Guanidino-graphene catalysed synthesis of flavones via Aldol-Michael-oxidation

Article abstract of DOI:10.1166/jnn.2017.12644

Guanidino-graphene has been synthesized by the reaction of bromoamine with reduced graphene oxide and characterized by FT-IR, Raman, TGA, powder XRD, TEM, SEM, and zeta potential. It is a cheap, heterogeneous and environmentally benign solid base catalyst used for cascade Aldol-Michael-oxidation in the synthesis of chalcone, flavonoids.

Full text of DOI:10.1166/jnn.2017.12644

Article
Journal of
Nanoscience and Nanotechnology
Vol. 17, 2525–2530, 2017
Copyright © 2017 American Scientific Publishers
All rights reserved
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Printed in the United States of America
Guanidino-Graphene Catalysed Synthesis of
Flavones via Aldol-Michael-Oxidation
Sweta Mishra, Smriti Arora, Ritika Nagpal, and Shive Murat Singh Chauhan∗
Bioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India
Guanidino-graphene has been synthesized by the reaction of bromoamine with reduced graphene
oxide and characterized by FT-IR, Raman, TGA, powder XRD, TEM, SEM, and zeta potential. It is
a cheap, heterogeneous and environmentally benign solid base catalyst used for cascade Aldol-
Michael-oxidation in the synthesis of chalcone, flavonoids.
Keywords: Guanidinium Based Graphene/Heterogeneous Base/Cascade Reaction/Flavonoids.
1. INTRODUCTION
phosphates17 modified with NaNO138 or KF.19 Herein, we
have synthesized a novel guanidine based graphene, and
employed it as a catalyst in a one-pot cascade reaction
for the synthesis of chalcone, flavanone and flavone which
Carbocatalysis, a promising field, is widely available
and inexpensive that has facilitated a broad variety of
reactions.1 The heterogeneous carbon materials offer many
offers several benefits including atom economy, as well as
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advantages such as easy work-up, recyclability and less
waste production.2ꢀ3 Catalysts based on graphene have
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minimum time, labor and resource management.
Copyright: American Scientific Publishers
been regarded as potential solid catalysts because of
high ratio of catalytically active surface area to weight.4
Graphene’s precursor, graphene oxide, has been used as
a powerful reagent for oxidizing various alcohols and
alkenes, as well as hydrating alkynes, to their corre-
sponding aldehyde or ketone compounds.5–7 Recently,
amino-functionalized carbon have been synthesized by
various methods8ꢀ9 and used for the transesterification of
triglycerides,10 biomass conversion11 and as an oxygen
reduction electrocatalyst.12 Hence, it would be interesting
to develop an guanidino graphene as a solid base catalyst.
Earlier, GO has been directly used as a catalyst for
synthesis of chalcone in which high amount of cata-
lyst has been used.13 This prompted us to use chemi-
cally modified amino graphene as a solid base catalyst
for the synthesis of flavonoids. Their synthesis has been
carried out through a variety of procedures, but the most
common one is performed via the Claisen-Schmidt con-
densation and subsequent intramolecular Michael addi-
tion to form flavanones followed by oxidation to form
flavones between the reaction of substituted benzaldehydes
and substituted 2-hydroxyacetophenones in basic or acidic
media under homogeneous conditions. Various solid cat-
alysts have been applied to flavanoid synthesis, such as
magnesium oxide,14 alumina,15 hydrotalcites16 and natural
2. EXPERIMENTAL DETAILS
2.1. Preparation of Graphene Based Catalysts
Graphite oxide (GO) was prepared from natural graphite
by the modified Hummers method.20 GO (300 mg) was
dispersed into ultrapure water (50 mL) and sonicated for
1 h followed by addition of NaHSO3 (16.2 mmol). The
ꢀ
mixture was heated at 100 C under stirring and the sus-
pension was filtered, washed several times with distilled
water, redispersed into water under the assistance of ultra-
sonication for 5 min and filtered again by washing with
distilled water several times to make the pH ∼ 7. The fil-
trated r-GO was dried.
Under N2 atmosphere, vacuum-dried r-GO (200 mg)
was suspended into THF (50 ml) and excess of lithium
diisopropylamide (2 M solution in heptane/THF) was
added. The mixture was vigorously stirred continuously
for 12 h at room temperature. Various bromoamines were
vacuum dried for 4 h and then added to the r-GO solution.
The mixture was continuously stirred for 14 h at room
temperature. At the end of the reaction, product was fil-
tered, rinsed with water and methanol in order to remove
the unreacted amine (Scheme 1).
2.2. Reaction Procedure for Flavanoid Synthesis
A mixture of o-hydroxyacetophenone (1 mmol), corre-
sponding aldehyde (1 mmol) and amino graphene (50 mg)
∗Author to whom correspondence should be addressed.
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doi:10.1166/jnn.2017.12644
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Guanidino-Graphene Catalysed Synthesis of Flavones via Aldol-Michael-Oxidation
Mishra et al.
X
X
OH
OH
NaHSO3
(i) LDA
GO
1
HOOC
(ii) BrCH2CH2X
3
X
COOH
2 (r-GO)
HOOC
4
X
a
b
X = –NMe2
X = –NH2
O
c
X =
N
NH
d
X =
HN
NH2
Scheme 1. Synthesis of Amino grafted graphene.
were dissolved in xylene (1 ml) and was refluxed for 14 h.
The progress of reaction was monitored by TLC. The reac-
tion mixture was filtered and solvent was removed under
reduced pressure. The products were isolated by column
chromatography. Catalyst was recovered by simple filtra-
tion and rinsing with dichloromethane and methanol.
which G band appear at 1589 cm−1 (ID/IG = 1.12) which
showed that maximum functionalization was achieved with
guanidinium type of functionality (Fig. 2).
In powder XRD (Fig. 3), the diffraction peak of GO
appears at 11.3ꢀ (001) with interlayer space (d-spacing)
of 0.76 nm, while r-GO exhibits a new diffraction peak
at 2ꢂ = 24.9ꢀ, demonstrating the formation of graphitic
structures during the reduction of GO. However in the
functionalized graphenes, the diffraction peak blue shifts
to 2ꢂ = 22.9ꢀ which is attributed to the intercalation of
amino groups between the stacked graphene layers, corre-
sponding to an increased d-spacing (3.87 Å).
3. RESULTS AND DISCUSSION
3.1. Structure Characterisation and Morphology of
Amino-Grafted Graphenes
Various functionalized graphenes used in this paper were
prepared through the covalent attachment of alkylamine
Elemental analysis was used to give the detailed chem-
ical information of graphene-based samples. Table I show
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onto the reduced graphene sheet (r-GO). LDA works better
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for proton abstraction as compared to BuLi as it is more
Copyright: American Scthieant taiffitcerPuambliinsohegrrsafting, the nitrogen content increased
stable and offers a cleaner reaction. The r-GO sheet consist
significantly from 0.32% to 3.7%, a 10-fold increase,
which confirms the successful introduction of amine
groups onto the surface of r-GO. Among the prepared
graphenes nitrogen content was found to be maximum in
guanidine based graphene (9.21%). The values of the ele-
mental analysis were in good agreement with the theoret-
ical calculated values.
of large number of chemically reactive vacancies and sp3
carbon atoms as compared to graphite and therefore, can
be used for covalent attachment of desired molecules via
C–C coupling reactions.
The structure of synthesized amino-graphenes has been
confirmed by FT-IR, Raman, TGA, powder XRD, TEM,
SEM, zeta-potential measurements. The nitrogen con-
taining graphene possess basic character with pKa ∼
9–11. Among all the synthesized graphene, guanidine
based graphene (Gdn-Graphene) was found to be most
basic. FTIR spectra of as-synthesized amino-graphene
indicate contributions from nitrogen functional groups.
Peaks 3430–3420 cm−1 contribute for N–H stretching,
1645 cm−1 for C N stretching, 1552–1546 cm−1 for N–
H bending, 1152–1132 cm−1 for C–N stretching (Fig. 1).
Absence of peaks at 1730 for ꢁC O, 1091 for ꢁC–O indi-
cates complete reduction of GO. N-bromoamines did not
react with –COOH and –OH as no corresponding peaks
were observed in IR.
We also examined the thermal stability of the prepared
graphenes and compared it with r-GO using TGA under
In Raman spectroscopy, r-GO has two characteristic
peaks around 1353 and 1576 cm−1, corresponding to the
defect-induced D band and G band respectively.21 A red-
shifted G band after amino-grafting, attributed to slight
reduction of C C and introduction of new functional
groups on the graphene sheets was observed.22 The max-
imum shifting was observed in case of compound 4d in
Figure 1. FT-IR spectra of (a) NH2-Graphene, (b) Gdn-Graphene.
J. Nanosci. Nanotechnol. 17, 2525–2530, 2017
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Mishra et al.
Guanidino-Graphene Catalysed Synthesis of Flavones via Aldol-Michael-Oxidation
Table I. Elemental analysis of GO, r-GO and the prepared graphenes.
Sample
H (%)
C (%)
N (%)
GO (1)
rGO (2)
–NMe2 (4a)
–NH2 (4b)
Mor-Graphene (4c)
Gdn-Graphene (4d)
2.23
0.81
2.32
2.11
2.70
2.90
67.18
73.70
71.30
71.97
71.60
71.90
0.61
0.32
3.70
3.10
3.60
9.21
helps in effective dispersion. SEM images display flower-
like curled characteristics of amino graphene.
The zeta potential measurements (Fig. 6) have been
widely used to study surface charge on a variety of car-
bons materials. The zeta potential of r-GO is negative
(ꢃ = −30 to −38 mV) indicating the negatively charged
state of exfoliated r-GO.24 The observed zeta (ꢃ) potential
for amino-grafted graphene (Gdn-graphene) is +32 mV
indicating the presence of positively charged amine groups
on the graphene sheet.
Figure 2. Raman Spectra of (a) r-GO, (b) Gdn-graphene.
ꢀ
a nitrogen flow over a temperature range of 25–900 C
ꢀ
with flow rate of 10 C per min (Fig. 4). Generally for
ꢀ
r-GO, there is nearly no weight loss below 145 C, as the
3.2. Synthesis of Chalcones, Flavanones and Flavones
The reaction with equimolar quantities of 2-hydroxy-
acetophenone (5) and anisaldehyde (6a) in presence of
synthesized amino-graphene under reflux conditions, gave
chalcone (7a), flavanone (8a) and flavone (9a) (Table II,
entry 1) (Scheme 2). Absence of catalyst did not yield any
oxygen functionalities have been removed upon reduction
of GO. On the other hand, after amino-grafting, a large
weight loss appeared from 200–400 ꢀC, which is attributed
to the thermal decomposition of amine moiety covalently
attached to the sheet. The results, thus, proves the success-
ful functionalization of various amines on r-GO sheet. All
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product even after 24 h. The optimized reaction was con-
of the other prepared graphenes show similar findings in
thermo-gravimetric analysis.
IP: 46.161.58.107 On: Sun, 07 May 2017 13:29:02
ꢀ
ducted at 140 C with 50 mg of catalyst (10 wt%), 1 ml
Copyright: American Scientific Publishers
solvent and 1 mmol of reactants. With different synthe-
sized graphenes varying conversion rate were obtained.
Gdn-graphene dramatically improved the conversion to
98% in which product yields were 40% chalcone, 40%
flavanone, 13% flavones in 14 h. Control experiment using
GO produced only chalcone (∼35% yield) in xylene as
solvent. Control experiment using guanidine hydrobromide
gave only chalcone in 40% yield.
Detailed surface morphology can be explained by TEM
and SEM images (Fig. 5). As can be seen in TEM images,
r-GO exist as few layers of graphene sheets and the similar
sheet with greater degree of crumpling was achieved for
amino-graphene. The crumpled sheet helped in two ways,
firstly, made the reactants easily accessible to the active
sites on both sides of the sheets which may also facili-
tate the diffusion of the product molecules,23 and secondly,
Figure 4. Thermo-gravimetric analysis of r-GO and Gdn-
Graphene (4d).
Figure 3. XRD pattern of Gdn-Graphene (4d).
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Guanidino-Graphene Catalysed Synthesis of Flavones via Aldol-Michael-Oxidation
Mishra et al.
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IP: 46.161.58.107 On: Sun, 07 May 2017 13:29:02
Figure 5.
TEM images of (a) r-GO, (b) Gdn-Cgraopphyenreig(h4dt:),A(cm, de)rSicEaMnimSacgieesnotfifGicdnP-gurabplhisenhee(r4sd).
Zeta Potential Distribution
The one pot synthesis of chalcone, flavanone
and flavones starting with aldehyde and 2-hydroxy
acetophenone as precursors has not been reported till now
and usually metals are used for the oxidation purpose,25–28
herein, we report the synthesis using a metal free catalyst.
Although, the results of different solid catalysts used so
far has been compiled in the Table II.
250000
Record 241: SBL 1
200000
150000
100000
50000
0
–100
0
100
200
Apparent Zeta Potential (mV)
During the course of above reaction, chalcone is formed
(2–3 h), followed by flavanone (3–4 h). On further
Figure 6. Zeta-potential curve of Gdn-graphene (4d).
Table II. Catalytic performance of the amino functionalized graphene with different amino loadings in the condensation of 2-hydroxyacetophenone
and anisaldehyde.
% Yieldb
Entry
Catalyst
Time (h)
Temp (ꢀC)
Solvent
% Conversiona
Chalcone
Flavanone
Flavone
1
2
3
4
5
6
7
8
9
10
(-NMe2-G)
(-NH2-G)
(Mor-G)
(Gdn-G)c
16
16
16
16
24
14
12
2
130
130
130
130
130
130
160
60
Xylene
Xylene
Xylene
Xylene
–
68
50
75
98 (80)
45
35
90
90
91
–
30
20
30
43
35
35
21
87
35
–
30
19
32
37
–
–
69
–
7
9
8
13
–
–
–
–
–
–
Guanidinium hydrobromide
GO
Xylene
DMSO
CH2Cl2
N-tetradecane
Xylene
MgO
Hydrotalcite
KF/Natural phosphate
No catalyst
2
24
100
130
52
–
Notes: Reactants = 1:1; Solvent = 1 mL; Amount of catalyst = 50 mg; Reaction time = 12–18 h; abased on substrate; bisolated yields; cyields after 3 runs.
2528
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Mishra et al.
Guanidino-Graphene Catalysed Synthesis of Flavones via Aldol-Michael-Oxidation
R1
R1
R1
R2
R3
R2
R3
R2
CHO
COCH3
OH
(4)
O
O
O
O
OH
O
R3
+
G-CH2CH2X
+
+
R1
Solvent
R3
R2
Chalcone
Flavanone
8
Flavone
5
6
7
9
(a) R1 = -H , R2 = -H, R3 = -H
(b) R1 = -H , R2 = -CH3, R3 = -H
(c) R1 = -H , R2 = -OCH3, R3 = -H
(d) R1 = -OCH3 , R2 = -H, R3 = -OCH3
(e) R1 = -H , R2 = -OH, R3 = -H
(f) R1= -H, R2= -Cl, R3 = -H
(g) R1 = -H , R2 = -Br, R3 = -H
(h) R1 = -H , R2 = -NO2, R3 = -H
Scheme 2. Synthesis of chalcone (7), flavanone (8) and flavone (9) using amino-graphene.
prolongation of reaction by 3–6 h flavanone was oxidized
to flavone. Flavanone and 2ꢁ-hydroxychalcone exist in
equilibrium between the pH range 10.5 and 13,29 therefore,
both are present as end-products with Gdn-graphene while
only chalcone was formed when GO (pH ∼ 4) was used.
The reaction with Gdn-graphene was performed under
N2 as well as O2 atmosphere for 24 h, and no change
in yield was observed. Therefore, we suggested graphitic
structure is responsible for the oxidative dehydrogenation
and defects are induced upon oxidation of graphite which
experimentally remain on the surface of graphene even
after the reduction of GO.30 These defects trap molecular
oxygen and help in oxidation.31
Flavone formation occurred due to these trapped oxy-
gen molecules in graphene defects via radical mechanism,
which was proved by the addition of radical quencher
NaN3 (no flavone appeared). To test its reusability, the cat-
alyst was removed from the reaction mixture by filtration
and dried to remove water and soluble impurities. The iso-
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and not molecular oxygen. A number of oxygen groups
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lated catalyst was used directly in the next run by adding
the same amount of starting material as the initial run.
After 5 consecutive runs, Gdn-Graphene still provided an
average conversion of 80%. Raman spectrum of the used
catalyst show same peaks as before. However, XRD reveal
an extra peak at 18ꢀ which might arise due to some reac-
tants adsorbed on graphene surface still after washing.
The reaction was explored by using different solvents
and substituents on the aromatic ring (Tables III, IV). The
substituents have found to have a great impact on the selec-
tivity of product. With electron-withdrawing substituents at
para-position of aldehyde favour higher selectivity towards
flavanone unlike other solid base catalysts.32 The reaction
worked best in non-polar solvents as the graphite sheet is
hydrophobic in nature so reactants get solvated by polar
solvents and thus, may interfere with the catalytic process.
Copyright: American Scientific Publishers
Table III. Reaction of 2ꢁ-hydroxyacetophenone and different aldehydes
with guanidine based amino graphene (4d).
% Yieldb
Entry Aldehyde % Conversiona Chalcone Flavanone Flavone
1
2
3
4
5
6
7
8
a
b
c
d
e
f
70
95
98
65
40
72
75
80
30
42
43
29
7
28
28
10
30
38
37
29
26
33
35
46
8
15
13
6
6
9
g
h
10
20
Notes: Reactants = 1:1; Solvent = 1 mL; Amount of catalyst = 50 mg; Reaction
time = 12–18 h; abased on substrate; bisolated yields.
Table IV. Reaction of 2ꢁ-hydroxyacetophenone and anisaldehyde with
guanidine based amino graphene (4d) in different solvents.
4. CONCLUSION
% Yieldb
In conclusion, a useful catalytic cascade synthesis of chal-
cone, flavonones and flavones with guanidino graphene
based catalyst in non-polar solvent has been developed.
Several factors play a decisive role: substituents, solvents
and amount of catalyst. The advantages of this solid cat-
alyst over other basic heterogeneous catalysts are the
high catalytic turnover, low catalyst loading, simplicity
of the catalyst preparation, ready availability, low price of
the precursors, and the ease of reuse. These results open
Entry
Solvent
% Conversiona Chalcone Flavanone Flavone
1
2
3
4
5
Xylene
DMF
Toluene
Ethanol
No solvent
98
80
65
45
65
43
32
31
23
15
37
39
15
12
22
13
7
18
5
25
Notes: Reactants = 1:1; Solvent = xylene (1 ml); Reflux; Amount of catalyst =
50 mg; Reaction time = 12–18 h; abased on substrate; bisolated yields.
J. Nanosci. Nanotechnol. 17, 2525–2530, 2017
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Guanidino-Graphene Catalysed Synthesis of Flavones via Aldol-Michael-Oxidation
Mishra et al.
the way to the use of inexpensive solid as a basic cata-
lyst for the applications in other organic reactions. Owing
to this reaction, the reasonable timings, eco-friendly con-
ditions, recyclability of guanidino graphene and excellent
yields proves this method superior over other methods.
13. H. P. Jia, D. R. Dreyer, and C. W. Bielawski, Adv. Synth. Catal.
353, 528 (2011).
14. M. T. Drexler and M. D. Amiridis, J. Catal. 214, 136 (2003).
15. R. S. Varma, G. W. Kabalka, L. T. Evans, and R. M. Pagni, Synth.
Commun. 15, 279 (1985).
16. M. J. Climent, A. Corma, S. Iborra, and A. J. Velty, J. Catal.
221, 474 (2004).
17. S. Sebti, A. Saber, A. Rhihil, R. Nazih, and R. Tahir, Appl. Catal.,
A 206, 217 (2001).
18. S. Sebti, A. Solhy, R. Tahir, S. Abdelatif, S.Boulaajaj, J. A. Mayoral,
J. I. Garcia, J. M. Fraile, A. Kossir, and H. Oumimoun, J. Catal.
213, 1 (2003).
Acknowledgments: Authors are grateful to DST,
CSIR-UGC, Delhi and University of Delhi for financial
assistance.
19. D. J. Mcquarrie, R. Nazih, and S. Sebti, Green Chemistry 4, 56 (2002).
20. W. S. Hummers, Jr. and R. E. Offeman, Journal of American Chem-
ical Society 80, 1339 (1958).
21. A. C. Ferrari, J. C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri,
F. Mauri, S. Piscanec, D. Jiang, K. S. Novoselov, S. Roth, and A. K.
Geim, Phys. Rev. Lett. 97, 187401 (2006).
References and Notes
1. (a) A. D. Todd and C. W. Bielawski, Catalysis Science and Technol-
ogy 3, 135 (2013); (b) D. R. Dreyer, K. A. Jarvis, P. J. Ferreirab, and
C. W. Bielawski, Polymer Chemistry 3, 757 (2012); (c) D. R. Dreyer
and C. W. Bielawski, Advanced Functional Materials 22, 3247
(2012); (d) S. Yang, X. Feng, X. Wang, and K. Müllen, Angewandte
Chemie International Edition 50, 5339 (2011).
22. K. N. Kudin, B. Ozbas, H. C. Schniepp, R. K. Prudhomme, I. A.
Aksay, and R. Car, NanoLetters 8, 36 (2007).
2. (a) H. Hattori, Chemical Review 95, 537 (1995); (b) H. Hattori,
Journal of the Japan Petroleum Institute 47, 67 (2004).
23. J. Ji, G. Zhang, H. Chen, S. Wang, G. Zhang, F. Zhang, and X. Fan,
Chemical Sciences 2, 484 (2011).
3. M. J. Lee, B. H. Kim, Y. Lee, B. T. Kim, and J. B. Park, Bull. Korean
Chem. Soc. 35, 1979 (2014); (b) K. Tanabe and W. F. Holderich,
Applied Catalysis A: General 181, 399 (1999).
4. D. R. Dreyer and C. W. Bielawski, Chemical Science 2, 1233 (2011).
5. D. R. Dreyer, H. P. Jia, and C. W. Bielawski, Angewandte Chemie
International Edition 49, 6813 (2010).
24. Y. R. Lee, I. Y. Kim, T. W. Kim, J. M. Lee, and S. J. Hwang, Chem.
Eur. J. 18, 2263 (2012).
25. M. S. Khanna, O. V. Singh, C. P. Garg, and R. P. Kapoor, Journal
of Chemical Society, Perkin Trans. 1, 2565 (1992).
26. N. Ahmed, H. Ali, and J. E. Van Lier, Tetrahedron Lett. 46, 253 (2005).
27. P. S. Kulkarni, D. D. Kondhare, R. Varala, and P. K. Zubaidha,
Journal of Serbian Chemical Society 78, 909 (2013).
28. A. S. Zambarea, J. N. Sangshettia, N. D. Kokarea, and D. B.
Shindea, Chin. Chem. Lett. 20, 171 (2009).
6. H. P. Jia, D. R. Dreyer, and C. W. Bielawski, Advanced Synthesis
and Catalysis 4, 528 (2011).
7. J. Pyun, Angewandte Chemie International Edition 50, 46 (2011).
8. S. Chatterjee, R. K. Layek, and A. K. Nandi, Carbon 52, 509 (2013).
29. A. Cisak and C. Mielczarek, Journal of Chemical Society Perkin
Delivered by Ingenta to: State University of New York at Binghamton
IP: 46.161.58.107 On: Sun,300.7TVMr.aGansey.o2r2g,0a1k16il07a3s,1(1M39.:92O29)t.y:e0p2ka, A. B. Bourlinos, V. Chandra, N. Kim,
9. C. Yuan, W. Chen, and L. Yan, Journal of Material Chemistry
22, 7456 (2012).
10. A. Villa, J. P. Tessonnier, O. Majoulet, DC. So.pSyur,iganhdt:RA. mScehlröigcla, n Scientific Publishers
K. C. Kemp, P. H. R. Zboril, and K. S. Kim, Chemical Reviews
112, 6156 (2012).
Chemical Communnication 4405 (2009).
11. (a) J. P. Tessonnier, A. Villa, O. Majoulet, D. S. Su, and R. Schlögl,
Angew. Chem. Int. Ed. 48, 6543 (2009); (b) J. Boro, L. J. Konwar,
and D. Deka, Journal of Bioprocess Engineering and Biorefinery
2, 54 (2013).
12. Y. Zhang, K. Fugane, T. Mori, L. Niu, and J. J. Ye, Chem. Mater.
22, 6575 (2012).
31. C. Su, M. Acik, K. Takai, J. Lu, S. J. Hao, Y. Zheng, P. Wu,
Q. Bao, T. Enoki, Y. J. Chabal, and K. P. Loh, Nature Communica-
tion 3, 1298 (2012).
32. (a) M. J. Climent, A. Corma, S. Iborra, and J. Primo, J. Catal.
151, 60 (1995); (b) D. J. Macquarrie, R. Nazih, and S. Sebti, Green
Chemistry 4, 56 (2002).
Received: 4 July 2015. Accepted: 2 December 2015.
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