One-pot synthesis of a high-surface-area zirconium oxide material with hierarchically three-length-scaled pore structure

Article abstract of DOI:10.1039/b402915a

A new type of hierarchically three-length-scaled porous zirconium oxide material with high BET surface area of > 900 m² g^-1, having a uniform macroporous (300-500 nm) structure of a supermicroporous (1.5 nm) nanoparticle (?25 nm in size) assembly with irregular mesovoids (20-60 nm) in the macroporous walls, was prepared by a simple one-pot method in the presence of alkyltrimethylammonium surfactant, which should be significant for practical applications in multiple fields including catalysis and separation.

Full text of DOI:10.1039/b402915a

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L E T T E R
One-pot synthesis of a high-surface-area zirconium oxide material
with hierarchically three-length-scaled pore structure
´
Aurelien Vantomme, Zhong-Yong Yuan 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: þ32-81-725414;
Tel: þ32-81-724531
Received (in Montpellier, France) 25th February 2004, Accepted 21st June 2004
First published as an Advance Article on the web 2nd August 2004
A new type of hierarchically three-length-scaled porous zirco-
nium oxide material with high BET surface area of 4 900
m2 gꢀ1, having a uniform macroporous (300–500 nm) structure
of a supermicroporous (1.5 nm) nanoparticle (B25 nm in size)
assembly with irregular mesovoids (20–60 nm) in the macropor-
ous walls, was prepared by a simple one-pot method in the pre-
sence of alkyltrimethylammonium surfactant, which should be
significant for practical applications in multiple fields including
catalysis and separation.
porous structure having three orders of length scale is of great
interest for bulk chemical applications. Suzuki et al.24 synthe-
sised mesoporous silica foams with hierarchical trimodal pore
structure (macrovoids and two kinds of mesopores ranging
around 3 and 40 nm) by the self-assembly of surfactant
micelles, silica nanoparticles and air bubbles. Sen et al.35
prepared hierarchically micro-meso-macroporous silicas with
ordering on three different scales in the presence of multiple
templates of polystyrene latex spheres, triblock copolymers
and co-surfactants (butanol or pentanol). In this letter, we
report the synthesis of hierarchically porous zirconia materials
with ordering on three different length scales by a simple one-
pot method in the presence of a single surfactant (see Experi-
mental) and extend their surface areas to over 900 m2 gꢀ1 This
novel zirconium oxide material, due to its extremely high
surface area and the hierarchically trimodal porous structure,
can find new applications, such as a bioactive ceramic.
Materials with high and multi-scale porosity and high sur-
face area play key roles in industrial processes, from catalysis
and surface chemistry to gas storage, purification and separa-
tion. Various synthetic pathways, including exo-templating
and endo-templating strategies, have been developed to create
porous and high-surface-area inorganic materials.1,2 Many
metal oxides, such as ZrO2,3,4 TiO2,5,6 CeO2,7 and Al2O3,8
have been synthesised, owing to their great potential applica-
tions in the field of catalysis. However, the design of high-
surface-area materials with multi-scaled porous structures still
remains an experimental challenge.
The synthesised zirconia particles are mainly tens of micro-
meters in size with a regular array of macropores, as shown in
the SEM image of Fig. 1(a). The diameters of the macropores
range from 300 to 500 nm. The macropores are uniformly
distributed in the particles [Fig. 1(b)], similar to with those
obtained previously for macroporous oxides of niobium32 and
zirconium.33,34 The regularity of the macropores can be con-
firmed by the cross-sectional TEM image in Fig. 1(c). A careful
observation shows that the macroporous walls are composed
of nanoparticles of about 25 nm in size, and the small irregular
voids ranging between 20 and 60 nm are the interparticle
spaces resulting from the aggregation of these nanoparticles.
These mesovoids are randomly distributed in the macroporous
walls. The high-magnification TEM images also reveal that
these nanoparticles are mesostructured with a disordered
wormhole-like assembly of accessible meso-/micropores [Fig.
1(d)]. This kind of wormhole-like meso(micro)structure was
previously observed in silica- and alumina-based mesostruc-
tured material synthesised by using non-ionic surfactants.36
Fig. 2 shows the X-ray diffraction patterns of the synthesised
samples. The wide-angle diffraction only gives a broad feature
in the 2y range of 20–401, which indicates that the zirconia
frameworks possess amorphous walls. One single broad dif-
fraction peak is present in the low-angle region, suggestive of
the packing of regularly sized ZrO2 nanoparticles, giving the
mesovoids. This is consistent with the TEM analysis.
Zirconium oxide is of particular interest because of its ion
exchange, redox, and acid-basic properties. Much effort has
been devoted to the synthesis of mesoporous zirconia materials
using supramolecular templating techniques with cationic qua-
ternary ammonium surfactants,3,9–13 anionic surfactants,14–17
primary amines,18–20 non-ionic surfactant21 and block copoly-
mers.22 However, the surface areas of these previously reported
mesoporous zirconias rarely exceed 700 m2 gꢀ1 3,9–22
Pacheco
.
et al.23 synthesised microporous zirconias using anionic (Nia-
proof 4) and nonionic (Tergitol 7) surfactants; their surface
areas were only in the range of 100–250 m2 gꢀ1. Antonelli4
synthesised sulfated meso- and microporous zirconias by using
chelating carboxylate surfactants; their surface areas were on
the order of 400–650 m2 gꢀ1
.
Practical approaches require the preparation of mesoporous
materials having hierarchical porous structures at different
length scales in order to achieve highly organised func-
tions.24,25 Several groups have reported the preparation of
macroporous materials with microporous or mesoporous walls
by dual templating methods with the utilisation of colloidal
polymer latex,25–28 starch gel,29 inorganic salts,30 emulsions31
or vesicles32 as templates for creating the macropores. A simple
method for the synthesis of hierarchical bimodal mesoporous-
macroporous zirconias by a single surfactant templating meth-
od has also been developed recently; the surface area could
Fig. 3 shows the typical nitrogen adsorption-desorption
isotherm of the synthesised material. The isotherm is of type
IV, according to the IUPAC classification. A high BET
(Brunauer–Emmet–Teller) surface area of 903 m2 gꢀ1 is ob-
tained from this material with the total pore volume of 1.01
cm3 gꢀ1. (Although the specific surface area determined by the
BET method, based on the assumption of uniform monolayer-
reach 700 m2 gꢀ1 33,34
This method is quite facile without the
.
need for polymeric spheres or vesicles to act as a template that
generates the macroporous structure. On the other hand, a
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 3 – 1 0 8 5
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Fig. 1 (a, b) SEM images of the synthesised zirconia particles showing uniform macroporosity; (c) low-magnification TEM image of a cross-
section of the synthesised zirconia showing the uniform macropore structure with mesovoids in the walls; (d) high-magnification TEM image of a
region of the macropore walls, showing the assembly of zirconia nanoparticles into wormhole-like supermicropores with irregular mesovoids.
multilayer formation with the absence of micropores, may be
slightly overestimated for hierarchical porous materials, we
used the BET method here for the sake of simplicity. The BET
surface area value presented here is still informative.) The
adsorption isotherm exhibits a high uptake of N2 at low
relative pressure (P/P0), indicating the presence of supermicro-
pores with a pore size if the range of 1–2 nm (between
micropore and mesopore size). The analysis of the pore size
distribution by the Barret–Joyner–Halenda method from the
adsorption branch of the isotherm reveals a narrow pore size
distribution centred at 1.5 nm (Fig. 3). At relative pressures
higher than 0.85, a strong increase in nitrogen adsorbed
volume is observed, evident of an appreciable amount of
secondary porosity, that is the large mesopores or the inter-
particle porosity. This secondary porosity can be attributed to
the mesovoids observed in the macroporous walls. The macro-
pores, confirmed by TEM and SEM images, are too large to be
measured by N2 adsorption analysis. Therefore, TEM and
SEM observations and N2 adsorption analysis reveal that the
current material exhibits the trimodal pore structure of a
micro-meso-macroporous system.
This hierarchical structure is synthesised at a high concen-
tration of surfactant CTMABr with a high surfactant-to-Zr
ratio. It is known that the pore size of mesostructured zirconias
will decrease with increasing surfactant concentration, and
zirconias with a pore size of about 1.8 nm can be prepared at
low surfactant concentration (e.g., Surf : Zr ratio of 0.33).34
Although the role of surfactant molecules in the creation of
macroporous structures remains unclear, it is reasonable on the
basis of previous13,33,34 and present observations to believe that
the supermicropores of the current zirconia are induced by
surfactant molecules. Since the hydrolysis and precipitation
rates of the zirconium alkoxide are very fast, nanometer-sized
particles of supermicrostructured surfactant–zirconia compo-
site with surface hydroxyl groups could form as soon as the Zr
precursor is added to the surfactant micellar solution. The un-
consumed surfactant molecules cover the nanoparticles of the
supermicrostructured surfactant–zirconia composition due to
the affinity between the hydroxyl groups of the nanoparticles
and the hydrophilic heads of the surfactant molecules.24 The
presence of surfactant molecules surrounding the surface im-
proves the size homogeneity and promotes the gentle assembly
of the nanoparticles, driving the formation of the mesovoids
(interparticle spaces) in the aggregation of the nanoparticles.
Meanwhile, a large amount of propanol molecules are
generated quickly by the hydrolysis and condensation of
Fig. 2 XRD patterns of the synthesised zirconia material. Inset is the
low-angle diffraction pattern.
Fig. 3 N2 adsorption-desorption isotherms of the synthesised zirconia
and (inset) the corresponding BJH adsorption pore size distribution.
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analysis (Micrometrics Tristar 3000), SEM (Philips XL-20 at
15 keV) and TEM (Philips TECNAI-10 at 100 keV).
Acknowledgements
This work was financially supported by the European Program
of InterReg III (Programme France-Wallonie-Flandre, FW-
2.1.5) and the Belgian Federal Government PAI-IUAP 01/5
project. A.V. thanks FNRS for a FRIA scholarship.
References
1
2
F. Schuth, Angew. Chem., Int. Ed., 2003, 42, 3604.
¨
T. J. Barton, L. M. Bull, W. G. Klemperer, D. A. Loy, B.
McEnaney, M. Misono, P. A. Monson, G. Pez, G. W. Scherer,
J. C. Vartuli and O. M. Yaghi, Chem. Mater., 1999, 11, 2633.
M. J. Hudson and J. A. Knowles, J. Mater. Chem., 1996, 6, 89.
D. M. Antonelli, Adv. Mater., 1999, 11, 487.
S. Cabrera, J. El Haskouri, A. Beltran-Porter, D. Beltran-Porter,
M. D. Marcos and P. Amoros, Solid State Sci., 2000, 2, 513.
H. Yoshitake, T. Sugihara and T. Tatsumi, Chem. Mater., 2002,
14, 1023.
D. Terrible, A. Trovarelli, J. Llorca, C. de Leitenburg and
G. Dolcetti, J. Catal., 1998, 178, 299.
T. Z. Ren, Z. Y. Yuan and B. L. Su, Langmuir, 2004, 20, 1531.
U. Ciesla, S. Schacht, G. D. Stucky, K. K. Unger and F. Schuth,
¨
Angew. Chem., Int. Ed. Engl., 1996, 35, 541.
3
4
5
6
7
8
9
10 U. Ciesla, M. Froba, G. Stucky and F. Schuth, Chem. Mater.,
1999, 11, 227.
¨
¨
11 J. S. Reddy and A. Sayari, Catal. Lett., 1996, 38, 219.
12 J. A. Knowles and M. J. Hudson, J. Chem. Soc., Chem. Commun.,
1995, 2083.
13 J. L. Blin, R. Flamant and B. L. Su, Int. J. Inorg. Mater., 2001, 3,
959.
Fig. 4 Schematic representation for the formation of hierarchical
supermicro-meso-macroporous zirconia.
zirconium propoxide, which might produce microphase-sepa-
rated domains of ZrO2 nanoparticles and water/alcohol chan-
nels which are the initiators of the macrochannels.37,38 Thus, a
hierarchical structure of uniform macrochannels with meso-
voids in the walls of a supermicrostructured nanoparticle
assembly would form during the synergistic packing of the
surfactant–zirconia nanoparticles. The existence of a very high
surface area should be compatible with this pore architecture
of three-length-scaled ordering. The proposed mechanism for
the formation of such a hierarchical trimodal pore structure of
zirconia is illustrated in Fig. 4.
14 G. Pacheco, E. Zhao, A. Garcia, A. Sklyarov and J. J. Fripiat,
Chem. Commun., 1997, 491.
15 G. Pacheco, E. Zhao, A. Garcia, A. Sklyarov and J. J. Fripiat,
J. Mater. Chem., 1998, 8, 219.
16 M. S. Wong and J. Y. Ying, Chem. Mater., 1998, 10, 2067.
17 G. Larsen, E. Lotero, M. Nabity, L. M. Petkovic and D. S. Shobe,
J. Catal., 1996, 164, 246.
18 N. Ulagappan, V. N. Raju and C. N. R. Rao, Chem. Commun.,
1996, 2243.
19 Y.-Y. Huang, T. J. McCarthy and W. M. H. Sachtler, Appl. Catal.
A, 1996, 148, 135.
20 D. J. McIntosh and R. A. Kydd, Microporous Mesoporous Mater.,
2000, 37, 281.
In conclusion, a hierarchically supermicro-meso-macropor-
ous zirconium oxide with high surface area has been prepared
for the first time by a simple one-pot synthetic pathway using
only a single surfactant as the directing agent of supermicro-
pores and mesovoids. The significant asset of the hierarchically
three-length-scaled pore system and the exceptionally high
surface area allow easy molecular diffusion to the reaction
sites, especially in catalysis. Therefore, this novel material may
find potential applications in multiple fields, such as catalysis,
adsorption, separation, chemical sensors and solid oxide fuel
cell electrode materials, as well as bioactive ceramics.
21 V. Idakiev, L. Ilieva, D. Andreeva, J. L. Blin, L. Gigot and B. L.
Su, Appl. Catal. A, 2003, 243, 25.
22 (a) P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D.
Stucky, Nature (London), 1998, 396, 152; (b) P. Yang, D. Zhao,
D. I. Margolese, B. F. Chmelka and G. D. Stucky, Chem. Mater.,
1999, 11, 2813.
23 G. Pacheco, E. Zhao, E. D. Valdes, A. Garcia and J. J. Fripiat,
Microporous Mesoporous Mater., 1999, 32, 175.
24 K. Suzuki, K. Ikari and H. Imai, J. Mater. Chem., 2003, 13, 1812.
25 P. Yang, T. Deng, D. Zhao, P. Feng, D. Pine, B. F. Chmelka,
G. M. Whitesides and G. D. Stucky, Science, 1998, 282, 2244.
26 B. Lebeau, C. E. Fowler, S. Mann, C. Farcet, B. Charleux and
C. Sanchez, J. Mater. Chem., 2000, 10, 2105.
27 M. Antonietti, B. Berton, C. Goltner and H. Hentze, Adv. Mater.,
1998, 10, 154.
¨
28 B. T. Holland, L. Abrams and A. Stein, J. Am. Chem. Soc., 1999,
121, 4308.
29 B. J. Zhang, S. A. Davis and S. Mann, Chem. Mater., 2002, 14, 1369.
30 D. Zhao, P. Yang, B. F. Chmelka and G. D. Stucky, Chem.
Mater., 1999, 11, 1174.
Experimental
In a typical preparation, a 15 wt % micellar solution of
cetyltrimethylammonium bromide (CTMABr) was prepared
by dissolving CTMABr in an aqueous acidic solution (pH ¼ 2)
at 40 1C under stirring for at least 3 h. An appropriate amount
of zirconium propoxide [Zr(OC3H7)4] was added dropwise into
the above solution to give a surfactant : Zr molar ratio of 1.65.
After further stirring for 1 h, the mixture was transferred into a
Teflon-lined autoclave and heated at 60 1C for 2 days. The
product was filtered by Soxhlet extraction over ethanol for at
least 30 h in order to remove the surfactant species, and then
dried at 60 1C in vacuum. No trace of a C–H stretch was
observed in the infrared spectrum of the product, indicating a
template-free material. Characterisation was performed by
XRD (Philips PW 1820 with Cu-Ka radiation), N2 adsorption
31 Z. Y. Yuan, T. Z. Ren and B. L. Su, Adv. Mater., 2003, 15, 1462.
32 D. M. Antonelli, Microporous Mesoporous Mater., 1999, 33, 209.
33 J. L. Blin, A. Le
Cheetham and B. L. Su, Angew. Chem., Int. Ed., 2003, 42, 2872.
34 Z. Y. Yuan, A. Vantomme, A. Leonard and B. L. Su, Chem.
Commun., 2003, 1558.
´
onard, Z. Y. Yuan, L. Gigot, A. Vantomme, A. K.
´
35 T. Sen, G. J. T. Tiddy, J. L. Casci and M. W. Anderson, Angew.
Chem., Int. Ed., 2003, 42, 4649.
36 S. A. Bagshaw, E. Prouzet and T. J. Pinnavia, Science, 1995, 269,
1242.
37 A. Collins, D. Carriazo, S. A. Davis and S. Mann, Chem.
Commun., 2004, 568.
38 T. Z. Ren, Z. Y. Yuan and B. L. Su, Chem. Phys. Lett., 2004, 388, 48.
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