Hierarchical microtubular nanoporous zirconia with an extremely high surface area and pore volume

Article abstract of DOI:10.1016/j.cplett.2004.02.069

Hierarchical nanoporous zirconias with an aligned microtubular structure of inner diameter 0.5-1.5 μm and length 5-30 μm and an extremely high surface area and large pore volume (up to 1100 m²/g and 3.0 cm ³/g, respectively) have been prepared by a simple method from a mixture of zirconium propoxide and chloroform solutions in the presence of nonionic polyethylene oxide surfactant. The tubular walls are composed of wormhole-like nanopores, resulting in very high surface areas and large pore volumes of hierarchical porous materials for multi-applications.

Full text of DOI:10.1016/j.cplett.2004.02.069

Chemical Physics Letters 388 (2004) 46–49
www.elsevier.com/locate/cplett
Hierarchical microtubular nanoporous zirconia with
an extremely high surface area and pore volume
Tie-Zhen Ren, Zhong-Yong Yuan, Bao-Lian Su *
Laboratory of Inorganic Materials Chemistry, I.S.I.S., The University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
Received 31 January 2004; in final form 31 January 2004
Published online: 18 March 2004
Abstract
Hierarchical nanoporous zirconias with an aligned microtubular structure of inner diameter 0.5–1.5 lm and length 5–30 lm and
2
3
an extremely high surface area and large pore volume (up to 1100 m /g and 3.0 cm /g, respectively) have been prepared by a simple
method from a mixture of zirconium propoxide and chloroform solutions in the presence of nonionic polyethylene oxide surfactant.
The tubular walls are composed of wormhole-like nanopores, resulting in very high surface areas and large pore volumes of hi-
erarchical porous materials for multi-applications.
Ó 2004 Elsevier B.V. All rights reserved.
Porous and high-surface-area materials are of great
interest to many scientific communities [1]. Such mate-
rials with a high degree of control over their structural
and textural properties are quite desirable due to their
application perspective. Much effort has been directed to
tyltrimethylammonia or nonionic polyethylene oxide
surfactant [20,21], but the particles had a dense layer on
one face, which might limit their applications.
The tubular structures of zirconia might have some
potential applications in the fields of heterogeneous ca-
talysis, adsorption, separation, chemical sensors and so
forth. However, only a few zirconia tubes were reported
to data and were prepared by sol-gel coating of carbon
nanotubes [22], alumina membrane [23], or eggshell
membrane [24]. The walls of such exo-templated tubes
are dense or sintered with a very low surface area
the preparation of ZrO -based mesoporous materials
2
using cationic quaternary ammonium surfactants [2–7],
anionic surfactants [8–11], primary amines [12–14] and
block copolymers [15,16] as the templating agents, since
ZrO2 is an important functional material. Ordered
mesoporous zirconia thin films have also been prepared
by evaporation-induced self-assembly [17]. However, the
surface areas of those previously reported mesoporous
2
(655 m /g). In this Letter, we report a simple strategy to
make a hierarchical structure of microtubular nanopor-
ous zirconia with an extremely high surface area and
2
zirconias can rarely exceed 700 m /g [2–16,18,19]. Thus,
2
3
new challenges arise in the preparation of ZrO2-based
porous structures including the increase and preserva-
tion of their surface areas and endowing a hierarchy of
different length scales with well-controlled pore sizes.
Antonelli [18] synthesized sulfated meso- and micropo-
rous zirconias by using chelating carboxylate surfac-
large pore volume (up to 1100 m /g and 3.0 cm /g, re-
spectively). The synthesized zirconia materials are mainly
in a form of bundles of microtubules with wormhole-like
nanoporous walls, having higher surface areas than those
previously reported for porous or tubular zirconia.
In our synthesis procedure, a 15 wt% micellar solu-
tion of Brij 56 [C (EO) ] was prepared by dissolving
2
tants, and their surface areas were 400–650 m /g.
Hierarchically mesoporous–macroporous zirconias with
1
6
10
the surfactant in a H SO aqueous solution of pH 2 at
2 4
2
a high surface area up to 700 m /g have synthesized
recently by surfactant templating of either cationic ce-
60 °C. A mixture of zirconium propoxide and chloro-
form (CHCl3) with different Zr/CHCl3 molar ratio was
added dropwise into the above medium (surf./Zr ratio
was fixed in the range of 0.33–0.5) under stirring. After
a further stirring for 1 h at room temperature, the
*
Corresponding author. Fax: +32-81-725414.
E-mail address: bao-lian.su@fundp.ac.be (B.-L. Su).
0
009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2004.02.069

T.-Z. Ren et al. / Chemical Physics Letters 388 (2004) 46–49
47
2
1
1
000
500
000
CHCl
CHCl
CHCl
CHCl
3
3
3
3
/Zr = 0
/Zr =3/7
/Zr =5/5
/Zr =7/3
/
Zr = 0
CHCl
CHCl
CHCl
CHCl
3
3
3
3
/Zr =3/7
/Zr =5/5
/Zr =7/3
0.3
0
0
0
.2
.1
.0
5
00
0
0
.0
0.2
0.4
0.6
0.8
1.0
0
4
8
12
16
20
24
(
a)
Relative pressure, P/P
(b)
Pore diameter (nm)
0
Fig. 1. Nitrogen adsorption–desorption isotherms (a) and their corresponding pore size distribution curves (b) of the zirconias synthesized from the
precursors with different CHCl3/Zr ratios. The volume adsorbed was shifted by 50, 100, 200 and dV/dD value was shifted by 0.05, 0.1, 0.2 for the
curves of CHCl3/Zr ¼ 3/7, 5/5, 7/3, respectively.
obtained mixture was transferred to a Teflon-lined au-
toclave and heated at 80 °C for 24 h under static con-
dition. The product was filtered and washed by Soxhlet
extraction over ethanol for 36–48 h to remove the sur-
factant species, and dried at 60 °C.
Fig. 1 shows the nitrogen adsorption–desorption iso-
therms and the corresponding pore size distributions of
the zirconias synthesized with different CHCl3/Zr ratios.
The pore size distribution curves were obtained by BJH
method using the adsorption branches of the isotherms.
It is seen that the pore sizes of the materials slightly de-
creased from 1.7 to 1.4 nm with the addition of CHCl3
solution in the synthesis mixture (Table 1). And an evi-
dent change was seen in the part of isotherms at relative
pressure greater than 0.85, indicative of the presence of
an appreciable amount of secondary porosity. With the
improve the surface area and porosity of the resultant
zirconia material. This is the first time to report the
mesoporous zirconias with such extremely high surface
areas and large pore volumes. To our knowledge, the
pore volume of the current zirconia material is the
highest ever reported in the metal oxide materials. Yo-
shitake et al. [25] synthesized the wormhole-like meso-
2
porous titania with BET surface area over 1200 m /g by
primary amine templating, but the pore volume of their
3
titania was not larger than 0.65 cm /g. Such large pore
volume of the current zirconia material is ever larger
than those of most of previously reported silica-based
mesoporous materials, including mesocellular silica
3
foams (up to 2.4 cm /g) [26], and comparable to the re-
ported highest pore volume of mesoporous silica MCM-
3
41 (3.31 cm /g) which obtained after post-treatment with
N,N-dimethyldecylamine [27].
increase of the content of CHCl , the adsorbed volume
3
of nitrogen increased significantly, suggesting an
improved secondary porosity. The BET (Brunauer–
Emmett–Teller) surface areas also increased strikingly
The previously reported mesoporous zirconias have
typically yielded macroscale particles of fairly random
shape [2–16]. However, a featured morphology of mi-
crotubular structure was observed in the zirconias syn-
thesized in the present work. Fig. 2 shows typical
scanning electron microscopic (SEM) images of the
synthesized zirconias from the mixture of zirconium
propoxide and chloroform, revealing a microtubular
structure. The particles are in a form of well-aligned
hollow tubules with inner diameters of 0.5–1.5 lm and
lengths ranging from 5 to 30 lm. From the view of the
profiles of the particles, it can be seen the tubes are ar-
rayed highly ordered and uniaxially into bundles but
with open tips. Single tubules can also be seen in the
samples with a shorter length. Such a morphological
formation, induced by the participation of chloroform
in the synthesis, should be compatible with the signifi-
cant increase of the surface areas and porosity of the
resultant zirconias. This microtubular morphology is
2
from 593 to 1071 m /g with the pore volumes from 0.502
3
to 2.928 cm /g. This clearly indicates that a mixture of
zirconium propoxide and chloroform can obviously
Table 1
Structural properties of the microtubular zirconia materials synthe-
sized from the precursors with different CHCl3/Zr ratio
a
CHCl
3
/Zr ratio
S
BET
2
V
pore
(cm /g)
D
meso
(nm)
3
(
m /g)
0
593
878
0.502
1.344
2.613
2.928
1.7
1.5
1.4
1.4
3
5
7
/7
/5
/3
1071
987
a
Pore diameters calculated by using the BJH model on the ad-
sorption branch of the isotherms.

48
T.-Z. Ren et al. / Chemical Physics Letters 388 (2004) 46–49
Fig. 2. (a)–(c) Typical scanning electron microscopic images of the resultant microtubular zirconias. (b) Image viewed along the direction of tubules.
d) TEM image of the tubular walls showing wormhole-like mesostructure.
(
quite distinct from those previously reported of porous
zirconias [20,21].
mechanism to the present materials. Although the for-
mation mechanism is not totally clear and further work
should be done, it should be significant that the micro-
tubular structure of nanoporous zirconia can retain af-
ter thermal treatment at the temperature above 300 °C.
X-ray diffraction shows that the zirconia frameworks
possess amorphous walls (Fig. 3). One diffraction peak
is present in the small-angle region, which is indicative
of a disordered mesostructure without long-range order
in the pore arrangement. High-magnification transmis-
sion electron microscopic (TEM) images of the cross-
sectional specimens also reveal that the tubular walls are
composed of nanoparticles with accessible mesopores of
a disordered wormhole-like array (Fig. 2d).
It is expected that the participant chloroform should
affect the hydrolysis and precipitation rates of the Zr
precursor, as well as the formation of the surfactant
bilayer structure and supermicelles, which may further
affect the morphology and structural property of the
resultant zirconia. The surfactant-stabilised emulsions
or microemulsions might be formed in the synthesis
procedure, which would be predominant to direct the
formation of microtubular structure with ultra high
surface area. Or a co-operative effect of surfactant-
templating and emulsion-templating might be a real
2
A high surface area of 350–550 m /g can still be ob-
tained for these 300 °C-calcined microtubular zirconia
materials, revealing the high thermal stability.
In summary, the hierarchically mesostructured zir-
conia materials with a microtubular structure and an
extremely high surface area and large pore volume have
been synthesized, which should be promising for prac-
tical applications in the fields of catalysis, adsorption,
separation, chemical sensors and solid oxide fuel cell
electrode material [28,29]. The synthesis route described
here is very simple, low cost, environmentally benign
and able to be modified in many ways so that varied
product engineering is possible. By this strategy, the
synthesis of hierarchical nanostructure of other metal
oxides, such as titanium oxide, with extremely high
surface areas can be realizable.
Acknowledgements
3
CHCl /Zr=3/7
This work was financially supported by the European
Program of InterReg III (Programme France-Wallonie-
Flandre, FW-2.1.5) and the Belgian Federal Govern-
ment PAI-IUAP-5/01 project.
2
4
6
8
10
2
θ (degree)
CHCl /Zr
3
7
5
3
/3
/5
/7
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