Ordered bimodal mesoporous silica with tunable pore structure and morphology

Ordered bimodal mesoporous silica with tunable pore structure and morphology

Microporous and Mesoporous Materials 98 (2007) 6–15 www.elsevier.com/locate/micromeso Ordered bimodal mesoporous silica with tunable pore structure a...

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Microporous and Mesoporous Materials 98 (2007) 6–15 www.elsevier.com/locate/micromeso

Ordered bimodal mesoporous silica with tunable pore structure and morphology Fuqiang Zhang, Yan Yan, Yan Meng, Yulin Xia, Bo Tu, Dongyuan Zhao

*

Department of Chemistry and Molecular Catalysis, Innovative Materials Lab, Fudan University, Shanghai 200433, PR China Received 26 June 2006; received in revised form 12 August 2006; accepted 15 August 2006 Available online 27 September 2006

Abstract Ordered bimodal mesoporous silica materials with uniform framework large pores of 30 nm and small pores of 5–10 nm have been synthesized using triblock copolymer P123 as a template and liquid paraffin as a swelling agent on the water/oil surface following a solution sol–gel pathway. XRD, TEM, SEM and nitrogen sorption were used to characterize the obtained bimodal mesoporous silica samples. Due to the low solubility of liquid paraffin in P123 solution, two types of micelles (P123 micelles and P123-coated liquid paraffin microemulsions) may exist in such water-in-oil system at the same time. Thus, homogeneously interconnected bimodal mesopores were derived from the synchronous assemblies of the two types of micelles with inorganic precursors on the water/oil surface. The bimodal mesoporous materials can be obtained only at a low water/oil volume ratio of 2/100. The two scale pores were directly observed in TEM images and indirectly proved by the two step increase in nitrogen sorption isotherms. The small pores were derived from P123 micelles and the pore size can be easily tuned from 5 to 10 nm by varying the aging temperature during the synthesis procedure. The bimodal mesoporous materials display a sheet or a hollow sphere shell morphology, with a thickness of 100–200 nm, which may be influenced by the P123/water ratio in the mixture. Furthermore, a desirable amount of micropores are contained on the pore wall of such bimodal mesoporous materials, which may endow such materials with promising properties in sorption, catalysis, etc.  2006 Elsevier Inc. All rights reserved. Keywords: Bimodal; Mesoporous silica; Liquid paraffin; Block copolymer; Swelling agent

1. Introduction Since the discovery of M41S family in 1992 [1,2], mesoporous materials have attracted more and more interests for their potential applications in sorption, catalysis and separation, etc. Up to now, a variety of highly ordered mesoporous silica materials (M41S [1,2], SBA [3,4], MSU [5], FDU [6], HMS [7], KIT [8], etc.) have been successfully synthesized. The pore size of MCM-41 is restricted in the range of 2–8 nm [1,2], while that of the SBA-15 materials can be tuned from 5 to 20 nm [3]. The SBA-15 materials contain a considerable amount of micropores on the pore silica walls [9,10], which may endow such materials with exciting properties in sorption, catalysis, etc. *

Corresponding author. Tel.: +86 21 6564 2036; fax: +86 21 6564 1740. E-mail address: [email protected] (D. Zhao).

1387-1811/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2006.08.013

Recently, various types of hierarchically (macro–micro [11], macro–meso [12], meso–micro [13], and meso–meso [14–23]) porous materials are synthesized by using two or three templates. Such materials may have great advantage in applications in sorption and catalysis of size-selective reactions. For these applications, the bimodal porous materials must have well-controllable pore size and structures. Commonly, pores in different length scale are derived from the template of different size. The macropores are obtained from colloidal particles or poly(dimethylsiloxane) (PDMS) molds, and the mesopores are from surfactants templating and the micropores are from the structuredirecting agents (such as tetramethylammonium hydroxide, TMAOH, tetraethylammonium hydroxide, TEAOH, tetrapropylammonium hydroxide, TPAOH, etc.). Most of the hierarchically porous materials can be synthesized by using mixing templates of different length scales. However, such

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mixing templates strategy does not necessarily results in the desired bimodal mesopores, because often the co-template just leads to a mono-modal pore system. Some previous works described the bimodal mesopore system with small pores (2–10 nm) derived from the surfactant micelles and large pores (>10 nm) from the interparticle spacing of silica grains [14–21]. Unfortunately, the obtained hierarchical pores are mixtures of framework and textural pores. It is very difficult to obtain ordered and well-controlled larger pore from such strategy. Recently, Smarsly et al. [22] reported the synthesis of ordered bimodal mesoporous materials (small pore of 2 nm and large pore of 10 nm) by using mixing templates of block copolymers and ionic surfactant employing a solvent evaporation induced assembly (EISA) approach. Groenewolt and Antonietti [23] also synthesized similar bimodal mesoporous materials by using mixing templates of fluorocarbon/ hydrocarbon block copolymer employing the EISA method. However, it is still a great challenge to synthesize ordered bimodal mesoporous materials with small pores of 2–10 nm and large pores of >20 nm following the EISA method mentioned above, although such bimodal pore system is of great importance to the bulky molecules reactions. Moreover, to the best of our knowledge, there are no literatures that described the synthesis of ordered bimodal mesoporous materials using mixing templates following the solution sol–gel pathway, while the solution sol–gel pathway is considered to be a more versatile and effective method in the synthesis of highly ordered mesoporous materials. Mesostructured cellular foams (MCFs) with uniform pore size (15–30 nm) can be synthesized by using triblock copolymers as templates and 1,3,5-trimethylbenzene (TMB) as a swelling agent [24,25]. But commonly only mono-modal mesopores can be obtained in such system. In addition, for the bimodal mesoporous materials, the pore-size tunability is also an important factor that influences their applications. The pore size of the reported bimodal porous materials [14–23] is restricted to the size of the template and cannot be easily tuned. In this study, we report the synthesis of bimodal ordered mesoporous silica materials possessing tunable small pore of 5–10 nm and large pore of 30 nm by using triblock copolymer P123 as a template and liquid paraffin as a swelling agent in the water-in-oil (W/O) system following a solution sol–gel pathway. The solubility of liquid paraffin in P123 solution is much smaller than that of TMB or other short chain hydrocarbon [26]. Thus, two types of micelles may exist in the liquid paraffin/P123/HCl/H2O solution. After the addition of TEOS (tetraethyl orthosilicate), bimodal mesoporous materials are formed on the W/O surface as a result of the co-assembly of the two types of micelles with inorganic precursors (TEOS) at the same time. The two length scale pores are all uniform and well-controlled framework pores and homogeneously interconnected. The small pores are derived from the micelles of P123 and the pore size can be easily tuned from 5 to 10 nm by varying the aging temperature. The large pores are

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derived from the microemulsions of P123-coated liquid paraffin droplets. Moreover, the hierarchical porous system also contains a desirable amount of micropores (up to 0.08 cm3/g) on the pore wall. The bimodal mesoporous materials display morphologies of thin sheets or shells of hollow spheres, with a thickness of 100–200 nm, which can be tuned by varying the P123 concentration. 2. Experimental section 2.1. Chemicals Triblock poly(ethylene oxide)-b-poly(propylene oxide)b-poly(ethylene oxide) copolymer Pluronic P123 (Mw = 5800, EO20PO70EO20) was bought from Aldrich Chemical Inc. Liquid paraffin with a chain length of C18–C20 (q = 0.835–0.855 g/ml at 20 C, bp = 298– 302 C) was bought from Shanghai Feida Chemical Company. Other chemicals were purchased from Shanghai Zhenxing Chemical Company. All chemicals were used as received without further purification. Millipore water was used in all experiments. 2.2. Synthesis Bimodal mesoporous materials were synthesized in the water/liquid paraffin system using EO20PO70EO20 (P123) as a template and liquid paraffin as a swelling agent. In a typical synthesis, 1.0 g of EO20PO70EO20 (P123) was dissolved in 35 ml of 2 M HCl solution at room temperature to obtain a clear solution. Then 2 ml of the obtained solution was added to 100 ml of liquid paraffin. The mixture was stirred at a rate of 1000 rpm for 4 h at 40 C, and then 0.12 g of TEOS was then added to the mixture. After stirred for 1 min, the mixture was aged at 40 C for 24 h for gelation with or without stirring. The obtained mixture was then aged at 40–120 C for another 24 h. The products were collected by filtration, washed with petroleum ether and ethyl alcohol, dried in air, and calcined at 550 C for 5 h to remove the template. 2.3. Characterization Small-angle powder X-ray diffraction (XRD) patterns were recorded with a Bruker D4 powder X-ray diffractometer using CuKa radiation. Small angle X-ray scattering (SAXS) patterns were recorded on a Nanostar U smallangle X-ray scattering system using CuKa radiation. Nitrogen adsorption–desorption isotherms were measured with a Micromeritics Tristar 3000 analyzer at 77 K. All the samples were outgassed at 180 C for 8 h before the analysis. The Brunauer–Emmett–Teller (BET) method was utilized to calculate the surface areas. The pore-size distributions of the small pores were derived from the adsorption branch between the relative pressure range (0.2–0.8) of the isotherms by using the BJH method. The pore size of the large pores were derived from the

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adsorption branch in the relative pressure range (0.8–1.0) by also using BdB method with a spherical pore model [27]. The micropore volume (Vm) and micropore surface area were calculated by using the V–t plot method. The t values were calculated as a function of the relative pressure ˚ ) = [13.99/(log(p0/p) + using the de Boer equation, t (A 1/2 0.034)] . The micropore volume (Vm) was calculated using the following equation, Vm = I · 0.001547 (cm3), where I represents the Y-intercept in the V–t plot. Transmission electron microscopy (TEM) images were taken with a JEOL JEM2011 electron microscope operating at 200 kV. For the TEM measurements, the samples were dispersed in ethanol with the aid of supersonic and then dried on a holey carbon film Cu grid. Scanning electron microscopy (SEM) images were taken with a Philips XL30 electron microscope operating at 20 kV. 3. Results and discussion Bimodal ordered mesoporous materials can be synthesized in the water-in-oil system using triblock copolymer P123 as a template and liquid paraffin as a swelling agent. The samples synthesized by systematically varying the component ratio and synthetic condition are summarized in Table 1. Sample S-1 was synthesized under stirring condition in the gelation step. Sample S-2 was prepared from the same component ratio as S-1 except the static gelation step. By comparing the two samples, we may have a better understanding of the effect of stirring in the gelation. TEM and SEM images of S-1 (Fig. 1A, C, and E) and S-2 (Fig. 1B, D, and E) are shown in Fig. 1. S-1 show a shell-like morphology and the shell is formed by SBA-15-like rods connected by the sheet with large pore (30 nm). The XRD pattern of S-1 (Fig. 2A) further confirms the ordered p6m symmetry of the SBA-15-like rods. The channels in the rods of S-1 are parallel to the short axis, as can be seen from Fig. 1C, a TEM image of large magnification. The sample S-2 displays a sheet-like morphology, as shown in the SEM image of S-2 (Fig. 1F). Sample S-2 has a thickness of 100–200 nm, which can be roughly measured from the

Fig. 1. TEM images (A, B, C, D) and SEM images (E, F) of bimodal mesoporous silica sample S-1 (A, C, E) and S-2 (B, D, F). The magnification of images C, D is higher than that of A, B.

SEM image. It can be seen from TEM images (Fig. 1B and D) that the sample S-2 is formed by of uniform and homogeneous interconnected large pores (30 nm) and small domains of cylindrical small pores (<10 nm). The XRD pattern of sample S-2 (Fig. 2A) shows only one weak peak, while the SAXS patterns (Fig. 2A inset) show three resolved diffraction peaks which can be indexed to 1 0, 1 1, 2 0 reflections of 2D hexagonal mesostructure, suggesting that the cylindrical small pores in S-2 sample can still be packed in p6m symmetry in small domain. Such small domain size may cause strong scattering and lead to poor-resolved one wide diffraction peaks in XRD patterns.

Table 1 Synthesis conditions of bimodal mesoporous silica materials with different component ratios Sample

P123 (g)

TEOS (g)

2 M HCl solution (ml)

Liquid paraffin (ml)

Water/oil ratio

Aging temperature (C)

Stirring during the step of gelation?

S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12

2/35 2/35 2/35 2/35 2/35 10/35 50/35 100/35 100/35 100/35 2/10 2/50

0.12 0.12 0.12 0.12 0.12 0.60 3.0 6.0 6.0 6.0 0.42 0.084

2 2 2 2 2 10 50 100 100 100 2 2

100 100 100 100 100 100 100 50 10 2 100 100

2/100 2/100 2/100 2/100 2/100 10/100 50/100 100/50 100/10 100/2 2/100 2/100

40 40 80 100 120 100 100 100 100 100 100 100

Yes No No No No No No No No No No No

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Fig. 2. XRD patterns (A), N2 sorption isotherms (B) and BJH pore-size distribution curves (inset of B) of samples S-1 and S-2. Small angle X-ray scattering (SAXS) pattern of sample S-2 (inset of A).

The N2 sorption isotherms and corresponding pore-size distribution curves of S-1 and S-2 are shown in Fig. 2B. There are two obvious capillary condensation steps (0.5 < P/P0 < 0.7, 0.80 < P/P0 < 0.95) in the isotherms of sample S-2, associated with the small pores of 5 nm and large pores of 30 nm, respectively. While only one capillary condensation step of sample S-1 is observed and the secondary rapid increasing adsorption step is not as obvious as that of S-2, suggesting that sample S-1 is mainly composed with hexagonally ordered small mesopores. The pore volume of large pore of S-2 calculated from the

condensation step is 0.11 cm3/g, which is about 200% larger than that of S-1 (0.04 cm3/g). Sample S-2 possesses quite different pore structures compared to S-1. The two types of mesopores for S-1 sample are largely separated in domain, while the domain size of small pores of S-2 is much smaller than that of sample S-1. As a result, more homogeneously interconnected bimodal mesopores system in sample S-1 can be observed by TEM. The structure of sample S-2 is a desirable bimodal structure for applications in catalysis and sorption. Static condition in the gelation step is considered to be a crucial

Fig. 3. N2 sorption isotherms (A) and corresponding pore-size distribution curves (B) of samples S-2, S-3, S-4 and S-5. For clarity, the isotherms of S-2, S3, S-4 and S-5 are offset along Y-axis for 0, 60, 300 and 450 cm3/g, respectively.

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factor for the formation of bimodal mesoporous materials with desirable interconnected pore system. The pore-size tunability of small pores in bimodal porous materials plays an important role in widening their application fields. Similar to mesoporous SBA-15 materials, we can easily tune the pore size of bimodal mesoporous silica materials by varying the aging temperature during the synthesis [3]. Herein, we synthesized samples S-3, S-4, and S-5 from the same component ratios as S-2 at the aging temperature of 80, 100 and 120 C, respectively. The nitrogen sorption isotherms and corresponding pore-size distribution curves of samples S-2, S-3, S-4 and S-5 are shown in Fig. 3A and B. The sizes of the small pores are calculated by using BJH method from the adsorption branch at relative pressure range 0 < P/P0 < 0.8, and those of large pores are calculated by the same method with a spherical model at the pressure range of (0.8 < P/P0 < 1.0). All of the four samples display bimodal mesoporosity, which is greatly effected by the aging temperature. The volumes of large pores for samples S-3, S-4 and S-5 are much larger than that of sample S-2. Increasing the aging temperature from 40 to 120 C, the small pore changes greatly. The small pore diameter of the four samples as a function of the aging temperature is shown in Fig. 4A. The size of the small pores of the bimodal mesoporous materials can be tuned from 5 to 10 nm by varying the aging temperature. The tunable small pores may endow the bimodal mesoporous materials with desirable and interesting properties in sorption, catalysis of bulky molecules. Compared to the small pore, the large pore shows much wider pore-size distribution. When the aging temperature is increased from 40 to

120 C, the pore-size distribution curves move to larger pore slightly, which can be directly observed in the TEM images of the samples S-3, S-4 and S-5 (Fig. 6). It was reported that MCFs materials can be obtained by using P123 as a template and hydrocarbon (TMB, benzene, hexane, etc.) as a swelling agent. P123-coated hydrocarbon droplets can be obtained by the addition of such hydrocarbon to P123/HCl solutions [3,24,25]. The P123-coated hydrocarbon droplets may lead to the formation of MCFs materials [25]. In our synthetic strategy, a required amount of P123/HCl solution is dispersed in the liquid paraffin and thus a water-in-oil system is obtained. Liquid paraffin is composed of long-chain hydrocarbon, its solubility in P123 solution is much smaller than that of TMB, n-hexane, etc. [26]. As a result, the P123-coated liquid paraffin microemulsions formed in the water droplets are not so stable as those of TMB. Thus, two types of micelles may be contained in the water droplets dispersed in the oil, as shown in Scheme 1. One is the cylinder type micelles formed by triblock copolymer P123 and the other is the spherical P123-coated liquid paraffin microemulsions, similar to the P123-coated TMB microemulsions [25]. The two types of micelles may be stable at the inner part of the water droplets. While on the water/oil surface the two types of micelles may transform to each other. After the addition of TEOS, the TEOS molecules may disperse from oil to water phase. The two types of micelles may assemble with the inorganic precursors on the water/oil surface at the same time, and then the bimodal mesostructured materials are formed as a result. In the gelation step, stirring may facilitate the micelle transformation from P123-coated

Fig. 4. (A) Small pore diameters of bimodal mesoporous silica materials as a function of the aging temperature. Large pore diameters of bimodal mesoporous materials versus the aging temperature (B), water/oil ratio (C) and P123/water ratio (D).

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Scheme 1. The formation mechanism of the bimodal mesoporous silica materials.

Fig. 5. Nitrogen sorption isotherms (A) and XRD patterns (B) of calcined samples S-4, S-6, S-7, S-8, S-9 and S-10. For clarity, the isotherms of S-4, S-6, S7, S-8, S-9 and S-10 are offset along Y-axis for 0, 100, 450, 700, 1100 and 1300 cm3/g, respectively.

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hydrocarbon emulsion to cylinder micelles on the water/oil surface due to the extraction effect. Thus, materials synthesized under static condition may possess higher pore volume of large pores compared to those synthesized under stirring condition. Stirring has great influence on the pat-

terns of the bimodal mesoporous materials and may facilitate the movements and aggregations of the cylindrical micelles and inorganic precursors in the gelation step. Thus, the cylindrical pore may aggregate to SBA-15-like rods in large domains. Under static condition, such process

Fig. 6. TEM images of sample S-3 (A), S-4 (B), S-5 (C), S-7 (D), S-9 (E), S-10 (F), S-11 (G) and S-12 (H).

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may be inhibited. As a result, the domains of hexagonal packed pores are very small and more homogeneously interconnected bimodal mesoporous silica materials are obtained. The size of small pores derived from the P123 micelles can be easily tuned by varying the aging temperature, due to the temperature-dependent hydrophilicity of PEO blocks [3]. The mesostructured bimodal materials are formed before the post-synthesis treatment process. Thus, higher aging temperature does not lead to larger amount of liquid paraffin coated with P123. It can explain why the large pore diameter changes slightly when aged at higher temperature. 3.1. Water/oil ratios Five samples S-6, S-7, S-8, S-9 and S-10 were synthesized systematically by varying the water/oil ratio to 10/

Table 2 Structure parameters of samples S-1 to S-12 Sample

SBET (m2/g)

V (cm3/g)

Vs (cm3/g)

VL (cm3/g)

DS (nm)

DL (nm)

S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12

480 550 900 560 570 650 690 830 690 780 590 450

0.59 0.77 1.1 0.90 0.94 1.5 1.4 1.7 1.2 1.1 0.90 0.86

0.15 0.24 0.36 0.28 0.31 0.37 – – 0.28 – 0.28 0.25

0.12 0.20 0.39 0.28 0.31 0.73 – – 0.39 – 0.26 0.33

5.3 5.4 6.8 8.1 10.0 8.0 – – 8.1 8.2 7.5 7.9

– 28.2 27.8 38.0 28.3 27.6 28.0 22.8 29.0 – 17.0 29.0

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100, 50/100, 100/50, 100/10 and 100/2, respectively. The nitrogen sorption isotherms and XRD patterns of samples synthesized with a water/oil ratio of 2/100, 10/100, 50/100, 100/50, 100/10 and 100/2 are shown in Fig. 5. When the w/ o ratio is increased from 2/100 (S-4) to 10/100 (S-6), the volume percentage of the large pore increased greatly. There is only one weak diffraction peak in the XRD pattern of either S-4 or S-6, indicating poor structure regularity of the two samples. When the w/o ratio is increased up to 50/ 100 (S-7) and 100/50 (S-8), only MCF-like structure with pore size 30 nm is obtained, as can be shown from the nitrogen sorption isotherms and XRD patterns (Fig. 5) of samples S-7 and S-8. The TEM images of sample S-8 (Fig. 6D) further confirm the MCF structures of S-7. When the w/o ratio is further increased to 100/10 (S-9), two capillary condensation steps can be observed from the nitrogen sorption isotherm of S-9. The XRD pattern of sample S-9 shows three well-resolved diffraction peaks, indexed as 10, 11 and 20 reflections of p6m symmetry. The TEM image (Fig. 6E) shows that the two modal pore systems of S-9 are domainially separated from each other, while those of S-4 are homogeneously interconnected. At a w/o ratio of 100/2 (S-10), mesoporous silica materials with highly ordered p6m symmetry are obtained, as is proved by the XRD patterns (Fig. 5B) and nitrogen sorption isotherms (Fig. 5A). When the water/oil ratio is increased to 100/ 10, the large pore diameter did not change a lot (Figs. 4C and 5A), while the volume ratio of the two types of pores is increased greatly (Table 2). The products with interconnected bimodal mesopores could not be obtained when the water/oil was above 50/100. The water/oil ratio is an essential factor that influences the formation of bimodal mesopores. When the water/oil ratio is low enough (2/100), the water droplets can be dispersed very well in the oil phase

Fig. 7. Nitrogen sorption isotherms (A) and pore-size distribution (B) of samples S-4, S-11, and S-12. For clarity, the isotherms of S-4, S-11 and S-12 are offset along Y-axis for 200, 350 and 0 cm3/g, respectively.

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and the transformation of two types of micelles occurs on the w/o surface. Thus two types of micelles are contained in the water droplets, which may derive the formation of thin sheets with desirable bimodal pores under static condition during the gelation step. When the w/o ratio is increased up to 50/100, it can be observed that the water phase are separated from the oil phase. As a result, few micelles transformation may happen on the w/o surface and few cylinder type P123 micelles will exist in the water phase. As a result, only MCFs-type materials are obtained after gelation in samples S-7 and S-8. 3.2. P123/water ratios Two samples S-10 and S-11 with different P123/water weight ratios (1/10, 1/50) were synthesized with a water/ oil ratio 2/100 (Table 1). The weight ratio of TEOS/P123 was restricted to 2.1/1 during the synthesis process. The nitrogen sorption isotherms of three samples prepared from different P123/water ratio 1/10 (S-11), 1/35 (S-4) and 1/50 (S-12) are shown in Fig. 7. Two capillary condensation steps in the nitrogen sorption isotherms are clearly observed, indicating bimodal mesoporosity of the three samples. Compared to the sample synthesized from the P123/water ratio of 1/35 (S-4) and 1/50 (S-12), sample prepared from the ratio of 1/10 (S-11) possess relatively less uniform pores (Fig. 7B), suggesting that low P123/water ratio may favor the formation of the bimodal mesostructures. Moreover, the large pore diameter of sample S-11 is smaller compared to those of samples S-4 and S-12 (Figs. 4D and 7B), indicating that low P123/water ratio may lead to larger pore diameter. The TEM images of the two samples are shown in Fig. 6. It can be measured from the TEM images that the hollow sphere has a shell thickness of 100– 200 nm. The materials synthesized with P123/water ratio of (1/35)–(1/50) display a sheet-like morphology. When the ratio is increased to 1/10, mesoporous silica hollow spheres with bimodal mesopores can be obtained. The hollow sphere morphology can further prove that the mesostructured shells are formed on the water/oil surface. During the formation of the bimodal mesoporous materials, the TEOS was dissolved in the oil phase. Thus the hydrolyzation and condensation of TEOS occurred on the water/oil interface and shells are formed as a result. In case of materials from low P123/water ratio, the shells may be too thin and easily broken, and only sheet-like materials are obtained. When the P123/water ratio is increased to 1/10, the shell is robust enough to form hollow spheres. 3.3. Microporosity The micropore volumes of the samples (S-2, S-3, S-4 and S-5) can be calculated from the Y-intercept (Fig. 8). The four samples contain a desirable amount of micropores. The micropore volume of S-3 (0.07 cm3/g) and S-4 (0.08 cm3/g) are relatively higher than those of S-2 (0.01 cm3/g) and S-5 (0.01 cm3/g). The aging tempera-

Fig. 8. V–t plots of samples S-2, S-3, S-4 and S-5.

ture has great influence on the micropore volume of the bimodal mesoporous materials. Samples prepared at the aging temperature of 80–100 C contain larger micropore volume. Similar to SBA-15, in the bimodal porous materials, the micropores should be derived from the PEO blocks embedded in the pore walls [9,10]. 4. Conclusion In summary, narrow distributed bimodal mesoporous materials with uniform large pore of 30 nm and small pores of 5–10 nm have been successfully prepared by using P123 as a template and liquid paraffin as a swelling agent in a water-in-oil system following a solution sol–gel pathway. The bimodal mesopores are all framework pores and homogeneously interconnected. The pore size of small pores in such materials can be easily tuned from 5 to 10 nm by varying the aging temperature. In addition, the materials display morphologies of thin sheets or shells of hollow spheres (100–200 nm). The obtained bimodal mesoporous materials are expected to have wide potential application field in bulky molecules sorption, catalysis, etc. Acknowledgments This work was supported by National Natural Science Foundation of China (20421303, 20233030, 20521140450), State Key Basic Research Program of PRC Shanghai Science and Technology Committee (05DZ22313, 04JC14087), China National Petroleum Corp. Research Grant (040803-03-00), Shanghai HuaYi Chemical Group and Fudan Graduate Innovation Funds. References [1] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992) 710. [2] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.W. Chu, D.H. Olson, E.W. Sheppard, S.B.

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