Efficiently Converting CO2 into C2H4 using a Porphyrin-Graphene Composite Photocatalyst

Article abstract of DOI:10.1071/CH15141

In this work, a photocatalyst consisting of porphyrin and graphene was designed to reduce CO2 to hydrocarbons under visible light. This catalyst can (1) effectively reduce CO2 to hydrocarbons, particularly to C2H4; (2) selectively control the photogenerated electrons transfer path due to the physico-chemical properties of porphyrin and graphene; and (3) reduce the complexity of investigating this photocatalytic process because the photocatalyst has fewer defects, thus preventing the introduction of interference factors.

Full text of DOI:10.1071/CH15141

CSIRO PUBLISHING
Aust. J. Chem. 2016, 69, 27–32
Full Paper
http://dx.doi.org/10.1071/CH15141
Efficiently Converting CO2 into C2H4 using a
Porphyrin–Graphene Composite Photocatalyst
A
A
A
A B
,
Meihua Piao, Nan Liu, Yanshu Wang, and Chunsheng Feng
A
Department of Anesthesiology, First Hospital of Jilin University, Jilin University,
Changchun 130023, China.
B
Corresponding author. Email: csfeng@jlu.edu.cn
In this work, a photocatalyst consisting of porphyrin and graphene was designed to reduce CO2 to hydrocarbons under
visible light. This catalyst can (1) effectively reduce CO2 to hydrocarbons, particularly to C2H4; (2) selectively control the
photogenerated electrons transfer path due to the physico-chemical properties of porphyrin and graphene; and (3) reduce
the complexity of investigating this photocatalytic process because the photocatalyst has fewer defects, thus preventing the
introduction of interference factors.
Manuscript received: 24 March 2015.
Manuscript accepted: 28 May 2015.
Published online: 26 June 2015.
generated in small amounts,[23–25] and hence were not investi-
gated thoroughly. And reports on directly converting CO2 to
multi-carbon compounds by photocatalytic process are still
scarce.[8] This subject has not gained much attention.
Introduction
Currently, energy and environment are two subjects of consid-
erable importance worldwide. In the past several decades, the
level of carbon dioxide in the atmosphere has risen significantly
owing to the combustion of hydrocarbon fuels. Accordingly, the
shortage of hydrocarbon fuels will be an inevitable problem in
the near future. Artificial photosynthesis, a solar energy-based
technology, for recycling carbon dioxide into a readily trans-
portable hydrocarbon fuel, would help to reduce atmospheric
CO2 levels and partly fulfil energy demands within the present
hydrocarbon-based fuel infrastructure.[1] Moreover, artificial
synthesis, using photoenergy is a compelling approach to drive
the conversion of methane and other single-carbon compounds
into more valuable molecules at room temperature.[2,3] For this
reason, through suitable conversion, single-carbon carbohy-
drates may be used as substitutes for the dwindling petroleum
resources as chemical feedstock. Therefore, much effort has
been devoted to convert single-carbon carbohydrates into multi-
carbon compounds under mild conditions.[4–7] As a conse-
quence, converting CO2 into multi-carbon compounds by pho-
tocatalytic methods will be of considerable importance,
whereby the two processes, i.e. reducing CO2 to one carbon
compound and the subsequent reduction to multi-carbon com-
pounds, are combined.[8]
Research on CO2 conversion by photocatalytic method has
progressed quickly in recent years. And various photocatalysts
have been developed and trialled to achieve high conversion
rates and selectivity such as organic compounds and transition
metal coordination compounds,[9–11] semiconductors,[12–18]
metal–organic frameworks,[19] perovskite-structured com-
pounds,[20] and hybrid photocatalysts.[21,22] However, the pro-
ducts obtained from the photo-conversion process were mainly
CH4, CO, CH3OH, and some other single-carbon molecules. In
former research, even though multi-carbon compounds were
detected in the products, they were only reported as by-products
In this work, a novel photocatalytic system based on a
porphyrin and graphene composite presented high efficiency
of hydrocarbon conversion; not only was a higher conversion
rate of CH4 attained, but also the conversion of CO2 to ethylene
was possible under visible light irradiation. Considering that the
conversion of solar energy into chemical energy is becoming
the hot spot of future energy investigation, this work provides a
simple and promising path to fabricate multi-carbon chemicals
from CO2. Moreover, graphene plays a crucial role in this
composite material in facilitating conversion from CO2 into
C2H4 that has also been thoroughly investigated.
Experimental
Preparation of Photocatalyst
The preparation of the graphene sheets (GS) was performed
according to the method by Wu et al.[8] The film was prepared
by an extremely convenient method involving mist spray. The
typical process was as follows: commercially available copper
tetra(hydroxyphenyl)porphyrin (CuTHPP, 65 mg) was dis-
solved in 1,2 dichloroethane (DCE; 100 mL) containing a sus-
pension of GS (0.2 mg mLꢀ1). Then, the dispersion was ejected
from a spray lance onto a solid substrate (quartz), driven by N2 at
a certain pressure, while the substrate was maintained at 1008C.
The prepared films were then placed in a vacuum drying
chamber at 1008C for 2 h to evaporate solvent molecules
adsorbed onto the photocatalyst. In addition, a control experi-
ment of porphyrin, in the absence of graphene, was carried out in
film form on a quartz substrate. The concentration of porphyrin,
size of substrate, and the method employed for film preparation
were the same as that used for the preparation of GS/CuTHPP.
Journal compilation Ó CSIRO 2016
www.publish.csiro.au/journals/ajc

28
M. Piao et al.
Electrochemical Measurement of Porphyrin
CuTHPP was modified on a glassy carbon electrode (GCE)
using acetone solution and dried at room temperature. A Pyrex
electrolytic cell was employed, filled with Ar-purged 0.5 M
Na2SO4 (20 mL). A Pt wire and Ag|AgCl electrode were
employed as the counter and reference electrodes, respectively.
Impedance measurements were recorded using a CHI660 elec-
trochemical workstation.
C2H4
CuTHPP
LUMO
eꢀ
CO2
eꢀ
eꢀ
eꢀ
ꢁ
Photocatalytic Measurement
H2O
A double-sided photocatalytic film with an appropriate area of
2 ꢁ 10 cm ꢁ 20 cm was introduced into a 1-L quartz chamber
equipped with valves for evacuation and gas feeding. Following
loading of the sample, the chamber was evacuated and sealed to
,10 mTorr using a mechanical pump. Carbon dioxide (CO2,
99.99 % pure) was forced to pass through a bubbler containing
deionized water before entering the reaction chamber. These
two processes of evacuation and CO2 pumping were repeated
thrice. The approximate excess pressure is less than 1.0 psi. All
CO2 conversion experiments were performed under irradiation
O2
Scheme 1. Transfer process of photogenerated electrons for CuTHPP/
graphene composite. Under illumination, the photoexcited electrons are
transferred from the porphyrin molecules passing through graphene sheets.
Due to the hydrophobicity of graphene, the transfer of electrons from
graphene to H2O molecules is difficult.
of a solar simulator. The light power density was 100 mW cmꢀ2
.
2.72 eV, as shown in Fig. 1b. To estimate the conduction band
potential (ECB), Mott–Schottky plot for CuTHPP was con-
structed under the condition of pH ¼ 7.0, as shown in Fig. 1a.
It can be seen that the slope of the plot was positive, thus
suggesting that CuTHPP is an n-type semiconductor. When
illuminated, the generated electrons are transferred from the
porphyrin molecules to graphene, while the holes remain in the
porphyrin because of the properties of these two materials
mentioned above. The ECB of CuTHPP was approximately
ꢀ0.74 V versus Ag|AgCl (ꢀ0.54 V versus NHE (normal hydro-
gen electrode)). According to the band gap and ECB of CuTHPP,
we can achieve the relationship between the energy bands of this
porphyrin and the energy levels of the redox couple, as clearly
seen in Fig. 1. In this case, theoretically, CO2 can be reduced to a
carbohydrate, and H2O can be oxidized to O2 using the present
photocatalyst.
Owing to the large number of defects in reduced graphite
oxide (RGO), the transfer of electrons will be greatly hindered,
and the defects will also lead to the introduction of some trap
levels in the band gap of graphene. These traps will result in a
difficulty in transferring electrons from the GS to the adsorbed
molecule for following reactions.[22] In consequence, the prep-
aration of graphene using conventional methods (graphite oxide
reduction) is not sufficiently effective. Therefore, the presence
of fewer defects and the higher conductivity of graphene are
desirable in this photocatalytic composite.
The equilibrium temperature of the samples was ,408C (ꢂ58C).
Although the experiments have also been conducted at lower
temperatures (,358C), no definite influence of temperature on
product formation rates has been found.
Results and Discussion
In order to construct an outstanding photocatalyst with high
selectivity, two types of special materials were used as shown in
Scheme 1. CuTHPP was chosen as the antenna (light exciter)
rather than inorganic materials because CuTHPP has a greater
ability to absorb light than inorganic materials. Compared with
inorganic catalyst materials, organic molecules possess rela-
tively simple light absorption suitable for investigating, with no
interference from the effect of surface state and impurity energy
levels. More importantly, organic molecules as catalysts do not
possess surface dangling bonds, which are otherwise abundant
on the surface of inorganic materials. Thus, the interaction
between porphyrin and reactants is simpler to control. All above
characteristics are beneficial to improve the selectivity of pho-
tocatalysts. Another important reason to choose such porphyrin
molecule as antenna is its excellent photostability.
Graphene was introduced into this photocatalyst system as a
charge transfer mediator for its high electrical conductivity and
tuneable band gap properties.[26–28] Moreover, graphene is an
outstandingCO2 absorberaccordingtoliteraturereports,ofwhich
the theoretical maximum uptake of CO2 is 37.93 wt-%.[29] After
combining these two components, under light irradiation, the
excited electrons would move from the antenna to the CO2
molecules while easily passing through the graphene component,
thus greatly enhancing the conversion rate effectively. Moreover,
the hydrophobic property of graphene allows the catalytic reac-
tion to proceed on the surface in a more controllable fashion
because H2O molecules are unable to accept photogenerated
chargesfromthegraphenesurface.Therefore, these twomaterials
werecombinedtorealize hydrocarbonphotogeneration, asshown
in Scheme 1.
After preparation, a series of characterizations were per-
formed to investigate the quality of the graphene sheets, as
shown in Fig. 2. The exfoliation state of the material was first
ascertained by scanning electron microscopy (SEM) measure-
ments (Fig. 2a). After exfoliation, the thickness of the flakes
decreased significantly when compared with that of graphite, as
clearly shown in the SEM image. Transmission electron micro-
scopy (TEM) was used to reveal the number of layers in the GS.
The high-resolution TEM image (Fig. 2b) shows that the
structure of GS consisted of a few layers.
The structure of graphene was further investigated by Raman
spectroscopy, as shown in Fig. 2c. The G band (,1580 cmꢀ1
)
In order to confirm whether this photocatalyst can reduce
CO2 into hydrocarbon, the energy level of this material was
investigated using the Mott–Schottky method and UV-visible
measurement technique (Fig. 1a, b). Through the UV-visible
measurements, the energy gap of CuTHPP was estimated as
and 2D band (,2700 cmꢀ1) were observed clearly in graphene,
and a weak peak for D band (,1350 cmꢀ1) was visible that is
attributed to edge effects.[30] However, the signal intensities of
the D peak are obviously different from that of the RGO reported

Artificial Photosynthesis
29
(b)
2.0
1.5
1.0
0.5
0
70 ꢂ 1012
60 ꢂ 1012
50 ꢂ 1012
40 ꢂ 1012
30 ꢂ 1012
20 ꢂ 1012
10 ꢂ 1012
0
(a)
CuTHPP
CuTHPP/G
G
CuTHPP
0.4
200
300
400
500
600
700
ꢀ1.0 ꢀ0.8 ꢀ0.6 ꢀ0.4 ꢀ0.2
0
0.2
Potential [V] vs. Ag|AgCl
Wavelength [nm]
Vacuum
E
ꢀ1.0
NHE
(c)
ꢀ3.5
ꢀ4.5
ꢀ5.5
ꢀ6.5
CuTHPP
CO2/HCOOH
CO2/HCHO
CO2/C2H4 ꢀ0.341 V
ꢀ0.61 V
ꢀ0.48 V
TiO2
CO2/CO ꢀ0.53 V
ꢀ0.54 V
2Hꢁ/H2
ꢀ0.42 V
CO2/CH4
ꢀ0.24 V
0
3.2 eV
H2O/O2 0.82 V
2.72 eV
1.0
2.0
H2O/H2O2 1.35 V
H2O/OH 2.32 V
pH 7.0
pH 7.0
Fig. 1. (a) Mott–Schottky plot for the conduction band of CuTHPP by investigating the relationship between impedance and potential change at a
fixed frequency in 0.5 M Na2SO4 at pH¼ 7.0. (b) UV-Visible measurements of the band gaps of CuTHPP, graphene (G), and their composite. (c) Band
potentials of CuTHPP (at pH¼ 7.0) in contact with the redox potential for H2O and CO2 reactions at pH¼ 7.0 with respect to NHE or vacuum.
G
2D
(c)
(a)
(e)
D
Graphene
2100
1200
1500
1800
2400
2700
3000
Raman shift [cmꢀ1
]
C 1s
(d)
1 µm
Carbon: 96.9 %
Oxygen: 3.1 %
(b)
Graphene
O 1s
1 µm
5 nm
0
200
400
600
800 282 284 286 288 290 292
Binding energy [eV]
Binding energy [eV]
Fig. 2. (a) SEM image of GS. (b) High-resolution TEM image of GS with few layers. (c) Raman spectrum (using a laser excitation wavelength of 514.5 nm) of
graphene on a SiO2 substrate. (d) XPS spectrum of GS confirming the presence of oxygen and carbon atoms and corresponding narrow XPS scan of C 1s.
(e) SEM image of GS/CuTHPP composite.
in the literature, thereby demonstrating that the exfoliation
process did not introduce significant amounts of additional
structural defects such as epoxides covalently bound to the basal
plane.[31] In the Raman spectrum, the 2D peak can be used to
ascertain the number of layers of the graphene sheets.[30] As
shown in Fig. 2c, the 2D band of the as-prepared graphene
shifted clearly to lower energies. Based on the peak profile
and position, the as-prepared graphene can be classified as a

30
M. Piao et al.
Control (heat in dark)
Control (in O2)
CH4
CH4
C2H4
C2H4
Control (in N2)
Time [s]
1.0
Control on CUTHPP
(a)
(b)
0
0.5
C2H4
1.5
2.0
(c)150
150
100
50
CH4
30
20
10
0
100
50
0
4
3
6
5
4
3
0
2
2
1
1
0
1
2
3
4
5
6
0
Time [h]
Fig. 3. (a) Plots of hydrocarbon generation as a function of time over porphyrin/G catalyst via gas–solid phase reduction method and associated control
experiments. (b) Hydrocarbon generation rate. (c) Activity stability measurements. The red closed markers represent CH4 generation, open markers stand for
C2H4 generation.
few-layer graphene (FLG) with a thickness corresponding to
5 layers.[30]
the UV component. Reaction products were analyzed using a
gas chromatograph equipped with a flame ionization (FI)
detector for the detection of hydrocarbons and a thermal
conductivity (TC) detector for the detection of hydrogen. Each
interval data is an average result obtained from the detection
measurements conducted thrice. Gas sample analysis of the
reaction products revealed that ethylene was predominant,
whereas methane was found in relatively lower concentrations.
Fig. 3 shows the yield and rate of hydrocarbons generation on
this composite photocatalyst. The production rates of ethylene
X-Ray photoelectron spectroscopy (XPS) was used to exam-
ine the chemical composition of the as-prepared graphene, as
shown in Fig. 2d. The oxygen content of the sample is 3.1 %. The
exfoliation process introduced only small amounts of oxygen,
resulting from the small cut sheets in the process. Nevertheless,
the as-prepared graphene had few defects compared with RGO.
This can be further confirmed from the C 1s XPS spectrum,
whereby only a single peak at ,284.5 eV, which is associated
with graphitic carbon, can be observed. Therefore, the result
indicted that graphene was prepared successfully by the exfoli-
ation method mentioned above.
The morphology of the as-prepared thin film photocatalysts
was examined by SEM and shown in Fig. 2e. As observed, the
nano-sized CuTHPP crystal grew on the graphene sheets,
resulting in a roughened surface, which indicated the integration
of the two components in the photocatalyst. Because of the large
size (50–100 mm) and wrinkle of GS, the composite sheets
cannot spread smoothly. Consequently, this film was uneven;
the thickness is not uniform and varies from 100 nm to 30 mm
(from the flat region to the crinkled region) based on the SEM
and optical microscopy analyses. This structure means that the
photogenerated electrons can be transferred from CuTHPP to
graphene efficiently. It is worth noting that after combining
CuTHPP with GS, the UV signal of CuTHPP did not shift (as
shown in Fig. 1b) that suggested that the intermolecular ordering
of porphyrin was the same as that of porphyrin without gra-
phene. Additionally, CuTHPP contains a large amount of
hydrophilic OH groups, which result in slight adsorption of
water onto the film. However, this hydrophilic property is not
inconsistent with the hypothesis mentioned above. Although the
OH groups of porphyrin make the film hydrophilic, the hydro-
phobic character of graphene remains unchanged. We hypothe-
sized that the hydrophobicity of graphene and hydrophilicity of
porphyrin could be used to achieve individual adsorption (water
or CO2) onto different components of the graphene–porphyrin
composite, consequently resulting in separated reactions via
different mechanisms.
(,23.17 mmol gꢀ1 hꢀ1) and methane (,14.94 mmol gꢀ1 hꢀ1
)
were obtained from the CuTHPP/graphene (CuTHPP/G) sam-
ple. In the most recent studies, nanoparticles have been primar-
ily employed as photocatalysts.[12,13,15,19,20,22] Compared with
our composite systems, porphyrin molecules were used as the
antenna; its high absorbance enhanced the conversion of CO2 to
a certain extent. The lifetime of photogenerated carriers can be
greatly increased by the low-defect graphene present in this
photocatalyst, thereby providing a large surface for capturing
abundant CO2 molecules. Consequently, this photocatalyst
presented excellent hydrocarbon generation owing to the syn-
ergistic effect of the two components. Regarding the overall
yield of hydrocarbon, our photocatalyst exhibited comparative
performance to noble metal co-loaded nanocatalysts
(,25 mmol gꢀ1 hꢀ1).[15] The absence of H2 signals indicated
that the amount of H2 evolved in this work was not significant
or non-existent. This result can be attributed to the hydrophopic
property of graphene, which hindered reduction of H2O.
Signals associated with some other potential products with
larger molecular weights, such as HCO2H, CH2O, and CH3OH,
may be neglected as they are probably difficult to form.
To confirm that the hydrocarbons were generated through
catalytic reaction rather than through organic decomposition of
the photocatalysts themselves, control experiments were per-
formed. The dark control experiment was conducted by heating
the catalysts at 508C in the presence of CO2, and hydrocarbons
were not detected after 8 h of reaction. The photocatalyst films
were also irradiated under an N2 atmosphere in the chamber for
8 h, and no hydrocarbons was detected either (as shown in
Fig. 3a). Similarly, as shown in the Fig. 3a, another control
experiment was carried out in H2O and O2 atmosphere. In this
case, no CH4 or C2H4 was detected, thereby confirming that the
The prepared photocatalyst was tested in an enclosed quartz
chamber with a Xenon lamp as the light source using a high-
pass filter with a ‘cut-on’ wavelength of 400 nm to remove

Artificial Photosynthesis
31
HO
H
O
O
C
C
O
O
•ꢀ
•ꢀ
CO2
ꢀ
O
ꢀ
C
•ꢀ
C
O
ꢀ
O
OH
O
HO
O
HO
HO
OH
OH
2eꢀ
2Hꢁ
C
C
C
C
C
C
ꢀ
O
HO
OH
HO
C
C
OH
•
O
O
C
C
C
C
O
O
2Hꢁ
ꢁ
ꢁ
HO
O
•
•
ꢁ
ꢁ
•
•
•
•
ꢃ
C
C
HO
C
C
OH
•
2eꢀ
O
OH
HO
2eꢀ
4Hꢁ
ꢀ
C
ꢀ
C
HC
2Hꢁ
CH
HO
O
C
C
OH
2Hꢁ
HO
OH
2Hꢁ
HO
HO
OH
CH CH
OH
OH
ꢁ
ꢁ
OH2
ꢁ
H2O
C
C
H
H
O
4eꢀ 2Hꢁ
2eꢀ
HC
CH
HC
CH
H
ꢁ
O
O
H
CH
HC
2Hꢁ
2eꢀ
ꢁ
HC
ꢁ
CH ꢁ
4eꢀ
HO
HC
2eꢀ
ꢀ
HC
CH ꢀ
CH
2Hꢁ
CH2
ꢁ
OH
2Hꢁ
2eꢀ
H2C
ꢁ
H2O
HO
HC
4Hꢁ
•
•
CH
H2C
CH2
ꢁ
OH
OH2
Fig. 4. Proposed mechanism of the photo-reduction of CO2 to C2H4 on graphene.
products were generated by the photocatalytic process. With the
aim of investigating the role of graphene in this photocatalytic
process, a control experiment was conducted involving
CuTHPP and no graphene (Fig. 3a). In this control experiment,
only CH4 was detected in trace amounts; C2H4 was not detected.
This result suggests that the generation of C2H4 was determined
by graphene in this composite system that can be likely ascribed
to the outstanding ability of graphene as an excellent electron
transfer mediator and adsorber for CO2. Furthermore, the
process was successively repeated for five times, and no obvious
decay in activity could be observed (Fig. 3c) that demonstrates
that the photocatalysts are stable.
electronic structure, which can be attached to the graphene
through p–p non-covalent bond and receive electrons continu-
ously. Under this circumstance, the potential of the transition
states can be greatly decreased, as well as the stability of the
intermediates.
Conclusion
In summary, due to the synergistic effect of porphyrin and
graphene, the as-prepared photocatalyst presented a high CO2
conversion rate and reaction selectivity of H2O and CO2 mole-
cules. In particular, C2H4 was produced in a remarkable amount
under visible light. Because the present porphyrin–graphene
composite as photocatalyst for converting CO2 into multi-
carbon compounds is a novel system, experimental trials
involving different porphyrins would benefit the enrichment of
the current developed system. Changing the central metallic ion
and grafting branch is expected to enhance the catalytic activity
and selectivity. Converting single-carbon inorganic compounds
into multi-carbon compounds via photocatalysis if of significant
The potential mechanism of the photocatalytic conversion of
CO2 into C2H4 over graphene can be deduced as illustrated in
Fig. 4. According to the mechanism of catalytic reduction of
CO2 on Cu surface,[32–34] the key step in the conversion of CO2
into bi-carbon compounds is the self-coupling of CH2Oꢃ radi-
ꢃ
cals, HCO2 radicals, CHOꢃ radical, COꢀ2 radical, or inter-
coupling of other radicals. As assumed by Wu et al.,[8] in the
reaction process, all the intermediates have a delocalized

32
M. Piao et al.
importance. To date, research in this area is scarce.[1,8,24] Thus,
this new method is expected to further progress in the use of new
materials to effectively convert solar energy into chemical
energy, and provides a new means to convert CO2 into chemi-
cals. It will add to the investigation on artificial photosynthesis,
and provide a potential means of solving the carbon emission
and energy shortage simultaneously.
[16] S. Asal, M. Saif, H. Hafez, S. Mozia, A. Heciak, D. Moszynski,
M. S. A. Abdel-Mottaleb, Int. J. Hydrogen Energy 2011, 36, 6529.
doi:10.1016/J.IJHYDENE.2011.02.066
[17] C. Zhao, A. Kroll, H. Zhao, Q. Zhang, Y. Li, Int. J. Hydrogen Energy
2012, 37, 9967. doi:10.1016/J.IJHYDENE.2012.04.003
[18] A. D. Handoko, J. Tang, Int. J. Hydrogen Energy 2013, 38, 13017.
doi:10.1016/J.IJHYDENE.2013.03.128
[19] C. Wang, Z. G. Xie, K. E. deKrafft, W. L. Lin, J. Am. Chem. Soc. 2011,
133, 13445. doi:10.1021/JA203564W
Acknowledgements
[20] K. Iizuka, T. Wato, Y. Miseki, K. Saito, A. Kudo, J. Am. Chem. Soc.
2011, 133, 20863. doi:10.1021/JA207586E
[21] P. D. Tran, L. H. Wong, J. Barber, J. S. C. Loo, Energy Environ. Sci.
Financial support from the National Natural Science Foundation of China
(Grant No. 81271215 ) is gratefully acknowledged.
2012, 5, 5902. doi:10.1039/C2EE02849B
[22] Y. T. Liang, B. K. Vijayan, K. A. Gray, M. C. Hersam, Nano Lett.
2011, 11, 2865. doi:10.1021/NL2012906
[23] M. Subrahmanyam, S. Kaneco, N. Alonso-Vante, Appl. Catal., B
References
[1] S. C. Roy, O. K. Varghese, M. Paulose, C. A. Grimes, ACS Nano
2010, 4, 1259. doi:10.1021/NN9015423
[2] L. Li, G. D. Li, C. Yan, X. Y. Mu, X. L. Pan, X. X. Zou, K. X. Wang,
J. S. Chen, Angew. Chem., Int. Ed. 2011, 50, 8299. doi:10.1002/ANIE.
201102320
[3] L. Li, Y. Y. Cai, G. D. Li, X. Y. Mu, K. X. Wang, J. S. Chen, Angew.
Chem., Int. Ed. 2012, 51, 4702. doi:10.1002/ANIE.201200045
[4] J. H. Lunsford, Catal. Today 2000, 63, 165. doi:10.1016/S0920-5861
(00)00456-9
[5] R. A. Periana, O. Mironov, D. Taube, G. Bhalla, C. J. Jones, Science
2003, 301, 814. doi:10.1126/SCIENCE.1086466
[6] A. Holmen, Catal. Today 2009, 142, 2. doi:10.1016/J.CATTOD.2009.
01.004
[7] R. Balasubramanian, S. M. Smith, S. Rawat, L. A. Yatsunyk, T. L.
Stemmler, A. C. Rosenzweig, Nature 2010, 465, 115. doi:10.1038/
NATURE08992
[8] T. S. Wu, L. Y. Zou, D. X. Han, F. H. Li, Q. X. Zhang, L. Niu, Green
Chem. 2014, 16, 2142. doi:10.1039/C3GC42454E
[9] A. J. Morris, G. J. Meyer, E. Fujita, Acc. Chem. Res. 2009, 42, 1983.
doi:10.1021/AR9001679
1999, 23, 169. doi:10.1016/S0926-3373(99)00079-X
[24] O. K. Varghese, M. Paulose, T. J. LaTempa, C. A. Grimes, Nano Lett.
2009, 9, 731. doi:10.1021/NL803258P
[25] X. J. Zhang, F. Han, B. Shi, S. Farsinezhad, G. P. Dechaine,
K. Shankar, Angew. Chem., Int. Ed. 2012, 51, 12732. doi:10.1002/
ANIE.201205619
[26] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V.
Dubonos, I. V. Grigorieva, A. A. Firsov, Science 2004, 306, 666.
doi:10.1126/SCIENCE.1102896
[27] M. Y. Han, B. Ozyilmaz, Y. B. Zhang, P. Kim, Phys. Rev. Lett. 2007,
98, 206805. doi:10.1103/PHYSREVLETT.98.206805
[28] Y. B. Zhang, T. T. Tang, C. Girit, Z. Hao, M. C. Martin, A. Zettl,
M. F. Crommie, Y. R. Shen, F. Wang, Nature 2009, 459, 820.
doi:10.1038/NATURE08105
[29] A. Ghosh, K. S. Subrahmanyam, K. S. Krishna, S. Datta,
A. Govindaraj, S. K. Pati, C. N. R. Rao, J. Phys. Chem. C 2008, 112,
15704. doi:10.1021/JP805802W
[30] A. C. Ferrari, J. C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri,
F. Mauri, S. Piscanec, D. Jiang, K. S. Novoselov, S. Roth, A. K. Geim,
Phys. Rev. Lett. 2006, 97, 187401. doi:10.1103/PHYSREVLETT.97.
187401
[10] M. Cokoja, C. Bruckmeier, B. Rieger, W. A. Herrmann, F. E. Kuhn,
Angew. Chem., Int. Ed. 2011, 50, 8510. doi:10.1002/ANIE.201102010
[11] H. Takeda, K. Koike, H. Inoue, O. Ishitani, J. Am. Chem. Soc. 2008,
130, 2023. doi:10.1021/JA077752E
[31] S. Stankovich, D. A. Dikin, G. H. B. Dommett, K. M. Kohlhaas, E. J.
Zimney, E. A. Stach, R. D. Piner, S. T. Nguyen, R. S. Ruoff, Nature
2006, 442, 282. doi:10.1038/NATURE04969
[12] E. E. Barton, D. M. Rampulla, A. B. Bocarsly, J. Am. Chem. Soc. 2008,
130, 6342. doi:10.1021/JA0776327
[32] H. Yano, F. Shirai, M. Nakayama, K. Ogura, J. Electroanal. Chem.
[13] S. C. Yan, S. X. Ouyang, J. Gao, M. Yang, J. Y. Feng, X. X. Fan, L. J.
Wan, Z. S. Li, J. H. Ye, Y. Zhou, Z. G. Zou, Angew. Chem., Int. Ed.
2010, 49, 6400. doi:10.1002/ANIE.201003270
[14] N. M. Dimitrijevic, B. K. Vijayan, O. G. Poluektov, T. Rajh, K. A.
Gray, H. Y. He, P. Zapol, J. Am. Chem. Soc. 2011, 133, 3964.
doi:10.1021/JA108791U
[15] Q. Liu, Y. Zhou, J. H. Kou, X. Y. Chen, Z. P. Tian, J. Gao, S. C. Yan,
Z. G. Zou, J. Am. Chem. Soc. 2010, 132, 14385. doi:10.1021/
JA1068596
2002, 519, 93. doi:10.1016/S0022-0728(01)00729-X
[33] A. A. Peterson, F. Abild-Pedersen, F. Studt, J. Rossmeisl, J. K.
Norskov, Energy Environ. Sci. 2010, 3, 1311. doi:10.1039/
C0EE00071J
[34] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ.
Sci. 2012, 5, 7050. doi:10.1039/C2EE21234J