Gold Bull
DOI 10.1007/s13404-013-0094-9
ORIGINAL PAPER
One-pot synthesis of Au nanoparticles/reduced graphene oxide
nanocomposites and their application for electrochemical H2O2,
glucose, and hydrazine sensing
Xiaoyun Qin & Qingzhen Li & Abdullah M. Asiri &
Abdulrahman O. Al-Youbi & Xuping Sun
# The Author(s) 2013. This article is published with open access at SpringerLink.com
Abstract In this paper, Au nanoparticles/reduced graphene
oxide (AuNPs/rGO) nanocomposites were prepared through
a one-pot strategy, carried out by heating the mixture of
HAuCl4 and graphene oxide solution at 90 °C under alkaline condition. The resultant AuNPs/rGO nanocomposites
were found to exhibit good catalytic performance toward
H2O2 reduction and oxidation as well as hydrazine oxidation. The electrochemical sensing application of the
nanocomposites for H2O2, glucose, and hydrazine was also
demonstrated successfully.
Keywords Au nanoparticles . Reduced graphene oxide .
Electrochemical detection . H2O2 . Glucose . Hydrazine
Introduction
Graphene, a two-dimensional aromatic sheets composed of sp2bonded carbon atoms, has received enormous interest in various
areas of research owing to its large specific surface area, excellent
thermal and electrical conductivity, strong mechanical strength,
good biocompatibility, and low manufacturing cost [1–3]. On the
X. Qin : Q. Li : X. Sun
Chemical Synthesis and Pollution Control Key Laboratory of
Sichuan Province, School of Chemistry and Chemical Industry,
China West Normal University, Nanchong 637002 Sichuan, China
A. M. Asiri : A. O. Al-Youbi : X. Sun
Chemistry Department, Faculty of Science, King Abdulaziz
University, Jeddah 21589, Saudi Arabia
A. M. Asiri : A. O. Al-Youbi : X. Sun (*)
Center of Excellence for Advanced Materials Research, King
Abdulaziz University, Jeddah 21589, Saudi Arabia
e-mail: sun.xuping@hotmail.com
other hand, noble metal nanostructures are a class of functional
materials with unique physical and chemical properties [4, 5].
Furthermore, the integration of two-dimensional graphene with
zero-dimensional noble metal nanoparticles (NPs) into hybrid
structures has received increased attention in the past few years
[6–12]. These noble metal NPs/graphene nanocomposites not
only combine the merits of each component, but possess interesting structural, electrochemical, electromagnetic, and other
properties that are not available in their respective components.
We have fabricated noble metal NPs/graphene nanocomposites
via chemical reduction and photocatalytic strategies [13–23].
Zhou et al. demonstrated the one-step synthesis of AgNPs on
graphene oxide (GO) and reduced graphene oxide (rGO) surfaces absorbed on 3-aminopropyltriethoxysilane-modified
Si/SiOx substrates without using any surfactant or reducing agent
[24]. Similarly, our group has also successfully reduced GO to
rGO in liquid phase and decorated AgNPs onto thus obtained
rGO under strong alkaline conditions without any reducing agent
[25, 26]. In this process, AgNPs are deposited onto rGO by
chemical reduction of silver ions by hydroxyl group of GO
accompanied with the conversion of GO into rGO under strong
alkaline conditions as well as heat treatment process [27–30].
However, high temperature or multistep reactions are required.
Accordingly, from a point view of material science, synthesis of
noble metal NPs/graphene nanocomposites by a more facile
method and exploiting their catalytic applications are still highly
desirable. Herein, we prepared AuNPs/rGO nanocomposites
through a one-pot route by heating the mixture of HAuCl4 and
GO solution under alkaline condition at 90 °C for 30 min. It
suggests that the resultant AuNPs/rGO nanocomposites show
good catalytic performance toward H2O2 reduction and oxidation as well as hydrazine oxidation. We further demonstrate the
electrochemical sensing application of the nanocomposites for
H2O2, glucose, and hydrazine.
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Material and methods
Reagents and materials
Graphite powder, NaCl, NaH2PO4, Na2HPO4, HAuCl4, and
H2O2 (30 %) were from Aladin Ltd. (Shanghai, China).
Glucose, NaNO3, H2SO4 (98 %), and KMnO4 were purchased
from Beijing Chemical Corp. glucose oxidase (GOD) was
purchased from Aldrich Chemical Inc. All chemicals were
used as received without further purification. The water used
throughout all experiments was purified through a Millipore
system and a fresh solution of H2O2 was prepared daily.
Phosphate-buffered saline (PBS) was prepared by mixing
stock solutions of NaH2PO4, Na2HPO4, and NaCl.
Preparation of GO
GO was prepared from natural graphite powder through a
modified Hummers method [31]. In a typical synthesis, 1 g
of graphite was added into 23 mL of 98 % H2SO4, followed
by stirring at room temperature over a 24-h period. After
that, 100 mg of NaNO3 was introduced into the mixture and
stirred for 30 min. Subsequently, the mixture was kept
below 5 °C by ice bath, and 3 g of KMnO4 was slowly
added into the mixture. After being heated to 35–40 °C, the
mixture was stirred for another 30 min. After that, 46 mL of
water was added into above mixture during a period of
25 min. Finally, 140 mL of water and 10 mL of 30 %
H2O2 were added into the mixture to stop the reaction.
After the unexploited graphite in the resultant mixture was
removed by centrifugation, as-synthesized GO was dispersed into individual sheets in distilled water at a concentration of 0.5 mg/mL with the aid of ultrasound for further
use.
counter electrode. All potentials given in this work were
referred to the Ag/AgCl electrode. All the experiments were
carried out at ambient temperature. The modified electrode
was prepared via a simple casting method. Prior to the surface
coating, the GCE was polished with 1.0 and 0.3 μm alumina
powder, respectively. After that, the GCE was rinsed with
distilled water, followed by sonication in ethanol and distilled
water, respectively. Then, the electrode was allowed to dry in a
stream of nitrogen. For the determination of H2O2, 3 μL of
AuNPs/rGO nanocomposites was dropped on the surface of
pretreated GCE and left to dry at room temperature. Then,
4 μL of 38 mg/mL GOD aqueous solution was dropped on the
resulting AuNPs/rGO/GCE to dry at 4 °C for 3 h. For current
time experiment, 2 μL of 1 wt% chitosan solution was used as
a fixative and additionally casted on the surface of the above
materials modified GCE and dried at 4 °C for 2 h before
electrochemical experiments.
Instruments
UV–vis spectra were obtained on a UV5800 spectrophotometer. Raman spectra were obtained on J-Y T64000
Raman spectrometer with 514.5 nm wavelength incident
laser light. Powder X-ray diffraction (XRD) data were
recorded on a Rigaku D/MAX 2550 diffractometer with
Cu Kα radiation (λ=1.5418 Å). Transmission electron microscopy (TEM) measurements were made on a Hitachi H8100 EM (Hitachi, Tokyo, Japan) with an accelerating applied potential of 200 kV. The sample for TEM characterization was prepared by placing a drop of the dispersion on
carbon-coated copper grid and drying at room temperature.
Results and discussion
Preparation of AuNPs/rGO nanocomposites
Characterization of AuNPs/rGO nanocomposites
In a typical experiment, 155 μL of HAuCl4 aqueous solution (24.3 mM) was mixed with the 4,650-μL 0.25 mg/mL
of GO and 195 μL 8 M NaOH. Then, the mixture was
heated to 90 °C for 30 min in a hot bath. The products were
collected by centrifugation and washed with water three
times. Finally, the resulting precipitates were redispersed
in water for characterization and further use.
Figure 1 shows the Raman spectra of aqueous dispersion of
GO (curve a) and the products (curve b). It is seen that GO
exhibits a D band at 1,361 cm−1 and a G band at 1,608 cm−1,
while the corresponding bands of the products are 1,354 and
1,579 cm−1, respectively. The G band of the products redshifts from 1,608 to 1,579 cm−1, which is attributed to the
high ability for recovery of the hexagonal network of carbon
atom [32]. It is also found that the products show relative
higher intensity of D to G band (0.97) than that of GO
(0.79), further confirming the formation of new graphitic
domains [33]. These observations confirm the successful
conversion of GO to rGO after the heat treatment process
under alkali conditions.
Figure 2 shows the UV–vis spectra of aqueous dispersion
of GO and resulting products. As expected, GO exhibits
strong bands centered at 230 and 290 nm, corresponding to
Electrochemical measurements
The electrochemical measurements were performed with a
CHI 660D electrochemical analyzer (CH Instruments, Inc.,
Shanghai). A conventional three-electrode cell was used, including a glassy carbon electrode (GCE) (geometric area=
0.07 cm2) as the working electrode, a Ag/AgCl (3 M KCl)
electrode as the reference electrode, and platinum foil as the
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Fig. 1 Raman spectra of (curve a) GO and (curve b) the products
obtained
π–π* transitions of aromatic C=C band and n–π* transitions
of C=O band in GO, respectively (curve a) [34]. It is clearly
seen that the adsorption peak of the obtained composites
gradually red-shifts from 230 to 260 nm, and the absorbance
in the whole spectral region increases after heat treatment
(curve b), suggesting the successful reduction of GO [13,
35]. It is worthwhile mentioning the obvious color change
from pale yellow to black after heat treatment of the mixture
in alkaline conditions, revealing another piece of evidence
to support the formation of rGO. Additionally, a new absorption band appears at 528 nm ascribing to the characteristic of the colloidal Au surface plasmon resonance band,
indicating the formation of AuNPs [36].
The XRD pattern of the products obtained is shown in
Fig. 3. The four peaks located at 38.2, 44.5, 64.8, and 77.6°
are assigned to 111, 200, 220, and 311 faces of a Au crystal,
respectively, demonstrating the formation of metallic Au
Fig. 2 UV–vis absorption spectra of aqueous dispersions of (curve a)
GO and (curve b) the products obtained
Fig. 3 XRD pattern of products obtained
(JCPDS 04-0784). The broad peak at 2θ=20–30° appears,
indicating the disordered stacking of rGO sheets in the
composites [37]. All of these observations confirm the formation of AuNPs/rGO nanocomposites after the heat treatment of the mixture of HAuCl4 and GO solution under
alkali conditions.
The formation of AuNPs/rGO nanocomposites was further confirmed by TEM observations. Figure 4 shows typical TEM images and the corresponding energy-dispersed
spectrum (EDS). Low magnification image (Fig. 4a) indicates that numerous nanoparticles are attached onto the
surface of rGO. A higher magnification image reveals the
AuNPs are about 40 nm in diameter and the shape is mostly
spherical (Fig. 4b). The chemical composition of the
nanocomposites was determined by EDS (Fig. 4c), further
confirming the existence of C, O, and Au elements. Other
peaks originate from the ITO-coated glass substrate.
Fig. 4 Typical TEM images at (a) low and (b) high magnifications and
(c) corresponding EDS of the obtained AuNPs/rGO nanocomposites
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The reducing nature of GO under alkaline conditions has
been discussed by Kannan and Zhou et al. The hydroxyl
groups of the molecules attached to the hexagonal basal
plane make GO a proper agent to reduce AuCl4− under
alkaline conditions [27]. Because the electrons in the negatively charged rGO can participate in the reduction of metal
complex, AuCl4− could obtain the electrons in the negatively charged rGO surface to form AuNPs. The big difference
between the reduction potential of rGO and AuCl4− also
help to the spontaneous reduction process [24]. Meanwhile,
the alkaline conditions can also accelerate the formation of
rGO and AuNPs [28–30]. The strong alkali, NaOH, plays a
dual role in the conversion of GO and the formation of
AuNPs in this system. In this way, AuNPs are deposited
onto rGO by chemical reduction of AuCl4− by hydroxyl
group of GO accompanied with the conversion of GO into
rGO under strong alkaline conditions as well as heat treatment process.
Electrocatalytic effect toward H2O2 of AuNPs/rGO/GCE
To demonstrate the sensing application of AuNPs/rGO
nanocomposites, we first constructed an enzymeless H2O2
sensor by immobilizing AuNPs/rGO nanocomposites with
chitosan as a fixative onto a GCE surface. Figure 5a shows
cyclic voltammograms (CVs) of bare GCE and the
AuNPs/rGO/GCE in 0.2 M PBS at pH 7.4 in the presence of
1 mM H2O2. It is seen that the response of the bare GCE
toward H2O2 is quite weak. In contrast, the AuNPs/rGO/GCE
exhibits notable catalytic current in the process of both reduction and oxidation of H2O2. It is also important to note that the
AuNPs/rGO/GCE exhibits no electrochemical response in the
absence of H2O2. All these observations indicate that such
AuNPs/rGO nanocomposites exhibit notable electrocatalytic
activity toward both the reduction and oxidation of H2O2. The
typical current–time curve of the AuNPs/rGO/GCE was
shown in Fig. 5b. The amperometric response of the sensor
was studied by successively dropping the H2O2 solution with
different concentrations into the PBS under optimized conditions at an applied potential of −0.3 V vs. Ag/AgCl electrode.
The linear range of the H2O2 detection was from 0.1 to 9 mM
(r=0.999), and the detection limit was estimated to be 1.5 μM
based on the criterion of a signal-to-noise ratio of 3.
Determination of glucose at GOD/AuNPs/rGO/GCE
Based on the high electrocatalytical activity of
AuNPs/rGO/GCE toward H2O2, a glucose sensor was further developed by immobilizing GOD onto the surface of
AuNPs/rGO/GCE. The sensing mechanism is that GOD can
selectively catalyze the oxidation of glucose in the presence
of oxygen to form H2O2, which can be electrochemically
detected [38]. Differential pulse voltammogram (DPV) has
Fig. 5 a CVs of different electrodes in N2-saturated 0.2 M PBS at pH
7.4 in the presence and absence of 1 mM H2O2 (scan rate, 50 mV s−1).
b Typical steady-state response of the AuNPs/rGO/GCE to successive
injection of H2O2 into the stirred N2-saturated 0.2 M PBS at pH 7.4
(applied potential, −0.3 V). Inset: the fitting of the experimental data by
the regression line
higher sensitivity than CV and is used for quantitative measurements in the current study. Figure 6 shows the typical
DPVs of the GOD/AuNPs/rGO/GCE in 0.2 M PBS solution
at pH 7.4 with various concentrations of glucose in saturated
O2. It is seen that well-defined anodic peaks at −0.07 V are
observed, which can be attributed to the electrochemical
oxidation of H2O2. It is also found that the oxidation current
increases with the increased amount of glucose in saturated
O2. The inset in Fig. 6 shows the calibration curves to
corresponding amperometric responses. Good linear relationships are observed between the catalytic current and
glucose concentration at ranges from 0 to 1 mM (r=0.998)
and from 3 to 21 mM (r=0.996), respectively. The detection
limit is estimated to be 20 μM with a signal-to-noise ratio of
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potential of 0.3 V vs. Ag/AgCl electrode (Fig. 7b). When
an aliquot hydrazine was dropped into the stirred PBS
solution, the oxidation current rose steeply to reach a
stable value. The sensor could accomplish 96 % of the
steady state current within 3 s, indicating a fast amperometric response behavior. The inset in Fig. 7b shows
the calibration curve of the sensor. The linear detection
range is estimated to be from 5 to 900 μM (r=0.999),
and the detection limit is estimated to be 0.08 μΜ at a
signal-to-noise ratio of 3. Note that our present sensing
system gives lower detection limit than that of platinum
screen-printed electrodes (0.12 μM) [42], AuNPs on
thiolated single-stranded DNA-modified Au electrode
Fig. 6 DPVs of GOD/AuNPs/rGO/GCE in O2-saturated 0.2 M PBS at
pH 7.4 with various concentrations of glucose (from down to top 0,
0.2, 0.4, 0.6, 0.8, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21 mM). Inset: the
calibration curves corresponding to the responses at −0.07 V
3. Note that our present sensing system gives lower detection
limit than that of GOD/AuNPs/rGO/chitosan-based system
(180 μM) [39], GOD/AuNPs/rGO/ionic liquid (IL) biosensor
(130 μM) [40] and GOD-chemically modified graphene-IL
(376 μM) [41], etc. The relative standard deviation of the
response to 1 mM of glucose is 1.9 % for ten successive
measurements, indicating the good reproducibility of
GOD/AuNPs/rGO/GCE. To evaluate the long-term stability
of the glucose biosensor, the GOD/AuNPs/rGO/GCE was
stored at 4 °C when not in use. The response to glucose at
the GOD/AuNPs/rGO/GCE decreased to about 95 % of its
initial response current on the third day and about 91 % after
10 days. The loss of the response current may be ascribed to
the decrease of the enzyme activity during these days.
Electrocatalytic effect toward hydrazine of AuNPs/rGO/GCE
It is found that the resultant AuNPs/rGO composites exhibit
good catalytic performance toward hydrazine oxidation.
Figure 7a shows the electrocatalytic responses of bare
GCE and AuNPs/rGO/GCE toward the oxidation of hydrazine in 0.2 M PBS at pH 7.4 in the presence of 10 mM
hydrazine. The response of the bare GCE toward the oxidation of hydrazine is quite weak. In contrast, the
AuNPs/rGO/GCE shows a notable current peak about
75 μA in intensity centered at 0.3 V vs. Ag/AgCl; however,
it exhibits no electrochemical response in the absence of
hydrazine. These observations indicate that the observed
current peak originates from hydrazine oxidation and the
nanocomposites can effectively catalyze the electrochemical
oxidation of hydrazine. The amperometric response of the
hydrazine sensor was studied by successively dropping the
hydrazine aqueous solution into the PBS at an applied
Fig. 7 a CVs of different electrodes in 0.2 M PBS at pH 7.4 in the
presence and absence of 10 mM hydrazine (scan rate, 50 mV s−1). b
Typical steady-state response of the AuNPs/rGO/GCE to successive
injection of hydrazine into the stirred 0.2 M PBS at pH 7.4 (applied
potential, 0.3 V). Inset: the fitting of the experimental data by the
regression line
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(0.56 μM) [43], and hybrid nickel hexacyanoferratefunctionalized multiwalled carbon nanotube/GCE [44].
Conclusions
In summary, heating treatment of HAuCl4 and preformed
GO solution under alkaline condition has been proven to be
an effective strategy to one-pot preparation of AuNPs/rGO
nanocomposites without an extra reducing agent. Such
nanocomposites exhibit good electrocatalytic activity toward H2O2 reduction and oxidation as well as hydrazine
oxidation. Electrochemical detection of H2O2, glucose, and
hydrazine is also demonstrated successfully. Our present
study is important because it provides us a simple method
for preparing noble metal nanoparticles/rGO composites for
sensing and other applications.
Open Access This article is distributed under the terms of the Creative
Commons Attribution License which permits any use, distribution, and
reproduction in any medium, provided the original author(s) and the
source are credited.
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