Synthesis of Nanosized Multilayered Silica Vesicles with High

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Synthesis of Nanosized Multilayered Silica Vesicles with High Hydrothermal Stability Xin Gu, Changlin Li, Xiaohui Liu, Jiawen Ren, Yanqin Wang,* Yanglong Guo, Yun Guo, and Guanzhong Lu* Laboratory for AdVanced Materials, Research Institute of Industrial Catalysis, East China UniVersity of Science and Technology, Shanghai 200237, People’s Republic of China ReceiVed: December 7, 2008; ReVised Manuscript ReceiVed: February 18, 2009

Nanosized multilayered silica vesicles have been synthesized through a dual-template way by using cetyltrimethylammonium bromide (CTAB) and C3F7O(CFCF3CF2O)2CFCF3 CONH(CH2)3N+(C2H5)2CH3I(FC-4) as the cotemplates and tetraethyl orthosilicate (TEOS) as the siliceous precursor. According to transmission electron microscopy, X-ray diffraction, and N2 sorption analysis, the formation of the multilayered silica vesicles passed through the route of the normal mesoporous silica spheres (MCM-41) to irregular hexagonal structures with cavities inside MCM-41 spheres and finally to the small-sized multilayered siliceous vesicles with the increase of FC-4/CTAB molar ratio. The possible mechanism of the two kinds of micelles cooperation was discussed. The synthesized silica vesicle spheres were 30-40 nm with a few shells that may facilitate the transport of the molecules. Furthermore, the vesicular structure was also obtained by aging at 150 °C, which maintained high surface area even after hydrothermal treatment in boiling water for 48 h. The higher hydrothermal stability, high surface area, and pore volume would benefit the loading of catalysts and increase the adsorption capacity. 1. Introduction There are millions of fancy structures in nature that formed by living creatures, and these structures always have delicate and peculiar functions in special areas. Directly imprinting the shape and the texture will benefit human life. By use of silica vesicle as an example, it can be used in drug delivery, encapsulation, nanocatalyst, high-capacity adsorptions, and so on. Hollow mesoporous silica has been used in controllable release of drugs after modification.1 “Onion” silica with magnetized nano-Fe3O4 core was easy to be separated.2 Lipase immobilized in the multilayered silica vesicles could catalyze the hydrolysis of tributyrin with high activity,3 and much more ibuprofen molecules could stored in the mesoporous shell monolayer silicate vesicles than general MCM-41 materials.4 In addition, the synthesis of silica vesicles with different structures might further explore its potential applications. As the result, many researchers are attracted by the marvelous morphologies and potential applications of silica vesicles. Silica vesicles which were synthesized from the vesicletemplating (VT) technique can produce hard vesicles with relatively high mechanical and hydrothermal stabilities. Various structures of vesicular silica can be achieved by changing the type of surfactants, adjusting the components of surfactant mixtures or controlling other factors such as temperature,5,6 pH value,7 or stirring rates.8 Pinnavaia started the research of vesicular silicas, and multilayered vesiclelike MSU-V and MSU-G have been synthesized by using bola-amphiphiles9,10 and Gemini surfactants11 as the templates, respectively. By use of the Gemini surfactant as the template, small siliceous vesicles (30-40 nm) with several layers were also synthesized.12 Other researchers also got good results, such as hollow siliceous monolamellar vesicles (200-800nm) with mesoporous shells have been synthesized in a cationic-anionic-neutral block * To whom correspondence should be addressed. E-mail: wangyanqin@ ecust.edu.cn (Y.W.); [email protected] (G.L.).

copolymer ternary-surfactant system.13 Onionlike mesoporous siliceous spheres have been synthesized by using Jeffamine D2000 surfactant as the template.5 But most of the surfactant templates were homemade or expensive. Recently, Yu’s group did a lot of works on vesicular silica and functionalized vesicular silica by using different kinds of surfactants. When triblock copolymer P123 was used as the structure directing agent in a mild pH solution, the foamlike and raspberrylike monolayer vesicles have be synthesized with the assistance of salt or pore size expander or delicately adjusting the pH value and temperature.14-16 By use of Pluronic P85 as the single template, multilayered organosiliceous vesicles with spongelike walls and controllable shell numbers were also synthesized by adjusting the pH value of solutions.7 When taking fluorocarbon surfactant C3F7O(CFCF3CF2O)2CFCF3CONH(CH2)3N+(C2H5)2CH3I- (FC-4) with cetyltrimethylammonium bromide (CTAB) as the structure directing agents and BTME (1,2bis(trimethoxysilyl)ethane) as the silica precursor, monolayer organosiliceous vesicles (100-200nm) that had ca. 20 nm thick shells with tunable mesopores have been synthesized.17 The hydrocarbon surfactant was the template of mesopores, and the fluorocarbon surfactant was the vesicle template. The transition from silica rods to vesicles was modeled in the perfluorooctanoic acid (PFOA) and CTAB system. For fluorocarbon chains taking part in the morphology formation, the g factor of micelles and the result silica structures could be adjusted by increasing the molar ratio of PFOA/CTAB.18 In the same way, PFOA and nonionic block copolymer (Pluronic P123) binary surfactants system showed transition from hexagonal mesoporous rodlike silica to multilayer vesicles by varying the molar ratio of PFOA/ P123.19 Surfactants with fluorocarbon chain such as FC-4, which are larger and more rigid than hydrocarbon chains, could easily self-assemble into separate molecular aggregates, like highly stable, heat-sustained vesicles.20 From this point, FC-4 are favor to be used as vesicle template for building solid vesicular silicas,

10.1021/jp810749s CCC: $40.75  2009 American Chemical Society Published on Web 03/26/2009

Synthesis of Nanosized Multilayered Silica Vesicles

J. Phys. Chem. C, Vol. 113, No. 16, 2009 6473

Figure 1. TEM images of sample S0.72 synthesized with the FC-4/CTAB molar ratio of 0.72.

and the assistant of mesoporous surfactant templates will build this hollow silicas with mesoporous shells. The monolayer silica vesicles may facilitate the separation of the large molecules and improve the activity of catalysts due to their mesoporous structure, large surface area and high pore volume. Besides the advantages of monolayer silica vesicles, the multilayered silica vesicles have higher mechanical stability. For the synthesis of silica vesicles, normally, special surfactants were used as the template, and the synthesis temperature was always at room temperature or lower than 100 °C, which could lead to the lower hydrothermal stability. Up till now, there were fewer reports on silica vesicles, which cover high hydrothermal stability, multilayered vesicle structure, accessible thin shells, and small sizes by using common silicate as precursors; the morphology could be sustained while aged at higher temperature. In this paper, multilayered silica vesicles, which were just 30-40 nm spheres with 3-5 layers, have been synthesized in the cotemplate system. The surface area and pore volume were up to 762 m2 g-1 and 0.86 cm3 g-1, respectively. The morphology transitions from MCM-41 spheres to the vesicular spheres were observed by increasing the molar ratio of FC-4/ CTAB and a possible mechanism was proposed and discussed in details. Furthermore, the vesicular structure was also obtained by aging at 150 °C, which maintained high surface area even after hydrothermal treated in boiling water for 48 h. 2. Experimental Section Chemicals. FC-4 was purchased from Shanghai Sinyca Corporation Limited; CTAB, tetraethyl orthosilicate (TEOS) and sodium hydroxide (NaOH) were obtained from Shanghai Chemical Co. All chemicals were used without further purification. Synthesis. In a typical synthesis, 0.36 g of FC-4, 0.2 g of CTAB (molar ratio of FC-4/CTAB ) 0.72), and 0.7 mL of 2 M NaOH were dissolved in 96 g of deionized water. The temperature was raised to 80 °C, and the solution was kept stirring till it turned to transparent. Then 1.108 g of TEOS was dropped into the homogeneous solution with vigorous stirring and sustained for 2 h. The resulting solution was aged at 100 °C for another 24 h. Thus obtained white precipitate were filtrated, washed with deionized water, and dried at 60 °C overnight. Finally, the powder was calcinated at 550 °C for 5 h to remove the organic surfactants. To investigate the influence of the molar ratio of FC-4/CTAB on the mesostructure and formation mechanism, calculated amount of FC-4 was added

to the synthesis mixture with the molar ratios of 0.08, 0.3, 0.6, and 1.0, respectively. The samples were defined as Sx, in which x was the molar ratios of FC-4/CTAB, such as S0.72 was synthesized at the molar ratio of FC-4/CTAB ) 0.72. To investigate the thermal stability, S0.72 was also aged at 150 °C for 24 h, which was denoted as S0.72-150. For comparison, the sample synthesized with only CTAB or FC-4 was named as SCTAB and SFC-4, respectively. 3. Results and Discussion Transmission electron microscopy (TEM) is used to observe the morphology and the detailed structures. Figure 1 shows the morphology and structure of S0.72, which are well-dispersed, small-sized silica vesicles (30-40nm) with 3-5 layers. The spaces between two layers were about 3.7 nm. The detailed insights show that the vesicular shells are porous. The small-angle X-ray diffraction (XRD) pattern in Figure 2 (left) shows one broad peak, indicating the disordered mesostructure in the vesicular shells. N2 adsorption/desorption isotherm was measured to investigate the surface and pore properties of the sample. Figure 2 (right) displays the isotherm of sample S0.72, which shows the typical type IV adsorption isotherm. The adsorption steps at the relative pressures of 0.2-0.4 and 0.4-0.5 signified the filling of two kinds of mesopores, and the uptake at higher relative pressure of 0.8-1.0 comes from the void space between the nanosized silica vesicles. The surface area is 762 m2 g-1, and the pore volume is 0.86 cm3 g-1. The pore size distribution calculated from the Barret-Joyner-Halenda (BJH) method clearly shows two kinds of mesopores, centered at 2.58 and 3.52 nm, respectively. We proposed that the smaller pores were attributed to the porous shell templated by CTAB micelles, and the larger pores were attributed to the width of spaces between two shells which were templated by FC-4 vesicles. This is well agreed with the TEM images that contain mesopores in the shell and spaces between shells. This proposal was further confirmed by changing the molar ratio of FC-4/CTAB and will be discussed later. If pure FC-4 was used as the template, siliceous vesicles with the diameter of 150-250 nm can be obtained with one dense layer, but there were porous silicas inside and outside the vesicles (Figure 3a). Further studies showed that it was attributed to the instability of the siliceous vesicles during hydrothermal treatment, because the multilayered siliceous vesicles with the diameter of 60-120 nm were obtained before hydrothermal treatment (Figure 3b). So, we can propose that the formation

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Figure 2. Small-angle XRD pattern (left) and N2 sorption (right) of sample S0.72.

Figure 3. TEM images of the sample synthesized by using FC-4 as the template (a) after aging and (b) before aging.

of the small, stable siliceous vesicles structure was not only attributed to the FC-4 vesicle template but also to the contribution of the cooperation between CTAB and FC-4. To further study the cooperation of CTAB with FC-4 and the formation mechanism, the phase transition was investigated by changing the molar ratio of FC-4/CTAB. Figure 4 shows the changes of the mesostructures and morphologies of silica at different molar ratios of FC-4/CTAB. When only CTAB was used as the template, the spheres of MCM-41 were obtained (Figure 4a); the small-angle XRD pattern in Figure 5a also confirmed the hexagonal structure. When FC-4 was added to the synthetic system with the molar ratio of 0.08, the small cavities (∼20 nm), which were templated by FC-4 vesicles, were enfolded in the MCM-41 spheres and the mesoporous particles split into joined spheres. Around the small hollow cores, all these particles had well-arranged hexagonal structure that was approved by XRD pattern shown in Figure 5b. Further increasing the molar ratio of FC-4/CTAB to 0.3, more cavities were enveloped in the mesoporous silica spheres and these spheres become slim and branched, as shown in Figure 4c. In this case, only a wide peak was observed in XRD pattern (Figure 5c) at lower 2θ degree, which shows the appearance of the disordered mesostructures and the enlargement of the cell parameter. When the molar ratio of FC-4/CTAB reached 0.6, both the MCM-41 spheres with cavities inside the mesostructures and the pure multilayered silica vesicles coexisted, indicating that with the addition of FC-4 the silica vesicles transformed from MCM-41 spheres. To confirm this mechanism, samples with FC-4/CTAB ) 1 were also synthesized, and its TEM image was presented in parts e and f of Figure 4,

respectively. It shows that the vesicular structures have 3-5 layers and that the diameter is ca. 12 nm. The XRD pattern in parts d, e, and f of Figure 5 could also get the similar result that more FC-4 would lead to the more disordered mesostructures. N2 sorption isotherms were used to investigate the changes of the textural properties of the samples at different molar ratios of FC-4/CTAB. As shown in Figure 6, the MCM-41 spheres have a typical type IV adsorption isotherm with a sharp uptake step at the relative pressure of 0.2-0.4, indicating the narrow pore size distribution. The isotherm of S0.08 is similar to MCM41 spheres, and the pore size distribution is also narrow. But in the case of S0.3, the hysteresis loop is not so sharp and moves to higher relative pressures. BJH pore size distribution shows two peaks, centered at 2.68 and 3.82 nm, respectively. This result is similar to that of the vesicular silica, sample S0.72, but the relative pore volume at the larger pore size range of 3-4 nm is smaller than that of sample S0.72. Sample S0.6 shows the similar phenomenon, but the relative pore volume at the larger pore size range of 3-4 nm is larger than that of S0.3 and smaller than that of S0.72. Table 1 is the collections of the textural properties of all samples, which clearly shows that the percentage of pore volume at larger pore size range (3-4 nm), which is related to the multilayered vesicles increase from 0 to 6, 21, 27, and 46% with the increase of the FC-4/CTAB from 0 to 0.08, 0.3, 0.6, and 0.72, indicating the increase of the contribution of FC-4. To further confirm the contribution of FC-4 to the final structural properties, thermogravimetric/differential thermal analysis measurements were carried out on samples SCTAB, S0.3, and S0.72, respectively, before removing the organic templates.



Figure 4. The TEM images of the samples: (a) SCTAB; (b) S0.08; (c) S0.3; (d) S0.6; (e and f) S1.0.

Because of overlap of the decomposition temperature, it was difficult to point out the exact molar ratio of the two templates in the resulting materials. However, the temperature that attributed to the full decomposition of FC-4 surfactant was shifted from 510 °C for sample S0.3 to 550 °C for sample S0.72, which indicated the increased amount of FC-4 involved in the formation of the multilayered vesicle silicates. In combination with the N2 sorption analysis and TEM images, it can be proposed that the pore diameter around 2.6 nm signified the filling of the mesopores that were templated by CTAB micelles, and the peak of 3.8 nm showed the spaces of alternative shells of silica multilayered vesicles. Usually, dynamic light scattering (DLS) is a useful technique to measure the size of micelles in surfactant solutions, so we

investigated the miscibility of these two surfactants solution before the addition of TEOS. The micelle size in pure surfactants solutions increased from 0.85, 2, 23, and 33 to 56 nm for pure CTAB, FC-4/CTAB ) 0.3, FC-4/CTAB ) 0.72, FC-4/CTAB ) 1, and pure FC-4, respectively, indicating the micelle sizes become larger with the increase of FC-4/CTAB in solution. But it is hard to know the exact size and situation of micelles in the synthesis system after the addition of TEOS and during aging process. Actually, the aging process will influence the interactions between CTAB and FC-4 and lead to the reconstruction of the final structures. Figure 7 shows the TEM images of two representative samples before aging and can be compared with Figure 4. When the molar ratio of FC-4/CTAB was lower, for example 0.08, there were small helix rods without phase


Gu et al.

Figure 5. Small-angle XRD patterns of (a) SCTAB; (b) S0.08; (c) S0.3; (d) S0.6; (e) S0.72; (f) S1.0.

separation; after hydrothermal treatment, the sample shows hexagonal mesoporous structures with small cavities encapsulated inside it (Figure 4b). These indicate that the high aging temperature causes the segregation of CTAB and FC-4, with FC-4 micelles surrounded by CTAB micelles. While, when increasing the molar ratio of FC-4/CTAB, such as 0.6, the sample has separated phases, which are silicate vesicles and wormlike mesoporous silica; after aging, there is only one kind of structure (Figure 4d), which is multilayered vesicles combined with hexagonal mesoporous arrays, and no separate wormlike structures were found. So we can propose that the two surfactants micelles reconstructed with each other in the aging process. Scheme 1 illustrates the possible formation mechanism at different molar ratios of FC-4/CTAB. It was reported before that the surfactants with fluorocarbon chains could form stable and heat-sustained self-assembled aggregates.20,21 The properties

of the mixture of fluorocarbon-hydrocarbon surfactants with the same charge had been studied for several years.22-24 The fluorocarbon chain took part in the morphology formation that caused transition from silica rods to vesicles.18,19 In our work, the process is not exactly the same as reported before. As shown in Scheme 1, when the molar ratio of FC-4/CTAB is low, the involved silica-surfactant interactions facilitate the assembly of helix rodlike silicate micelles or the formation of small sphere particles in the dilute solution.25 The included cavities verified the theory that the fluorocarbon and hydrocarbon surfactants hardly mixed together to form one kind of micelle,22 but the fluorocarbon-rich and hydrocarbon-rich micelles could coexist in solution.24,26 In this condition, the major CTAB-rich micelles and few FC-4-rich vesicles coexisted and adhered together. Because the environment of FC-4-rich vesicles has changed a lot with the coexistence of CTAB, the cavities in the MCM-41 that formed by FC-4-rich vesicles are much smaller than the vesicles with only FC-4 surfactant as template. The hexagonal mesoporous silica spheres were assembled by the cooperation of CTAB-rich micelles and silica precursors as shown in Scheme 1. According to the previous reports, fluorocarbon and hydrocarbon surfactants would have different miscibility when changing the ratio of these two surfactants, the concentration of solution or even the temperature.22-24,26 When the molar ratio of FC-4/CTAB increased, more FC-4 double molecular layers mix with CTAB micelles. As a result, a new morphology which possesses both the properties of multilayered vesicle structures and small sizes were obtained, as shown in Scheme 1. The TEM images shows the whole transition procedure from MCM-41 spheres to irregular hexagonal structures with holes inside and finally the small sized siliceous vesicles with several layers. The S0.72 had comparatively uniform phase and further increasing FC-4 surfactant would obtain much smaller vesicles with 12 nm and some of which even had only one layer.

Figure 6. (right) N2-adsorption/desorption isotherms and (left) BJH pore size distributions of (a) SCTAB; (b) S0.08; (c) S0.3; (d) S0.6; (e) S0.72; (f) S1. Isotherms for S0.08, S0.3, S0.6, S0.72, and S1 were shifted vertically by 150, 250, 350, 450, and 550 cm3 g-1, respectively.

TABLE 1: Structural Properties of the Multilayered Silica Vesicles sample

FC-4/CTAB

D100 (nm)

SBET m2g-1

pore size nm

a b c d e f g

0 0.08 0.3 0.6 0.72 1 ∞

3.8 4.0 4.3 4.4 5.0 12.8

1070 888 873 847 762 776 301

2.58 2.50 2.68/3.82 2.58/3.82 2.58/3.52 2.75/3.53 3.79/10.5

V2-3/relative percenta cm3 g-1/%

V3-4/relative percentb cm3 g-1/%

0.75/100 0.59/94 0.57/79 0.46/73 0.31/54 0.27/48

0.061/6 0.15/21 0.17/27 0.26/46 0.29/52

VT cm3 g-1 0.95 0.75 0.87 0.83 0.86 0.96 1.38

Relative percent of the pore volume V2-3/(V2-3 + V3-4). b Relative percent of the pore volume V3-4/(V2-3 + V3-4). For V2-3, the pore volume at the pore size range from 2 to 3 nm. For V3-4, the pore volume at the pore size range from 3 to 4 nm. a



Figure 7. The TEM images of the samples before aging at 100 °C. (a) S0.08; (b) S0.6.

SCHEME 1: Possible Mechanism of the Formation of Silica Vesicles

The reason why the hexagonal arrays patterned around the FC-4 surfactant vesicles can be summarized as the S+I- (S+ ) CTAB+ or FC-4+, S- ) -OSi-) synthetic route and the aggregation between silicon ester. Initially, because of the Coulomb forces, the anionic siliceous precursor polymerized around both ionic CTAB and FC-4 surfactant micelles. Then, when silica-wrapped CTAB micelles come across silica-wrapped FC-4 surfactant vesicles, the insufficiently hydrolysis silica precursors will further condense and aggregate with each other and form such kind of structure which had vesicle framework in the hexagonal arrays. Aside from the synthesis of the special organic group decorated silica, in most cases, the siliceous precursors were usually TEOS or sodium aluminates and sometimes were tetramethyl orthosilicate (TMOS). The size of our silica vesicles were smaller than that reported in the same surfactant system with different silica precursor.11 The presumable reason might be that the silica precursor had effects on the morphologies and the structures. Fluorocarbon surfactant has higher thermal stability than hydrocarbon surfactant. Xiao’s group27,28 had demonstrated the

successful synthesis of the hydrothermal-stable mesoporous silica with the mixture of fluorocarbon and hydrocarbon surfactants as templates at high aging temperature. To investigate the hydrothermal stability of the FC-4 surfactant cotemplated multilayered vesicular silica in high aging temperature, the sample S0.72 was also aged at 150 °C, and its structure was characterized. Because of the higher condensation, the TEM image in Figure 8 (left) shows that the size of the particles decreased to 20-30 nm and the shells became thicker and denser, indicating the shrinkage of the whole framework, however, the multilayered vesicle structures were still sustained. N2 sorption in Figure 8 (right) also has an obvious step at the relative pressure of 0.3-0.4. In addition, the BJH pore size distribution, which has two main peaks at 2.7 and 3.3 nm, also confirms the shrinkage, the size between layers decreased. The surface area and pore volume of sample S0.72-150 is 657 m2 g-1 and 0.77 cm3 g-1, respectively, which are smaller than that of S0.72. The hydrothermal stability of sample S0.72-150 was investigated by treating with boiling water for 48 h. TEM image in Figure 9 (right) shows that there was no change of the vesicular


Gu et al.

Figure 8. (left) TEM image of S0.72-150 hydrothermal treated at 150 °C. (right) N2 adsorption/desorption isotherm and BJH pore size distributions of S0.72-150.

Figure 9. (left) TEM image of S0.72-150 after hydrothermal treatment at 100 °C for 48 h. (right) N2 adsorption/desorption isotherm and BJH pore size distributions of S0.72-150 after hydrothermal treatment at 100 °C for 48 h.

structure, and N2 sorption in Figure 9 (left) shows that the mesoporous structure becomes less ordered and the surface area can be maintained over 63%, which is much higher than that of MCM-41, indicating the high hydrothermal stability. This should be attributed to the full hydrolysis and condensation of silicon precursors at high aging temperature. The surface area and pore volume of sample S0.72-150 after hydrothermal treatment is 409 m2 g-1 and 0.45 cm3 g-1, respectively. The pore size distribution, which is calculated from the desorption isotherm, shows two distinctive peaks which center at 2.4 and 3.7 nm. The decrease of the pore size in shells and enlargement of spaces between layers suggest that hydrothermal treatment will cause slight break and shrinkage of mesoporous structure in shells but have hardly any effect on the multilayered morphologies. Compared with S0.72-150, the hydrothermal stability of S0.72 is worse. After boiling in water at 100 °C for just one day, the surface area of S0.72 is 58% left (762 vs 438 m2 g-1), and the total pore volume decreases to 0.56 cm3g-1. 4. Conclusion Nanosized multilayered silica vesicles had been synthesized in a CTAB/FC-4 hydrocarbon-fluorocarbon templates system. TEM, XRD, and N2 sorption analysis showed that the formation of the multilayered silica vesicles passed through the route of the normal MCM-41 spheres to irregular hexagonal structures with cavities inside and finally to the small size multilayered

siliceous vesicles with the increase of FC-4/CTAB molar ratio. The synthesized silica vesicle spheres were 30-40 nm with a few shells that may facilitate the transport of the molecules. Thus synthesized silica vesicles could remain the multilayered vesicle structures even aged at 150 °C. The high hydrothermal stability, large surface area, and pore volume will benefit the catalysis reactions and further exploration of the potential applications. Acknowledgment. This project was supported financially by theNationalBasicResearchProgramofChina(No.2004CB719500), the New Century Excellent Talents in University (NCET-05415), the National Natural Science Foundation of China (No. 20673037), and the Commission of Science and Technology of Shanghai Municipality, China (08JC1407900). References and Notes (1) Zhu, Y. F.; Shi, J. L.; Shen, W. H.; Dong, X. P.; Feng, J. W.; Ruan, M. L.; Li, Y. S. Angew. Chem., Int. Ed. 2005, 44, 5083. (2) Zhang, L.; Qiao, S. Z.; Jin, Y. G.; Chen, Z. G.; Gu, H. C.; Lu, G. Q. AdV. Mater. 2008, 20, 805. (3) Zhou, G.; Chen, Y.; Yang, S. Microporous. Mesoporous. Mater. In press. (4) Zhu, Y. F.; Shi, J. L.; Chen, H. R.; Shen, W. H.; Dong, X. P. Microporous. Mesoporous. Mater. 2005, 84, 218. (5) Hossain, K. Z.; Sayari, A. Microporous. Mesoporous. Mater. 2008, 114, 387.

Synthesis of Nanosized Multilayered Silica Vesicles (6) Zhang, L. X.; Li, P. C.; Liu, X. H.; Du, L. W.; Wang, E. AdV. Mater. 2007, 19, 4279. (7) Zhang, Y.; Yu, M.; Zhou, L.; Zhou, X.; Zhao, Q.; Li, H.; Yu, C. Chem. Mater. 2008, 20, 6238. (8) Tan, B.; Lehmler, H. J.; Vyas, S. M.; Knutson, B. L.; Rankin, S. E. AdV. Mater. 2005, 17, 2368. (9) Tanev, P. T.; Pinnavaia, T. J. Science 1996, 271, 1267. (10) Tanev, P. T.; Liang, Y.; Pinnavaia, T. J. J. Am. Chem. Soc. 1997, 119, 8616. (11) Kim, S.-S.; Liu, Y.; Pinnavaia, T. J. Microporous. Mesoporous. Mater. 2001, 44-45, 489. (12) Karkamkar, A. J.; Kim, S. S.; Mahanti, S. D.; Pinnavaia, T. J. AdV. Func. Mater. 2004, 14, 507. (13) Yeh, Y. Q.; Chen, B. C.; Lin, H. P.; Tang, C. Y. Langmuir 2006, 22, 6. (14) Wang, H. N.; Wang, Y. H.; Zhou, X.; Zhou, L.; Tang, J.; Lei, J.; Yu, C. Z. AdV. Func. Mater. 2007, 17, 613. (15) Yu, M. H.; Wang, H. N.; Zhou, X. F.; Yuan, P.; Yu, C. Z. J. Am. Chem. Soc. 2007, 129, 14576. (16) Wang, H. N.; Zhou, X. F.; Yu, M. H.; Wang, Y. H.; Han, L.; Zhang, J.; Yuan, P.; Auchterlonie, G.; Zou, J.; Yu, C. Z. J. Am. Chem. Soc. 2006, 128, 15992. (17) Djojoputro, H.; Zhou, X. F.; Qiao, S. Z.; Wang, L. Z.; Yu, C. Z.; Lu, G. Q. J. Am. Chem. Soc. 2006, 128, 6320.

J. Phys. Chem. C, Vol. 113, No. 16, 2009 6479 (18) Yang, S.; Zhou, X. F.; Yuan, P.; Yu, M. H.; Xie, S. G.; Zou, J.; Lu, G. Q.; Yu, C. Z. Angew. Chem., Int. Ed. 2007, 46, 8579. (19) Yuan, P.; Yang, S.; Wang, H. N.; Yu, M. H.; Zhou, X. F.; Lo, G. Q.; Zou, J.; Yu, C. Z. Langmuir 2008, 24, 5038. (20) Krafft, M. P.; Riess, J. G. Biochimie 1998, 80, 489. (21) Wang, K.; Karlsson, G.; Almgren, M.; Asakawa, T. J. Phys. Chem. B 1999, 103, 9237. (22) Asakawa, T.; Hisamatsu, H.; Miyagishi, S. Langmuir 1996, 12, 1204. (23) Davey, T. W.; Warr, G. G.; Almgren, M.; Asakawa, T. Langmuir 2001, 17, 5283. (24) Kadi, M.; Hansson, P.; Almgren, M.; Furo, I. Langmuir 2002, 18, 9243. (25) Cai, Q.; Luo, Z. S.; Pang, W. Q.; Fan, Y. W.; Chen, X. H.; Cui, F. Z. Chem. Mater. 2001, 13, 258. (26) Funasaki, N.; Hada, S. J. Phys. Chem. 1980, 84, 736. (27) Han, Y.; Li, D.; Zhao, L.; Song, J.; Yang, X.; Li, N.; Di, Y.; Li, C.; Wu, S.; Xu, X.; Meng, X.; lin, K.; Xiao, F. Angew. Chem., Int. Ed. 2003, 42, 3633. (28) Li, D.; Han, Y.; Song, J.; Zhao, L.; Xu, X.; Di, Y.; Xiao, F. S. Chem.-Eur. J. 2004, 10, 5911.

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Synthesis of Nanosized Multilayered Silica Vesicles with High

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