The mesoporous nanocrystalline zircoina was synthesized via solid state reaction-structure directing method in the presence of Laponite. The introduction of Laponite renders the higher thermal stability and lamellar track to the zirconia. Laponite acts as inhibitor for crystal growth and also hard template for the mesostructure. The role of Laponite is attributed to the interaction between the zirconia precursors and the nano-platelets of Laponite via the bridge of hydrophilic segments of surfactant. It results in the formation of Zr-O-Mg-O-Si frameworks in the direction of Laponite layer with the condensation of frameworks during the calcination process, which contributes the higher stability and lamellar structure to the nano-sized zirconia samples

A. Ziehfreund

D. Terribile

E. Sominski

F. Kleitz

F. P. F. van Berkel

F. Schuth

G. K. Chuach

Gaoqing Lu

H. Verveij

J. S. Reddy

M. Mamak

M. S. Wong

P. D. Yang

Q. Huo

S. D. Shen

U. Ciesla

X. M. Liu

Xinmei Liu

Zifeng Yan

Crossref

Stabilization of mesoporous nanocrystalline zirconia with Laponite

Liu, Xinmei

Yan, Zifeng

Lu, Gaoqing

University of Queensland eSpace

 
 
 
 
ARTICLES 
360 Chinese Science Bulletin  Vol. 50  No. 4  February  2005 
Chinese Science Bulletin 2005 Vol. 50 No. 4 360—364 
Stabilization of mesoporous 
nanocrystalline zirconia with  
Laponite 
LIU Xinmei1,2, YAN Zifeng1,2 & LU Gaoqing2 
1. Key Laboratory for Heavy Oil Processing, Key Laboratory of Cataly-
sis, CNPC, University of Petroleum, Dongying 257062, China; 
2. ARC Centre for Functional Nanomaterials, University of Queensland, 
QLD 4072 Australia 
Correspondence should be addressed to Liu Xinmei (e-mail: zfyancat@ 
hdpu.edu.cn) 
Abstract  The mesoporous nanocrystalline zircoina was 
synthesized via solid state reaction——structure directing 
method in the presence of Laponite. The introduction of La-
ponite renders the higher thermal stability and lamellar 
track to the zirconia. Laponite acts as inhibitor for crystal 
growth and also hard template for the mesostructure. The 
role of Laponite is attributed to the interaction between the 
zirconia precursors and the nano-platelets of Laponite via 
the bridge of hydrophilic segments of surfactant. It results in 
the formation of Zr-O-Mg-O-Si frameworks in the direction 
of Laponite layer with the condensation of frameworks dur-
ing the calcination process, which contributes the higher 
stability and lamellar structure to the nano-sized zirconia 
samples.  
Keywords: mesoporous nanocrystalline zirconia, Laponite, stabiliza-
tion mechanism. 
DOI: 10.1360/982004-83 
ZrO2 has attracted much attention because of its high 
performance as structural materials, electrode materials, 
electronics and oxygen sensors, supports and catalysts[1—6]. 
However, a major problem of this nonsiliceous oxide is its 
thermal stability. The surfactant removal by calcination, as 
used for porous silicates, leads to structure collapse be-
cause of phase transformation, hydrolysis and redox reac-
tion occurring at elevated temperature, which results in the 
loss of surface area and porosity. In addition, nano-sized 
particles prefer to aggregate to resist its higher surface 
energy. It means that for mesostructured or nanocrystal-
line zirconia, thermal stability is always a challenging 
area. 
Recently, many synthesis routes have been proposed 
for the synthesis of thermally stable zirconia. The major 
approaches are  to tune its electronic property or to 
enlarge the pore wall[7—11]. For example, the inorganic 
framework is either phosphate or sulfate groups as stabi-
lizers[12—14]. These anions can inhibit the crystallization of 
precursor species during the calcination. The introduction 
of phosphate or sulfate groups can be achieved by the 
self-assembly process of organic and inorganic species 
using the surfactant with phosphate or sulfate hydrophilic 
head or by post treatment with these anions after the ma-
terials are obtained. Also, aliovalent and tetravalent 
dopants, such as Na+, Ca2+, Y3+, Si4+, Ce4, Th4+, etc. have 
been used to reinforce the nanocrystalline structures[15—19]. 
The stabilization was believed to be achieved by strong 
surface interaction between dopants ions and zirconia or 
by higher coordination number via addition of large size 
dopants.  
The zirconia prepared via solid-state reaction——
structure directing method——bear large surface area and 
optimum pore structure[20]. Its phase can be tailored 
among amorphous, tetragonal and monoclinic phase by 
controlling the synthesis parameters. In order to improve 
the thermal stability of the zirconia with MSU structure, 
Laponite was introduced into the inorganic framework. 
This study demonstrates that electronic and structural ef-
fects of Laponite render good stability to zirconia. 
1  Experimental 
(ⅰ) Sample preparation.  The approach to synthe-
sizing the mesoporous nanocrystalline zirconia is the same 
as that of ref. [20]. The stabilization of framework was 
also solid-state reaction. In a typical synthesis, a certain 
amount of Laponite was milled together with zirconyl 
chloride (ZrOCl2⋅8H2O), and then PEO-block-PPO sur-
factant (F.W. = 5800) was introduced into the above mix-
ture by vigorously stirring. After that, the mixture reacted 
with milled sodium hydroxide whose amount is quarter 
mole of zirconyl chloride. The product was then trans-
ferred into an autoclave and kept at a 383 K for 48 h. 
Subsequently, the sample was washed with deionized water 
until it was free of Cl− ions, and then washed with ethanol 
twice to remove water and surfactant contained in the 
solid. Finally, the samples were dried at 383 K overnight.  
(ⅱ) Characterization.  Nitrogen adsorption and de-
sorption isotherms at 77.3 K were carried out with Auto-
sorb-1C (Quantachrome, USA) after degassing at 200℃ 
for 10 h. The mesopore size distribution was calculated 
from the desorption branch of the isotherms. X-ray pow-
der diffraction (XRD) patterns were obtained with a 
Bruker Axs (Germany) diffractometer, using Co Kα radia-
tion with a tube voltage of 40 KV, and a tube current of 20 
mA. Transmission electron microscopic (TEM) images 
were taken using a Philips CM200 Microscope in bright 
field transmission model. The samples for TEM were 
prepared by directly dispersing the zirconia particles 
treated by ultrasonic dispersion onto holey carbon grids. 
Energy-disperse X-ray (EDX) spectra were taken on a 
Gatan detector connected to the electron microscope. 
2  Results and discussion 
The data in Table 1 and Fig. 1 demonstrate that La-
ponite is a good stabilizer for zirconia. When incorporat-
 
 
ARTICLES 
ing 7% mass ratio of Laponite into the synthesis, the sur-
face area and pore diameter of the sample calcined at    
450℃ can be comparable with as-made product. The 
BET surface area is still up to 231.2 m
 
2·g−1 even calcined 
at 600℃ for 20 h. It is worthywhile to note that the pore 
structure can be almost retained at this high elevated tem-
perature. Fig. 1 shows that the pore diameter of pure zir-
conia is distinctly enlarged with an increase in calcination 
temperature; otherwise, it is nearly duplicated for the sta-
bilized samples calcined at any investigated temperature. 
Moreover, in the presence of Laponite, the mesoporous 
system is more developed and pore distribution tends to be 
narrower. It means that the incorporation of Laponite to 
the inorganic framework can resist the expanding of pore 
mouth, thus rendering higher surface area to the zirconia.  
 
Table 1  Role of Laponite to the surface area and pore structure  
of zirconia 
Sample BET/m2.g-−1 Pore volume /cm3.g−1 Pore diameter /nm
As-made 397.2 0.412 4.61 
450℃ 103.3 0.279 6.12 
600℃ 40.0 0.267 17.80 
As-made 356.5 0.454 4.08 
450℃ 360.9 0.472 4.10 
600℃ 231.2 0.411 4.56 
Chinese Science Bulletin  Vol. 50  No. 4  February  2005 361 
 
 
 
Fig. 1.  Mesopore size distribution of zirconia calcined at different 
temperatures. Inset: pore size distribution of samples stabilized by Lapo-
nite. 
 
XRD studies on samples indicate that nanocrystalline 
zirconia can be synthesized via this novel method and 
crystallization can occur during the calcination. The dif-  
fraction peaks of calcined stabilized sample shown in Fig. 
2 are more broadened than the as-made pure zirconia. This  
means that Laponite must have been incorporated into the  
zirconia framework and there formed a strong interaction  
with Zr4+. The intimate interaction between zirconia pre-
cursors and inorganic species of the Laponite is so strong  
that Zr-O-Mg-O-Si network may be formed at elevated  
temperature. This network inhibits the crystal growth dur-
ing calcination, and consequently there form more fine 
nanocrystallites. In addition, Si, Mg species also act as the 
barriers for the Zr species, resisting the aggregation of 
nanosized zirconia particles. This proposal is further con-
firmed by TEM images.  
 
 
 
Fig. 2.  XRD pattern of calcined zirconia before and after stabilization. 
 
TEM images in Fig. 3 show that all the samples bear 
MSU structure and nanosized particles. Selected-area 
electron diffraction patterns indicate that the pore walls of 
zirconia are made up of nanocrystalline with characteristic 
diffuse electron diffraction rings. This crystalline structure 
effectively sustains the local strain caused by the crystal-
lization and prevents the mesostructure from collapsing, 
which contributes good thermal stability to the sam-
ples[10,11]. The particle size of the sample stabilized with 
Laponite is much smaller than pure zircona. This phe-
nomenon is prominent for calcined samples. The size of 
zirconia modified with 7% mass ratio of Laponite and 
calcined at 600℃ is only 2.0 nm or so. It can be com-
pared with the as-made sample. For pure zirconia, it is 
increased from 1.5nm of as-made sample to 6.0—7.0 nm 
of sample calcined at 450℃. This result is consistent with 
the XRD diffraction lines. The mesoporous structure and 
lattice finger of pure zirconia calcined at 450℃ are ap-
parently exhibited in Fig. 3(c). The pore diameter is about 
6.2 nm, which corresponds to the value of 6.1 nm calcu-
lated by BJH method.  
Interestingly, the mesostructure of Laponite stabi-
lized samples looks more ordered than that in the pure 
zirconia. The local lamellar structure can be observed in 
the mesostructure of the calcined sample. It indicates that 
Laponite can act as hard template during the mesostruc-
ture formation. Its templating is achieved by the synergy 
with soft template (surfactant). In the solid-state synthesis, 
the precursor of zirconia and inorganic species in Laponite 
can interact via hydrogen boning between the PEO seg-
ments of surfactant and various inorganic species. This 
interaction may be extended in the direction of Laponite 
platelet layer. The Zr-O-Mg-O-Si network is formed upon  
 
 
 
 
ARTICLES 
 
 
Fig. 3.  TEM images of pure and stabilized zirconia before and after calcination. (a) As-made pure zirconia; (b) zirconia stabilized by 7% 
Laponite; (c) pure zirconia calcined at 450℃; (d) zironia stabilized with 7% Laponite and calcined at 600℃. 
 
condensation of inorganic pore wall at high temperature. 
That is why the mesostructure of calcined Laponite stabi-
lized sample is more ordered.  
The stabilization mechanism of Laponite to the zir-
conia is illustrated in Fig. 4. In the solid-state synthesis 
system, zirconia chloride, Laponite and surfactant are suf-
ficiently mixed first, and then react with NaOH. Subse-
quently, the product is crystallized in autoclave. In the 
crystallization, the hydrogen bonding is formed between 
hydrophilic segments and precursor of zirconia, simulta-
neously, formed between hydrophilic segments and Si 
or/and Mg species in Laponite layer. However, these 
weaken hydrogen bonding transform to M-O bond with 
the condensation of skeleton hydroxyl at higher tempera-
ture, which contributes to the connection among various 
inorganic species via oxygen atoms. Let it be noted here 
that the interaction among various inorganic species can 
be extended in the direction of Laponite platelet layer. 
This is why local lamellar structures can be observed in 
the zirconia mesostructure. The Zr-O-Mg-O-Si networks 
with large covalent bonds induce stronger interaction for 
the framework.  It is believed that the introduction of 
Laponite not only renders the lamellar structure but also 
form the solid mesoporous skeleton. It is the large cova-
lent bonds network that contributes the higher stability to 
the mesostructure.  
N2 adsorption/desorption isotherms showing IV or V 
type with hysteresis loop are obtained for the zirconia 
modified with different amounts of Laponite, which fur-
ther confirmed that zirconia prepared with solid-state re-
action—structure directing method are representative of 
mesoporous materials. The more introduction of Laponite 
into the framework, the larger of hysteresis loop is ob-
served as shown in Fig. 5. The change of hysteresis loop is 
believed to be related to the pore structure. The mesopore 
size tends to be larger and pore distribution is broadened. 
The Barrett-Joyner-Halenda (BJH) analyses in Fig. 5(b) 
show that the zirconia stabilized with above 7% mass ratio 
of Laponite exhibit bimodal distribution, and pore size can 
be up to 10 nm. While for sample prepared with lower 
than 7% ratio, there is just one narrow peak, and pore is 
concentrated on 4.1nm. The change of pore structure is 
attributed to the modification of mesostructure with 
amount of addition of Laponite. The local lamellar struc-
ture can be extended to long distance with zirconia pre-
cursors incorporated into more Laponite layers. The con-
nection of Zr-O-Si-O-Mg network renders larger 
mesopore to the samples. Simultaneously, the pore vol-
ume is increased and surface area reaches maximum value 
with Laponite introduction. All these results are listed in 
Table 2. 
The data in Table 2 also show that the particle size of 
362 Chinese Science Bulletin  Vol. 50  No. 4  February  2005 
 
 
ARTICLES 
 
 
Fig. 4.  Schematic of stabilization mechanism of Laponite to the zirconia. 
 
 
 
Fig. 5.  Surface area and pore structure of stabilized zirconia with increase of Laponite (mass ratio to ZrOCl2•8H2O). 
 
Table 2  The effect of introduction amount of Laponite on physical  
properties of zirconia 
Sample Particle size /nm 
BET 
/m2·g−1
Pore volume 
/cm3·g−1
Pore 
diameter/nm
Zr-Lap-3 2.7 287.9 0.383 4.08 
Zr-Lap-5 2.1 282.2 0.334 4.10 
Zr-Lap-7 2.0 360.9 0.472 4.10 
Zr-Lap-10 1.8 309.7 0.582 4.12, 5.80 
Zr-Lap-30 1.5 276.2 0.914 6.34, 9.87 
Chinese Science Bulletin  Vol. 50  No. 4  February  2005 363 
The number in sample name is depicted as the mass ratio of lapo-
nite to the ZrOCl2•8H2O. 
 
stabilized zirconia is decreased with the increase of Lapo-
nite introduction. This can be demonstrated from XRD 
patterns showing weakened intensity (Fig. 6). The asym- 
 
Fig. 6.  Effect of introduction of Laponite on the XRD patterns of zir-
conia. 
 
 
 
 
ARTICLES 
364 Chinese Science Bulletin  Vol. 50  No. 4  February  2005 
. 
metry peak of sample prepared with high presence of La-
ponite indicates the transformation of mesostructure. 
3  Conclusion 
The results demonstrate that Laponite acted as in-
hibitor of nano-sized zirconia agglomeration and hard 
template for the ordered mesostructure formation. It not 
only improves the thermal stability but also positively 
render the more ordered mesoporous structure. Under the 
synthesis condition, the zirconia precursors intimately 
interact with the nano-platelets of Laponite via the bridge 
of hydrophilic segments with hydrogen bond and the 
Zr-O-Mg-O-Si frameworks were formed in the direction 
of Laponite layer with the condensation of frameworks 
during the calcination process. It is the formation of 
Zr-O-Mg-O-Si network that resists the crystallization of 
zirconia precursor and renders local lamellar structure to 
the nanocrystalline zirconia.  
Acknowledgements  The authors thank Dr. J. Riches of Microscopy 
and Microanalysis Center, University of Queensland, Australia for his 
assistances, and  Mr. L. Bekessy and Ms. A.J.E. Yago of Chemistry, 
University of Queensland, Australia for XRD experiments. 
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Stabilization of mesoporous nanocrystalline zirconia with Laponite

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