Fullerene-catalyzed reduction of azo derivatives in water under UV irradiation

Article abstract of DOI:10.1002/asia.201200701

Metal-free fullerene (C₆₀) was found to be an effective catalyst for the reduction of azo groups in basic aqueous solution under UV irradiation in the presence of NaBH₄. Use of NaBH₄ by itself is not sufficient to reduce the azo dyes without the assistance of a metal catalyst such as Pd and Ag. Experimental and theoretical results suggest that C ₆₀ catalyzes this reaction by using its vacant orbital to accept the electron in the bonding orbital of azo dyes, which leads to the activation of the N=N bond. UV irradiation increases the ability of C₆₀ to interact with electron-donor moieties in azo dyes. Filling a vacancy: Experimental and theoretical methods have been combined to show that C₆₀-catalyzed reductions of azo compounds form aromatic amines under UV irradiation (see scheme). The obtained results show that C₆₀ acts as an electron acceptor to catalyze the reduction of azo compounds, and the role of UV irradiation is to increase the ability of C₆₀ to interact with electron-donor moieties in azo compounds. Copyright

Full text of DOI:10.1002/asia.201200701

DOI: 10.1002/asia.201200701
Fullerene-Catalyzed Reduction of Azo Derivatives in Water under UV
Irradiation
[
a]
[a]
[a]
[a]
[b]
Yong Guo, Wengang Li, Jingjing Yan, Basem Moosa, Maꢀan Amad,
[
c]
[a]
Charles J. Werth, and Niveen M. Khashab*
Abstract: Metal-free fullerene (C )
and Ag. Experimental and theoretical
results suggest that C60 catalyzes this
reaction by using its vacant orbital to
accept the electron in the bonding orbi-
tal of azo dyes, which leads to the acti-
vation of the N=N bond. UV irradia-
tion increases the ability of C60 to inter-
act with electron-donor moieties in azo
dyes.
6
0
was found to be an effective catalyst
for the reduction of azo groups in basic
aqueous solution under UV irradiation
in the presence of NaBH . Use of
4
Keywords: amines
·
azo
NaBH4 by itself is not sufficient to
reduce the azo dyes without the assis-
tance of a metal catalyst such as Pd
compounds · electron transfer · ful-
lerenes · heterogeneous catalysis
Introduction
cluding methyl orange (MO), methyl red (MR), and azoben-
zene-4,4’-dicarboxylic acid (AA)) under UV irradiation with
Developing carbon catalysts is crucial because carbon is
the presence of sodium borohydride (NaBH ) (Scheme 1).
4
[1–3]
cheap and easy to obtain. Su et al.
found that surface-
NaBH is a common reductant. However, it is not sufficient
4
modified carbon nanotubes and nanodiamonds catalyzed
the oxidative dehydrogenation of hydrocarbons. Yuan
to reduce azo compounds without the assistance of metal
[8]
[9]
catalysts, such as Pd and Ag. The obtained results sug-
gest that C60 catalyzes this reaction by using its vacant orbi-
tal to accept the electron in the bonding orbital of azo dyes,
which leads to activation of the N=N bond. UV irradiation
increases the ability of C60 to interact with electron-donor
moieties in azo dyes. Azo compounds are common organic
[4]
et al. reported that mesoporous carbon dehydrogenated
[5]
propane into propylene. Most recently, Bielawski et al. re-
viewed the application of carbon catalysts in synthetic
À
À
chemistry. They reported that C , C , and C /C
60
cata-
lyzed the hydrogenation of nitrobenzene into aniline under
6
0
60
60
[6]
UV irradiation and dark conditions. But Kukula and Bok-
contaminants that are usually removed by expensive metal-
[7]
À
[8,9]
hoven et al. proved that the activity of C60 under dark
conditions resulted from the residual nickel in the reaction
mixture. Until now, the catalytic activity of C60 under UV ir-
radiation has not been fully investigated. Herein, detailed
experimental and theoretical studies have been combined to
investigate C -catalyzed reductions of azo compounds (in-
catalyzed processes.
The C -catalyzed reduction reaction
60
provides a better way to deal with this class of potentially
toxic materials at low cost. On the other hand, reduction of
azo compounds is a good source of primary amines that are
useful in organic synthesis.
60
Results and Discussion
[
a] Dr. Y. Guo, Dr. W. Li, Dr. J. Yan, Dr. B. Moosa, Prof. N. M.
Khashab
The reaction proceeded by dissolving azo compounds
10 mg) in basic aqueous solution (pH 11), followed by the
Controlled Release and Delivery Lab (CRD)
Center of Membrane and Porous Materials
Chemical and Life Sciences and Engineering Division
King Abdullah University of Science and Technology (KAUST)
Thuwal 23955-6900 (Kingdom of Saudi Arabia)
E-mail: niveen.khashab@kaust.edu.sa
(
addition of NaBH4 (150 mg) and C60 (10 mg). The whole
system was irradiated under UV light with constant stirring
for 5 h to reach completion. Since C60 did not dissolve in
water, the mixture was centrifuged and the supernatants
were analyzed by UV-visible spectroscopy and a high-per-
formance liquid chromatography/photodiode array detector
coupled with a mass spectrometry detector (HPLC-PDA-
MS).
According to Figure 1, NaBH4 alone cannot effectively
reduce methyl orange (MO) under UV irradiation as the ab-
sorption peak around 460 nm of the N=N bond in MO does
not decrease (Figure 1a), which is consistent with previous
[
b] Dr. M. Amad
Analytical Chemistry Core Laboratory
King Abdullah University of Science and Technology (KAUST)
Thuwal 23955-6900 (Kingdom of Saudi Arabia)
[
c] Prof. C. J. Werth
Department of Civil and Environmental Engineering
and Department of Chemistry
University of Illinois at Urbana-Champaign
Urbana, Illinois 61801 (USA)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200701.
[8,9]
reports.
And this is true when using C60 only (Figure 1b).
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in 5 h in the presence of C60
and NaBH under UV irradia-
4
tion.
The UV result of methyl red
(
MR) reduction is shown in
Figure S2 (see the Supporting
Information). MR dissolves in
an aqueous basic solution with
a UV absorption peak of the
[10]
N=N bond around 430 nm.
The absorption peak of the N=
N bond decreases within 5 h in
the presence of C60 and NaBH4
under UV irradiation (see the
Supporting Information). Two
4
Scheme 1. Fullerene-catalyzed reduction of azo compounds under UV irradiation in the presence of NaBH .
R=R or R ; R’=R’ , R’ or R’ .
1
2
1
2
3
reduced species of MR, C H NO and C H N , were identi-
7
7
2
8
12
2
fied with the HPLC-PDA-MS method (see the Supporting
Information). The reduction rate of MR is shown in Fig-
ure S3 (see the Supporting Information). Approximately
9
2% of MR was reduced by NaBH and C under UV irra-
4 60
diation within 5 h. C60 can also effectively catalyze the re-
duction of azobenzene-4,4’-dicarboxylic acid (AA) in the
presence of NaBH under UV irradiation (see the Support-
4
ing Information). The reduced species of AA, C H NO ,
7
7
2
was identified by the HPLC-PDA-MS method (see the Sup-
porting Information). According to Figure S5 in the Sup-
porting Information, approximately 90% of AA is reduced
in 5 h.
It has been reported that C H species can be formed by
6
0
2
the reaction of C60 with BH –THF complex+H O in toluene
3
2
[11,12]
or NaBH +CH CH OH in toluene.
To clarify whether
4
3
2
Figure 1. Comparison experiments to verify that UV light, C60, and
NaBH are essential for the reduction of methyl orange (MO).
4
C H is involved in the C -catalyzed reduction of azo com-
pounds, we have investigated the reaction of C60 with
6
0
2
60
NaBH +H O and NaBH +CH CH OH in toluene, respec-
4
2
4
3
2
Without UV irradiation, C60 and NaBH cannot reduce MO
tively. The color of the solution of C60 in toluene became
4
as well (Figure 1c). After 5 h under UV irradiation in the
yellow from purple after NaBH +CH CH OH was added,
4
3
2
presence of C60 and NaBH , the absorption peak at 460 nm
and the UV spectra was different from that of C (Figure 2,
60
4
[11,12]
in MO decreases greatly and a new peak appears at 245 nm
a versus c).
However, the color of the C60 solution was
[8]
(
Figure 1d). The HPLC-PDA chromatogram method has
been used for characterizing the products of C -catalyzed
6
0
MO reduction (a detailed description is provided in the Sup-
porting Information). Prior to UV irradiation, the HPLC-
PDA chromatogram results show that only one chromato-
graphic peak at a retention time of 36 min with m/z 306
+
[
M+H] was found, which corresponded to MO. After 2 h
of UV irradiation, two additional peaks were clearly detect-
ed. The chromatographic peak at a retention time of 4 min
À
had a molecular ion peak at m/z 172 [MÀH] , which was at-
tributed to a reduced species (C H NSO ) of MO (see the
6
7
3
Supporting Information). The other reduced species
C H N ) of MO was detected at a retention time of 6 min
(
8
12
2
+
with m/z 137 [M+H] . No other degradation products of
MO were detected in the samples after UV irradiation. Con-
versions rather than yield are often used to describe the re-
duction of MO as the produced aromatic amines are very
[
8,9]
unstable in water.
The reduction rate of MO is shown in
Figure 2. UV spectra of
CH CH OH in toluene.
C
60
,
C
60-NaBH
4
-H
2
O, and
4
C60-NaBH -
the Supporting Information. Nearly 96% of MO is reduced
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C -Catalyzed Reduction of Azo Derivatives
60
the same as that after NaBH +H O was added, and their
tween MO and C . It has been reported that Ag nanoparti-
4
2
60
UV spectra were identical as well (Figure 2, a versus b).
cles have the best catalytic performance among Ag, Au, and
Pt nanoparticles as MO is most easily adsorbed on its sur-
This suggested that C60 did not react with NaBH +H O
4
2
[9]
under UV irradiation to form C H species. We also consid-
face and activated. Thus, C -catalyzed MO reduction is
6
0
2
60
ered the possibility of C (OH) and C anion as reaction
most likely initiated by adsorption of MO on the C60 cluster
surface by using its vacant orbital to accept the electrons of
the bonding orbital in azo compounds under UV irradiation.
This possibly leads to the activation of MO.
6
0
n
60
intermediates. It has been reported that C (OH) dissolves
6
13]
0
n
[
in water to form a yellow aqueous solution and the forma-
[7]
tion of the C60 anion changes the solution color as well.
From samples b and c shown in Figure S6 (see the Support-
ing Information), it can be seen that the color of the toluene
layer (top) did not change and the water layer (bottom) was
colorless. Furthermore, the UV spectra of C , C -NaBH -
For a deeper understanding of MO activation by C
60
[16]
under UV irradiation, the unrestricted M062X method in
[17]
the Gaussian 09 program was adopted to investigate the
interaction between C and MO under UV irradiation since
6
0
60
4
60
[18]
H O-dark, and C -NaBH -H O-UV were identical (see the
a recent report recommends this functional for the fuller-
ene system. In our study, C60 does not dissolve in water and
acts as a heterogeneous catalyst to promote the reduction of
2
60
4
2
Supporting Information), thereby implying that C (OH)
n
6
0
and C60 anions did not form by the reaction of C60 with
[8]
[9]
NaBH +H O under UV irradiation. It has been reported
azo compounds, just like the Pd and Ag nanoparticle. To
simplify the calculation, one C60 molecule was chosen as
a model to investigate the interaction between C60 and MO.
Based on calculation results, C60 in the ground state (singlet
C ) has vacant bonding orbitals (orbitals with negative ener-
4
2
[13]
that the C (OH) species can dissolve in water. However,
60
n
the C (OH) species was not detected in the reaction solu-
60
n
tion by electrospray ionization, atmospheric pressure photo-
ionization, or atmospheric-pressure chemical ionization
mass spectrometries.
6
0
gies from 181 to 183, Figure 3), which indicate that it is
a electron acceptor. This is consistent with a previous
An inductively coupled plasma (ICP) emission spectrome-
ter was used to detect the metal contaminates in C . Trace
[19]
report and means that using the C60 molecule as a model
60
amounts (i.e., ppm) of Co, Cr,
Cu, Fe, and Ag were detected
(
see the Supporting Informa-
[6]
tion). These metal contami-
nants were removed by treating
C60 successively with HCl (12m)
and HNO (0.5m). ICP analysis
3
was carried out for the acid-
treated C60 and no residual
metal
contaminants
were
found. According to Figure S7
in the Supporting Information,
13
the C NMR spectrum of C60 is Figure 3. HOMO orbitals and the corresponding orbital energies of singlet (left) and triplet C60 (right). Bond-
ing orbitals have negative energy.
the same as that of acid-treated
C . This is also true for UV
60
spectra of C60 and acid-treated
C60 (see the Supporting Information). This means that C60
kept its structure after acid treatment. Then the treated C60
was used to reduce MO under UV irradiation in the pres-
can provide reliable information for the investigated system.
After C60 is irradiated by UV light, electrons are generally
excited into orbital 181 from orbital 180 and triplet C60 is
formed. An unrestricted M062X calculation was performed
for the triplet species to obtain orbital information. From
Figure 3, the energies of the half-occupied orbitals of triplet
C60 (orbital 180 and 181) are lower than those of the unoc-
cupied orbital of singlet C60 (orbital 181). Thus, C60 accepts
electrons more easily in the excited state than in the ground
state. The interaction energy between singlet C and MO is
ence of NaBH . From Figure S9 in the Supporting Informa-
4
tion, the treated C60 still effectively catalyzed MO reduction.
Thus, metal contaminants are not the driving force behind
fullerene catalytic activity.
It is well known that C60 is a better electron acceptor
[14,15]
under light irradiation than under dark conditions.
Also,
azo compounds contain N atoms and aromatic rings, which
are all electron-donor moieties. Therefore, C60 might cata-
lyze the reduction of azo compounds by using its vacant or-
bital to accept the electrons of the bonding orbital in azo
compounds. According to Figure S10 in the Supporting In-
formation, a small amount of MO molecules are adsorbed
on the C60 surface without UV irradiation. After UV irradia-
tion for 2h, the UV peak of MO clearly decreases, which
implies that UV irradiation can increase the interaction be-
6
0
À1
24.5 kcalmol , and smaller than that between triplet C
60
À1
and MO (54.0 kcalmol ). This accounts well as to why MO
is more easily adsorbed on the C60 surface under UV irradia-
tion than without UV irradiation (see the Supporting Infor-
mation). Singlet C60 interacts with MO to form a complex
(C SMO), whereas the complex from the interaction be-
60
tween triplet C60 and MO is named as C TMO. From
60
Figure 4, it can be seen that the length of the N=N bond is
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Niveen M. Khasab et al.
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Figure 4. The optimized geometries of MO, C60SMO, and C60TMO.
Figure 5. The optimized geometry of the MO–CNT complex.
1
.28 ꢁ in MO, 1.29 ꢁ in C SMO, and 1.33 ꢁ in C TMO.
6
0
6
0
Clearly, MO is more activated by triplet C60 than singlet C60.
The distance between the N=N bond and triplet C60 in
C TMO is larger than that in C SMO, owing to triplet C
formed to investigate the change of the N=N bond before
and after interacting with CNT. According to Figures 4 and
5, the length of the N=N bond in the MO–CNT complex is
identical to that in MO. This means that the p–p stacking in-
teraction cannot activate the N=N bond of MO.
60
60
60
accepting electrons from the aromatic ring of MO. As there
is a conjugation between the N=N bond and the aromatic
ring in MO (see the Supporting Information), the interac-
tion between C60 and the aromatic ring of MO will also lead
to the activation of the N=N bond. It has been reported that
the phosphane–borane compound can activate the HÀH
In addition, we found that water also played a significant
role in the azo dye reduction by C60 and NaBH under UV
4
irradiation.
bond by using the vacant orbital of the boron center to
MR rather than MO was chosen to test whether it can be
accept the electron in bonding orbitals of the HÀH bond
reduced in ethyl acetate by C60 and NaBH under UV irradi-
4
[20–22]
with the assistance of the phosphorus center.
Fullerene
ation as MO does not dissolve well in this organic solvent.
C60 still works as a heterogeneous catalyst because it does
not dissolve well in ethyl acetate. From Figure 6, it can be
has been found that can accept the lone-pair electrons of
carbene using its vacant orbital to form a Lewis acid–base
[23]
adduct. Most recently, Alcarazo et al. suggested that full-
erene may work as a carbon-based catalyst to activate small
[24]
[25]
molecules. Our previous work also showed that the ac-
ceptor property of C60 greatly influences the way that the
carbonyl group on the rim of the C60 orifice reacts with
a phosphite compound. So, it is very possible that C60 also
activates MO under UV irradiation by using its vacant orbi-
tal to accept the electron in the bonding orbital of MO, simi-
lar to that of the transition metal accepting the electron in
[21]
the bonding orbital with its vacant d orbital.
It is well known that aromatic molecules can also adsorb
on the carbon-nanotube (CNT) surface through p–p stack-
[26]
ing interactions.
To confirm that MO activation is not
from the p–p stacking interactions as C60 is a conjugated
system as well, the possibility of using CNTs to catalyze the
MO reduction was also checked. Commercial carboxylic
acid functionalized carbon nanotubes were used because
any possible metal residue should be removed during the
acid-treatment process. ICP analysis for the CNT sample
was performed and no metal residues were found. An IR
Figure 6. UV spectra of C60-catalyzed MR reduction under UV irradia-
tion in the presence of NaBH in ethyl acetate. This reaction is monitored
4
by taking the supernatants of the solution at different time intervals for
UV characterization.
À1
peak was found at 1726.75 cm , which corresponds to the
C=O stretching vibration of the carboxylic groups (see the
[27]
Supporting Information).
A TEM image of the CNT
sample showed that its diameter is about 15 nm (see the
Supporting Information). As illustrated in Figure S14 in the
Supporting Information, it was found that CNT cannot cata-
lyze the reduction of MO with and without UV irradiation
as the absorption peak around 460 nm of the N=N bond in
MO decreases a little as a result of the adsorption of MO
on the CNT surface. Theoretical calculations have been per-
seen that MR cannot be reduced in ethyl acetate by C60 and
NaBH under UV irradiation as the UV absorption peak of
4
MR around 400 nm decreases only a little after the reaction
has proceeded for 5h. However, the UV absorption peak of
MR around 400 nm completely decreases in 5h after the ad-
dition of water (5 mL), which suggests that water also plays
a role in MR reduction. A previous report shows that the
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C -Catalyzed Reduction of Azo Derivatives
60
NaBH –H O complex can be formed through dihydrogen
vation of the N=N bond. This work provides new insight
into the catalytical performance of fullerene and is helpful
in the design of novel, green, carbon-based catalysts.
4
2
+
À
À
[28]
bonding: O···H ··· HÀB between BH and H O.
Theo-
4
2
retical calculations have been performed to investigate the
À
interaction between BH and H O. A simplified model just
4
2
À
containing one BH4 anion and one water molecule was
adopted. Given that anions are involved, solvent effects
have been considered in all optimizations by using the PCM
Experimental Section
Reagents
[29]
model with water as solvent. From Figure 7, the optimized
Fullerene, sodium hydroxide, sodium borohydride, methyl orange, methyl
red, and azobenzene-4,4’- dicarboxylic acid were purchased from Sigma
Aldrich (USA).
Reduction of Azo Compounds under UV Irradiation
Reduction of MO was carried out in a 50 mL beaker. NaOH solution
(
1m, 0.5 mL), distilled water (40 mL), sodium borohydride (150 mg), and
4À
2
4À
2
Figure 7. The optimized geometries of BH
models. Mulliken charges of some atoms are given in parentheses in red.
,
H
O, and BH –H
O
MO (10 mg) were added into the beaker. The pH of this solution was
about 11. Then, C60 (10 mg) was added to form a suspension, followed by
stirring under UV irradiation (UVLS-26 EL series UV lamp, 365 nm) at
room temperature for 5 h. The supernatants of all samples after centrifu-
gation were characterized with UV/Vis spectroscopy and HPLC-PDA-
MS analysis. The reduction procedure of methyl red (MR) and azoben-
zene-4,4’-dicarboxylic acid (AA) in water was similar to that mentioned
above.
+
À
H ··· H distance is 1.832 ꢁ, which is consistent with the re-
[28]
ported distance range (1.77 ꢁ–1.95 ꢁ).
adopted model can provide reliable information for the in-
Therefore, the
vestigated system. The length of the BÀH bond in the
À
Reaction of Fullerene with NaBH
4 2 4 3 2
+H O and NaBH +CH CH OH
BH –H O model is 1.236 ꢁ, which is slightly longer than
4
2
À
that in BH4 (1.230 ꢁ). In addition, the charge on the B-
C
60 (0.6 mg) was dissolved in toluene (10 mL) to form a light purple solu-
+
À
tion, then NaBH4 (10 mg) was added to the solution. After the addition
of water (1 mL) to the solution, the toluene/water mixture layered: the
upper layer (toluene phase) was still light purple and the lower layer
(water phase) was colorless. It was true for the same reaction proceeding
under UV irradiation. However, the addition of ethanol (1 mL) to the so-
lution turned the C60 toluene solution yellow from purple immediately,
which implied the formation of new species.
bound hydride in O···H ··· H-B is À0.100 e, and more nega-
À
tive than that in BH (À0.086 e). This suggests that the hy-
4
dride in the NaBH –H O complex should be more reactive
4
2
than that in NaBH , which explains well how H O partici-
4
2
pates in the reduction of MR catalyzed by C60 and NaBH4
under UV irradiation. It is well known that methanol can in-
crease the reduction ability of NaBH in organic synthesis
through the formation of dihydrogen bonding.
ICP Emission Spectrometer for Fullerene
4
[30]
Fullerene (100.0 mg; Aldrich) was put in the crucible and was heated in
a muffle furnace at 5008C under air to oxide all the samples, then 12m
HCl (1 mL) aqueous solution was added in the crucible to make a clear
transparent solution, which was transferred into a 10 mL volumetric flask
for ICP measurements.
We also collected a C60 sample after the reaction was
completed. The collected C60 was used to catalyze MO re-
duction again. As shown in Figure S15 in the Supporting In-
formation, the collected C60 effectively catalyzes MO reduc-
tion as well, which implies that C60 can be recycled for this
reaction. Based on Figure S16 in the Supporting Informa-
tion, more than 90% of MO is reduced by the catalysis of
Treatment of Fullerene with HCl and HNO
3
For the removal of the residual metals in C60, C60 (100 mg) was first treat-
ed with 12m HCl for 30 min, then 0.5m HNO3 for another 30 min. Subse-
quently, Milli-Q water was used to wash these samples until the pH of
the supernatant was neutral. These samples were dried in a vacuum oven
at 508C overnight.
C60 ACHTUNGTRENNUNG( 15 mg) and C ACHTUNGTRENNUNG( 5 mg) in 5h under UV irradiation. Thus,
60
even small amounts of C60 can effectively catalyze the reduc-
tion of MO, which supports evidence that C60 works as a cat-
alyst rather than a reactant. The reduction rate using C -
Computational Section
6
0
ACHTUNGTRENNUNG( 15 mg) is just a little faster than that by C ACHTUGNTRENNU(GN 5 mg), which
60
indicates that the catalytic efficiency of C60 for this reaction
is so high that there is little difference whether using 5 or
All calculations were performed with the M062X/3-21g method in Gaus-
sian 09 since recent reports recommended this functional for the fuller-
ene system. For triplet C60 and the triplet C60–MO complex, the unre-
stricted M062X method was used. The interaction energy between C60
and MO was obtained by using the sum of the electronic energy of C60
and MO to deduct the electronic energy of the C60–MO complex.
15 mg C60 to catalyze MO reduction.
All figures were drawn with the GaussView 5.0 program based on the op-
timized species.
Conclusion
In summary, experimental and theoretical methods have
been combined to illustrate C -catalyzed reductions of azo
Acknowledgements
6
0
compounds in water under UV irradiation. The obtained re-
sults show that C60 acts as an electron acceptor to catalyze
the reduction of azo compounds and the role of UV irradia-
tion is to increase the ability of C60 to accept the electron in
the bonding orbital of the azo dyes, which leads to the acti-
We are grateful to King Abdullah University of Science and Technology
(
KAUST) for financial support.
Chem. Asian J. 2012, 00, 0 – 0
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Received: July 31, 2012
Revised: August 23, 2012
Published online: && &&, 0000
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www.chemasianj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

FULL PAPER
Filling a vacancy: Experimental and
theoretical methods have been com-
bined to show that C -catalyzed
reductions of azo compounds form
aromatic amines under UV irradiation
Fullerenes
Yong Guo, Wengang Li, Jingjing Yan,
Basem Moosa, Maꢀan Amad, Charles J.
Werth, Niveen M. Kha-
6
0
(
see scheme). The obtained results
shab*
&&&& — &&&&
show that C60 acts as an electron
acceptor to catalyze the reduction of
azo compounds, and the role of UV
irradiation is to increase the ability of
C60 to interact with electron-donor
moieties in azo compounds.
Fullerene-Catalyzed Reduction of Azo
Derivatives in Water under UV Irradi-
ation
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
7
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&
These are not the final page numbers! ÞÞ