Surfactant-assisted synthesis of unprecedented hierarchical meso-macrostructured zirconia

Article abstract of DOI:10.1039/b303272h

A surfactant-assisted one-step synthesis route was developed, leading to the formation of a very high surface area (600 m² g^-1) of zirconia and unprecedented hierarchical meso-macroporous structure with wormhole-like mesoporous walls and a novel, uniform assembly of macropores ranging in size from 300 to 500 nm.

Full text of DOI:10.1039/b303272h

Surfactant-assisted synthesis of unprecedented hierarchical
meso-macrostructured zirconia
Zhong-Yong Yuan, Aurélien Vantomme, Alexandre Léonard and Bao-Lian Su*
Laboratory of Inorganic Materials Chemistry, The University of Namur (FUNDP), 61 Rue de Bruxelles,
B-5000 Namur, Belgium. E-mail: bao-lian.su@fundp.ac.be; Fax: +32-81-725414; Tel: +32-81-724531
Received (in Cambridge, UK) 26th March 2003, Accepted 16th May 2003
First published as an Advance Article on the web 3rd June 2003
A surfactant-assisted one-step synthesis route was devel-
oped, leading to the formation of a very high surface area
long-range order in the mesopore arrangement — this is
consistent with the TEM image. No significant diffraction in the
wide-angle range except a broad feature in the 2q range of
20–40° was observed, which indicates that the zirconia
frameworks possess amorphous walls.
Representative nitrogen adsorption–desorption isotherms
and the corresponding pore size distributions are shown in Fig.
2
21
(
600 m g ) of zirconia and unprecedented hierarchical
meso-macroporous structure with wormhole-like mesopor-
ous walls and a novel, uniform assembly of macropores
ranging in size from 300 to 500 nm.
The fabrication of hierarchically-ordered porous structures at
multiple scales has recently attracted considerable attention for
both fundamental and practical reasons.1 Mesoporous oxide
materials with macroporous structures are of much interest as
potential catalysts and sorbents, partly because the textural
mesopores and intrinsic interconnected pore systems of macro-
structures should be able to efficiently transport guest species to
framework binding sites. The combination of surfactant tem-
3. A strong uptake of N
a relative pressure (P/P
plateau at P/P of 0.80. This kind of isotherm indicates that the
2
due to capillary condensation occurs in
0
) range of 0.14–0.40 and reaches a
,2
0
final materials belong to the mesoporous family. The pore size
3
4
plating techniques and colloidal crystal templating methods
allows the construction of hierarchically bimodal mesoporous-
5
macroporous silicas. Sponge-like silica membranes with three-
dimensional meso-macrostructures were synthesised from an
electrolyte phase of block copolymer/silica systems, though
inorganic salt crystals inevitably grew along with the silica
membrane.6 Antonelli7 reported the synthesis of macro-
mesoporous niobium oxide by means of a NaCl-promoted
vesicle templating method using a niobium ethoxide/amine gel.
In this communication, we describ a simple method to
synthesise a novel hierarchical structure of meso-macroporous
zirconia in one step using a single surfactant. This method does
not require polymeric spheres to generate the macropore
structure nor does salt need to be added to form templatable
vesicles.
Zirconia is an important functional material. Much research
has focused on the synthesis of mesoporous zirconia by using a
surfactant, such as cetyltrimethylammonium bromide
8
(
CTMABr), as the structure-directing template agent. How-
ever, the mesoporous zirconias that have been reported have
typically yielded macroscaled particles of fairly random shape.
The mesoporous zirconia synthesised in this work exhibits an
unusual morphology of macroporous structure.† The particles
have a size of tens of micrometers with one flat but dense layer
with a smooth surface (Fig. 1). Above this layer, a regular array
of macropores occurs. In size, the macropores range from 300 to
Fig. 1 (a–c) SEM images of the synthesised meso-macroporous zirconia
particles; (d) low-magnification TEM image of a cross-section of meso-
macrostructured zirconia along the macrochannel direction; (e) high-
magnification TEM image of the macroporous structure, showing that the
macrostructure framework is composed of wormhole-like mesopores.
500 nm. The hollow macrochannels are practically parallel to
each other and perpendicular to the flat dense layer of the
monolithic particles. A view of the monolithic particles’
profiles shows that these macrochannels extend throughout
almost the whole particle. Such a macroporous structure is
unprecedented and quite different from those previously
reported, including the structures of vesicle-templated and latex
sphere-templated macroporous oxide materials.4 The particles
containing such a macrostructure have a good yield of over
,7
6
0%, which is estimated by SEM observations. A TEM image
of a cross-sectional zirconia specimen also reveals that the
macroporous framework is composed of accessible mesopores
with a disordered wormhole-like array (Fig. 1e).
Fig. 2 shows the X-ray diffraction (XRD) patterns of the
synthesized meso-macrostructured zirconia. The presence of a
single broad diffraction peak in the low-angle range is
indicative of a disordered mesostructure with no discernible
Fig. 2 XRD pattern of the synthesised meso-macrostructured zirconia.
1
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This journal is © The Royal Society of Chemistry 2003

Fig. 4 Schematic representation of meso-macrostructure formation.
This hierarchical meso-macrostructured material should be
significant for its applications in catalysis and separation
technology. It can also be employed in the design of inorganic
membranes which may be applied in various domains such as
process filtration, cell culture, and biomolecule separation and
storage. Additionally, it can be used as templating material for
the inverted synthesis of new advanced materials such as
nanotubes and nanowires. Functionalisation of this material by
chemical modification of the internal pore surface may lead to
more practical applications.
We wish to acknowledge financial support from the Euro-
pean Program of InterReg III (Programme France-Wallonie-
Flandre, FW-2.1.5) and the Belgian Federal Government PAI-
IUAP-5/01 project and Wallonie WDU project-Gredecat.
2
Fig. 3 N adsorption–desorption isotherms of the meso-macrostructured
zircona. The corresponding pore size distribution curve (insert) is obtained
from the adsorption branch of the isotherm using the BJH (Barrett–Joyner–
Halenda) method.
distribution curve obtained by the BJH method using the
adsorption branch of the isotherm is centered at about 1.8 nm.
The macropores, confirmed by SEM and TEM images, are too
large to be measured by N
2
adsorption analysis. The BET
surface area is 600 m g with a pore volume of 0.510 cm3
2
21
2
1
g
.
The synthesis of such a well-structured zirconia with
mesoporous walls separating the parallel macrochannels can be
performed in a wide range of experimental conditions, having a
good reproducibility with a yield of 40 to 90%. Only one
surfactant of CTMABr is needed to direct the production of
meso-macrostructure. The variation of the molar ratio of
surfactant to zirconium from 0.5 to 10, or the ratio of water to
zirconium from 20 to 300 did not affect the formation of the
meso-macrostructure, though the surface area of the production
Notes and references
† The synthesis was performed in the presence of the surfactant CTMABr.
A 10 wt% micellar solution of CTMABr was prepared by dissolving the
surfactant at room temperature in an aqueous solution over 3 h. A zirconium
3 7 4
propoxide [Zr(OC H ) ] solution was added dropwise into the above
medium, followed by further stirring for 3 h at room temperature. The
obtained mixture was then transformed to a Teflon-lined autoclave and
heated at 60 °C for 2 days under static conditions. The product was filtered
and washed by Soxhlet extraction over ethanol for 24–48 h in order to
remove the surfactant species. It was then dried at 60 °C in a vacuum.
Infrared spectroscopy revealed that all surfactant species were removed
after extraction. Characterisation was performed by XRD (Philips PW1820
2
21
could vary within the range of 518 to 670 m g while the
mesopore size could vary within the range of 1.8 to 2.5 nm. The
precipitation rate is known to be very fast when the ratio
between the concentration of water and zirconium is higher than
9
4
. Thus, hydrolysis and condensation occurred as soon as
3 7 4
Zr(OC H ) was added to the micellar solution of surfactant,
and the primary particles of mesostructured surfactant/zirconia
composite were formed with a large number of surface hydroxyl
groups due to incomplete condensation. Meanwhile, the
surfactant molecules in the solution can be adsorbed onto the
surface of primary particles to form a bilayer structure at the
interface. The further aggregation of these primary hybrid
particles and surfactant molecules could result in the vesicula-
tion of bilayer structures and the formation of supermicelles by
the coalescence of multiple micelles and the inter-aggregate
with Cu-Ka radiation), N
2
adsorption analysis (Micromeritics Tristar
000), SEM (Philips XL-20 at 15 keV) and TEM (Philips TECNAI-10 at
00 kV).
3
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0–12
This cooperative self-assembly process would
lead to the production of an ordered array of macrochannels
Fig. 4). The removal of the surfactant species then gives a
4
B. T. Holland, C. F. Blanford and A. Stein, Science, 1998, 281, 538; S.
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(
5
M. Antonietti, B. Berton, C. Göltner and H. Hentze, Adv. Mater., 1998,
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6
structures with a vesicular architecture have been well-
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orderliness of mesopore-composed macroporous walls are thus
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accessible pores can be well-preserved after calcination at 300
1
1
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1
1
°
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1
1
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though the mesostructure has been damaged due to sintering,
which is revealed by XRD, SEM and N
2
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13 A. Lind, B. Spliethoff and M. Lindén, Chem. Mater., 2003, 15, 813.
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