Fabrication and photocatalytic activity of fullerodendron/CaCO3 composites

Article abstract of DOI:10.1246/bcsj.79.1983

Novel composite materials consisting of fullerodendrons and CaCO ₃ particles were fabricated to have better efficiency as photosensitizers in singlet photooxygenation reactions compared to pristine fullerodendrons. Moreover, fullerodendrons in

Full text of DOI:10.1246/bcsj.79.1983

ꢀ
2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 12, 1983–1987 (2006) 1983
Fabrication and Photocatalytic Activity of
Fullerodendron/CaCO Composites
3
Bandana Talukdar, Yutaka Takaguchi, Yasushi Yanagimoto,1
1
Ã1
1
2
2
Sadao Tsuboi, Masahiro Ichihara, and Kazuchika Ohta
1
Graduate School of Environmental Science, Okayama University, Tsushima, Okayama 700-8530
Faculty of Textile Science and Technology, Shinshu University, Ueda, Nagano 386-8567
2
Received May 1, 2006; E-mail: yutaka@cc.okayama-u.ac.jp
Novel composite materials consisting of fullerodendrons and CaCO3 particles were fabricated to have better
efficiency as photosensitizers in singlet photooxygenation reactions compared to pristine fullerodendrons. Moreover,
fullerodendrons in composites demonstrate the ability to control CaCO3 polymorphism through formation of thermo-
dynamically least stable form of CaCO3: vaterite.
Organic–inorganic hybrid materials have been drawing
great attention in research for acquisition of better insights into
natural processes like biomineralization and to create new and
more-advanced materials for better and novel applications.
Among various kinds of hybrid materials studied so far, com-
Herein, we report the synthesis of a new composite material
consisting of the least thermodynamically stable form of
CaCO3, i.e., vaterite, stabilized by carboxylate salts of a full-
erodendron, and the investigation of photosensitizing ability
of a fullerodendron within an organic–inorganic hybrid. Dur-
ing our investigation, we found that this new composite mate-
rial serves as an efficient heterogeneous photocatalyst through
incorporation of spherical vaterite crystals of CaCO3 to the
fullerodendrons. This photocatalyst is demonstrably more effi-
cient than pristine fullerodendron.
1
posites of CaCO3 with different organic motifs have been stud-
2
ied extensively. Particularly, the controlled formation of crys-
tal polymorphs of CaCO3, i.e., vaterite, aragonite, and calcite,
in the presence of different organic moieties has been the focus
of intense research.2 In this context, dendrimers, which are
monodispersed macromolecules with a regular and highly
branched three-dimensional architecture, are better candidates
for studying crystal nucleation and growth of CaCO3 than are
–4
Results and Discussion
The composite material (Fig. 1) was prepared by carrying
out CaCO3 crystallization in the presence of fullerodendron
3
other synthetic linear polymers. Recently, Naka and co-work-
ers demonstrated the controlled formation of vaterite using the
poly(amidoamine) (PAMAM) dendrimer with carboxylate
8
(I) (Fig. 2) under the same conditions as those of our previous
5
work (see Experimental Section). The dendrimer content in
4
groups at the external surface. Although many studies have
been devoted so far to the control of crystal polymorphs of
the crystalline CaCO3 was found to be approximately 34 wt %,
which was determined from the UV–vis spectra according to
the same method (see Experimental Section) as applied in
2
,3
CaCO3, there are only a limited number of reports con-
cerning the chemistry of a photoreactive dendrimer within
organic–inorganic hybrid materials. In this regard, recently,
we fabricated a new composite material consisting of anthryl
5
our previous report. After preparation of the composite mate-
rial, the crystal phases of CaCO3 were characterized using
FT-IR analysis, XRD, and SEM. The FT-IR spectrum of the
À1
5
dendron and vaterite particles of CaCO3. Furthermore, we ob-
composite showed bands at 877 and 746 cm (Fig. 3), indi-
cating the formation of vaterite, whereas characteristic bands
served photodimerization of the anthracene unit, showing that
the photoreactivity of the anthryl dendron is preserved within
the composite, despite effects of light-scattering and low con-
5
centration. Meanwhile, the development of fullerene-based
photosensitizers have been drawing much attention because
of their widespread application in the field of synthetic organic
chemistry and photodynamic therapy.7 Nakamura reported
that C60, C70, and their derivatives are synthetically useful
photosensitizers for the photooxygenation of olefins with sin-
6
6
m
glet oxygen. Recently, we developed a method for facile
8
synthesis of fullerodendron, which can act as a homogeneous
9
photocatalyst. Although homogeneous photosensitizers for
reactions with singlet oxygen based on fullerene derivatives
have been widely reported, there have been only a few reports
of heterogeneous photocatalysts containing fullerenes.1
0–13
Fig. 1. Photograph of fullerodendron/CaCO3 composite.
Published on the web December 13, 2006; doi:10.1246/bcsj.79.1983

1
984 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Composites of Fullerodendron/CaCO3
-
K O
3000
O
-
K O
2
2
1
1
500
000
500
000
O
N
O
-
O K
NH
N
O
N
HN
O
-
O K
5
00
0
O
O
NH
0
10
20
30
40
2θ [0]
Fig. 4. XRD of the fullerodendron/vaterite composite. The
asterisk ( ) denotes the diffraction angle caused by calcite,
Ã
indicating negligible contamination.
Fig. 2. Structure of fullerodendron (I).
746
877
Fig. 5. SEM image of fullerodendron/vaterite composite
material (scale bar = 3 mm).
Fig. 3. FT-IR spectrum of CaCO3 crystals in the fullero-
dendron/vaterite composite.
of calcite at 874 and 712 cm were barely detectable.14 The
diffraction pattern, which was observed through XRD of the
composite materials, indicates the presence of vaterite crystals
in the composite with negligible calcite contamination
À1
In a typical photooxygenation reaction, a solution of furan-
2-carboxylic acid (1) (115 mg, 1 mmol) in CDCl3 (7 mL) in
presence of the composites (5 mg) was irradiated using a
500 W high-pressure mercury lamp through a Pyrex filter at
room temperature. During irradiation, oxygen was bubbled
through the reaction mixture. After irradiating for 90 min, the
corresponding lactone (5) was obtained in 95% yield (see
Scheme 1, Eq. 1). The photooxygenation reaction of 2,3-di-
methyl-2-butene (2) gave the corresponding photooxygenat-
ed product 3-hydroperoxy-2,3-dimethyl-2-butene (6) in 61%
yield using the composite material (5 mg) as a photocatalyst
(Eq. 2). The ene reaction of 4-methylpent-3-ene-2-ol (3) with
singlet oxygen generated by photosensitization with the com-
posite gave compounds 7 and 8 in 98 and 1.6% yields, respec-
tively (Eq. 3). The observed regioselectivity and stereose-
lectivity of the products conform to the known selectivity
of singlet oxygen reactions,6m indicating that the composite
material-sensitized reaction generates free singlet oxygen.
Moreover, photooxygenation of dibenzyl sulfide (4) gave the
corresponding sulfoxide in 96% yield (Eq. 4). In this case, a
mixture of chloroform and methanol was used as the solvent,
according to the observation of Foote and Peters that protic
solvents minimize the physical quenching of singlet oxygen
to afford better yields of sulfoxides than aprotic ones.18 When
we used pure chloroform as the solvent for the photooxygena-
tion reaction, sulfoxide (5) was obtained in 30% yield. The
crystal phase of CaCO3 did not change after the photoreac-
tions, which was confirmed by using FT-IR spectroscopy after
the photoreactions.
(
Fig. 4). Finally, SEM observation (Fig. 5) showed spherical
vaterite crystals, which might be attributable to aggregation
of numerous small vaterite nanoparticles.15 Although the com-
plete phase transformation of vaterite into the thermodynami-
cally stable calcite occurs within 80 h in aqueous solution, the
obtained vaterite crystals did not change the crystal morphol-
ogy even after incubation in water for 20 days. According to
similar results using PAMAM dendrimer reported by Naka
and co-workers, we speculated that the vaterite surface was
stabilized by the carboxylate-terminated fullerodendron, i.e.,
the surface of vaterite might be covered with fullerodendrons.
The color of the composite (Fig. 1), brown-orange surface, is
consistent with this speculation.
To examine the scope of the composite material as a photo-
sensitizer and to investigate the nature of the generated reac-
tive species, we carried out a photooxygenation reaction with
various olefins sensitized using fullerodendron/CaCO3 com-
posites. The Diels–Alder reaction and the ene reaction are
two widely used applications of singlet oxygen with olefins.17
Therefore, we examined the Diels–Alder conversion of furan-
1
6
2
-carboxylic acid (1) to it’s corresponding lactone as well as
the ene reaction of 2,3-dimethyl-2-butene (2) and 4-methyl-
pent-3-en-2-ol (3). Oxidation of benzyl sulfide (4) was also
examined. All of these reactions were catalyzed by the compo-
site materials under heterogeneous conditions (Scheme 1).

B. Talukdar et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1985
hν (> 300 nm), O2
COOH
HO
(1)
O
O
O
fullerodendron/CaCO3
composite
1
5
CDCl , 90 min
3
hν (> 300 nm), O2
(
2)
OOH
HOO
fullerodendron/CaCO3
composite
2
6
CDCl , 90 min
3
OH
OH
hν (> 300 nm), O2
OH
HOO
81:19
(
(
3)
4)
fullerodendron/CaCO3
composite
toluene, 4.5 h
7
8
3
O
S
hν (> 300 nm), O2
S
fullerodendron/CaCO3
composite
4
9
CHCl /CH OH, 110 min
3
3
Scheme 1. Photooxygenation reactions carried out with the composite material in heterogeneous condition.
The heterogeneous photosensitizer fullerodendron/CaCO3
composite was recovered easily at the end of the reaction by
centrifugation. It was recycled by washing (CHCl3, MeOH,
and H2O) and drying. When reused in subsequent runs, the
composite materials afforded the corresponding products, but
in noticeably lower yields, showing that the effectiveness of
the sensitizer gradually decreases. For example, photooxyge-
nation of dibenzyl sulfide (4) gave the corresponding sulfoxide
(
9) in 96% yield in the first run, and after recycling of the full-
erodendron/CaCO3 composite, 61 and 47%, in a second and
third run, respectively. This might be attributed to a slight
decomposition of the fullerodendron during the photooxygena-
tion reaction. A similar result was observed when pristine full-
Fig. 6. SEM image of the fullerodendron/calcite composite
(scale bar = 20 mm).
9
erodendron (I) was used as a catalyst.
Comparison of the photocatalytic ability of the composite
material with that of the fullerodendron showed that the
heterogeneous photocatalyst fullerodendron/CaCO3 compo-
site is more efficient than our previous homogeneous catalyst
can be attributed to better isolation of the individual photoac-
tive C60 moieties in the composites as compared to that of pris-
tine fullerodendron, which prevents self-quenching of excited
state of C60.
9
fullerodendron. For example, the photooxygenation of diben-
zyl sulfide (4) with the composite (containing 1.7 mg of fullero-
dendrimer) gave 96% of the desired product (9) when irradi-
ated with high-pressure mercury lamp for 110 min, whereas
the homogeneous photooxygenation reaction using the same
amount of fullerodendron (I) (1.7 mg) for the same duration
gave a 70% yield of 9. The catalytic turnover of the hetero-
geneous photocatalyst was estimated for the photooxygenation
reaction of dibenzyl sulfide (4) to be >450, which was calcu-
lated based on the fullerodendron content in the composite.
However, that number is expected to be even greater because
only the fullerodendrons on the surface of the composite were
expected to exhibit photoreactivity. The photoreactivity of
fullerodendrons within the composite might be inhibited
because of the light-scattering effects. The turnover number
of the composite (>450) is apparently more than 1.5 times
higher than that of fullerodendron (300). The reason for this
enhanced photoreactivity of fullerodendron/CaCO3 composite
Finally, in order to clarify the unique reactivity of our full-
erodendron/vaterite composite, we fabricated a fulleroden-
dron/calcite composite and investigated it’s photocatalytic
activity. The calcite composite of fullerodendron was prepared
by delaying the addition time of fullerodendron. After the for-
mation of calcite of CaCO3, fullerodendron (I) was added to a
dispersion of calcite crystals. The dispersion was then stirred
for 3 days with the expectation of surface modification of cal-
cite crystal of CaCO3 and separated by filtration. It is notable
that this new composite seems to be less stable than our previ-
ous composite of vaterite since most of the fullerodendrons in
the calcite composite gets washed away with water. This is
evident from the comparison of the fullerodendron contents
of both of the composites, which is 9 and 34 wt % for calcite
and vaterite composite, respectively. Figure 6 shows a SEM
image of the fullerodendron/calcite composite, in which rhom-
bohedral calcite crystals were observed. The FT-IR spectrum

1
986 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Composites of Fullerodendron/CaCO3
À1
of the composite had bands around 874 and 712 cm , indicat-
ing the formation of calcite. In order to compare the photoca-
talytic activity of the fullerodendron/calcite composite with
the fullerodendron/vaterite composite, we investigated the
photooxygenation reaction of dibenzyl sulfide (4) using these
two composites. For example, the photooxygenation of diben-
zyl sulfide (4) with the calcite composite containing 1.7 mg of
fullerodendrimer gave 87% of the desired product 9 when irra-
diated with a 500 W high-pressure mercury lamp for 110 min,
whereas, for the same duration, the vaterite composite contain-
ing the same amount of fullerodendron (1.7 mg) gave 96% of
added to the reaction mixture after incubation for 6 h. The disper-
ꢀ
sion was then kept at 30 C for 3 days under gentle stirring. The
crystalline CaCO3 was collected after 3 days and washed several
times with water.
Estimation of the Content of Fullerodendron (I) in the Com-
posite Material. 5 mg of the composite material was dissolved in
3
0
0 mL of 1 M HCl. Absorbance of the solution at 400 nm was
.454. According to the molecular extinction coefficient (") that
was calculated by measurement of pristine fullerodendron (I),
content of the fullerodendron (I) in the composite material of
vaterite was estimated to be 34 wt %. Similarly, the wt % of the
calcite composite was estimated to be 9%.
9
. On comparision of the photocatalytic activity of both com-
posite materials, we found that the photoreactivity of fullero-
dendron/calcite composite is lower than fullerodendron/vater-
ite composite as evident from the yields of their photooxygen-
ated products.
This work was partly supported by the Kurata Memorial
Hitachi Science and Technology Foundation, Industrial Tech-
nology Research Grant Program in 2004 from the New Energy
and Industrial Technology Development Organization (NEDO)
of Japan, and a Grant-in-Aid for the Scientific Research
Conclusion
(Nos. 15550036 and 15750036) from the Ministry of Educa-
tion, Culture, Sports, Science and Technology (MEXT), Japan.
In conclusion, this work demonstrates that the photoreactiv-
ity of the fullerodendron does not diminish on fabrication of a
hybrid material; in fact, its photoreactivity is further enhanced.
When pristine C60 was used as a photosensitizer as shown by
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based on the formation of the more active spherical vaterite,
which is important for better catalytic performance. Further
work is in progress to explore applications and advantages of
organic–inorganic hybrid based on the fullerodendron.
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