Synthesis of Pt nanoparticle-loaded 1-aminopyrene functionalized reduced graphene oxide and its excellent electrocatalysis

Article abstract of DOI:10.1039/c3ra47107a

Pt nanoparticle (NP)-loaded 1-aminopyrene functionalized reduced graphene oxide composites (Pt/1-AP-rGO) were synthesized by a simple polyol process. The morphology and structure of the resulting composites were characterized by transmission electron microscopy, Raman spectroscopy and X-ray diffraction. In comparison with Pt/-rGO, the resulting Pt/1-AP-rGO exhibited much better dispersibility. Higher dispersion and smaller size of Pt NPs was also observed on 1-AP functionalized rGO. As a result, Pt/1-AP-rGO showed higher catalytic activity, better anti-poisoning ability and stability for methanol oxidation. Meanwhile, it also displayed better electrocatalytic performance toward H ₂O₂. The strategy presented here offers an efficient way for the preparation of high-performance electrocatalysts, which will find promising applications in biosensors and fuel cells. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3ra47107a

RSC Advances
View Article Online
View Journal | View Issue
COMMUNICATION
Synthesis of Pt nanoparticle-loaded 1-aminopyrene
functionalized reduced graphene oxide and its
excellent electrocatalysis
Cite this: RSC Adv., 2014, 4, 13733
Received 28th November 2013
Accepted 4th March 2014
*
Dong Liu, Lu Yang, Jian She Huang, Qiao Hui Guo and Tian Yan You
DOI: 10.1039/c3ra47107a
www.rsc.org/advances
Pt nanoparticle (NP)-loaded 1-aminopyrene functionalized reduced composites have been extensively explored in the eld of fuel
graphene oxide composites (Pt/1-AP–rGO) were synthesized by a cells and biosensors.18–21 Various state-of-the-art approaches,
simple polyol process. The morphology and structure of the resulting such as in situ growth,22 self-assembly23 and one-pot method,24
composites were characterized by transmission electron microscopy, have been developed for the preparation of graphene-supported
Raman spectroscopy and X-ray diffraction. In comparison with Pt/– NPs composites. Unfortunately, the easy aggregation of the
rGO, the resulting Pt/1-AP–rGO exhibited much better dispersibility. graphene sheets leads to the decrease of the effective surface
Higher dispersion and smaller size of Pt NPs was also observed on 1-AP area and eventually detrimental to the electrochemical appli-
functionalized rGO. As a result, Pt/1-AP–rGO showed higher catalytic cations.25 To address this issue, an effective strategy is by
activity, better anti-poisoning ability and stability for methanol oxida- covalent or non-covalent attaching certain molecule onto gra-
tion. Meanwhile, it also displayed better electrocatalytic performance phene surface.26 Even more important, the attached molecules
toward H2O2. The strategy presented here offers an efficient way for with suitable groups, such as amino group, could also serve as
the preparation of high-performance electrocatalysts, which will find nucleating sites of the NPs.27 Non-covalent functionalization of
promising applications in biosensors and fuel cells.
graphene with aromatic molecule takes the advantages of
simple decoration process and well-maintained intrinsic elec-
tronic properties of graphene. Pyrenecarboxylic acid, perylene
tetracarboxylic acid and pyrenesulfonic acid sodium salt-func-
tionalized graphene showed improved dispersibility and excel-
lent electrochemical performance.28–31
1-aminopyrene (1-AP) could be a suitable molecule for the
functionalization of graphene which contains both benzene
ring structure and amino group.32,33 In this work, we utilized
1-AP as the non-covalent functional reagent to prepare Pt
NPs-loaded reduced graphene oxide (rGO) composites.
Results demonstrate that Pt NPs supported on 1-AP func-
tionalized rGO showed better dispersity and smaller size
than that on rGO. The resulting composites exhibited high
electrocatalytic activities towards methanol oxidation and
H2O2 reduction.
Introduction
Due to their unique structure and composition, nanoparticles
have shown excellent optical, electrical and catalytic properties
in various elds.1–5 For instance, Pt nanoparticle based catalysts
are the most used electrocatalysts in fuel cells.6–9 Previous
investigations demonstrate that effectively controlling the size
and dispersion of Pt NPs is a prerequisite for high catalytic
performance. What's more, loading of Pt NPs on the surface of
catalyst support is another way to improve the catalytic perfor-
mance of Pt NPs.10–12 In fact, nding suitable catalyst support is
crucially important for the construction of biosensors and fuel
cells.13 The desirable catalyst support should possess large
specic surface area for the efficient dispersion of catalyst NPs,
high electrical conductivity for promotion the fast electron
transfer and excellent chemical stability for maintaining the
stable catalyst structure.14
Experimental
Materials and apparatus
Recently, due to various intriguing properties, graphene has
emerged as one of the most promising catalyst support.15–17 In
particular, graphene-supported Pt and PtM (M ¼ Pd, Fe etc.) NPs
Graphite ake, Platinum tetrachloride (PtCl4) and 1-amino-
pyrene (1-AP) were purchased from Aldrich. Methanol, ethylene
glycol (EG), dimethyl formamide (DMF) and H2O2 (30%) were
obtained from Beijing Co. (China). Chloroplatinic acid
(H2PtCl6) solution was obtained from the PtCl4 dissolved in
hydrochloric acid. All chemicals were used as received.
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China. E-mail:
youty@ciac.jl.cn
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 13733–13737 | 13733

View Article Online
RSC Advances
Communication
UV-Vis analysis was performed with a UV-3000PC spectro-
photometer. Particle size and morphology were obtained on
transmission electron microscope (TEM, HITACHI H-8100 EM).
X-ray diffraction (XRD) patterns were acquired using a D8
ADVANCE X-ray diffractometer (Bruker AXS, Germany) with Cu
Results and discussion
The Pt/1-AP–rGO composite was synthesized via a simple polyol
process (Scheme 1). Firstly, 1-AP was non-covalently assembled
onto GO surface via p–p interaction between the pyrenyl groups
of 1-AP and graphene sheets. The amino groups of 1-AP became
weakly positive charged when the solution was adjusted to acid
condition (pH ¼ 6.0). Such an acid condition fairly facilitated
the self-assembly of negatively charged PtCl62ꢁ, forming a
uniform dispersion of Pt precursor on the surface of GO.
˚
Ka radiation (l ¼ 1.54056 A). Raman spectra were recorded on a
Renishaw Raman microscope (model RM2000) with laser exci-
tation wavelength of 514.5 nm. Pt-loading in the composites
was determined by inductively coupled plasma optical emission
spectroscopy (ICP-OES, Thermo Fisher).
2ꢁ
Finally, 1-AP–GO and PtCl6 were reduced simultaneously by
ethylene glycol, obtaining the highly dispersed Pt nanoparticle-
loaded rGO. The inset image of Fig. 1A shows the photographs
of Pt/rGO and Pt/1-AP–rGO dispersed in ethylene glycol. Obvi-
ously, Pt/1-AP–rGO can be well dispersed in ethylene glycol,
while Pt/rGO forms precipitate and oating particles. Thus, the
presence of 1-AP could effectively avoid the aggregation of rGO.
UV/visible spectra were used to conrm the successful non-
covalent binding of 1-AP. As shown in Fig. 1A, Pt/rGO shows a
typical featureless spectrum (curve c). The two additional peaks
around 355 and 281 nm observed in the spectrum of Pt/1-AP–
rGO could be ascribed to the characteristic peaks of 1-AP at 360
and 285 nm (curve a), suggesting that rGO has been successfully
functionalized by 1-AP.32
Raman spectroscopy is an effective method to distinguish
the ordered and disordered structure of carbon in carbonaceous
materials. The Raman spectrum of GO, Pt/rGO and Pt/1-AP–rGO
are shown in Fig. 1B. Two prominent scattering peaks located at
1350 and 1595 cmꢁ1 can be assigned to the E2g phonon of sp2
carbon atoms (D-band) and breathing mode of k-point phonons
of A1g symmetry (G-band), respectively. The intensity ratio of D
to G band (ID/IG) could be used to evaluate the degree of
modication or defects of rGO. In this work, the ID/IG value of
GO, Pt–rGO and Pt/1-AP–rGO is 0.97, 1.13 and 1.06. The
increased ID/IG value when GO was reduced to rGO reveals a
decrease in the average size of sp2 domains in rGO compared
with GO.35 However, the ID/IG values decrease slightly for 1-AP–
Synthesis of graphite oxide
Graphite oxide was synthesized according to modied Humm-
er's method.34 Briey, graphite akes (1 g) was added into a
mixture of concentrated H2SO4 (15 mL), K2S2O8 (5 g), and P2O5
(5 g). Then, the solution was kept at 80 ꢀC for 6 hours. Aer
cooling to room temperature, the mixture was diluted with
double distilled water, ltered, and washed until the pH of the
rinse water was about 6.5. Thereaer, the as-treated graphite
ꢀ
was added to a mixture of cold (0 C) concentrated H2SO4 (23
mL) and NaNO3 (0.5 g). Subsequently, 3 g of KMnO4 was added
slowly with violent agitation. Then the solution was stirred at 40
ꢀC for 2 h, the reaction was kept for 15 min aer adding double
distilled water (46 mL). Finally, 140 mL water and 10 mL 30%
H2O2 was added to terminate the reaction, followed by washing
and ltration.
Synthesis of Pt/1-AP–rGO
As a typical procedure to synthesize the Pt/1-AP–rGO, 5 mg
graphite oxide was dispersed in 10 mL ethanol by ultrasonic
treatment for 60 min (200 W). Subsequently, 5 mg 1-AP was
added with stirring at room temperature for 12 h. The obtained
ꢀ
solution was centrifuged and dried at 60 C and denoted as 1-
AP–GO. Then, 5 mg 1-AP–GO and 65 mL H2PtCl6 solution (100
mM) were dispersed in 10 mL ethylene glycol solution. The pH
value of the solution was adjusted to 6.0 with 1.0 M KOH
aqueous solution. Thereaer, the above dispersion was trans-
ꢀ
ferred into a 50 mL three-necked bottle and reuxed at 130 C
for 6 h. Finally, the blended solution was washed with ethanol
and dried in vacuum at 80 ꢀC overnight, obtaining Pt/1-AP–rGO.
Similarly, Pt/rGO composite was prepared with the same
procedure without the use of 1-AP.
Electrode modication and electrochemical measurements
Prior to the modication, glassy carbon electrode (GCE) was
polished with alumina slurry and cleaned by ultrasonic. 2 mL
well-dispersed Pt/1-AP–rGO suspensions (1.0 mg mLꢁ1
)
was dropped onto GCE and dried at room temperature.
Then mL 0.5% naon solution was covered on the
1
modied electrode. For comparison, Pt/rGO modied GCE
(Pt/rGO–GCE) was prepared with the same procedure. Elec-
trochemical measurements were performed on a CHI 832
electrochemical workstation (China). Ag/AgCl/(sat. KCl)
and platinum wire were used as reference and auxiliary
electrodes, respectively.
Scheme 1 Schematic illustration of the synthetic process of Pt/1-
AP–rGO.
13734 | RSC Adv., 2014, 4, 13733–13737
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
RSC Advances
Fig. 1 UV-visible spectra of (a) 1-AP, (b) Pt/1-AP–rGO and (c) Pt/rGO
in ethanol. Inset: photographs of (1) Pt/rGO and (2) Pt/1-AP–rGO in
ethylene glycol. Raman spectra of GO, Pt/rGO and Pt/1-AP–rGO.
Fig. 3 XRD patterns of Pt/rGO and Pt/1-AP–rGO. Inset image is the
XRD pattern of GO.
rGO compared with rGO, which could be attributed to the
coverage of the defect sites on rGO by 1-AP.33
Fig. 2A and B displays the TEM images of Pt/rGO and Pt/1-
AP–rGO. Obviously, Pt NPs on 1-AP functioned rGO exhibit a
better dispersion than that on pristine rGO. In fact, Pt/1-AP–rGO
possessed smaller Pt size (3.3 nm) than Pt/rGO (4.8 nm) with a
narrower size distribution. This result demonstrates that the
presence of 1-AP on GO may provide more effective active sites
for the nucleation of Pt NPs and benet the achievement of Pt
NPs with small size. Moreover, the aromatic group in 1-AP could
also prevent the aggregation of rGO, leading to larger surface
area and more active sites for the loading of Pt NPs.
Fig. 4 (A) CVs of Pt/rGO (black line) and Pt/1-AP–rGO (red line)
modified GCE in 0.5 M H2SO4; (B) CVs and the modified electrodes in
1.0 M KOH containing 1.0 M CH3OH. Scan rate: 50 mV sꢁ1
.
XRD patterns of GO, Pt/rGO and Pt/1-AP–rGO are shown in
Fig. 3. The sharp diffraction peak at 2q ¼ 10.8ꢀ corresponds to
the interlayer spacing of 0.87 nm for GO. However, a new wide
diffraction peak appeared at 2q ¼ 25.1ꢀ for Pt/rGO and Pt/1-AP–
rGO, conrming the successful reduction of GO to rGO. The
three diffraction peaks located at 2q ¼ 39.5ꢀ, 45.8ꢀ and 67.4ꢀ
could be indexed to the (111), (200) and (220) planes of face-
centered cubic Pt crystals. Moreover, the broader diffraction
peaks of Pt/1-AP–rGO suggest smaller size of Pt NPs on 1-AP–
rGO than that on rGO, which is consistent with the TEM results.
Fig. 4A shows the cyclic voltammograms (CVs) of Pt/1-AP–
rGO–GCE and Pt/rGO–GCE in 0.5 M H2SO4. Both electrodes
exhibit the typical characteristics of hydrogen adsorption and
desorption behavior on platinum, conrming the successful
loading of Pt NPs on rGO. The electrochemical active surface
area (ECSA) is an important data to evaluate the number of the
available catalytic active sites, and are estimated from hydrogen
desorption peaks from ꢁ0.2 to 0.2 V. In this work, ECSA for Pt/1-
AP–rGO and Pt/rGO are calculated to be 35.1 and 25.2 m2 gꢁ1
respectively. The increased ECSA of Pt/1-AP–rGO compared with
Pt/rGO may originate from the smaller size of Pt NPs. We
suppose that the improved dispersibility of Pt/1-AP–rGO also
contribute to the increased ECSA.
,
The electrocatalytic activity of the as-prepared Pt/1-AP–rGO
was rstly evaluated by investigating for methanol oxidation.
Fig. 4B shows the typical CVs of methanol oxidation at Pt/1-AP–
rGO–GCE and Pt/rGO–GCE, respectively. Both electrode present
the typical CVs of methanol oxidation in alkaline condition,
with a forward anodic peak current density (jf) which is attrib-
uted to the oxidation of methanol to CO2 and Pt adsorbed
carbonaceous intermediates, as well as a back anodic peak
current (jb) originating from the additional oxidation of carbo-
naceous intermediates species to CO2. The CVs of Pt/1-AP–rGO
displays a jf of 814 mA mgꢁ1 at ꢁ0.208 V in the forward scan,
which is 2.1-fold higher than that of Pt/rGO (387 mA mgꢁ1),
indicating a higher electrocatalytic activity of Pt/1-AP–rGO. The
ratio of the jf to jb (jf/jb), is an important index of the catalyst
tolerance to poisoning species generated during methanol
oxidation. The calculated jf/jb of Pt/1-AP–rGO (3.39) is evidently
larger than that of Pt/rGO (2.74), suggesting better tolerance to
poisoning species. Furthermore, the jf/jb value for methanol
oxidation on Pt/1-AP–rGO is also higher than that on Pt–GCFM36
and Pt NPs@POM/CNT.37 The long-time stability of Pt/1-AP–rGO
towards methanol oxidation was examined by chro-
noamperometry at ꢁ0.2 V (not shown here). The results show
Fig. 2 TEM images of Pt/rGO (A) and Pt/1-AP–rGO (B). Insets are the
corresponding Pt NPs size distribution.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 13733–13737 | 13735

View Article Online
RSC Advances
Communication
facile approach could be extended to the preparation of other
NPs-loaded rGO composites.
Acknowledgements
We are grateful for the nancial support from the National
Natural Science Foundation of China (no. 21222505).
Notes and references
Fig. 5 (A) CVs of modified electrode in 0.2 mM PBS (pH ¼ 7.0) with 5
mM H2O2 at a scan rate of 50 mV sꢁ1 (B) I–t curves of the modified
electrode for successive injection of 1 mM H2O2 at ꢁ0.1 V, inset:
calibration curves between amperometric current and concentration
of H2O2 (black line: Pt/rGO–GCE, red line: Pt/1-AP–rGO–GCE).
1 X. W. Zhou, R. H. Zhang, Z. Y. Zhou and S. G. Sun, J. Power
Sources, 2011, 196, 5844.
2 X. W. Zhou, Y. L. Gan, Z. X. Dai and R. H. Zhang,
J. Electroanal. Chem., 2012, 685, 97.
3 H. T. Li, Z. H. Kang, Y. Liu and S. T. Lee, J. Mater. Chem.,
2012, 22, 24230.
4 P. V. Kumar, N. M. Bardhan, S. Tongay, J. Q. Wu,
A. M. Belcher and J. C. Grossman, Nat. Chem., 2014, 6, 151.
that the current decreased rapidly at the rst few minutes and
then reached a steady state current. The current density of Pt/1-
AP–rGO remains 37.1%, while 25.1% for Pt/rGO aer 7200 s
continuous testing. The results above demonstrate that
Pt/1-AP–rGO possesses superior electrocatalytic activity, anti-
poisoning ability and good stability for methanol oxidation in
comparison with Pt/rGO.
´
5 C. Lavorato, A. Primo, R. Molinari and H. Garcıa, ACS Catal.,
2014, 4, 497.
6 Y. J. Kuang, B. H. Wu, Y. Cui, Y. M. Yu, X. H. Zhang and
J. H. Chen, Electrochim. Acta, 2011, 56, 8645.
7 M. S. Ahmed, D. Kim and S. Jeon, Electrochim. Acta, 2013, 92,
168.
8 K. Ji, G. Chang, M. Oyama, X. Z. Shang, X. Liu and Y. B. He,
Electrochim. Acta, 2012, 85, 84.
9 X. J. Bo and L. P. Guo, Electrochim. Acta, 2013, 90, 283–290.
10 R. Lv, T. X. Cui, M. S. Jun, Q. Zhang, A. Y. Cao, D. S. Su,
Z. J. Zhang, S. H. Yoon, J. Miyawaki, I. Mochida and
F. Y. Kang, Adv. Funct. Mater., 2011, 21, 999.
11 Z. Y. Ji, X. P. Shen, G. X. Zhu, K. M. Chen, G. H. Fu and
L. Tong, J. Electroanal. Chem., 2012, 682, 95.
12 J. Yang, C. G. Tian, L. Wang and H. G. Fu, J. Mater. Chem.,
2011, 21, 3384.
We further studied the electrocatalytic activity of Pt/1-AP–
rGO towards H2O2 reduction. Fig. 5A shows the CVs of Pt/1-AP–
rGO–GCE and Pt/rGO–GCE in PBS (pH ¼ 7.0) with 5 mM H2O2.
Both electrodes exhibit remarkable reduction peak at about 0 V,
while the reduction peak current at Pt/1-AP–rGO–GCE is
about 2-fold as that at Pt/rGO–GCE. I–t curves of Pt/1-AP–rGO–
GCE and Pt/rGO–GCE were obtained by successive injection of
H2O2 at the potential of ꢁ0.1 V as shown in Fig. 5B. Pt/1-AP–
rGO–GCE displays fast response to H2O2, and could reach
95% of the steady-state current in 2 s. The corresponding
calibration curves (inset of Fig. 5B) reveal that Pt/1-AP–rGO
exhibits higher sensitivity (3.47 mA mMꢁ1
) than Pt/rGO
(1.83 mA mMꢁ1). Although the Pt/1-AP–rGO–GCE does not
exhibit wide linear range toward H2O2 as that for biosensors
based on spherical porous Pd nanoparticle assemblies38 and
Au–graphene–HRP–chitosan biocomposites,39 it shows rela-
tively fast response to H2O2.
13 S. D. Yang, C. M. Shen, Y. Y. Liang, H. Tong, W. He, X. Z. Shi,
X. G. Zhang and H. J. Gao, Nanoscale, 2011, 3, 3277.
14 E. Antolini, Appl. Catal., B, 2009, 88, 1.
15 E. J. Lim, S. M. Choi, M. H. Seo, Y. Kim, S. Lee and W. B. Kim,
Electrochem. Commun., 2013, 28, 100.
16 R. Liu, H. H. Zhou, J. Liu, Y. Yao, Z. Y. Huang, C. P. Fu and
Y. F. Kuang, Electrochem. Commun., 2013, 26, 63.
17 G. B. Zhu, P. B. Gai, L. Wu, J. H. Zhang, X. H. Zhang and
J. H. Chen, Chem.–Asian J., 2012, 7, 732.
18 S. Park, Y. Y. Shao, H. Y. Wan, P. C. Rieke, V. V. Viswanathan,
S. A. Towne, L. V. Saraf, J. Liu, Y. H. Lin and Y. Wang,
Electrochem. Commun., 2011, 13, 258.
The enhanced electrocatalytic performance can be ascribed
to following factors: the larger ECSA of Pt/1-AP–rGO provide
more active sites for the reduction of H2O2; Pt/1-AP–rGO can
easily form a uniform lm on the GCE surface, which could
facilitate the diffusion of H2O2 and increase the response
sensitivity, while Pt/rGO shows inhomogeneous aggregations
on the GCE surface.
19 H. Q. Ji, M. G. Li, Y. L. Wang and F. Gao, Electrochem.
Commun., 2012, 24, 7.
20 S. Nandini, S. Nalini, R. Manjunatha, S. Shanmugam,
J. S. Melo and G. S. Suresh, J. Electroanal. Chem., 2012, 689,
232.
Conclusions
We developed a simple but efficient polyol process for the
preparation of Pt-loaded 1-AP–rGO composites. Characteriza-
tions demonstrate that Pt NPs exhibited smaller size and better 21 H. Zhang, X. Q. Xu, Y. J. Yin, P. Wu and C. X. Cai,
dispersion on the 1-AP functioned rGO in comparison with that
J. Electroanal. Chem., 2013, 690, 19.
on rGO. The as-prepared Pt/1-AP–rGO exhibited higher elec- 22 A. N. Cao, Z. Liu, S. S. Chu, M. H. Wu, Z. M. Ye, Z. W. Cai,
trocatalytic activities towards methanol oxidation and H2O2
reduction than Pt/rGO. Our work provides a novel nanomaterial
Y. L. Chang, S. F. Wang, Q. H. Gong and Y. F. Liu, Adv.
Mater., 2010, 22, 103.
as high-performance platform for fuel cells and biosensor. This 23 W. Ren, Y. X. Fang and E. K. Wang, ACS Nano, 2011, 5, 6425.
13736 | RSC Adv., 2014, 4, 13733–13737
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
RSC Advances
24 Y. M. Li, L. H. Tang and J. H. Li, Electrochem. Commun., 2009, 32 S. Y. Wang, X. Wang and S. P. Jiang, Langmuir, 2008, 24,
11, 846. 10505.
25 H. Liu, J. Gao, M. Q. Xue, N. Zhu, M. N. Zhang and T. B. Cao, 33 Z. Lin, L. W. Ji, W. E. Krause and X. W. Zhang, J. Power
Langmuir, 2009, 25, 12006. Sources, 2010, 195, 5520.
26 X. Yang, M. S. Xu, W. M. Qiu, X. Q. Chen, M. Deng, 34 N. I. Kovtyukhova, P. J. Ollivier, B. R. Martin, T. E. Mallouk,
J. L. Zhang, H. D. Iwai, E. Watanabe and H. Z. Chen,
J. Mater. Chem., 2011, 21, 8096.
S. A. Chizhik, E. V. Buzaneva and A. D. Gorchinskiy, Chem.
Mater., 1999, 11, 771.
27 J. B. Liu, S. H. Fu, B. Yuan, Y. L. Li and Z. X. Deng, J. Am. 35 S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas,
Chem. Soc., 2010, 132, 7279.
28 D. Parviz, S. Das, H. S. T. Ahmed, F. Irin, S. Bhattacharia and
M. J. Green, ACS Nano, 2012, 6, 8857.
29 J. H. Jang, D. Rangappa, Y. U. Kwonc and I. Honma, J. Mater.
Chem., 2011, 21, 3462.
30 X. H. An, T. Simmons, R. Shah, C. Wolfe, K. M. Lewis,
A. Kleinhammes, Y. Y. Jia, Y. Wu, S. T. Nguyen and
R. S. Ruoff, Carbon, 2007, 45, 1558.
36 Y. Z. Chang, G. Y. Han, M. Y. Li and F. Gao, Carbon, 2011, 49,
5158.
37 S. W. Li, X. L. Yu, G. J. Zhang, Y. Ma and J. N. Yao, Carbon,
2011, 49, 1906.
M. Washington, S. K. Nayak, S. Talapatra and S. Kar, Nano 38 M. Han, S. L. Liu, J. C. Bao and Z. H. Dai, Biosens.
Lett., 2010, 10, 4295. Bioelectron., 2012, 31, 151.
31 F. H. Li, H. F. Yang, C. S. Shan, Q. X. Zhang, D. X. Han, 39 K. F. Zhou, Y. H. Zhu, X. L. Yang, J. Luo, C. Z. Li and
A. Ivaskab and L. Niu, J. Mater. Chem., 2009, 19, 4022.
S. R. Luan, Electrochim. Acta, 2012, 55, 3055.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 13733–13737 | 13737