Characterization of pore structure of copolymer-templated periodic mesoporous organosilicas

Studies in Surface Science and Catalysis 156 M. Jaroniec and A. Sayari(Editors) 9 2005 ElsevierB.V. All rights reserved

673

Characterization of pore structure of copolymer-templated periodic mesoporous organosilicas Oksana Olkhovyk, Michal Kruk, # Rebecca Sutton + and Mietek Jaroniec*

Department of Chemistry, Kent State University, Kent, Ohio 44242, USA

The diameters of entrances to the large cage-like mesopores (7-10 nm) of triblockcopolymer-templated periodic mesoporous organosilicas (PMOs) with ethylene (-CH2-CH2-) bridging groups were determined on the basis of nitrogen and argon adsorption isotherms for unmodified and organosilane-modified materials. The polymers used for the PMO synthesis were Pluronic P123 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EOz0POv0EO20) and B50-6600 poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) (EO39BO47EO39).Hysteresis loops of argon adsorption isotherms for unmodified PMOs closed at the lower limit of adsorption-desorption hysteresis, thus indicating the pore entrance diameter below 4 nm. The pores of the PMO templated with EO39BO47EO39 triblock copolymer were largely blocked after the surface modification with octyldimethylsilyl groups, thus suggesting the pore entrance size below ~2.9 nm. The PMO templated by EOz0PO70EO20 copolymer still exhibited accessible porosity after the modification with the latter groups, which in combination with the results of argon adsorption points to the pore entrance diameter between 2.9 and 4.0 nm.

I. INTRODUCTION The combination of sol-gel synthesis approach with supramolecular templating afforded a new class of materials with hybrid organic-inorganic frameworks and periodic mesoporous structures [1-3], which were named PMOs (periodic mesoporous organosilicas). The incorporation of organic groups into silica-based frameworks has been achieved through condensation of organosilanes, whose structure is composed of an organic group decorated with two or more silicon atoms bearing hydrolysable alkoxy groups [1-5]. Typically, the organosilane has a structure (R'O)3Si-R-Si(OR')3, where hydrolysable groups (R'O-) are methoxy or ethoxy groups, and the bridging group R is ethylene, ethane, methylene, phenylene, thiophene, biphenylene and so forth [1-10]. The introduction of different organic groups into silica-based frameworks changes the density, hardness, modulus and dielectric constant when compared to the unmodified silica [11]. An additional fine-tuning of these *Corresponding author- M. Jaroniec, e-mail:[email protected] # Current address: Departmentof Chemistry, Carnegie Mellon University,Pittsburgh, PA 15213. +REU student from the Department of Chemistry, Purdue University,West Lafayette, IN 47907.

674 properties can be achieved by co-condensation of (R'O)3Si-R-Si(OR')3 silanes (or other PMO precursors) with tetraethyl or tetramethyl orthosilicates [3,11]. Materials with low, tunable dielectric constants are of much interest from the viewpoint of development of a new generation of low-k dielectric materials for electronic applications [11 ]. PMOs are also promising as adsorbents for organic molecules [2,12] and templates for nanostructures [13, 14]. Their surface and chemical properties can also be tuned by co-condensation of the PMO precursors with organotrialkoxysilanes [15-17], which may lead, for instance, to PMOs with ion binding properties [ 16] or catalytic properties [18,19]. Alternatively, one can incorporate inorganic heteroatoms, which was demonstrated for titanium, in the PMO frameworks and obtain materials suitable for catalytic applications [20,21 ]. Over the last three years, there was much interest in expanding the pore size domain achievable for PMOs. First PMOs were templated by alkylammonium surfactant templates [1-3] and micelle expanders were not used, so the pore diameters of these materials were below 5 nm. In 2001 a successful synthesis of large-pore (diameter above ~5 nm) PMOs templated by block copolymers has been reported [22-25]. With exception of Zhu et al. work [24], which reported large-pore 2-D hexagonally ordered ethylenesilica PMO, these materials were formed via co-condensation with tetraethyl orthosilicate (TEOS), thus having only moderate content of framework organic groups [22], or they exhibited a poor framework ordering [23,25]. It should be noted that the use of oligomeric and polymeric templates for the PMO synthesis was originally reported in 2000, but little information about porous structures of these materials was provided [11]. In 2002, we reported the first example of PMO with periodic structure of cage-like mesopores synthesized from pure (R'O)3Si-R-Si(OR')3 precursor, that is, without co-condensation of TEOS [26]. Over the last two years, the synthesis procedures of large-pore PMOs with a variety of structures, pore diameters, and framework compositions were reported using oligomeric or polymeric surfactant templates [27-39] or alkylammonium surfactants with addition of micelle expanders [40]. Some of these materials exhibited highly ordered three-dimensional pore structure of cubic Im3m symmetry (body-centered cubic structure) [33,37]. The pore geometry and connectivity in PMOs is expected to largely influence the properties of these materials as adsorbents, catalysts, and templates for nanostructures. Most PMOs feature cylindrical mesopores, although spherical mesopores are also quite common [1,26,33,37,41]. In the case of spherical mesopores, the entrances to them are usually much narrower than the mesopore interiors [42-47], which may have a significant influence on diffusion of gases and accessibility of pores to large molecules [48]. Moreover, even in the case of cylindrical mesopores, the occurrence of constrictions and porous "plugs" may largely influence pore accessibility [49,50]. Therefore, the identification of currently available methods and perhaps the development of new methods for the determination of the pore entrance size in PMOs are important from the viewpoint of prospective applications of these materials. Electron crystallography is a powerful technique for the elucidation of the structure of 3-dimensionally ordered mesoporous materials, including their pore entrance size [42,51 ]. This method is potentially applicable for PMOs with an appreciable degree of structural ordering and sufficiently large size of ordered domains. In the case of entrances having diameter up to about 1 nm, their size can also be effectively probed on the basis of size exclusion of adsorbates of different molecular dimensions [44]. On the other hand, entrances having diameter above ~4 nm can be characterized by analyzing desorption branches of hysteresis loops on the gas adsorption-desorption isotherms [45-47]. Recently, we proposed a method to determine the pore entrances in materials with cage-like

675 mesopores by performing a surface modification of a given material with a series of organosilanes of different sizes and monitoring the pore accessibility after the modification [43]. The size of the smallest surface-bonded group that is capable of making the mesopores of the studied material inaccessible to nitrogen, argon or other gas is related to the pore entrance size, as long as the surface-bonded groups attain extended conformations (this does not need to be valid for all the groups; for cylindrical or spherical pore geometries, even a small fraction of fully extended groups is expected to be sufficient to block the pores). This surface-modification/pore-accessibility-monitoring method [43,52,53] was demonstrated to be very useful in studies of FDU-1 silicas with close-packed spherical pores (cubic closepacked, Fm3m, with intergrowth of hexagonal close-packed structure) [46,54] and SBA-16 silicas with body-centered cubic structures of Im3m symmetry [42,55]. In the present work we show that the pore entrance size in large-pore PMOs can be elucidated using the surface-modification/pore-accessibility-monitoring method combined with argon and nitrogen adsorption. These methods are potentially useful for other PMO materials.

2. M A T E R I A L S AND M E T H O D S

N-butyldimethylchlorosilane was acquired from Petrarch System Inc. (Bristol, PA). Noctyldimethylchlorosilane and pyridine (anhydrous) was purchased from Aldrich (Milwaukee, WI). Toluene (p.a., water content below 0.02%), i-propanol (anhydrous), nhexyldimethylchlorosilane, and hydrochloric acid (ASC certified) were purchased from Fisher Scientific (Pittsburgh, PA). PMO samples were synthesized using bis(triethoxysilyl)ethane as the organosilica framework precursor. The sample denoted PMO1 was templated by poly(ethylene oxide)poly(butylene oxide)-poly(ethylene oxide) triblock copolymer (B50-6600, EO39BO47EO39 from Dow Chemicals). The sample PMO2 was templated by Pluronic P 123 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) template (EO20PO70EO20, BASF). The initial synthesis temperature was 40~ in both cases, whereas the hydrothermal treatment time was 6 hours for PMO 1 and 1 day for PMO2. The details of the synthesis were reported elsewhere [26]. The copolymer template was removed via calcination under nitrogen at 300~ for 10 hours. As was demonstrated earlier, this procedure does not lead to any appreciable cleavage of Si-C bonds characteristic for the PMO structure [26]. It should be noted that the PMO samples used in the present study were prepared via calcination of the same as-synthesized (polymer-containing) samples as those reported in Ref. [26], but in the present case, the calcined PMO samples had somewhat higher content of block copolymer left after calcination, as inferred from thermogravimetry. The surfaces of PMOs were modified via chemical reaction with butyldimethylchlorosilane (BDCS), hexyldimethylchlorosilane (HDCS), and octyldimethylchlorosilane (ODCS) in the presence of pyridine [56]. The typical modification procedure was as following. 0.2 g of the PMO sample was dispersed in 2.5 mL of silane, followed by addition of 15 mL of anhydrous pyridine. The mixture was refluxed (temperature about 120~ without stirring in a round-bottom flask for 24 h and, after cooling, the modified material was washed many times on the glass filter with small portions of toluene and isopropyl alcohol (total --200-250 ml) to remove an excessive amount of modifier, pyridine and possible products of hydrolysis of the silane. The samples were dried for 8 hours in a

676 vacuum oven at ~100~ The PMO samples modified with butyldimethylsilyl (BDMS), hexyldimethylsilyl (HDMS), octyldimethylsilyl (ODMS) groups are denoted PMOn-S, where S denote the silane used for the reaction (BDCS, HDCS or ODCS). Adsorption isotherms were measured on Micromeritics model ASAP 2010 volumetric adsorption analyzer (Norcross, GA) using nitrogen and argon of 99.998% purity. Measurements were performed in the range of relative pressure from 10-6 to 0.995 at -196~ on the samples degassed for 2 hours at 110~ under vacuum of about 10"3 Torr. The degassing temperature (110*C) was selected to avoid the decomposition of attached organic ligands and assure thermodesorption of physically adsorbed water. TA Instrument model TA 2950 (New Castle, DE) analyzer was used to carry out highresolution thermogravimetric measurements. The purging gas was nitrogen; the maximum heating rate was 5~ per minute over a temperature range from 25~ to 1000~ in all cases. The specific surface area was evaluated using the BET method [57]. The total pore volume was estimated from the amount adsorbed at a relative pressure of 0.99 [57]. The pore size distribution (PSD) was calculated using the algorithm based on the work of Barrett, Joyner and Halenda (BJH) [58] and the relation between the capillary condensation pressure and the pore diameter established by Kruk, Jaroniec and Sayari (KJS) [59]. The tcurve used in PSD calculations was reported elsewhere [60]. Nitrogen adsorption data for the PMOs under study were taken from Ref. [26].

3. RESULTS AND DISCUSSION The structure and adsorption properties of the periodic organosilicas under study were discussed in a recent communication [26]. The sample templated by EO39BO47EO39 copolymer exhibited a three-dimensionally ordered structure, presumably of cubic symmetry, which was not assigned primarily due to the small ordered domain size. The mesopores appeared to be cage-like, based on the shape of the hysteresis loop on the nitrogen adsorption isotherm (see Figure 1) and were large (10 nm, see Table 1 and Figure 2). The sample templated by EO20POToEO20 copolymer exhibited somewhat smaller pore diameter of about 7 nm (see nitrogen adsorption isotherm in Figure 3 and PSD in Figure 4), and a lower extent of structural ordering, although it had some periodic features, as inferred from the occurrence of a single peak on the XRD pattern [26]. A similar PMO templated by EO20PO70EO20 copolymer was reported by Muth et al. [23]. None of these earlier studies determined sizes of entrances to the mesopores of these PMOs, although the fact that the capillary evaporation of nitrogen at -196~ was delayed to the lower limit of hysteresis pointed to the pore entrance diameter below 5 nm [26]. In the case of argon at -196~ the capillary evaporation was also delayed to the lower limit of adsorption-desorption hysteresis, which is indicative of the pore entrance size below 4.0 nm, as discussed in detail elsewhere [45,47]. To further refine this rather crude estimate of the pore entrance size, surface modifications with butyl-, hexyl- and octyldimethylchlorosilanes were performed. As discussed elsewhere, these organosilanes are capable of reducing the pore diameter by not more than 1.5, 2.0 and 2.5 nm, respectively [43]. Therefore, entrances would have to be below 1.9, 2.4 and 2.9 nm, if the surface modification with the aforementioned three ligands renders them impenetrable for nitrogen molecules (this takes into account the size of nitrogen molecule).

677 0.12

500

o [] ;

P M O 1 (Ar) o

PMO1

~o 400 [-.

(N2)

vl= I

0.10

_ Well

~

r~

PMO1 PMO 1-BDCS PMOI~HDCS

0.08

o 300 .~ 0.06 O

<

200

"~ 0.04

100

"~ 0.02 O

~" 0.00 0

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure, P/Po

~

-

-

T

2

4

r

1

T

1

6

8

10

12

r-----

14

Pore width, nm

Fig. 1. Argon and nitrogen adsorption isotherms Fig. 2. Pore size distributions for the PMO1 for the PMO1 sample together with nitrogen sample after modification with alkylmonoadsorption isotherms for the PMO1 sample after chlorosilanes modification with alkylmonochlorosilanes.

Table 1. Structural parameters for unmodified and modified PMO samples. Sample

BET specific surface area (m 2 g-l)

PMO1

746

Pore diameter

Total pore volume

(nm)

(cm 3 g-l)

10.0

0.62

PMO1-BDCS

165

8.7

0.19

PMO1-HDCS

189

8.6

0.21

PMO1-ODCS

45

2

0.07

PMO2

743

7.2

0.63

PMO2-BDCS

572

6.7

0.45

PMO2-HDCS

387

6.5

0.36

PMO2-ODCS

379

6.3

0.36

As expected, the surface-bonding of organosilyl ligands led to a decrease in the adsorption capacity and in the pore diameter (see Table 1). However, the decrease in the adsorption capacity was more gradual in the case of PMO2 and its mesopores.still exhibited capillary condensation after the modification with the largest organosilyl groups studied (that is, octyldimethylsilyl groups). This suggests that the pore entrance size for this material was above 2.9 nm. Combined with the conclusions from argon adsorption data, the pore entrance diameters in PMO2 are in the range of 2.9-4.0 nm. It needs to be noted here that both the desorption behavior and blockage with organosilane depend on the accessibility of the pore in the particle of the material to the surrounding gas phase [53]. Therefore, these experiments do not probe the distribution of the pore entrance sizes, but rather provide

678 information about the widest pathway connecting the given mesopore with the surrounding gas phase. This information is critical for the assessment of the accessibility of pores to molecules of different sizes, but is not necessarily equivalent with the size of the widest entrance to a particular pore, and certainly not equivalent in most cases with the pore entrance size distribution (unless entrances are monodisperse in size). However, for mesoporous networks with many entrances to any given mesopore, many possible pathways exist from each pore to the surrounding and thus the considered experiments are likely to probe the sizes of the widest entrance to the particular pores. 500

0.25 o

PMO2 (At)| PMO2(N2

t

"

~

o o

v=E 0.20

400

5/-J

300

0.15

i

.~ O.lO

200 ~D

PMO2 PMO2-BDCS

. . . . . . .

O

<

100

~t"-o ~ ~

0.05

PMO2_BDCS PMO2-HI~S PMO2-ODCS

0.00

0 0.0

0.2

0.4

0.6

Relative pressure, P/Po

0.8

1.0

2

4

6

8

10

Pore width, nm

Fig. 3. Argon and nitrogen adsorption Fig. 4. Pore size distributions for the PMO2 isotherms for the PMO2 sample together with sample before and after modification with nitrogen adsorption isotherms for the PMO1 alkylmonochlorosilanes. sample after modification with alkylmonochlorosilanes. The modifications resulted in the decrease of the pore diameter and reduction of the adsorption capacity. This decrease was gradual for the PMO2 sample, and more abrupt for the PMO1 sample. For the latter, no capillary condensation was observed after the modification with octyldimethylsilyl groups, thus indicating that the pores do not have entrances wider than 2.9 nm. The mesopores of PMO 1 sample were largely accessible after the modification with smaller butyldimethylsilyl and hexyldimethylsilyl groups, but the height of the peak on the PSD was already diminished much more than in the case of PMO2, despite its smaller pore diameter (and thus larger loss of adsorption capacity expected after the introduction of a layer of surface group of a particular thickness). Therefore, it is likely that some of entrances to the mesopores of PMO 1 were actually of diameter well below 2.9 nn3.

In the case of modification of the silica surface with organosilanes, one can readily monitor the amount of organosilyl groups introduced by using high-resolution thermogravimetry [52]. This is because the weight loss under air (and in many cases, under nitrogen) above ~100~ is primarily due to the oxidative removal (under air) or decomposition (under nitrogen) of organic groups, whose content can be estimated on the basis of this weight loss. However, in the case of PMOs, the unmodified material already contains the organic groups and moreover, the template removal may be incomplete [15]. The TG data indicated that an appreciable amount of the copolymer template was indeed

679 present in the PMOs after calcination under nitrogen at 300~ as the weight loss under nitrogen was much higher than that corresponding to the loss of the ethylene groups. The presence of residual template before the PMO reaction with organosilanes made it impossible to evaluate the surface coverage of organic groups, as the residual template may be removed during the reaction with organosilanes [61]. In the case of the PMO samples subjected to the post-synthesis modification with organosilanes, there is additional weight loss on the TG curve related to the decomposition of attached organosilyl groups. The TG curves (Figure 5) as well as the corresponding differential (DTG) curves (Figure 6) are quite complex for the PMO samples subjected to the post-synthesis reaction with organosilanes. Thus, neither differences in the carbon content before nor after modification nor differences in the weight losses, provide information about the amount of bonded groups. Therefore, we are not able to ascertain that the coverages of alkyldimethylsilyl groups were sufficient to ensure that the assumption about blockage of entrances takes place in the case where the extended length of the surface-bonded groups approaches the pore radius, which was experimentally supported for silica materials [26]. Consequently, this study provides upper limit of the pore entrance sizes for the PMOs under study, whereas the actual values may be lower. Nonetheless, it is clear that the pore entrance diameter in PMOs can be just a fraction of the pore diameter (less than 1/3 in the case of PMO1 sample and that the larger pore diameter does not imply the larger pore entrance size (as seen for PMO 1 and PMO2). 100 0.16

0.14

95 --o I -"

90 ell

r..)

85

N

80

PMO1-TECS PMO1-HMCS PMO1-ODCS

PMO1-TECS --o-- PMO1-HMCS 9 PMO1-ODCS

0.12 q

0.10 0.08 0.06 0.04

75

70

0.02 i

'|

i

i

200

400

600

800

0.00 1000

Temperature, ~

Fig. 5. Thermogravimetric (TG) weight change curves recorded for selected PMO 1 samples after modification with alkylmonochlorosilanes.

200

400

600

800

1000

Temperature, ~

Fig. 6. Differential TG (DTG) curves for selected PMO 1 samples after modification with alkylmonochlorosilanes.

4. CONCLUSIONS The analysis of desorption branches of hysteresis loops on argon or nitrogen adsorption isotherms may provide useful information about sizes of entrances to the large mesopores of copolymer-templated organosilicas with cage-like structures. However, in the case where

680 the desorption takes place at the lower limit of adsorption-desorption hysteresis, as in the case of the samples discussed in the present study, only the upper limit of the pore entrance diameter (~4 nm in the case of Ar, ~5 nm in the case of N2 at -196~ can be estimated. In these cases, a more accurate determination of the pore entrance size can be based on the use of surface-modification/pore-accessibility-monitoring method. Herein, we demonstrated that this approach can indeed be very useful for characterization of PMOs. Ethanesilica templated by poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblockcopolymer was found to exhibit the pore entrance size below 2.9 nm, which is similar to that for purely siliceous, periodic material with cage-like mesopores, templated by the same polymer and synthesized at the same temperature and time of hydrothermal treatment. The PMO templated by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer exhibited larger pore entrance diameter despite its smaller pore diameter. On the basis of the accessibility of pores after surface modification and argon adsorption behavior, the pore entrance size of this material was estimated to be between 2.9 and 4.0 nm. Because of the presence of an appreciable amount of residual polymer template in the PMOs used for the reaction with organosilanes, it was impossible to determine the coverage of organosilyl groups introduced during surface modification. Therefore, the pore entrance diameter estimates for the PMOs under study are not expected to be as accurate and reliable as those for pure-silica materials, where the success of the surface modification can be readily monitored by TGA or elemental analysis.

5. ACKNOWLEDGMENT The authors acknowledge support from the National Science Foundation grants CHE0097538 (REU) and CHE-0093707. Dr. Jivaldo R. Matos from Instituto de Quimica da Universidade de S5o Paulo (Brazil) is acknowledged for the synthesis of the PMO samples. Dow Chemicals is acknowledged for providing the B50-6600 triblock copolymer.

REFERENCES

[1]

S. Inagaki, S. Guan, Y. Fakushima, T. Ohsuna, and O. Terasaki, J. Am. Chem. Soc., 121 (1999) 9611. [2] B. J. Melde, B. T. Holland, C. F. Blanford, and A. Stein, Chem. Mater., 11 (1999) 3302. [3] T. Asefa, M. J.MacLachlan, N. Coombs, and G. A. Ozin, Nature, 402 (1999) 867. [4] M. Kuroki, T. Asefa, W.Whitnal, M. Kruk, C. Yoshina-Ishii, M. Jaroniec, and G. A. Ozin, J. Am. Chem. Soc., 124 (2002) 13886. [5] K. Landskron, B. D. Hatton, D. D. Perovic and G. A. Ozin, Science, 302 (2003) 266. [6] T. Asefa, M. J. MacLachlan, H. Gondley, N. Coombs, and G. A. Ozin, Angew. Chem., Int. Ed., 39 (2000) 1808. [7] S. Inagaki, S. Guan, T. Oshuna, O. Terasaki, Nature, 416 (2002) 304. [8] C. Yoshina-Ishii, T. Asefa, N. Coombs, M. J. MacLachlan and G. A. Ozin, Chem. Commun. (1999) 2539. [9] G. A. Ozin, G. Temtsin, T. Asefa and S. Bittner, J. Mater. Chem., 11 (2001) 3202. [ 10] M.P. Kapoor, Q. Yang and S. Inagaki, J. Am. Chem. Soc., 124 (2002) 15176.

681 [ 11] Y. Lu, H. Fan, N. Doke, D. A. Loy, R. A. Assink, D. A. LaVan, C.J. Brinker, J. Am. Chem. Sot., 122 (2000) 5258. [12] M. C. Burleigh, M. A. Markowitz, M. S. Spector and B. P. Gaber, Environ. Sci. Technol., 2002, 36, 2515. [13] A. Fukuoka, Y. Sakamoto, S. Guan, S. Inagaki, N. Sugimoto, Y. Fukushima, K. Hirahara, S. Iijima and M. Ichikawa, J. Am. Chem. Soc., 123 (2001) 3373. [14] A. Fukuoka, H. Araki, Y. Sakamoto, S. Inagaki, Y. Fukushima and M. Ichikawa, Inorganica Chimica Acta, 350 (2003) 371. [15] T. Asefa, M. Kruk, M. J. MacLachlan, N. Coombs, H. Grondey, M. Jaroniec, and G. A. Ozin, J. Am. Chem. Soc., 123 (2001) 8520. [16] M. C. Burleigh, S. Dai, E. W. Hagaman and J. S. Lin, Chem. Mater., 13 (2001) 2537. [ 17] M. C. Burleigh, M. A. Markowitz, M. S. Specter and B. P. Gaber, J. Phys. Chem. B, 105 (2001) 9935. [18] S. Hamoudi and S. Kaliaguine, Microporous Mesoporous Mater., 59 (2003) 195. [19] X. Yuan, H. I. Lee, J. W. Kim, J. E. Yie and J. M. Kim, Chem. Lett. 32 (2003) 650. [20] K. Yamamoto, Y. Nohara and T. Tatsumi, Chem. Lett. 30 (2001) 648. [21 ] M. P. Kapoor, A. Bhaumik, S. Inagaki, K. Kuraoka and T. Yazawa, J. Mater. Chem., 12 (2002) 3078. [22] E.-B. Cho, K.-W. Kwon and K. Char, Chem. Mater., 13 (2001) 3837. [23] O. Muth, C. Schellbach and M. Froba, Chem. Commun., (2001) 2032. [24] H. Zhu, D. J. Jones, J. Zajac, J. Roziere, and R. Dutarte, Chem. Commun., (2001) 2568. [25] M. C. Burleigh, M. A. Markowitz, E. M. Wong, J.-S. Lin and B. P. Gaber, Chem. Mater., 13 (2001) 4411. [26] J. R. Matos, M. Kruk, L. P. Mercuri, M. Jaroniec, T. Asefa, N. Coombs, G. A. Ozin, T. Kamiyama, and O. Yerasaki, Chem. Mater., 14 (2002) 1903. [27] M. C. Burleigh, M. A. Markowitz, M. S. Spector and B. P. Gaber, J. Phys. Chem. B, 106 (2002) 9712. [28] S. Hamoudi and S. Kaliaguine, Chem. Commun., (2002) 2118. [29] A. Sayari and Y. Yang, Chem. Commun., (2002) 2582. [30] Y. Goto and S. Inagaki, Chem. Commun., (2002) 2410. [31] W. Guo, J.-Y. Park, M.-O. Oh, H.-W. Jeong, W.-J. Cho, I. Kim and C.-S. Ha, Chem. Mater. 15 (2003) 2295. [32] M. C. Burleigh, M. A. Markowitz, S. Jayasundra, M. S. Spector, C. W. Thomas and B. P. Gaber, J. Phys. Chem. B, 107 (2003) 12628. [33] W. Guo, I. Kim, and C. -S. Ha, Chem. Commun., (2003) 2692. [34] E.-B. Cho and K. Char, Chem. Mater., 16 (2004) 270. [35] M. C. Burleigh, S. Jayasundra, M. S. Spector, C. W. Thomas, M. A. Markowitz, and B. P. Gaber, Chem. Mater., 16 (2004) 3. [36] W. Wang, S. Xie, W. Zhou and A. Sayari, Chem. Mater., 16 (2004) 1756. [37] Z. Zhang, B. Tian, X. Yan, S. Shen, X. Liu, D. Chen, G. Zhu, D. Zhao and S. Qiu, Chem. Lett., 33 (2004) 1132. [38] X. Y. Bao, X. S. Zhao, X. Li, P. A. Chia and J. Li, J. Phys. Chem. B, 108 (2004) 4684. [39] X. Y. Bao, X. S. Zhao, S. Z. Qiao and S. K. Bhatia, J. Phys. Chem. B, 108 (2004) 16441. [40] Y. Liang and R. Anwander, Microporous Mesoporous Mater., 72 (2004) 153. [41 ] S. Guan, S. Inagaki, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc. 122 (2000) 5660.

682 [42] Y. Sakamoto, M. Kaneda, O. Terasaki, D. Y. Zhao, J. M. Kim, G. D. Stucky, H. J. Shin, R. Ryoo, Nature 408 (2000) 449. [43] M. Kruk, V. Antochshuk, J. R. Matos, L. P. Mercuri, M. Jaroniec, J. Am. Chem. Soc., 124 (2002) 768. [44] A. E. Garcia-Bennett, S. Williamson, P. A. Wright, I. J. Shannon, J. Mater. Chem., 12, (2002) 3533. [45] P. I. Ravikovitch and A. V. Neimark, Langmuir, 18 (2002) 9830. [46] J. R. Matos, M. Kruk, L. P. Mercuri, M. Jaroniec, L. Zhao, T. Kamiyama, O. Terasaki, T. J. Pinnavaia, and Y. Liu, J. Am. Chem. Soc., 125 (2003) 821. [47] M. Kruk and M. Jaroniec, Chem. Mater., 15 (2003) 2942. [48] M. Perez-Mendoza, J. Gonzalez, P. A. Wright and N. A. Seaton, Langmuir, 20 (2004) 7653; 20 (2004) 9856. [49] P. Van Der Voort, P. I. Ravikovitch, K. P. De Jong, M. Benjelloun, E. Van Bavel, A. H. Janssen, A. V. Neimark, B. M. Weckhuysen and E. F. Vansant, J. Phys. Chem. B, 106 (2002) 5873. [50] M. Kruk, M. Jaroniec, S. H. Joo and R. Ryoo, J. Phys. Chem. B, 107 (2003) 2205. [51] Y. Sakamoto, I. Diaz, O. Terasaki, D. Zhao, J. Perez-Pariente, J. M. Kim, G. D. Stucky, J. Phys. Chem. B, 106 (2002) 3118. [52] V. Antochshuk, M. Kruk, and M. Jaroniec, J. Phys. Chem. B., 107 (2003) 11900. [53] T. -W. Kim, R. Ryoo, M. Kruk, K. P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki, J. Phys. Chem. B, 108 (2004) 11480. [54] C. Yu, Y. Yu, and D Zhao, Chem. Commun. (2000) 575. [55] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka, and G. D. Stucky, J. Am. Chem. Soc., 120 (1998) 6024. [56] R. Ryoo, C. H. Ko, M. Kruk, V. Antochshuk, M. Jaroniec, J. Phys. Chem. B, 104 (2000) 11465. [57] S. J. Gregg and K. S. W. Sing, Adsorption, Surface Area and Porosity, Academic Press, London, 1982. [58] E.P. Barrett, L. G. Joyner, P. P. Halenda, J. Am. Chem. Soc., 59 (1951) 373. [59] M. Kruk, M. Jaroniec and A. Sayari, Langmuir, 13 (1997) 6267. [60] M. Jaroniec, M. Kruk and J. P. Olivier, Langmuir, 15 (1999) 5410. [61 ] V. Antochshuk and M. Jaroniec, Chem. Commun., (1999) 2373.