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Langmuir 2007, 23, 10788-10792
Preparation of Mesostructured Siloxane-Organic Hybrid Films with Ordered Macropores by Templated Self-Assembly Mikako Sakurai,† Atsushi Shimojima,§,⊥ Masaru Heishi,† and Kazuyuki Kuroda*,†,‡,§ Department of Applied Chemistry, Waseda UniVersity, Ohkubo-3, Shinjuku-ku, Tokyo, 169-8555, Japan, Kagami Memorial Laboratory for Materials Science and Technology, Waseda UniVersity, Nishiwaseda-2, Shinjuku-ku, Tokyo, 169-0051, Japan, and Core Research for EVolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Honcho 4-1-8, Kawaguchi-shi, Saitama, 332-0012, Japan ReceiVed May 31, 2007. In Final Form: July 21, 2007 Novel hierarchically ordered siloxane-based hybrid films with well-defined macropores and mesostructured pore walls have been prepared by the self-assembly process using oligomeric siloxane precursors bearing alkyl chains (CnH2n+1Si(OSi(OMe)3)3) in the presence of polystyrene opal films as a template. Either a two-dimensional (2D) hexagonal structure or a lamellar structure was formed depending on the alkyl chain length of the precursors (n ) 10 and 16, respectively). In both of the films, the mesostructures were oriented along the spherical surface of the template and were retained after removal of the template. Calcination of the 2D hexagonal hybrid produced ordered porous silica with both macro- and microporosities. The lamellar hybrid film exhibited a unique property of accommodating alkyl alcohols with an expansion of the interlayer spacings. These results provide a new concept for designing hierarchical hybrid materials that are potentially applicable as adsorbents, catalysts, sensors, and photonic crystals.
Introduction The elaboration of inorganic-organic composites is significant because of their potential applications in catalysis, photonics, and electronics and their use as structural and biomedical materials. The hierarchical organization of composites is one of the most challenging issues, leading to the emergence of multifunctions and the specific physical properties often observed in biological systems.1 Siloxane-based hybrids prepared by the hydrolysis and polycondensation of organoalkoxysilanes have important features such as good thermal and chemical stabilities, high optical properties, and biocompatibility.1 Although such materials are generally amorphous, recent research has shown that their structures can be controlled at the nanometer length scale through self-assembly. The use of surfactant assemblies as organic templates allows the formation of various hybrid mesostructures.2-4 Another interesting approach is based on the selfassembly of organoalkoxysilane molecules during hydrolysis and polycondensation in the absence of any structure-directing agents.5 There have been many reports on the synthesis of lamellar * Corresponding author. E-mail:
[email protected]. Fax: +81-3-52863199. Tel: +81-3-5286-3199. † Department of Applied Chemistry, Waseda University. ‡ Kagami Memorial Laboratory for Materials Science and Technology, Waseda University. § Japan Science and Technology Agency (JST). ⊥ Present address: Department of Chemical System Engineering, The University of Tokyo, Hongo-7, Bunkyo-ku, Tokyo 113-8656, Japan. (1) Sanchez, C.; Julia´n, B.; Belleville, P.; Popall, M. J. Mater. Chem. 2005, 15, 3559-3592. (2) Inagaki, S.; Guan, S.; Fukushima, Y.; Ohsuna, T.; Terasaki, O. J. Am. Chem. Soc. 1999, 121, 9611-9614. (3) Asefa, T.; MacLachlan, M. J.; Coombs, N.; Ozin, G. A. Nature 1999, 402, 867-871. (4) Melde, B. J.; Holland, B. T.; Blanford, C. F.; Stein, A. Chem. Mater. 1999, 11, 3302-3308. (5) (a) Shimojima, A.; Sugahara, Y.; Kuroda, K. Bull. Chem. Soc. Jpn. 1997, 70, 2847-2853. (b) Shimojima, A.; Umeda, N.; Kuroda, K. Chem. Mater. 2001, 13, 3610-3616. (c) Shimojima, A.; Kuroda, K. Langmuir 2002, 18, 1144-1149. (d) Shimojima, A.; Kuroda, K. Chem. Rec. 2006, 6, 53-63.
hybrids from bis-trialkoxysilylated precursors ((RO)3Si-R′Si(OR)3).6,7 Furthermore, we recently designed a new type of precursor, where three trialkoxysilyl groups are bonded to alkylsilane units (CnH2n+1Si(OSi(OMe)3)3), and succeeded in the synthesis of either lamellar or two-dimensional (2D) hexagonal hybrids depending on the alkyl chain length.8 Several strategies have recently been proposed for designing hierarchically ordered silica-based hybrids to impart new properties.9,10 Inagaki et al. synthesized mesoporous hybrids with molecularly ordered walls by the self-assembly of bis-trialkoxysilylated precursors having phenylene or biphenylene spacers in the presence of cationic surfactants.11,12 Nakanishi et al.13 and Huesing et al.14 reported the synthesis of hybrid monolith with continuous macropores generated by phase separation along with micro- and mesopores generated by amphiphilic triblock copolymer (P123) templates. In contrast to these systems, which usually require careful control of the reaction conditions, the use of colloidal crystals as templates provides a rather convenient way to create hierarchically ordered materials. Well-ordered, closely packed polystyrene (PS) beads have been widely used to produce macroporous materials with three-dimensional pore systems.15 By applying the self-assembly of surfactants or ionic liquids in combination with PS templating, silica-based materials with both interconnected macroporous and mesoporous structures (6) Moreau, J. J. E.; Vellutini, L.; Wong Chi Man, M.; Bied, C.; Bantignies, J.-L.; Dieudonne´, P.; Sauvajol, J.-L. J. Am. Chem. Soc. 2001, 123, 7957-7958. (7) Boury, B.; Corriu, R. J. P. Chem. Commun. 2002, 795-802. (8) Shimojima, A.; Liu, Z.; Ohsuna, T.; Terasaki, O.; Kuroda, K. J. Am. Chem. Soc. 2005, 127, 14108-14116. (9) Xia, Y.; Wang, W.; Mokaya, R. J. Am. Chem. Soc. 2005, 127, 790-798. (10) Brandhuber, D.; Peterlik, H.; Huesing, N. Small 2006, 2, 503-506. (11) Inagaki, S.; Guan, S.; Ohsuna, T.; Terasaki, O. Nature 2002, 416, 304307. (12) Kapoor, M. P.; Yang, Q.; Inagaki, S. J. Am. Chem. Soc. 2002, 124, 1517615177. (13) Nakanishi, K.; Kobayashi, Y.; Amatani, T.; Hirao, K.; Kodaira, T. Chem. Mater. 2004, 16, 3652-3658. (14) Huesing, N.; Raab, C.; Torma, V.; Roig, A.; Peterlik, H. Chem. Mater. 2003, 15, 2690-2692. (15) Holland, B. T.; Blanford, C.; Stein, A. Science 1998, 281, 538-540.
10.1021/la701590x CCC: $37.00 © 2007 American Chemical Society Published on Web 09/07/2007
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Scheme 1. Synthesis of Mesostructured Silica-Based Hybrids with Ordered Macropores
can be prepared.16-22 These bimodal porous materials have enhanced properties compared to the traditional MCM-type mesoporous materials because of increased mass transport. However, in the previously reported cases, amorphous regions are formed near the touching point of PS beads. This is because it is much easier for small silicate species to diffuse around the touching point compared to surfactant micelles, so that silicate species condense without the presence of any micelles.19 Such nonuniformity of the mesopores disturbs the important role of this type of material in the systematic study of the structureproperty relationship and in the elucidation of fundamental aspects of sorption theory. It will also affect the quality of the materials when it is used as molecular sensors, catalytic supports, and so on. In this paper, we report the synthesis of novel siloxane-based hybrid films with well-defined macropores and mesostructured walls by using designed siloxane precursors (CnH2n+1Si(OSi(OMe)3)3, 1(Cn), n ) 10 or 16) and PS opal films as a template. Because the inorganic group and the organic group are covalently attached, it is possible to fabricate hybrid films with a thoroughly uniform structure. Moreover, by varying the alkyl chain length, the pore size can be controlled in the range of micropore to mesopore, which is usually difficult to be accessed by the surfactant-directed approach. The formation process involves (1) partial hydrolysis and polycondensation of 1(Cn) in acidic EtOH solutions, (2) impregnation of the solutions into opal films by dip-coating, (3) evaporation-induced self-assembly and polycondensation of alkylsiloxane species, and (4) removal of PS to generate macropores (Scheme 1). Detailed analyses of these hierarchically ordered hybrid films revealed some specific features that are different from those for hybrid films without macropores derived from the same precursors. Experimental Section Materials. The siloxane precursors (1(Cn), n ) 10, 16) were synthesized by the procedure reported previously.8 A dispersion of PS beads (10 wt % dispersion in water, average diameter of 0.46 µm, Aldrich) was diluted to 2 wt % with purified water before use. Sulfuric acid (>96.0%, Kanto Chemical Co.), dehydrated ethanol (99.5%, Wako Pure Chemical Industries, Ltd.), 0.01 M hydrochloric acid (Wako Pure Chemical Industries, Ltd.), toluene (>99.5%, Kanto Chemical Co.), and n-decyl alcohol (>95.0%, Kanto Chemical Co.) were used as received. Synthesis. Fabrication of PS Opal Films. PS opal films were fabricated on cover glass substrates (24 × 13 mm2) by the dip(16) Lebeau, B.; Fowler, C. E.; Mann, S.; Farcet, C.; Charleux, B.; Sanchez, C. J. Mater. Chem. 2000, 10, 2105-2108. (17) Stein, A. Microporous Mesoporous Mater. 2001, 44-45, 227-239. (18) Zhou, Y.; Antonietti, M. Chem. Commun. 2003, 2564-2565. (19) Sen, T.; Tiddy, G. J. T.; Casci, J. L.; Anderson, M. W. Chem. Mater. 2004, 16, 2044-2054. (20) Kuang, D.; Brezesinski, T.; Smarsly, B. J. Am. Chem. Soc. 2004, 126, 10534-10535. (21) Oh, C.-G.; Baek, Y.; Ihm, S.-K. AdV. Mater. 2005, 17, 270-273. (22) Villaescusa, L. A.; Mihi, A.; Rodrı´guez, I.; Garcı´a-Bennett, A. E.; Mı´guez, H. J. Phys. Chem. B 2005, 109, 19643-19649.
coating method using a Nano dip coater (Eintesla, Inc.).23 The substrates were treated with sulfuric acid for 1 day and washed with purified water before use. They were vertically dipped in the 2 wt % dispersion of PS beads and withdrawn at 0.2 µm s-1 to form opal films. After being dried in air, the opal films were heated at 105 °C for 10 min so that the films were stabilized to some extent.24 Preparation of Hybrid Films (2(Cn)). Hydrolysis of 1(Cn) was carried out by stirring it in the mixture of ethanol, 0.01 M hydrochloric acid, and water at room temperature for 6 h. The starting molar ratio was 1(Cn)/EtOH/H2O/HCl ) 1:80:36:0.004. Ethanol was used as the solvent because it did not seem to deteriorate the PS opal film. The 29Si NMR spectrum of the solution after the reaction (Supporting Information, Figure S1) showed several signals at the T2, Q1, and Q2 regions, suggesting the formation of a trisiloxane ring and a tetrasiloxane ring via the hydrolysis and intramolecular condensation process.8 After the addition of water (1(Cn)/H2O ) 1:32), these precursor solutions were dip-coated on the opal films at a withdrawal rate of 0.5 mm s-1, and were dried in air to promote further polycondensation. The PS templates were removed by simply immersing the films in toluene for 1 day, yielding macroporous hybrid films (denoted as 2(Cn)). For further investigation, the 2(Cn) films were calcined in air at 500 °C for 8 h to give silica films without organic groups. Adsorption of Alcohols on Hybrid Films (2(Cn)). Macroporous hybrid films 2(C10) and 2(C16) were immersed in decyl alcohol at room temperature for 2 h. Before characterization, a minimal amount of hexane was poured on the films to remove the extra decyl alcohol on the surface. No further washing of the films was performed to avoid the desorption of alcohols. Characterization. The θ-2θ scanning X-ray diffraction (XRD) patterns of the products were obtained on a Mac Science M03XHF22 diffractometer with Mn-filtered Fe KR radiation. In-plane XRD patterns were recorded with a RIGAKU ATX-G diffractometer with a four-axis goniometer using Cu KR radiation, and a soller slit with a vertical divergence of 0.48° was used to obtain a parallel beam. The incident angle of the X-ray in the in-plane geometry was 0.2°. Field-emission scanning electron microscopic (FE-SEM) observations were performed with a JEOL JSM-6500F at an accelerating voltage of 15 kV. Before the observation, the samples were cut into an appropriate size (about 5 × 5 mm2) and were coated with carbon. Both surfaces and cross-sections of the samples were observed by tilting the substrates during the observation. Transmission electron microscopic (TEM) images were obtained by a JEOL JEM-2010 microscope at an accelerating voltage of 200 kV. Samples were prepared as follows: the hybrid films were peeled off from the substrates and were lightly ground before dispersion in ethanol. Then a carbon-coated TEM grid was immersed in this suspension and dried in air.
Results and Discussion Structural Analyses of 2(Cn). The morphologies of the films in the course of preparing 2(Cn) (n ) 10 and 16) were monitored by SEM. The SEM images of the PS opal film used as a template shows regularly packed PS beads (Figure 1). The film is (23) Gu, Z.-Z.; Fujishima, A.; Sato, O. Chem. Mater. 2002, 14, 760-765. (24) Zhou, Z.; Zhao, X. S. Langmuir 2005, 21, 4717-4723.
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Figure 1. FE-SEM images of the PS opal film: (a) top surface and (b) fractured surface.
Figure 3. XRD patterns of 2(Cn): (a) n ) 10; (b) n ) 16.
Figure 2. FE-SEM images of the hybrid films after removal of the PS template (2(Cn)): (a,b) n ) 10; (c,d) n ) 16.
polycrystalline with the domain sizes of only several micrometers. This is possibly due to the variation in the diameter of PS beads (from 420 to 500 nm). From the image of the fractured crosssection (Figure 1b), the thickness of the film is estimated to be ca. 7 µm, corresponding to about 18 layers of stacked PS beads. After impregnation of the hydrolyzed solutions of 1(Cn), hybrid xerogels were formed uniformly in the voids between the PS beads (Supporting Information, Figure S2). Also observed are some cracks, possibly formed during the drying step that should cause the shrinkage of siloxane networks. The films after treatment with toluene (2(Cn)) showed ordered arrays of spherical macropores formed by the removal of the template (Figure 2). The average diameters of the macropores are ca. 420 nm, which are connected to each other through small windows 40-100 nm in diameter. The small depressions at the top surface of the hybrid walls should be formed by the shrinkage of siloxane networks. The XRD patterns of 2(C10) and 2(C16) (Figure 3) exhibit peaks with d spacings of 2.94 and 3.33 nm, respectively. The second-order diffraction (d ) 1.67 nm) was also observed for 2(C16). Although the patterns are ill defined, the d spacings are close to those for the 2D hexagonal and lamellar hybrids prepared from 1(C10) and 1(C16), respectively, without PS templates.8 The difference in the d spacings of 2(C10) and 2(C16) (∆d ) 0.39 nm) is smaller than that in the alkyl chain lengths (0.78 nm, in all-trans state). This may be explained by the difference in the arrangement and/or conformation of the chains as well as the
Figure 4. TEM images of 2(Cn): (a,b) n ) 10; (c,d) n ) 16.
difference in the mesostructures.8 We note here that the treatment with toluene had essentially no effect on the mesostructures: almost identical patterns were observed for the samples before the removal of the template. (Supporting Information, Figure S3). The 2D hexagonal and lamellar structures of these films were evidenced by TEM (Figure 4). The TEM images of 2(C10) show both honeycomb and striped patterns that are characteristics of a 2D hexagonal mesostructure, while those of 2(C16) exclusively exhibit striped patterns due to a lamellar structure. In both cases, the structural periodicities basically correspond well to the d spacings measured by XRD. What is interesting is that the mesostructures seem to be oriented along the macropores, thus suggesting that hydrolyzed 1(Cn) self-assembled along the spherical surface of the PS beads. To obtain further information on the orientation of the mesostructures, the 2(Cn) films were characterized by in-plane XRD. In contrast to conventional θ-2θ scanning XRD patterns, where the peaks arise from the structural periodicity parallel to the substrate surface, in-plane XRD can elucidate the periodicity
Hierarchically Ordered Hybrid Films
Figure 5. In-plane φ-2θχ scanning XRD profiles of 2(Cn): (a) n ) 10; (b) n ) 16. The inset shows the scanning axes of the in-plane XRD geometry.
Figure 6. Hypothetical illustration of the orientation of cylindrical assemblies around the PS beads: (a) (10) plane is parallel to the substrate, (b) (12h) plane is parallel to the substrate, and mesochannels are (c) normal and (d) diagonal to the substrate surface. An image of the typical planes of a 2D hexagonal mesostructure is also shown.
normal to the surface.25 Figure 5 shows the in-plane XRD patterns (φ-2θχ scan) of the films. Single peaks with d ) 3.02 and 3.50 nm are observed for 2(C10) and 2(C16), respectively. These peaks should correspond to the structural periodicity observed in Figure 3, that is, the (10) and (01) planes of 2D hexagonal and lamellar structures, respectively. The slightly larger d spacings can be attributed to the lower lateral shrinkage of the films. Note that such in-plane XRD peaks cannot be observed in the hybrid films prepared without the PS templates,8 because the (10) and (01) planes are usually oriented parallel to the substrate surface. Thus the use of the template affected the orientation of the hybrid films, while the mesostructures are identical to those obtained without the template. On the basis of the above results, we discuss the orientation of the mesostructures precisely. For 2(C10), having the 2D hexagonal mesostructure, the existence of mesochannels oriented parallel to the substrate surface (Figure 6a) was evident because the (10) peak of a 2D hexagonal structure was observed in the θ-2θ XRD pattern. Moreover, the (10) peak also observed in the in-plane XRD pattern suggests two more possible orientations of the channels, as shown in Figure 6b,c. However, taking into account that the (12h) peak was absent in the θ-2θ XRD pattern, the mesochannels shown in Figure 6b do not exist actually; that is, mesochannels are partly oriented normal to the substrate surface (Figure 6c). Of course, it is plausible to consider that, in some (25) Miyata, H.; Kuroda, K. Chem. Mater. 1999, 11, 1609-1614.
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Figure 7. (A) XRD patterns of 2(Cn) after calcination at 500 °C for 8 h: (a) n ) 10; (b) n ) 16. (B) In-plane φ-2θχ scanning XRD profiles of the same samples: (a) n ) 10; (b) n ) 16.
region of the film, the mesochannels are oriented diagonally to the substrate (Figure 6d). Unfortunately, such periodicity can be detected by neither θ-2θ XRD nor in-plane XRD, so the details are yet to be understood. Such diversification of the orientations should be responsible for the relatively broad peaks observed in both θ-2θ and in-plane XRD patterns. In the case of 2(C16), where a lamellar mesostructure is formed, each layer should be formed along the surface of the PS beads so that the beads are isotropically covered with multilayered silica-organic shells. Calcination of the Macroporous Hybrid Films 2(Cn). To generate an additional porosity in the hybrid films, alkyl chains linked to the siloxane network were removed by calcination. The θ-2θ and φ-2θχ scanning XRD patterns of 2(Cn) after calcination are shown in Figure 7. The patterns for calcined 2(C16) showed no peaks (Figure 7A(b),B(b)), confirming that the lamellar structure completely collapsed by calcination. In contrast, a partial retention of the 2D hexagonal structure was confirmed for calcined 2(C10). The θ-2θ XRD pattern (Figure 7A(a)) shows only a very weak peak with d ) 2.63 nm, suggesting that the 2D hexagonal domains oriented parallel to the substrate almost collapsed. This result is similar to the case of the 2D hexagonal hybrid film prepared without the PS template, and may be due to the high shrinkage of siloxane networks along the direction normal to the substrate surface. However, the in-plane XRD pattern (Figure 7B(a)) shows a peak corresponding to a structural periodicity of d ) 2.66 nm, suggesting the retention of the 2D hexagonal structure. Actually, the TEM images (Figure 8) showed honeycomb patterns whose interpore distance is about 2.6 nm. This is a specific feature of this macroporous hybrid film where cylindrical assemblies are partly oriented normal to the substrate surface. These results suggest that a silica film with bimodal porosity was successfully synthesized. To obtain direct evidence of the porosity by nitrogen adsorption measurement, we freshly prepared the sample by using monolithic PS colloidal crystals as a template because of the difficulty in synthesizing a sufficient amount of the sample by using the PS opal film. The structure and morphology of this sample are very similar to those of 2(C10), as confirmed by XRD, SEM, and TEM (see Supporting Information, Figures S4-S10). The nitrogen adsorption isotherm of the calcined sample displayed a type I curve typical of
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Figure 8. TEM images of 2(C10) after calcination at 500 °C for 8 h. Views are (a) perpendicular and (b) parallel to the long axis of the cylindrical assembly.
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lamellar silica-surfactant composites are known,26,27 they are not suitable for use as reversible adsorbents because of the noncovalent interactions at the interfaces that should lead to the leaching of surfactant molecules. Similar adsorption behavior was also reported for alkylsilylated derivatives of crystallinelayered silicates;28,29 however, the morphological control, particularly in the form of thin films, has not been attained. Adsorption of various molecules is expected to be useful for controlling the optical properties (such as refractive index) of the hybrid films. It is also worth noting that the intercalation of certain molecules should trigger an increase in the macropore wall thickness and a decrease in the macropore diameter. In the above case, the ratio of the change reaches ∼37%, being estimated from the d spacings. These are very interesting for photonic applications such as photonic crystals with an environmentally responsive photonic bang gap structure.22,30,31 However, even the preliminary PS opal films did not show photonic band gap behavior: characteristic absorption was not observed during the UV/vis spectroscopy measurement in transmission mode. This is probably due to the lack of periodicities of the opal films. For future applications as photonic crystals, we will try to improve the periodicities of the films, and the research is currently underway in our laboratory.
Conclusions
Figure 9. XRD patterns of 2(C16) after (a) treatment with decyl alcohol and (b) washing with hexane. Insets show the proposed structural models of the interlayer spaces.
microporous silica (Supporting Information, Figure S11). The structural parameters, including the Brunauer-Emmett-Teller (BET) surface area and average pore diameter evaluated by the nonlocal density functional theory (NLDFT) method, are 600 m2 g-1 and ∼1.4 nm, respectively. From these data, the bimodal pore nature of the samples is successfully proven. Adsorption of Alcohols on 2(C16). We also found a unique intercalation behavior of the lamellar hybrid film (2(C16)) before calcination. Figure 9a shows the XRD pattern of 2(C16) after the treatment with decyl alcohol. A large increase in the d spacing by 1.22 nm was confirmed. Also, the in-plane XRD pattern of 2(C16) after the treatment showed an increase in the d spacing of 1.25 nm (Supporting Information, Figure S12). These results suggest that the alcohol molecules were intercalated into the expandable interlayer spaces of the lamellar structure. Importantly, deintercalation of alcohol molecules is also possible; the d spacing decreased to 3.53 nm by simply washing the film with hexane (Figure 9b). To the best of our knowledge, this is the first example of an inverse opal film that can accommodate guest molecules by intercalation. For 2(C10), such an increase in the d spacing was not observed, which strongly supports the idea that the film has a 2D hexagonal structure without the coexistence of a lamellar phase. The adsorption capability of the lamellar hybrid film (2(C16)) partly relies on its “hybrid” structure, where alkyl chains are covalently bonded to the siloxane layers. Although various
Novel mesostructured silica-based hybrid films with wellordered macropores were prepared by the self-assembly of designed alkylsiloxanes in the voids of PS opal films. Two types of mesostructures (i.e., lamellar and 2D hexagonal structures) were obtained by changing the alkyl chain length of the precursors. Calcination of the 2D hexagonal hybrid led to the formation of silica films with bimodal porosity. Incorporation of other metals such as Al or Ti into the frameworks of this bimodal pore system will lead to the development of novel efficient catalysts. The lamellar macroporous hybrid film exhibited a unique property: alkyl alcohol molecules are intercalated into the organic layers with the expansion of the interlayer spacings. Various applications are expected in the future by incorporating organic functional molecules, such as photofunctional molecules, into the interlayer spaces or cylindrical mesopores of such macroporous films. Acknowledgment. The authors are grateful to Y. Morioka for in-plane XRD measurement. This work was supported in part by a Grant-in-Aid for the 21st Century COE Program “Practical Nano-Chemistry” and was performed under the Global COE program “Practical Chemical Wisdom”. The A3 Foresight Program “Synthesis and Structural Resolution of Novel Mesoporous Materials” supported by the Japan Society for Promotion of Science (JSPS) is also acknowledged. Supporting Information Available: Experimental details and Figures S1-S12. This information is available free of charge via the Internet at http://pubs.acs.org. LA701590X (26) Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D. J. Am. Chem. Soc. 1998, 120, 6024-6036. (27) El-Safty, S. A.; Evans, J. J. Mater. Chem. 2002, 12, 117-123. (28) Ogawa, M.; Okutomo, S.; Kuroda, K. J. Am. Chem. Soc. 1998, 120, 7361-7362. (29) Shimojima, A.; Mochizuki, D.; Kuroda, K. Chem. Mater. 2001, 13, 36033609. (30) Choi, S. Y.; Mamak, M.; Freymann, G. von; Chopra, N.; Ozin, G. A. Nano Lett. 2006, 6, 2456-2461. (31) Fuertes, M. C.; Lo´pez-Alcaraz, F. J.; Marchi, M. C.; Troiani, H. E.; Luca, V.; Mı´guez, H.; Soler-Illia, G. J. de A. A. AdV. Funct. Mater. 2007, 17, 12471254.
