Titanium Dioxide/Graphene Oxide Nanocomposites as Heterogeneous Catalysts for the Esterification of Benzoic Acid with Dimethyl Carbonate

Article abstract of DOI:10.1002/cplu.201500080

Graphene oxide (GO) was prepared by modified Hummers' method starting from commercially available graphite. Different amounts of titanium dioxide nanoparticles (TiO₂) were loaded on the sheets of GO to obtain titanium dioxide/graphene oxide (TiO₂/GO) nanocomposites. The as-synthesized 5wt% TiO₂/GO nanocomposite was characterized by UV/Vis spectroscopy, photoluminescence spectroscopy, FTIR, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy techniques. The catalytic activity of the 5wt% TiO₂/GO nanocomposite was evaluated in the esterification of benzoic acid using dimethyl carbonate (DMC) as a green methylating agent. Furthermore, the activity of this nanocomposite for the conversion of benzoic acid was higher than that of the parent GO, TiO₂, TiO₂/activated carbon, and TiO₂/graphite.

Full text of DOI:10.1002/cplu.201500080

DOI: 10.1002/cplu.201500080
Full Papers
Titanium Dioxide/Graphene Oxide Nanocomposites as
Heterogeneous Catalysts for the Esterification of Benzoic
Acid with Dimethyl Carbonate
Durairaj Santhakumar Ruby Josephine,[a] Balasubramanian Sakthivel,[b]
Kunjithapatham Sethuraman,*[a] and Amarajothi Dhakshinamoorthy*[b]
Dedicated to Prof. K. Pitchumani on the occasion of his 60th birthday
Graphene oxide (GO) was prepared by modified Hummers’
method starting from commercially available graphite. Differ-
ent amounts of titanium dioxide nanoparticles (TiO2) were
loaded on the sheets of GO to obtain titanium dioxide/gra-
phene oxide (TiO2/GO) nanocomposites. The as-synthesized
5 wt% TiO2/GO nanocomposite was characterized by UV/Vis
spectroscopy, photoluminescence spectroscopy, FTIR, powder
X-ray diffraction, scanning electron microscopy, transmission
electron microscopy, and atomic force microscopy techniques.
The catalytic activity of the 5 wt% TiO2/GO nanocomposite
was evaluated in the esterification of benzoic acid using di-
methyl carbonate (DMC) as a green methylating agent. Fur-
thermore, the activity of this nanocomposite for the conver-
sion of benzoic acid was higher than that of the parent GO,
TiO2, TiO2/activated carbon, and TiO2/graphite.
Introduction
Graphene has received considerable attention for the fabrica-
tion of graphene-containing inorganic composites due to its
unique electronic properties,[1] high transparency,[2] flexible
structure, and large specific surface area.[3] Graphene oxide[4]
(GO) is obtained by an extensive oxidation of graphene thus
resulting a graphene nanosheet with carboxylic acid, hydroxy,
and epoxy groups attached to the surface. On the other hand,
it has been observed that the oxidation of graphene could
cause structural distortion of graphene.[5] Furthermore, it has
been reported that decorating inorganic materials with modi-
fied graphene could enhance their electronic[6] and photocata-
lytic properties.[7] Recently, GO and related materials have been
reported as catalysts for many organic transformations, thus
contributing to the development of green and sustainable
chemical processes.[8–12]
ing TiO2 with a carbonaceous substance on the surface can
also induce visible-light-responsive activity.[18]
Methyl halides, dimethyl sulfate, and diazomethane are com-
monly employed reagents for methylation reactions.[19] The al-
kylation of a carboxylic acid to the corresponding methyl ester
is a fundamental transformation in organic chemistry.[20]
A
number of reports including microwave-mediated process-
es[21,22] and zeolite-based catalysts[23–25] have been developed
for the esterification reaction. Dimethyl carbonate[26] (DMC) is
one of the alternative reagents for the replacement of dimeth-
yl sulfate and methyl halides in the development of green
chemical processes for the methylation of aromatics.[27–29]
In recent years, TiO2/GO composites[30] have been used as
heterogeneous photocatalysts for the degradation of pollu-
tants including Methylene blue,[31] Methyl orange[32] and Rhod-
amine B.[33] In contrast, TiO2/GO nanocomposites have not
been used as heterogeneous catalysts for organic transforma-
tions. Hence, in the present study we wish to report that TiO2/
GO can be used as a heterogeneous catalyst for the esterifica-
tion of benzoic acid with DMC as a green methylation reagent.
Also, we wish to compare the activity of TiO2/GO with that of
bare TiO2 and GO under identical reaction conditions.
TiO2 is one of the well-established photocatalysts under UV
light.[13,14] However, it has also been widely explored in the re-
search areas of energy conversion[15] and degradation[16] of pol-
lutants due to its cost-effective nature and chemical stability.
In recent years much effort has been devoted to developing
visible-light-active TiO2 by heteroatom doping because of its
obvious merit in solar energy utilization.[17] In addition, modify-
[a] D. S. R. Josephine, Prof. K. Sethuraman
School of Physics, Madurai Kamaraj University
Madurai-21, Tamil Nadu 625021 (India)
E-mail: sethuraman_33@yahoo.com
Results and Discussion
The 5 wt% TiO2/GO nanocomposite was characterized by UV/
Vis spectroscopy, photoluminescence spectroscopy, FTIR spec-
troscopy, powder X-ray diffraction (XRD), scanning electron mi-
croscopy (SEM), transmission electron microscopy (TEM), and
atomic force microscopy (AFM) techniques. GO provides a plat-
[b] B. Sakthivel, Prof. A. Dhakshinamoorthy
School of Chemistry, Madurai Kamaraj University
Palkalai Nagar
Madurai-21, Tamil Nadu 625021 (India)
E-mail: admguru@gmail.com
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form to anchor TiO2 with a uniform distribution through the
presence of various oxygen functionalities.
FTIR spectroscopy
FTIR measurements were carried out to explore the functional
groups present in the as-synthesized GO and 5 wt% TiO2/GO
nanocomposite samples. Figure 3 shows the FTIR spectrum of
GO with stretching frequencies at 1229 and 1061 cmÀ1 corre-
sponding to epoxide (CÀO) functional groups and the stretch-
ing frequency for carboxyl (C=O) groups is observed at
1728 cmÀ1. The FTIR spectrum of 5 wt% TiO2/GO nanocompo-
site typically shows no difference except lower intensities.
These studies clearly indicate that various oxygen groups such
as hydroxyl, carboxyl, epoxy, alkoxy, and carbonyl groups are
observed in the FTIR spectra of both GO and 5 wt% TiO2/GO
nanocomposite samples.
UV/Vis spectroscopy
The normalized UV/Vis spectrum of GO (Figure 1a) shows ab-
sorption bands at 230 and 298 nm. The absorption peak at
230 nm is attributed to the p–p* transition of C=C bonds
while the band at 298 nm corresponds to the n–p* transition
of C=O bonds, which further confirms the presence of carbonyl
groups. Further, the normalized UV/Vis spectrum of the 5 wt%
TiO2/GO nanocomposite (Figure 1b) clearly shows the presence
of the same bands with no possible shift implying that the
loading of TiO2 is very low in the 5 wt% TiO2/GO nanocompo-
site sample.
Figure 1. Normalized UV/Vis spectra of a) GO and b) 5 wt% TiO2/GO nano-
composite.
Figure 3. FTIR spectra of a) GO and b) 5 wt% TiO2/GO nanocomposite.
Photoluminescence spectroscopy
Powder XRD analysis
The photoluminescence (PL) spectra of GO and the 5 wt%
TiO2/GO nanocomposite are shown in Figure 2. The PL spec-
trum of GO shows an emission peak centered at 365 nm corre-
sponding to the crystalline graphitic C(sp2) network in GO. In
contrast, the PL spectrum of the 5 wt% TiO2/GO nanocompo-
site exhibits a similar emission pattern with a slight decrease in
its intensity, which is attributed to the interaction between GO
and TiO2.[34]
Powder XRD measurements were carried out to explore the
structural integrity of the as-prepared GO and 5 wt% TiO2/GO
nanocomposite samples (Figure 4). The powder XRD pattern of
GO exhibits a peak at 10.448 corresponding to the basal spac-
ing of 0.846 nm, which is a characteristic peak supporting the
existence of GO. Furthermore, the obtained diffraction peak
corresponds to the 002 plane, suggesting the formation of GO.
On the other hand, the 5 wt% TiO2/GO nanocomposite shows
peaks at 10.44, 25, and 458 representing the 002, 101, and 200
planes , respectively. The new peaks appearing at 25 and 458
correspond to the anatase phase of TiO2 loaded onto GO nano-
sheets. Also, it is interesting to note that the intensity of the
peak at 10.448 is higher for GO than for 5 wt% TiO2/GO, thus
suggesting that the oxygen-containing functional groups are
involved in the stabilization of TiO2.
Morphological studies
The morphological and layered features of the as-prepared
samples were examined through TEM, SEM, and AFM micro-
scopic techniques. The fact that the TiO2 nanoparticles are on
Figure 2. PL spectra of a) GO and b) 5 wt% TiO2/GO nanocomposite.
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composite to unravel their atomic structure and lattice atoms.
Figure 6a shows the presence of nanosheets with wrinkles and
edges spreading over a few microns in length indicating
a high aspect ratio, and Figure 6b shows the SAED pattern for
GO. The TEM image of the 5 wt% TiO2/GO nanocomposite
(Figure 6c) reveals that TiO2 nanoparticles are uniformly distrib-
uted on the surface of GO. In contrast, Figure 6e provides the
TEM image of the 5 wt% TiO2/GO nanocomposite after the cat-
alytic reaction with a slight agglomeration of TiO2 nanoparti-
cles as well as stacking of GO. The incorporation of TiO2 onto
the GO lattice prevents heavy agglomeration or restacking of
GO nanosheets. Furthermore, TiO2 nanoparticles are found to
be distributed uniformly on the surface of GO. The nanoparti-
cles deposited onto the sheets are found to be in the range of
5–10 nm. The SAED patterns of the 5 wt% TiO2/GO nanocom-
posite (Figure 6d,f) correspond to a diffused ring pattern indi-
cating the polycrystalline nature of the sample.
Figure 4. Powder XRD analysis of a) GO and b) 5 wt% TiO2/GO nanocompo-
site.
the surface of GO indicates a strong interaction between GO
and TiO2 via chemisorption. Also, the particle size and some of
the characteristic features of GO sheets will also be explored.
SEM analysis
SEM measurements were carried out to navigate the surface
features of the as-prepared GO and 5 wt% TiO2/GO samples
(Figure 5). The GO nanosheets show characteristic foldings/
wrinkles which can feasibly accommodate guest molecules. On
the other hand, the SEM image of 5 wt% TiO2/GO sample
shows that TiO2 nanoparticles are arranged on GO uniformly
without much agglomeration.
Figure 6. TEM images of a) GO, c) 5 wt% TiO2/GO nanocomposite, e) 5 wt%
TiO2/GO nanocomposite after the catalytic reaction; the respective SAED
patterns are given in (b,d,f).
AFM analysis
AFM measurements were carried out to explore the quality of
exfoliation of GO nanosheets, to authenticate the presence of
TiO2 nanoparticles on the sheets, and to determine the thick-
ness of the as-prepared nanosheets. AFM topograph and line
profiles of GO and 5 wt% TiO2/GO nanocomposite are given in
Figure 7a,b and Figure 8a,c, respectively. All these AFM images
confirm the sheet-like morphology. The line profiles of GO and
5 wt% TiO2/GO suggest that the thickness of GO is 1 nm and
the thickness of 5 wt% TiO2/GO nanosheets corresponds to
one monolayer with TiO2 nanoparticles and ranges between 5
and 10 nm. Figure 8a shows the AFM image of 5 wt% TiO2/GO
which clearly reveals the existence of TiO2 nanoparticles, which
appear as discrete bright dots homogenously distributed on
the surface of the GO. Further, the root mean square (rms)
values of roughness of GO and 5 wt% TiO2/GO are found to be
0.25 and 0.94 nm, respectively. An increase in the rms value of
roughness for the latter material compared to GO suggests the
interaction of TiO2 nanoparticles with GO. Also the surface of
Figure 5. SEM images of a,b) GO and c,d) 5 wt% TiO2/GO nanocomposite.
TEM analysis
TEM measurements were performed to explore the structural
features of the as-synthesised GO and 5 wt% TiO2/GO nano-
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thermore, the conversion of benzoic acid gradually increased
with the amount of TiO2 and reaches an optimum level. For in-
stance, 2 wt% TiO2/GO afforded 29% conversion of benzoic
acid after 8 h. In contrast, the 5 wt% TiO2/GO catalyst drastical-
ly enhanced the conversion of benzoic acid to 78% conversion
after 8 h. Under identical reaction conditions, the activities of
3 wt% TiO2/GO and 6 wt% TiO2/GO were examined and their
activities were similar to those of 2 wt% TiO2/GO and 5 wt%
TiO2/GO, respectively. On the other hand, a noticeable conver-
sion to 70% of benzoic acid was achieved using 10 wt% TiO2/
GO as catalyst under the optimized reaction conditions. Fur-
ther increasing the loading of TiO2 on GO to 20 wt% TiO2/GO
did not enhance the reaction further (74% conversion) after
8 h. On the other hand, the conversion of benzoic acid was de-
creased to 48% when the DMC volume reduced from 1 to
0.5 mL using 5 wt% TiO2/GO as catalyst. In contrast, the con-
version of benzoic acid using 5 wt% TiO2/GO was not further
enhanced when the volume of DMC was increased to 1.5 and
2 mL. Also, 0.5 mL of DMC was considered to be an optimal
volume for a uniform dispersion of substrate and catalyst.
Under identical reaction conditions, the catalytic activity of
5 wt% TiO2/GO was compared with that of other carbon mate-
rials such as graphite and activated carbon containing same
the weight percentage of TiO2 and the observed results are
summarized in Table 1. Conversions of 39 and 23% of benzoic
Figure 7. AFM images of GO (a,b); c) base plane corresponding to the line in
(b).
Table 1. Catalytic data for the esterification of benzoic acid using DMC
and various catalysts.[a]
Entry Catalyst
TiO2 loading DMC
t
T
Conv.
[mol%]
[mL]
[h] [8C] [%][b]
Figure 8. AFM images of 5 wt% TiO2/GO nanocomposite (a,c); b,d) base
planes corresponding to the lines in (a,c).
1
GO[c]
–
2.5
2.5
0.25
0.62
0.62
0.62
0.62
2.5
1.0
1.0
1.0
1.0
1.0
1.0
0.5
1.0
1.0
1.0
1.0
1.0
8
8
8
8
8
8
8
8
8
8
8
8
180
180
180
180
180
180
180
140
180
180
180
180
27
34
29
29
78
70
48
2
74
39
23
51
2
3
4
TiO2
TiO2 (Degussa)
2 wt% TiO2/GO
5 wt% TiO2/GO
10 wt% TiO2/GO
5 wt% TiO2/GO
5 wt% TiO2/GO
20 wt% TiO2/GO
5 wt% TiO2/AC
5
6
7
8
the GO nanosheets is found to be very smooth with base
plane and edges. These basal plane and edges are very effec-
tive for high performance in many applications. In particular,
edges are highly significant sites for the anchoring of guest
molecules. Among the various edge states of graphene-based
systems such as hexagonal, rectangular, and triangular edges,
it is observed that monolayer GO nanosheets with a highly dis-
torted rectangular lattice exhibit large area.
9
10
11
12
0.62
5 wt% TiO2/graphite 0.62
TiO2 +GO
–
[a] Reaction conditions: benzoic acid (100 mg), catalyst, DMC, required
time, and temperature. [b] Determined by GC. [c] 10 mg was used.
Catalytic performance
acid were achieved with 5 wt% TiO2/AC and 5 wt% TiO2/
graphite, respectively. In contrast, the physical mixture of GO
(9 mg) and TiO2 (1 mg) showed 51% conversion under identi-
cal reaction conditions; this conversion is lower than that with
5 wt% TiO2/GO but higher than with 5 wt% TiO2/AC and
5 wt% TiO2/graphite as catalysts. These experiments clearly in-
dicate the superior activity of 5 wt% TiO2/GO due to the syner-
gism between GO and TiO2 as well as optimal loading of TiO2
to achieve maximum conversion.
The catalytic activity of TiO2/GO was evaluated for the esterifi-
cation of benzoic acid using DMC as a green methylating
agent. A control experiment in the absence of catalyst afforded
no product, while in the presence of catalyst, product forma-
tion is observed. Furthermore, no and low conversions of ben-
zoic acid were observed at 90 and 1408C, respectively. The re-
action between benzoic acid and DMC using GO and TiO2 (7–
9 nm) as catalysts resulted in conversions of 27 and 34% after
8 h, respectively. On the other hand, commercially available
TiO2 (Degussa) was also examined as a catalyst and 29% con-
version of benzoic acid was observed after 8 h at 1808C. Fur-
One of the advantages of using heterogeneous catalysts is
the reusability after their recovery from the reaction mixture.
In this context, the catalyst reusability was also checked under
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the optimized reaction conditions (Table 1, entry 5). After the
required time, the autoclave was removed from the muffle fur-
nace and cooled to room temperature. The required volume of
acetonitrile (3 mL) was added to the reaction slurry and stirred
for 3 h. The analysis of the reaction mixture recovered from
the first reuse of the 5 wt% TiO2/GO catalyst showed 32% con-
version, which is lower than with fresh catalyst. It is very clear
that the activity of this catalyst is limited and further investiga-
tions are required to improve the stability of this catalytic
system. This decrease in catalytic activity was hypothesized to
be due to the agglomeration of TiO2 or partial stacking of GO
nanosheets during the catalytic reaction. This was further con-
firmed by subjecting 5 wt% TiO2/GO to TEM analysis and the
observed results are given in Figure 6. It can be seen clearly
that the particle size increased (13–18 nm) considerably after
the reaction (Figure 6e). Furthermore, powder XRD analyses of
fresh and used 5 wt% TiO2/GO catalysts reveal the broadening
of peaks corresponding to TiO2 (Figure 9). These results clearly
suggest that preserving the particle size of TiO2 as well as GO
in a single monolayer surface is highly essential to achieve
high conversion. A leaching experiment under the optimized
reaction conditions would provide evidence of the catalyst sta-
bility, but it is not performed here as one of the reactants
(DMC) is in the gas phase. Further work is in progress to ex-
plore this synergetic behavior in other organic transformations.
activity than 5 wt% TiO2/AC and 5 wt% TiO2/graphite as cata-
lysts. Among the various nanocomposites of TiO2/GO examined
for catalytic activity, 5 wt% TiO2/GO exhibits the highest activi-
ty under the present experimental conditions. The catalyst
could not be reused and suitable evidence was given for the
catalyst deactivation.
Experimental Section
Materials
Graphite powder and DMC were purchased from Sigma Aldrich.
Potassium permanganate (KMnO4, 99%), sulfuric acid (H2SO4 98%),
hydrogen peroxide (H2O2), hydrochloric acid (HCl), benzoic acid,
and DMC were purchased from Alfa Aesar. Titanium dioxide nano-
particles (7–9 nm) were purchased from SRL. All these materials
were of analytical grade and used as received without further pu-
rification.
Synthesis of TiO2/GO nanocomposite catalyst
GO was synthesized via modified Hummers’ procedure.[35] In a typi-
cal synthesis, 0.1 g of GO was suspended in 200 mL of deionized
water. After this mixture was stirred for about 10 min, it was soni-
cated for 2 h to exfoliate GO into nanosheets. Further 0.005 g of
TiO2 (5 wt%) was suspended in 200 mL of deionized water through
sonication for 10 min. This suspension was then mixed with the
dispersed GO and stirred for 24 h to obtain a homogenous distri-
bution of TiO2 on GO nanosheets. This mixture was then washed
with deionized water and centrifuged at 5000 rpm for 15 min to
remove unwanted residues and the resulting material was dried at
1008C. A similar procedure was also adopted for the synthesis of
5 wt% TiO2/AC and 5 wt% TiO2/graphite using activated carbon
(AC) and graphite instead of GO as the support.
Instrumentation details
The morphological studies were carried out using HR-TEM (Tecnai,
operated at 200 KV accelerating voltage), SEM [JEOL (JSM-5610LV)]
and AFM (noncontact mode, A100 SGS, APE Research). Powder
XRD was measured using a Brucker D8 Advance X-Ray diffractome-
ter with 2q ranging from 10 to 808, CuKa (1.540 Š). FTIR measure-
ments were performed using a Bruker instrument in the range of
400–4000 cmÀ1. Further, the absorbance and emission spectra were
carried out with a Shimadzu-UV 2450 double-beam spectropho-
tometer at room temperature in the wavelength range of 190–
900 nm and with a RF-5301 spectrofluorometer in the range of
300–800 nm, respectively.
Figure 9. Powder XRD analysis of a) fresh 5 wt% TiO2/GO and b) the used
5 wt% TiO2/GO catalyst.
Conclusion
Catalytic studies
In summary, GO/TiO2 nanocomposites were prepared and char-
acterized by UV/Vis spectroscopy, photoluminescence spectros-
copy, FTIR spectroscopy, powder XRD, SEM, TEM, and AFM
techniques. The catalytic activity of the 5 wt% TiO2/GO nano-
composite was compared with that of GO and bare TiO2 and
performance of the former is superior to that of its parents in
the esterification of benzoic acid using DMC as a green meth-
ylating agent. Furthermore, 5 wt% TiO2/GO exhibited higher
In general, benzoic acid (0.1 g), TiO2/GO, and DMC were added into
a Teflon container and stirred manually for uniform distribution.
This suspension was kept in an autoclave at 1808C for the required
time as shown in Table 1. The heterogeneous slurry was extracted
with acetonitrile by stirring for 3 h and filtered. The filtrate was
washed with water and the organic layer was dried over anhydrous
1
sodium sulfate. Product was characterized by GC-MS and H NMR
spectroscopy.
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[14] A. Dhakshinamoorthy, S. Navalon, A. Corma, H. Garcia, Energy Environ.
Sci. 2012, 5, 9217.
Acknowledgements
[15] G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, C. A. Grimes, Nano
Lett. 2006, 6, 215.
[16] Z. Y. Liu, X. T. Zhang, S. Nishimoto, T. Murakami, A. Fujishima, Environ.
Sci. Technol. 2008, 42, 8547.
[17] N. Luoa, Z. Jiang, H. Shi, F. Cao, T. Xiaoa, P. P. Edwards, Int. J. Hydrogen
Energy 2009, 34, 125.
[18] L. W. Zhang, H. B. Fu, Y. F. Zhu, Adv. Funct. Mater. 2008, 18, 2180.
[19] A. G. Shaikh, S. Sivaram, Chem. Rev. 1996, 96, 951.
[20] R. C. Larock, Comprehensive Organic Transformations, Wiley-VCH, Wein-
heim, 1989, chap. 9.
A.D.M. thanks University Grants Commission, New Delhi, for the
award of Assistant Professorship under its Faculty Recharge Pro-
gramme. A.D.M. also thanks the Department of Science and
Technology, India, for the financial support through Fast Track
project (SB/FT/CS-166/2013). K.S. acknowledges UGC-UPE for the
generous support through the HR-TEM facility. K.S. and D.R. also
acknowledge the DST-PURSE program of the School of Physics,
MKU, for the AFM facility.
[21] K. Ramalinga, P. Vijayalakshmi, T. N. B. Kaimal, Tetrahedron Lett. 2002, 43,
879.
[22] G. Pipus, I. Plazl, T. Koloimi, Chem. Eng. J. 2000, 76, 239.
[23] R. A. Sheldon, R. S. Downing, Appl. Catal. A 1999, 189, 163.
[24] A. Pandey, A. P. Singh, Catal. Lett. 1997, 44, 129.
[25] A. Corma, H. Garcia, S. Iborra, J. Primo, J. Catal. 1989, 120, 78.
[26] P. Tundo, M. Selva, Acc. Chem. Res. 2002, 35, 706.
[27] A. Dhakshinamoorthy, A. Sharmila, K. Pitchumani, Chem. Eur. J. 2010, 16,
1128.
[28] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Appl. Catal. A 2010, 378, 19.
[29] T. Subramanian, A. Dhakshinamoorthy, K. Pitchumani, Tetrahedron Lett.
2013, 54, 7167.
Keywords: dimethyl carbonate
heterogeneous catalysis · nanocomposites · TiO2
·
graphene oxide
·
[1] L. Zhi, K. Mullen, J. Mater. Chem. 2008, 18, 1472.
[2] R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Staub-
er, N. M. R. Peres, A. K. Geim, Science 2008, 320, 1308.
[3] S. Sun, L. Gao, Y. Liu, Appl. Phys. Lett. 2010, 96, 083113.
[4] X. Z. Zhou, X. Huang, X. Y. Qi, S. X. Wu, C. Xue, F. Y. C. Boey, Q. Y. Yan, P.
Chen, H. Zhang, J. Phys. Chem. C 2009, 113, 10842.
[5] L. Liu, S. Ryu, M. R. Tomasik, E. Stolyarova, N. Jung, M. S. Hybertsen,
M. L. Steigerwald, L. E. Brus, G. W. Flynn, Nano Lett. 2008, 8, 1965.
[6] D. H. Wang, D. W. Choi, J. Li, Z. G. Yang, Z. M. Nie, R. Kou, D. H. Hu, C. M.
Wang, L. V. Saraf, J. G. Zhang, ACS Nano 2009, 3, 907.
[7] J. Wu, X. Shen, L. Jiang, K. Wang, K. Chen, Appl. Surf. Sci. 2010, 256,
2826.
[30] R. K. Upadhyay, N. Soin, S. S. Roy, RSC Adv. 2014, 4, 3823.
[31] T.-D. Nguyen-Phan, V. H. Pham, E. W. Shin, H.-D. Pham, S. Kim, J. S.
Chung, E. J. Kim, S. H. Hur, Chem. Eng. J. 2011, 170, 226.
[32] X. Pu, D. Zhang, Y. Gao, X. Shao, G. Ding, S. Li, S. Zhao, J. Alloys Compd.
2013, 551, 382.
[33] Y. Min, K. Zhang, L. Chen, Y. Chen, Y. Zhang, Synth. Met. 2012, 162, 827.
[34] J. Liu, H. Bai, Y. Wang, Z. Liu, X. Zhang, D. D. Sun, Adv. Funct. Mater.
2010, 20, 4175.
[8] D. R. Dreyer, S. Park, C. W. Bielawski, R. S. Ruoff, Chem. Soc. Rev. 2010,
39, 228.
[9] B. F. Machado, P. Serp, Catal. Sci. Technol. 2012, 2, 54.
[10] C. Su, K. P. Loh, Acc. Chem. Res. 2013, 46, 2275.
[11] S. Navalon, A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem. Rev. 2014,
114, 6179.
[35] C. H. Lin, W. T. Yeh, C. H. Chan, C. C. Lin, Nanoscale Res. Lett. 2012, 7,
343.
[12] D. R. Dreyer, R. S. Ruoff, C. W. Bielawski, Angew. Chem. Int. Ed. 2010, 49,
9336; Angew. Chem. 2010, 122, 9524.
[13] A. Fujishima, K. Honda, Nature 1972, 238, 37–38.
Manuscript received: February 25, 2015
Final Article published: April 27, 2015
ChemPlusChem 2015, 80, 1472 – 1477
www.chempluschem.org
1477
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim