Electrochemical detection of hydroquinone by graphene and Pt-graphene hybrid material synthesized through a microwave-assisted chemical reduction process

Article abstract of DOI:10.1016/j.electacta.2010.12.046

We have synthesized graphene and Pt-graphene hybrid material by a microwave-assisted chemical reduction process and evaluated their application as electrode materials towards the electrochemical detection of hydroquinone. Graphene modified glass carbon electrode (GCE) showed a good performance for detecting hydroquinone due to the unique properties of graphene which increased the active surface area of the electrode and accelerated the electron transfer. The linear detection range of hydroquinone concentration was 20-115 μM with a sensitivity of 1.38 μA μM^-1 cm^-2; the detection limit was estimated to be 12 μM (S/N = 3). The electrocatalytic activity of the Pt-graphene modified GCE was further improved due to the enhanced electron transfer and the linear detection range was 20-145 μM with the sensitivity of 3.56 μA μM^-1 cm^-2, detection limit 6 μM (S/N = 3).

Full text of DOI:10.1016/j.electacta.2010.12.046

Electrochimica Acta 56 (2011) 2712–2716
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochemical detection of hydroquinone by graphene and Pt-graphene hybrid
material synthesized through a microwave-assisted chemical reduction process
Jing Lia,b, Chun-yan Liua,∗, Chao Chenga,b
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials of Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences, Zhongguancun, Beijing 100190, PR China
b Graduate School of the Chinese Academy of Sciences, Beijing 100806, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized graphene and Pt-graphene hybrid material by a microwave-assisted chemical
reduction process and evaluated their application as electrode materials towards the electrochemical
detection of hydroquinone. Graphene modified glass carbon electrode (GCE) showed a good performance
for detecting hydroquinone due to the unique properties of graphene which increased the active surface
area of the electrode and accelerated the electron transfer. The linear detection range of hydroquinone
concentration was 20–115 ␮M with a sensitivity of 1.38 ␮A ␮M−1 cm−2; the detection limit was esti-
mated to be 12 ␮M (S/N = 3). The electrocatalytic activity of the Pt-graphene modified GCE was further
improved due to the enhanced electron transfer and the linear detection range was 20–145 ␮M with the
sensitivity of 3.56 ␮A ␮M−1 cm−2, detection limit 6 ␮M (S/N = 3).
Received 17 June 2010
Received in revised form
17 September 2010
Accepted 14 December 2010
Available online 21 December 2010
Keywords:
Hydroquinone
Graphene
© 2010 Elsevier Ltd. All rights reserved.
Pt-graphene hybrid material
Electrochemical detection
Differential pulse voltammetry
1. Introduction
erties, strong mechanical strength, and its lower cost and easier
preparation in mass quantities compared with carbon nanotubes,
Hydroquinone is a phenolic compound which is important in a
wide number of biological and industrial processes such as coal–tar
production, paper manufacturing and photographic developers,
and is considered as an important xenobiotic micropollutant [1].
Several analytical methods have been used to detect hydroquinone,
including high performance liquid chromatography [2,3], flow
injectionanalysis [4,5], spectrophotometry [6,7], andelectrochemi-
cal methods [8,9], among which the electrochemical methods have
attracted great attentions owing to the advantages such as effi-
ciency, simplicity and quick response. In previous work, several
carbon-based materials such as mesoporous carbon [10], boron-
doped diamond [11], conductive carbon cement [12], carbon fibre
[13], and carbon nanotubes (CNTs) [14] have been explored for the
electrochemical detection of hydroquinone.
Graphene (G), a monolayer of carbon atoms packed into a dense,
honeycomb crystal structure as well as being a fundamental build-
ing block for fullerenes, carbon nanotubes, and graphite [15], has
shown fascinating properties and holds the promise for future
carbon-based device architectures [16–19]. Recently, graphene-
based materials have been explored for electrochemical sensor due
to its large surface area, extraordinary electronic transport prop-
typical examples including detection of glucose by metal deco-
rated graphene [20] and nitrogen-doped graphene [21] modified
glass carbon electrode, electrochemical detection of paracetamol
by graphene modified glass carbon electrode [22], and selective
detection of dopamine by graphene modified glass carbon elec-
trode [23]. However, to the best of our knowledgement, there is
no report about the eletrochemical detection of hydroquinone by
graphene-based materials.
Up to now, numerous methods have been developed to synthe-
size graphene such as micromechanical cleavage of graphite [24],
chemical vapor deposition technique [25], epitaxial growth on a
single-crystal silicon carbide by vacuum graphitization [26], and
chemical reduction of graphene oxide [27–31]. Among them, the
chemical reduction of graphene oxide, involving graphite oxida-
tion, exfoliation and reduction, is the most efficient approach to
bulk production of graphene-based sheets at low cost. In this con-
text, we synthesized graphene and Pt-graphene hybrid material by
a microwave-assisted chemical reduction process and evaluated
their application to electrochemical detection of hydroquinone.
2. Experimental
2.1. Preparation of graphene
∗
Graphene was prepared through a microwave-assisted chemi-
cal reduction of graphene oxide. In a typical procedure, graphite
Corresponding author. Tel.: +86 010 82543573; fax: +86 010 62554670.
E-mail address: cyliu@mail.ipc.ac.cn (C.-y. Liu).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.12.046

J. Li et al. / Electrochimica Acta 56 (2011) 2712–2716
2713
oxide (25 mg) prepared from natural graphite powders (Beijing
Chemical Factory of China) by Hummer’s method [32] was son-
icated in water (50 mL) for 2 h using a JK-300 ultrasonic cleaner
(300 W, 40 kHz) to achieve a clear, brown dispersion of graphene
oxide (0.5 mg/mL). 5 mL of hydrazine hydrate (80%) was added
into the graphene oxide and kept stirring for 3 h at 100 ◦C in a
microwave oven with program-control (Sineo MAS-II). The heat-
ing power was set to 300 W at the beginning of the reaction and
automatically reduced to as low as about 10 W when a given tem-
perature reached. The stirring rate was set to 700 rps. The black
graphene was obtained after centrifugation, washed with water
and ethanol, and naturally dried in air.
2.2. Preparation of Pt-graphene hybrid material
The route to prepare Pt-graphene hybrid material was similar
to graphene, except that 5 mL of hexachloroplatinic acid solution
(0.0193 M) was added to the graphene oxide solution and kept
stirring for 15 min at room temperature before the addition of
hydrazine hydrate.
2.3. Preparation of graphene and Pt-graphene modified glass
carbon electrode
Prior to modification, the glassy carbon electrodes (GCE) of 3 mm
diameter were polished with 0.5 ␮m alumina powder, washed with
deionized water and then dried in air. Graphene-based materials
were dispersed in N,N-dimethylformamide (DMF) by sonication
for 30 min to achieve a 2 mg/mL graphene-DMF suspension. Then,
5 ␮L of the suspension was coated onto GCE and allowed to dry in
air.
2.4. Characterization
The AFM images were recorded using a Multimode Nanoscope
IIIa AFM (Veeco Metrology LLC, Santa Barbara, CA). Tapping-mode
imaging was applied to provide the largest amount of structural
detail of the graphene oxide sheets as well as to prevent transloca-
tion of the sheets on the surface by the tip (Veeco MP-11100 silicon
cantilevers, force constant k = 60 N/m, radius of curvature r = 10 nm,
and resonance frequency f = 300 kHz). The sample was prepared
by depositing graphene oxide dispersion in water (0.05 mg/mL)
onto a new cleaved mica surface and dried under vacuum at room
temperature. The TEM images were taken with a JEM 2100F trans-
mission electron microscope, by using an accelerating voltage of
200 kV. The samples were dispersed in deionized water by sonica-
tion and dropped onto a conventional carbon-coated copper grid.
The XRD pattern was obtained with a Bruker D8 Foc◦us under Cu
Fig. 1. AFM images and height profile of graphene oxide.
istic of a fully exfoliated graphene oxide sheet [27,33,34]. Such
thickness was larger than that of single-layer pristine graphene
(0.34 nm), due to the presence of oxygen-containing functional
groups attached on both sides of the graphene sheet and the dis-
placement of the sp3-hybridized carbon atoms slightly above and
below the original graphene plane [27].
The TEM images of graphene sheets and Pt-graphene hybrid
material were shown in Fig. 2, where the transparent graphene
sheets with crumpled silk veil waves on the top of the carbon film
were observed (Fig. 2a), and the rumples was intrinsic to graphene
nanosheets [35]. A large number of Pt nanoparticles were sup-
ported on graphene sheets and few particles resided outside of the
support (Fig. 2b), which indicated the strong interaction between
the Pt nanoparticles and the graphene sheets. The size distribution
of Pt nanoparticles was 8–45 nm (Fig. 2c).
K␣ radiation at 1.54056 A with a scanning speed of 4 min−1. The
˚
XPS measurements were performed on a MICROLAB MK II spec-
trophotometer with Mg K␣ radiation. UV–vis absorption spectra
were recorded with a Shimadzu UV-1601 PC spectrophotome-
ter. The samples were dispersed in deionized water for optical
measurements. Differential pulse voltammetry (DPV) was car-
ried out at room temperature with a CHI 660C workstation (CH
Instruments, Chenhua, Shang-hai, China) connected to a personal
computer. A three-electrode configuration was employed, con-
sisting of a modified glassy carbon electrode (3 mm in diameter)
serving as the working electrode, saturated calomel electrode and
platinum wire serving as the reference and counter electrodes,
respectively.
In Fig. 3, graphite showed a sharp diffraction peak at 26.2◦ cor-
responding to (0 0 2) plane with d-spacing of 0.34 nm (Fig. 3a).
Compared with the graphite, the feature diffraction peak of
graphite oxide appeared at 10.4◦ corresponding to d-spacing of
0.85 nm (Fig. 3b), which was larger than that of graphite due to the
intercalated water molecules between layers [36]. After the exfo-
liation of graphite oxide by ultrasonic vibration and subsequent
chemical reduction, the obtained graphene showed a broadened
diffraction peak at 24.5◦ (Fig. 3c), meaning the layers of graphite
along c-axis were exfoliated and the carbon sp2 bond were restored.
The XRD pattern of Pt-graphene hybrid material is shown in Fig. 3d.
Apart from the peak at 24.5◦ assigned to graphene, all other peaks
can be indexed to Pt nanoparticles (face-centered cubic, JCPDS 04-
0802).
3. Results and discussion
AFM images of graphene oxide revealed the presence of
sheets with thickness of 1.199 nm (Fig. 1), which was character-

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J. Li et al. / Electrochimica Acta 56 (2011) 2712–2716
Fig. 3. XRD patterns of (a) graphite, (b) graphite oxide, (c) graphene, and (d) Pt-
graphene hybrid material.
The UV–vis spectrum of GO exhibited two characteristic peaks,
one was at 230 nm corresponding to ␲ → ␲* transitions of aromatic
C–C bonds, and a shoulder at 303 nm was attributed to n → ␲*
transitions of C O bonds (Fig. 5a) [40]. The peak at 230 nm was
red shift to 268 nm after the chemical reduction treatment (Fig. 5b
and c), which was an indication of the restoration of the electronic
conjugation within the G sheets [41].
The activity of the graphene modified GCE and Pt-graphene
modified GCE towards electrochemical detection of hydroquinone
were investigated by differential pulse voltammetry (DPV). The
GCE exhibited a weak and broad peak at 0.09 V corresponding to
Fig. 2. TEM images of (a) graphene sheets and (b) Pt-graphene hybrid material, (c)
the size distribution of supported Pt nanoparticles.
Compared with graphite oxide, the C 1s XPS spectrum of
graphene at 286–289 eV corresponding to oxygenated carbon
showed a significant decrease (Fig. 4a), confirming that most of the
epoxide, hydroxyl, and carboxyl functional groups were success-
fully removed through the reduction process. This observation was
in agreement with that found in previous studies [27,31]. Fig. 4b
represented the XPS signature of the Pt 4f doublet (4f7/2 and 4f5/2
)
for the Pt nanoparticles supported on graphene sheets. The Pt 4f7/2
and Pt 4f5/2 peaks appeared at 70.1 eV and 73.35 eV, respectively,
which shifted remarkably to the lower binding energy compared
with the standard binding energy of Pt 4f7/2 and Pt 4f5/2 for Pt0
state (70.83 eV and 74.23 eV) [37] due to the electron transfer from
the graphene sheet to Pt nanoparticles. Because the work func-
tion of graphene (4.48 eV) [38] is smaller than that of Pt (5.65 eV)
[39], electron transfer from the graphene sheets to Pt nanoparticles
would occurred during the formation of the Pt-graphene hybrid
structures.
Fig. 4. (a) C 1s XPS spectra of graphite oxide and graphene, and (b) Pt 4f spectra of
Pt-graphene.

J. Li et al. / Electrochimica Acta 56 (2011) 2712–2716
2715
the effective charge migration through the graphene. The effec-
tive transport of the electrons to the electrode in the Pt-graphene
matrix led to the efficient electrocatalytic oxidation of hydro-
quinone. We can observe in Fig. 6B and C that the peak current
increased with the increase of the hydroquinone concentration
(from the curve a to f). It could be seen from the curve a
in Fig. 6D that the current at graphene modified GCE linearly
increased with the increase of the concentration of hydroquinone
over the 20–115 ␮M range with sensitivity of 1.38 ␮A ␮M−1 cm−2
;
and the detection limit was estimated to be 12 ␮M (S/N = 3).
For Pt-graphene modified GCE (the curve b in Fig. 6D), a lin-
ear detection range was from 20 ␮M to 145 ␮M with sensitivity
of 3.56 ␮A ␮M−1 cm−2, the detection limit 6 ␮M (S/N = 3). Addi-
tionally, the current intensity at the Pt-graphene modified GCE
was higher than that at the graphene modified GCE in the whole
concentration range. These results indicated that the Pt-graphene
modified GCE showed higher current intensity, lower detection
limit, and higher sensitivity towards electrochemical detection of
hydroquinone compared with the pure graphene modified GCE,
possibly due to the enhanced electron transfer in the Pt-graphene
hybrid system.
The applicability of the graphene modified GCE to the selective
detection of hydroquinone in the presence of phenol was stud-
ied using DPV. Phenol and hydroquinone showed respectively an
oxidation peak at 0.218 eV (Fig. 7a) and 0.002 eV (Fig. 7b). For a
mixed solution of 0.15 mM hydroquinone and 10 mM phenol, there
were two well-distinguished peaks at the potential of 0.002 eV
and 0.218 eV, corresponding to the oxidation of hydroquinone and
phenol, respectively (Fig. 7c), indicating that hydroquinone can be
selectively detected in the presence of large concentration of phe-
nol.
Fig. 5. UV–vis absorption spectra of (a) graphene oxide, (b) graphene, and (c) Pt-
graphene hybrid material.
the oxidation of hydroquinone (curve a in Fig. 6A). The graphene-
modified GCE displayed a well-defined peak at 0.002 V with a
much higher current intensity as compared with the GCE (the
curve b in Fig. 6A), indicating the enhanced electrocatalytic activ-
ity towards hydroquinone, which could be due to the unique
properties of graphene that increased the active surface area of
the electrode and accelerated the electron transfer via improved
conductivity and the good affinity of graphene to hydroquinone.
When Pt nanoparticles were combined with graphene, the cur-
rent density further increased, maybe due to the enhanced electron
transfer in Pt-graphene hybrid system, which was attributed to
the charge hopping through the metallic Pt nanoparticles and
Fig. 6. DPV obtained at GCE (a), graphene modified GCE (b), and Pt-graphene modified GCE (c), using 115 ␮M hydroquinone in 0.05 M (pH 7.4) phosphate buffer solution
(A). DPV obtained at graphene modified GCE (B) and Pt-graphene modified GCE (C) with various concentration of hydroquinone: (a) 20 ␮M, (b) 29 ␮M, (c) 65 ␮M, (d) 83 ␮M,
(e) 115 ␮M and (f) 145 ␮M in 0.05 M (pH 7.4) phosphate buffer. DPV conditions: pulse amplitude = 0.05 V, sample width = 0.0167 s, pulse width = 0.15 s, pulse period = 0.4 s,
and quiet time = 2 s. (D) Calibration plots of background subtracted peak current at graphene modified GCE (a) and Pt-graphene modified GCE (b) versus the concentration
of hydroquinone.

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In conclusion, we have synthesized graphene and Pt-graphene
hybrid material through a microwave-assisted chemical reduction
process. The resulting graphene and Pt-graphene hybrid materials
have been used for the electrochemical detection of hydroquinone.
Graphene modified GCE showed a good performance for detect-
ing hydroquinone due to the unique properties of graphene, which
increased the active surface area of electrode and accelerated the
electron transfer. Compared with the pure graphene modified GCE,
the electrocatalytic activity of the Pt-graphene hybrid material was
further improved possibly due to the enhanced electron transfer in
the Pt-graphene hybrid system.
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