Layer-by-layer self-assembled hollow titania composite nanospheres containing [60]fullerene

Article abstract of DOI:10.1039/b719900g

Core-shell nanospheres, titania composite nanospheres containing [60]fullerene, were fabricated with sizes of about 100 nm by a layer-by-layer self-assembly procedure, and were characterized by TGA, FT-IR and XPS spectroscopy. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b719900g

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Layer-by-layer self-assembled hollow titania composite nanospheres
containing [60]fullerene
Wenfeng Jiang, Ying Yu, Dianqing Li, Yingjie Zhao, Maoyou Xu and
Zhiqiang Shi*
Received (in Montpellier, France) 3rd January 2008, Accepted 6th February 2008
First published as an Advance Article on the web 28th February 2008
DOI: 10.1039/b719900g
Core–shell nanospheres, titania composite nanospheres contain-
ing [60]fullerene, were fabricated with sizes of about 100 nm by a
layer-by-layer self-assembly procedure, and were characterized
by TGA, FT-IR and XPS spectroscopy.
bond and p–p interactions make it an ideal building block for
fabricating novel nanoarchitectures. With numerous hydroxyl
groups from b-CD and carboxyl groups from PTCA on the
C
60@2b-CD/PTCA nanoparticle surface, the composite na-
noparticle was further self-assembled with orthotitanic acid,
resulting in C60@2b-CD/PTCA/TiO composite nanospheres.
Developments in nanotechnology demand building blocks
of increasing structural and compositional complexity that can
be reproducibly self-assembled into functional materials. In
this regard, nanoparticles with core–shell morphologies repre-
sent a new type of construction unit, consisting of two
dissimilar compositional and structural domains. In recent
years, most attention has been paid to core–shell nanostruc-
2
In the composite nanospheres, both PTCA and b-CD are
thermally unstable. Hollow titania composite nanospheres
containing [60]fullerene with a core–shell structure were finally
obtained by calcination.
The perylene derivatives exhibited flat p-systems, as con-
firmed by the X-ray diffraction of several single crystals.
1
5,16
1
–3
tures owing to their important optical, electronic, magnetic
The strong p–p stacking and hydrogen bond interactions
enabled PTCA molecules to aggregate readily to form one-
dimensional nanorods of up to 400 nm in length (Fig. 1(a)).
However, after being assembled with C60@2b-CD, only
nanoparticles of less than 80 nm in diameter were observed
(Fig. 1(b)). It was noted that the morphologies and sizes of the
nanoparticles heavily depended on the molar ratio of C60@2b-
CD to PTCA used. In general, high excesses of PTCA resulted
in its dominative self-aggregation and a tendency to form rod-
like nanostructures, whereas high excesses of C60@2b-CD led
to larger particle sizes.
and catalytic applications, and as drug delivery carriers and
4
–10
nanoreactors.
In this field, layer-by-layer (LBL) self-as-
sembly approaches have been applied to fabricate hollow
composites using molecular precursors and nanoparticles as
1
,9,10
inorganic shell building blocks.
As kinds of photocataly-
tically active and photoconductive n-type semiconductors,
numerous nanosized titania materials have been synthesized
1
1,12
and investigated extensively.
Recently, several types of
titania hollow shell have been reported using the LBL techni-
1
,13
que.
TiO
and investigated their properties. But owing to the small
cavity in the TiO shell, it was difficult to observe hollow TiO
In our past work, we have fabricated C60@2b-CD-
(CD = b-cyclodextrin) nanospheres (15 nm in diameter)
The sample C60@2b-CD/PTCA (Fig. 1(b)) was obtained
using the ratio [C60@2b-CD]/[PTCA] = 0.55. These nanopar-
2
1
4
ticles were further coated with TiO
2
to form the C60@2b-CD/
PTCA/TiO composite nanospheres, which were calcined at
2
2
nanospheres with C60 cores. Bearing this mind, herein we
introduce 3,4,9,10-perylene tetracarboxylic acid (PTCA) to
form organic–inorganic C @2b-CD/PTCA/TiO composite
2
360 1C in a vacuum overnight to yield hollow titania nano-
spheres containing C60. The TEM images of the C60@2b-CD/
6
0
2
nanospheres that are 100 nm or so in diameter. By removing
the organic compounds, after calcination, hollow nanospheres
result.
2
PTCA/TiO composite nanospheres and the resulting hollow
nanospheres are shown in Fig. 1(c) and 1(d), respectively. The
color of the composite nanospheres was far deeper than the
The hollow titania composite nanospheres, containing
C
60@2b-CD/PTCA nanoparticles owing to the TiO
and the sizes of nanospheres were around 100 nm in diameter.
Compared to the C60@2b-CD/PTCA/TiO composite nano-
2
coating,
[
60]fullerene with a core–shell structure, were designed as
shown in Scheme 1. [60]Fullerene is highly symmetric, repre-
senting a special class of aromatic system. Because of water
insolubility and the absence of a driving force for self-assembly
with orthotitanic acid, the pristine C60 was capped with two
b-CD molecules, firstly to form a C @2b-CD inclusion
2
spheres, the surface of the hollow nanospheres were relatively
rough after calcination. When the 360 1C calcination time was
short, the composite nanospheres still had a solid core. A
hollowing effect was observed for those prepared by
6
0
complex, which was then self-assembled with PTCA to form
nanoparticles. PTCA is a unique water soluble compound with
four carboxyl groups and a flat p-system. Strong hydrogen
Department of Chemistry, Shandong Normal University, 88
Wenhuadonglu Road, Jinan, 250014, P. R. China. E-mail:
zshi@sdnu.edu.cn; Fax: +86 531-82615258; Tel: +86 531-8618254
Scheme 1 Synthesis scheme for the hollow titania nanospheres with a
[60]fullerene core.
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New J. Chem., 2008, 32, 581–583 | 581

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in total. It is suggested that most of the b-CD and PTCA were
decomposed by calcination. Further signals were visible from
4
1
60 1C, attributable to fullerene, with a mass reduction up to
0%. Compared with the C @2b-CD/PTCA/TiO composite
6
0
2
nanospheres, the decomposition temperature of fullerene in
hollow nanospheres is similar. This result demonstrates that
the hollow nanospheres containing fullerene were obtained by
the calcination of b-CD and PTCA.
Infrared spectra of the hollow nanospheres, the C60@2b-
CD/PTCA/TiO
2
nanospheres and the C60@2b-CD/PTCA
nanoparticles are shown in Fig. 3. In the spectrum of the
C
60@2b-CD/PTCA nanoparticles (Fig. 3(a)), strong vibration
À1
bands at 1614.7, 1638.7 and 1454 cm can be attributed to
CQC stretching and the aromatic perylene skeleton. The
À1
strong peak at 1659.6 cm
may be assigned to a CQO
stretching mode of the carboxylic acid group, which is re-
markably shifted towards a low wavenumber owing to the
formation of strong hydrogen bonds. The strong vibration
À1
Fig. 1 TEM images of (a) PTCA nanorods, (b) C60@2b-CD/PTCA
band at 1384.4 cm may be assigned to the –OCH
À1
3
group of
nanoparticles, (c) C60@2b-CD/PTCA/TiO
resulting hollow nanospheres.
2
nanospheres and (d) the
b-CD. Weak peaks at 575.6 and 526.2 cm can be attributed
to the fullerene. After being coated with orthotitanic acid, a
À1
broad band from 450 to 700 cm was observed, which can be
calcination in a vacuum overnight. It should be mentioned
that no such hollowing effect was observed in our previous
2
assigned to TiO (Fig. 3(b)). Compared with spectra a and b,
the FT-IR of the hollow nanospheres after calcination was
1
4
work.
simple. Peaks corresponding to CQO, –OCH from PTCA
3
To confirm the content and decomposition behavior of the
and b-CD disappeared, while the characteristic absorption
peaks of [60]fullerene at 575.6 and 526.2 cm verified the
À1
C @2b-CD/PTCA/TiO composite nanospheres and hollow
6
0
2
nanospheres, TGA investigations were carried out at a heating
À1
presence of fullerene. But there were also small peaks at
À1
rate of 5 1C min in a nitrogen atmosphere. Fig. 2 illustrates
1618.7, 1638.6 and 1400 cm , corresponding to a trace of
the TGA curves of the C60@2b-CD/PTCA/TiO
nanospheres and the hollow nanospheres containing [60]full-
erene. The TGA trace of the C60@2b-CD/PTCA/TiO com-
2
composite
perylene decomposed from PTCA.
2
The presence of C60 in the C60@2b-CD/PTCA/TiO nano-
2
spheres and hollow nanospheres was further confirmed by
measuring binding energy spectra of the C1s electrons. As
shown in Fig. 4, Gaussian analysis of the XPS data of C1s
displayed four main components. The binding energy for C60
was situated at 284.5 eV. The contribution at 285.5 eV could
be assigned to carbons associated with the core of the PTCA
molecule. All of the C-2–C-6 carbons of the glucose units in
b-CD were situated at 286.1 eV. The fourth broad contribu-
tion at 287.4 eV arose from carbonyl group carbons, hemiketal
carbons (C-1 carbon of the glucose units) and a shake-up
posite nanospheres (curve a) offers some interesting
observations, and shows ca. 14% weight loss until 120 1C that
is related to adsorbed water, but this amount could change,
depending on the relative humidity. The main decomposition
was found between 120 and 600 1C, and was clearly attribu-
table to the dehydration of b-CD, PTCA and C , with a
6
0
weight loss during this stage of 37%. Compared to the pristine
[
60]fullerene (curve c), the formation of the nanostructures
resulted in a remarkably early degradation of C60. Hollow
nanospheres (curve b) only showed a slight, steady decrease in
weight between 30 and 460 1C, amounting to no more than 4%
1
7
feature associated with the carbonyl groups. Compared with
the 60@2b-CD/PTCA/TiO nanospheres, the hollow
C
2
Fig. 2 TGA curves of (a) the C60@2ba
nanospheres, (b) the hollow nanospheres and (c) the pristine
60]fullerene.
˜
CD/PTCA/TiO
2
composite
Fig. 3 FT-IR spectra of (a) the hollow nanospheres, (b) the C60@2b-
CD/PTCA/TiO
2
nanospheres and (c) the C60@2b-CD/PTCA nano-
[
particles.
5
82 | New J. Chem., 2008, 32, 581–583
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C60@2b-CD/PTCA nanoparticles were dispersed by sonica-
4
tion in 175 mL n-butanol and added to the cold Ti(OH) stock
solution, and the mixture stirred at room temperature for 4 d.
The resulting solution was transferred to a Teflon-lined auto-
clave and aged at 120 1C for 24 h in order to grow the titania
nanospheres. Thereafter, the resulting mixture was centrifuged
at 4000 rpm for 30 min, and finally the supernatant liquid was
discarded. The precipitates were washed three times with
DMF and acetone, and were dried at room temperature under
vacuum for 1 d. The powder was then calcined at 360 1C in a
vacuum overnight.
The morphology and size of the samples were observed
using a Hitachi H-800 transmission electron microscope
(
TEM) at an accelerator voltage of 200 kV. Products were
analyzed in a Perkin-Elmer TGA7 under a dynamic nitrogen
À1
À1
atmosphere (20 mL min ) and a heating rate of 5 1C min
using platinum crucibles. The temperature range used was
from 20 to 650 1C. FT-IR spectra were recorded on a Bruker
Tensor-27 instrument. X-Ray photoelectron spectroscopy
data were obtained using an ESCALab220i-XL electron spec-
trometer from VG Scientific using 300 W Al-Ka radiation.
Fig. 4 C1s binding energy XPS spectra of the C60@2b-CD/PTCA/
TiO composite nanospheres (bottom) and hollow nanospheres (top).
2
FWHM = full width at half maximum.
nanospheres exhibited only traces of PTCA and b-CD com-
ponents. The C60 in the hollow nanospheres detached from the
b-CD molecules after calcination, and its binding energy
À9
The base pressure was about 3 Â 10 mbar. The binding
energies were referenced to the C1s line at 284.8 eV of
adventitious carbon.
1
8
shifted to 284.6 eV, closer to pristine C60 (284.7 eV). These
results indicate that the C60 structure in the hollow nanosphere
skeleton was retained.
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In conclusion, core–shell composite nanospheres, hollow
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fabricated successfully using a layer-by-layer self-assembly
strategy. The sizes of the nanospheres were about 100 nm in
diameter. The skeleton of [60]fullerene was retained un-
damaged, and is expected to be an ideal object for performing
investigations of [60]fullerene in nanospace.
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This journal is ꢀc The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008
New J. Chem., 2008, 32, 581–583 | 583