Chemistry Letters 2002
rotation barrier: 0.8 kJ/mol) and the Si–O bond can freely rotate.
983
8
(
500
That is the reason why even very long PDMS chain surfactants are
in liquid state at roomte mp erature (RT). In contrast, the
hydrocarbon surfactants tend to be in a solid state at RT since
Krafft temperatures for long and linear hydrocarbon-chain
4
4
50
00
350
8
surfactants are high. We suggest that silicone surfactants with
more flexible chains than conventional hydrocarbon surfactants
or copolymer would be responsible for the formation of this
3
2
00
50
0
.20
0.15
0
0
.10
.05
9
unusual lamellar silica mesophase. Even with substantial
200
changes in the concentration of silicone surfactant and HCl,
lamellar silica mesophase is also retained, suggesting that silicone
surfactant favors the formation of lamellar structure.
1
1
50
00
0.00
1
10
100
Pore diameter / nm
0
.0
0.2
0.4
0.6
0.8
1.0
TEM images of an ultrathin section of the as-made ZSU-4
product were shown in Figure 1b and c. Figure 1b shows that
lamellar silica mesophase similar to that observed in the ZSU-L
product is also retained in the ZSU-4 product templated from the
mixture of silicone surfactant and P123. Previously, in systems
Relative pressure (P/P0)
Figure 3. N2 adsorption-desorption isotherms and correspond-
ing BJH pore size distribution curve (Inset) for the calcined ZSU-
ꢀ
4
at 500 C for 6 h.
þ
with Pluronics family, CnEOm, CTA or their mixtures serving as
templates, a single mesophase such as hexagonal mesoporous
complex ordered mesostructures templated from the copolymer
blends are of interest fromthe viewpoint of biominerization, and
may find wide applications in catalysis, adsorption and separa-
tion. We believe that these findings have provided new insights
into the mechanistic issues involved in the formation of this new
interesting class of complex mesostructured materials. Further
investigation, however, will be required in order to adequately
explain the actual formation mechanisms of complex mesophases
formed in the mixed surfactant-templating systems. The possi-
bility of producing other oxide materials with this unusual
mesostructure using this novel method is also intriguing.
silica has been prepared.1
;7;10
Interestingly, we find here that
hexagonal pore channels were formed in the thick silica walls for
ZSU-4 (Figure 1c). Both the lamellae and hexagonal mesophase
are assembled in a single body, representing complex meso-
structures (structure within structure). No peaks are observed in
XRD patterns for the ZSU-L product, as observed in Figure 2a
(
ZSU-L lamellar phase was not detected by XRD analysis
because of its extremely large lattice constant). However, a high
degree of hexagonal mesoscopic order is observed for the
calcined ZSU-4 samples (Figure 2b). It appears that the lamellar
mesophase and hexagonal mesochannels in the walls were
separately templated from silicone surfactant and P123 in the
mixed surfactant templating systems, and thus hierarchically
ordered silica formed.
We acknowledge the support fromthe Guangdong Province
‘‘The Tenth Five-Year Plan’’ Key Project (20010185C).
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2
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Figure 2. XRD patterns of the as-made ZSU-L (a) and the
ꢀ
6
7
8
9
calcined ZSU-4 at 500 C (b).
N2 sorption isothermand the corresponding BJH (Barret-
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ꢀ
4
1
1
7
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ꢃ1
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6
.3 nm.
In conclusion, a novel silicone surfactant was first used to
synthesize lamellar silica mesophase. Silica materials with