and (b) the method uses easily available precursors and
equipment. Finally, we would like to mention some of the
steps to follow to enhance the capacity of this method. We are
of the opinion that the strength of a method is not only
dictated by its present capacity but also by its future capacity.
For example, even though the mesosize objects have a highly
accessible porosity for applications involving large molecules,
the intraparticle pore size should be increased. Here, the
intramesoporosity was obtained by using a low molecular
weight surfactant (Igepal). Replacing this surfactant, by for
example, block copolymers able to form inverse micelles with a
high loading capacity of precursors, could be a possible route
to increase the intraparticle pore size and pore structural
regularity of the mesosize colloids. Finally, crystallinity during
synthesis could be achieved by exploring microemulsion
systems with high stability at high temperatures.
I acknowledge financial support from the Spanish Ministerio
de Ciencia e Innovacion through MAT2008-03224/NAN.
Fig. 4 (A) TEM images, (B) XRD diffraction patterns and (C) N
adsorption–desorption isotherms (inset pore size distributions) for
ZrO , TiO and Y –ZrO nanostructures heated at 600/2 h (N
and then 350/24 h (air). The main diffraction peaks are labeled for each
2
Notes and references
2
2
2
O
3
2
2
)
1 H. Colfen and S. Mann, Angew. Chem., Int. Ed., 2003, 42,
2350.
sample. M, T and C represent monoclinic, tetragonal and cubic ZrO
while A represents anatase (TiO polymorph).
2
2
3
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C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and
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2
peaks due to the anatase phase (12 nm crystal size) of TiO
while Y –ZrO
size) phase of ZrO (after heating Y O forms a solid solution
2
Voigt-Martin, G. D. Stucky and F. Schu
D. Walsh, J. D. Hopwood and S. Mann, Science, 1994, 264, 1576;
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´ ´
C. J. Brinker, Nature, 1999, 398, 22; B. Julian-Lopez,
¨
th, Science, 1996, 273, 768;
2
O
3
2
presents peaks due the cubic (11 nm crystal
¨
2
2
3
within the zirconia crystalline structure). N2 isotherms
Fig. 4C) are similar for the three samples and show a
(
C. c. Boissiere, C. Chaneac, D. Grosso, S. Vasseur, S. Miraux,
`
´
relatively low irreversibility (large fraction of accessible pores).
This behavior suggests that capillary condensation–evaporation
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4
1
4
take place at similar pressure (isotherm type IVc). However,
no capillary condensation step is clearly observed, which could
be due to the significant fraction of open porosity. The BET
6
7
2
À1
specific surface areas are 95, 127, 94 m g for ZrO
2 2
, TiO and
F. Bai, D. Wang, Z. Huo, W. Chen, L. Liu, X. Liang, C. Chen,
X. Wang, Q. Peng and Y. D. Li, Angew. Chem., Int. Ed., 2007, 46,
Y
2
O
–ZrO , respectively. Pore size distributions based on
3 2
6
650.
the Barrett–Joyner–Halenda (BJH) model show a broad
mesopore population centered about the value of the particle
size (interparticle porosity) and a narrow mesopore population
corresponding to the intraparticle pores (about 4 nm for ZrO2
and Y O –ZrO , and 5 nm for TiO ).
8
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2
3
2
2
In summary, we have shown that a new method that
combines the thermally-controlled aggregation of surfactant-
stabilized liquid nanodroplets with gas reactants is suitable
for the generalized, predictable and facile synthesis of
dual mesosize–mesoporous structures. As an example we
are able to prepare water-dispersible materials of interest in
water purification and clean energy generation with good
crystallinity, high surface area, highly accessible and dual
mesoporosity, and sizes around the mesoscale. Advantages
of the method are: (a) the formation of the nanostructures is
reasonably predictable prior to carrying out the experiments
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230 | Chem. Commun., 2009, 3228–3230
This journal is ꢀc The Royal Society of Chemistry 2009