eidelman, Y. Lavie,
Y. Grunfeld, S. Ikher, M. Huszar, R. C. Zatcoff, M. Marikovsky,
Wound Repair Regen, 2010, 18, 266.
2
4
evaporated under reduced pressure. The residue was purified by
column chromatography. All products are known in the literature
and were characterized by FT-IR, NMR and melting points and

View Article Online
DOI: 10.1039/C4RA12552E
Page 7 of 7
RSC Advances
2
2
2
2
2 G. Borkow, R. C. Zatcoff, J. Gabbay, Medical Hypotheses,
002, 73, 883.
3 Y. Li, J. Liang, Z. Tao, J. Chen, Mat. Res. Bull., 2007, 43,
380.
Org. Lett., 2006, 8, 5089; (d) M. V. Nandakumar, Tetrahedron
Lett., 2004, 45, 1989; (e) A. G. Sergeev, G. A. Artamkina, I. P.
Beletskaya, Russ. J. Org. Chem., 2003, 39, 1741; (f) S. Gavade,
M. Shingare, D. Mane, Bull. Korean Chem. Soc., 2011, 32, 4167.
5
0
5
0
5
0
5
0
5
0
5
0
5
24 (a) L. C. Carnes, K. J. Klabunde, J. Mol. Catal. A Chem.,
003, 194, 227; (b) Z. Guo, X. Liang, T. Pereira, R. Scaffaro, H.
T. Hahn, Composites Science and Technology, 2007, 67, 2036.
70
2
2
2
5 (a) M. Nasrollahzadeh, M. Enayati, M. Khalaj, J. RSC Adv.,
014, 4, 26264; (b) M. Nasrollahzadeh, A. Ehsani, M. Maham,
1
1
2
2
3
3
4
4
5
5
6
6
Synlett, 2014, 25, 505.
2
2
2
6 M. V. Nandakumar, Tetrahedron Lett., 2004, 45, 1989.
7 J. Yin, S. L. Buchwald, J. Am. Chem. Soc., 2002, 124, 6043.
8 (a) M. Nasrollahzadeh, M. Maham, A. Ehsani and M. Khalaj,
RSC Adv., 2014, 4, 19731; (b) M. Nasrollahzadeh, A. Ehsani, A.
Rostami-Vartouni, Ultrason. Sonochem., 2014, 21, 275; (c) M.
Nasrollahzadeh, A. Zahraei, A. Ehsani and M. Khalaj, RSC Adv.,
2
2
2
014, 4, 20351; (d) M. Nasrollahzadeh, RSC Adv., 2014, 4,
9089.
9 (a) P. Fakhri, B. Jaleh, M. Nasrollahzadeh, J. Mol. Catal. A
Chem., 2014, 383-384, 17; (b) M. Nasrollahzadeh, B. Jaleh, A.
Jabbari, RSC Adv., 2014, 4, 36713; (c) P. Fakhri, M.
Nasrollahzadeh, B. Jaleh, RSC Adv., 2014, 4, 48691.
3
0 (a) M. Nasrollahzadeh, M. Maham, M. M. Tohidi, J. Mol.
Catal. A Chem., 2014, 391, 83; (b) M. Nasrollahzadeh, S. M.
Sajadi, M. Khalaj, J. RSC Adv., 2014, 4, 47313.
3
1 M. Nasrollahzadeh, F. Babaei, S. M. Sajadi and A. Ehsani,
Spectrochim. Acta A, 2014, 132, 423.
3
2
2 Z. Xiong, L. L. Zhang, J. Ma, X. S. Zhao, Chem. Commun.,
010, 46, 6099.
33 K. Jasuja and V. Berry, J. ASC Nano, 2009, 3(8), 2358.
3
3
0
3
4 R. K. Biroju and P. K. Giri, J. Phys. Chem. C, 2014, 118, 25.
5 A. Garahan, L. Pilon, J. Yin, J. Appl. Phys., 2007, 101,
14320.
6 E. D. Palik, Handbook of Optical Constants of Solids,
Academic Press, New York, USA, 1985.
3
1
3
1
7 R Swanepoel, Journal of Physics E: Scientific Instruments,
983, 16, 1214.
8 R Swanepoel, Journal of Physics E: Scientific Instruments,
984, 17, 896.
39 F. Babaei, Journal of Modern Optics, 2011, 58, 1292.
0 K. Anand, N. Kohli, O. Singh, A. Hastir, R. C. Singh, AIP
Conference Proceedings, 2013, 1512, 350.
4
4
4
1 K. Matsuda, Med. Res. Rev., 1994, 14, 271.
2 N. N. Melnikov, In Chemistry of Pesticides; J. D., Gunther,
Ed.; Springer-Verlag: Berlin, 1971, 225.
4
8
4
3 W. S. Jr. Hummers, R. E. Offeman, J. Am. Chem. Soc., 1958,
0, 1339.
4 N. I. Kovtyukhova, P. J. Ollivier, B. R. Martin, T. E. Mallouk,
S. A. Chizhik, E. V. Buzaneva, A. D. Gorchinskiy, Chem. Mat.,
1999, 11, 771.
4
5 I. B. Jeong, Y. S. Kim, B. Y. Lee, Y. H. Kim, B. S. Jeong, M.
S. Lee, Patent Application Publication Pub. No.: US
2
4
004/0221685A1, 2004.
6 G. Zhao, M. P. Pompeo, Patent Application Publication Pub.
No.: US 7517382B2, 2009.
A. Lakhtakia, R. Messier, Sculptured thin films
Nanoengineered Morphology and Optics, USA: SPIE; 2005.
4
7
4
2
8 A. Ehsani, F. Babaei, M. Nasrollahzadeh, Appl. Surf. Sci.,
013, 283, 1060.
49 V. C. Venugopal, A. Lakhtakia, Proceedings of the Royal
Society of London A, 2000, 456, 125.
5
0 (a) G. A. Artamkina, A. G. Sergeev, I. P. Beletskaya,
Tetrahedron Lett., 2001, 42, 4381; (b) A. G. Sergeev, G. A.
Artamkina, I. P. Beletskaya, Tetrahedron Lett., 2003, 44, 4719;
(c) M. C. Willis, R. H. Snell, A. J. Fletcher, R. L. Woodward,