Microporous and Mesoporous Materials 142 (2011) 98–103

Contents lists available at ScienceDirect

Microporous and Mesoporous Materials

journal homepage: www.elsevier .com/locate /micromeso

Novel eco-friendly synthesis of sucrose-templated mesoporous titaniawith high thermal stability

Dong-Wook Lee, Kew-Ho Lee ⇑National Research Laboratory for Functional Membranes, Environment and Resources Research Center, Korea Research Institute of Chemical Technology (KRICT),P.O. Box 107, Yuseong, Daejeon 305-606, Republic of Korea

a r t i c l e i n f o a b s t r a c t

Article history:Received 1 September 2009Received in revised form 20 October 2009Accepted 17 November 2010Available online 25 November 2010

Keywords:Mesoporous titaniaNonsurfactant templateSucroseThermal stability

1387-1811/$ - see front matter � 2010 Elsevier Inc. Adoi:10.1016/j.micromeso.2010.11.022

⇑ Corresponding author. Tel.: +82 42 860 7240; faxE-mail address: khlee@krict.re.kr (K.-H. Lee).

In this study, mesoporous titania with high surface area and pore volume was simply and eco-friendlysynthesized from titania nanosphere–sucrose nanocomposites without any kinds of surfactant templates,and we first report that environmentally friendly sucrose plays an important role as a nonsurfactant tem-plate for synthesis of mesoporous titania. The amorphous titania nanosphere–sucrose nanocompositeswere formed by simply dissolving sucrose in the 8 nm-sized titania sol at room temperature and dryingthe sol. After calcination of the nanocomposites, the mesoporous titania with three-dimensionally inter-connected wormhole mesostructure was successfully obtained along with formation of nanocrystalframework. The pore size of the mesoporous titania was easily controlled from 3.3 nm up to 7.1 nm bysimply changing the sucrose concentration in the nanocomposite sol. In addition, we investigated effectof a pre-calcination process under vacuum on the thermal stability of the mesoporous titania. The pre-calcination was conducted prior to a calcination process in air for elimination of templates, and nonpo-rous titania-carbon nanocomposites were formed during the pre-calcination process under vacuum. As aresult, mesostructure of the mesoporous titania prepared without the pre-calcination process totally col-lapsed at 700 �C, whereas the mesoporous titania synthesized with the pre-calcination process main-tained its mesostructure up to 800 �C. The improved thermal stability is attributed to the titaniananocrystal framework preformed among rigid carbon template networks during the pre-calcination pro-cess, leading to mild crystalline growth and slow anatase–rutile transformation during the calcinationprocess for template removal.

� 2010 Elsevier Inc. All rights reserved.

1. Introduction

Since Wei and coworkers [1,2] reported a novel, versatile, low-cost, and nontoxic synthetic method of mesoporous silica via anonsurfactant-templating route, several research groups have syn-thesized nonsurfactant-templated mesoporous silica with poly-meric silica (or silica nanospheres) and hydroxy-carboxylic acidcompounds (or amine-functionalized noble metal precursor) as asilica source and nonsurfactant template, respectively [3–13]. Inthe case of surfactant-templating methods, the hydrothermaltreatment is energy and time-consuming process and requiresexpensive autoclave equipment, and trying to find different surfac-tants for pore control is arduous work. Moreover, the use of surfac-tants as a templating agent and volatile solvents as a swellingagent is not environmentally friendly. In contrast, using the simpleand environmentally friendly nonsurfactant-templating route, thepore diameter of mesoporous silica can be easily controlled by sim-ply changing the concentration of environmentally friendly and

ll rights reserved.

: +82 42 860 7237.

cheap nonsurfactant templates. However, there have been only afew reports for synthesis of mesoporous non-silicate materials,especially titania, through the nonsurfactant templating method[14,15]. In addition, their pore size control with template concen-tration changed was not noticeable.

Here, we report simple one-pot synthesis of mesoporous titaniafrom titania nanosphere–sucrose (TN–S) nanocomposites. To thebest of our knowledge, this is the first report of nonsurfactant-templated mesoporous titania showing noticeable effect of thepore size control, and we first show that environmentally friendlysucrose plays an important role as a nonsurfactant template forsynthesis of mesoporous titania. The mesoporous titania with highsurface area and pore volume showed three-dimensionally inter-connected wormhole mesostructure.

Meanwhile, it is quite difficult to fabricate thermally stablemesoporous titania. The relatively low thermal stability of tita-nia-based mesoporous materials is often attributed to their phasetransformation, especially that of anatase to rutile [16]. From aviewpoint of catalytic application, it is very important to synthe-size mesoporous titania with high thermal stability. Recently,Aronson et al. synthesized titania-grafted MCM-41 and FSM-16

Table 1Synthesis conditions of mesoporous titania (KCT-2).

Samplecode

Sucrose/Timolar ratio

Pre-calcinationtemperature (�C)a

Calcinationtemperature (�C)

KCT-2-a 0 –b 400KCT-2-b 0.16 – 400KCT-2-c 0.32 – 400KCT-2-d 0.53 – 400KCT-2-e 1.59 – 400

KCT-2-f 0.32 – 300KCT-2-g 0.32 – 500KCT-2-h 0.32 – 600KCT-2-i 0.32 – 700KCT-2-j 0.32 – 800

KCT-2-k 0.32 600 600KCT-2-l 0.32 700 600

D.-W. Lee, K.-H. Lee / Microporous and Mesoporous Materials 142 (2011) 98–103 99

to improve the thermal stability by reacting TiCl4 in hexanes withas-synthesized silicate powder, in which surfactant remained [17].Yoshitake and coworkers improved thermal stability of template(primary amine)-extracted titania through CVD treatment of tita-nium isopropoxide [18]. Cassiers et al. synthesized NH3-treatedtitania, which is stable up to 600 �C [19]. In this study, we reportimprovement in the thermal stability of mesoporous titaniathrough introducing a pre-calcination process of TN–S nanocom-posites under vacuum prior to a calcination process for the tem-plate removal. That is, anatase nanocrystals are preformed in thepresence of carbon templates during the pre-calcination process,and then the carbon templates are eliminated during the calcina-tion process. The preformed anatase crystals lead to mild crystalgrowth during the calcination process, giving rise to higher ther-mal stability of the mesoporous titania.

KCT-2-m 0.32 800 600KCT-2-n 0.32 700 700KCT-2-o 0.32 800 800

a Prior to the calcination process, the pre-calcination process was carried outunder vacuum, resulting in formation of titania nanocrystal–carbon nanocompos-ites through carbonization of sucrose.

b The pre-calcination process was not conducted.

2. Experimental section

2.1. Synthesis of titania sol

Distilled water (100 mL) was added into the mixture of 14.8 mLtitanium(IV) isopropoxide (TIP: Aldrich, 97%) and 5 mL ethanol(Merck, 99.5%), followed by vigorous stirring at room temperaturefor 30 min, resulting in titania white precipitates. For peptizationof the titania precipitates, 1.33 mL of hydrochloric acid (Junsei,35%) was added into the solution including the titania precipitates,and removal of propanol from the solution was carried out by vig-orous stirring with flask neck opened at 90 �C for 2 h. Then, thesolution was diluted by addition of 100 mL distilled water. Afterthe reflux of final solution at 90 �C for 18 h, light milky titania solwith about 8 nm in particle size was obtained.

2.2. Synthesis of mesoporous titania

Sucrose of various concentrations was added to 50 mL of theas-prepared titania sol, followed by vigorous stirring at room tem-perature for 10 min. The amorphous titania nanosphere–sucrose(TN–S) nanocomposites with wormhole-like mesostructure wereobtained by drying the solution at room temperature with ablower. Subsequently, the wormhole-like mesoporous titania wassuccessfully synthesized by elimination of the sucrose from theTN–S nanocomposites through calcination in air at 300–800 �Cfor 2 h (ramping rate: 1 �C/min). The mesoporous titania is desig-nated as KCT-2 (Korea Research Institute of Chemical Technology,Titania Materials-2). For improvement in thermal stability ofKCT-2, a pre-calcination process under vacuum was introducedprior to the calcination process in air. The titania nanocrystalformation and carbonization of sucrose occurred simultaneouslyduring the pre-calcination process, resulting in titania nanocrys-tal–carbon nanocomposites. For the carbonization of sucroseduring the pre-calcination process, sulfuric acid was added intothe TN–S nanocomposite sol (a sulfuric acid/sucrose weightratio = 0.1), followed by drying the nanocomposite sol. Aftercarbon removal from the TN–S nanocomposites by calcination inair at 600–800 �C for 2 h (ramping rate: 1 �C/min), mesoporoustitania with improved thermal stability was synthesized. Themesoporous titania prepared under various synthetic conditionswas listed in Table 1.

2.3. Characterization

Nitrogen adsorption/desorption isotherms of the KCT-2 weretaken by a Micromeritics ASAP 2020 instrument. Pore size distribu-tion curves were obtained from desorption branch by using theBarrett–Joyner–Halenda (BJH) method. Transmission electron

microscopy (TEM) analysis was carried out using a FEI/TECNAIG2 instrument (operated at 200 kV). The X-ray diffraction (XRD)patterns were collected on a Rigaku D/MAX-2200 V instrumentusing CuKa radiation (operated at 1.6 kW). The each crystal sizefor anatase, rutile, and brookite was calculated from the (1 0 1)peak of anatase phase, the (1 1 0) peak of rutile phase, and the(1 2 1) peak of brookite phase using the Scherrer equation, respec-tively. Their weight ratio was calculated by the equation reportedby Zhang and Banfield [20].

3. Results and discussion

Fig. 1 shows TEM images of the mesoporous titania KCT-2 syn-thesized from TN–S nanocomposites. The low magnification imagedemonstrates that the KCT-2 has wormhole-like mesostructure,and its mesopores are three-dimensionally interconnected and dis-ordered. As shown in the high magnification image, it is revealedthat the pore wall of KCT-2 is composed of titania nanocrystalswith about 8 nm of primary particle size. The wormhole-like mes-ostructure of the KCT-2 was very similar to that of mesoporous sil-ica reported in our previous publications [10,12,13], which wassynthesized from nanocomposites of silica nanospheres and non-surfactant templates such as citric acid (CA) and tetraamineplati-num(II) hydroxide (TPH). It was confirmed that the silicananosphere–CA (or TPH) nanocomposites are formed through thehydrogen bonding interaction between silica nanospheres andthose nonsurfactant templates. Fig. 2 shows nitrogen sorption iso-therms of the KCT-2 with different sucrose/Ti molar ratio in theTN–S nanocomposite sol. The KCT-2 gave typical type IV isothermswith a H2 hysteresis loop as defined by IUPAC. The sharp inflectionof the hysteresis loop shifted toward higher P/Po value with anincrease of sucrose concentration in nanocomposite sol, whichimplies an increase in pore size. The increase in adsorbed nitrogenvolume indicated that the pore volume of KCT-2 gradually in-creased with an increase in the concentration of sucrose as a non-surfactant template. The sharp pore size distributions shown inFig. 2b clearly demonstrated the noticeable effect of pore size con-trol by only changing the sucrose concentration. As shown in Table2, the pore size of KCT-2 was easily controlled from 3.3 to 7.1 nmwith an increase in sucrose/Ti molar ratio from 0 to 1.59, and thepore volume increased from 0.12 to 0.42 cm3/g. Its surface areafluctuated in the range of 101 to 193 m2/g. One of the main fea-tures of nonsurfactant-templated mesoporous materials is tuning

Fig. 2. (a) Nitrogen sorption isotherms and (b) pore size distributions of the KCT-2,synthesized from TN–S nanocomposites, with different sucrose/Ti molar ratio.

Table 2Pore properties of mesoporous titania synthesized under various conditions.

Samplecode

BET S.A.(m2/g)a

Pore volume(cm3/g)b

Micropore volume(cm3/g)

Pore size(nm)c

KCT-2-a 101 0.12 0.005 3.3KCT-2-b 130 0.19 0.000 3.9KCT-2-c 132 0.25 0.012 5.7KCT-2-d 127 0.27 0.014 6.3KCT-2-e 193 0.42 0.003 7.1

KCT-2-f 282 0.23 0.007 3.2KCT-2-g 65 0.15 0.010 6.6KCT-2-h 14 0.11 0.009 12.5KCT-2-i –d – – –KCT-2-j – – – –

KCT-2-k 51 0.19 0.012 9.5KCT-2-l 52 0.17 0.013 9.1KCT-2-m 41 0.16 0.014 9.7KCT-2-n 21 0.12 0.013 15.2KCT-2-o 13 0.09 0.007 23.5

a BET surface area.b Total pore volume taken from the volume of N2 adsorbed at P/Po = 0.995.c BJH desorption average pore diameter.d The mesostructure totally collapsed.

Fig. 1. TEM images of the KCT-2-c: (a) a low magnification image (the scale bar is50 nm) and (b) a high magnification image (the scale bar is 5 nm).

100 D.-W. Lee, K.-H. Lee / Microporous and Mesoporous Materials 142 (2011) 98–103

the pore size through changing the nonsurfactant templateconcentration. Based on the change of pore properties shown inFig. 2 and Table 2, it can be concluded that sucrose plays animportant role as a nonsurfactant template for synthesis of meso-porous titania. To the best of our knowledge, this is the first reportof nonsurfactant-templated mesoporous titania showing suchnoticeable effect of pore size control.

Fig. 3 exhibits nitrogen sorption isotherms of the KCT-2 synthe-sized with different calcination temperature. The hysteresis loop ofKCT-2 shifted toward higher P/Po value with increasing calcinationtemperature from 300 to 800 �C. The KCT-2 showed the maximumof adsorbed nitrogen volume at 400 �C, and the adsorbed nitrogenvolume rapidly decreased from 500 to 800 �C. The KCT-2-j calcinedat 800 �C almost lost its hysteresis loop. Table 2 presents poreproperties calculated from the nitrogen sorption isotherms shownin Fig. 3. The pore size of KCT-2 increased from 3.2 to 12.5 nm withan increase in the calcination temperature from 300 to 600 �C. Themaximum pore volume was 0.25 cm3/g at 400 �C, and the surfacearea decreased from 282 to 14 m2/g with an increase in the tem-perature from 300 to 600 �C. However, above 700 �C, the meso-structure of KCT-2 totally collapsed.

In order to improve the thermal stability of KCT-2, a pre-calcination process under vacuum was introduced prior to acalcination process in air. The titania nanocrystal framework ispreformed and carbonization of sucrose occurs during the pre-calcination process under vacuum, resulting in titania nanocrys-tal–carbon (TN–C) nanocomposites. Subsequently, the calcinationprocess leads to the mild growth of titania crystalline and elimina-tion of the carbon templates from the TN–C nanocomposites. In

this study, the sucrose was employed as a carbon source of TN–Cnanocomposites as well as a nonsurfactant template for synthesisof mesoporous titania. In other words, the use of sucrose templates

Fig. 5. Nitrogen sorption isotherms of the KCT-2, synthesized from TN–C nano-composites, with different pre-calcination and calcination temperature.

Fig. 3. Nitrogen sorption isotherms of the KCT-2, synthesized from TN–S nano-composites, with different calcination temperature.

D.-W. Lee, K.-H. Lee / Microporous and Mesoporous Materials 142 (2011) 98–103 101

made it feasible to easily obtain TN–C nanocomposites withoutaddition of other carbon sources. Fig. 4 shows nitrogen sorptionisotherms of the KCT-2-k, l, and m calcined at 600 �C with differentpre-calcination temperature. Despite the pre-calcination process athigh temperature up to 800 �C, isotherms of KCT-2-k, l, and m werealmost constant in terms of the adsorbed nitrogen volume and rel-ative pressure where a hysteresis loop was located. As shown inTable 2, the KCT-2-k gave 51 m2/g of the surface area, 0.19 cm3/gof the pore volume and 9.5 nm of the pore size. The surface areaand pore volume slightly decreased with an increase in the pre-calcination temperature up to 800 �C.

For confirmation of the thermal stability of KCT-2 after theremoval of carbon templates from the TN–C nanocomposites, theKCT-2-k, n, and o was synthesized from the TN–C nanocompositewith varying the pre-calcination and calcination temperature upto 800 �C (Table 1). Fig. 5 exhibits nitrogen sorption isotherms ofthe KCT-2-k, n, and o synthesized from TN–C nanocomposites.Compared to the isotherms of the KCT-2-h, i, and j synthesizedfrom TN–S nanocomposites (Fig. 3), the KCT-2-k, n, and o showedmore stable mesostructure at high temperature. In the case ofthe KCT-2-h, i, and j, the mesostructure totally collapsed at700 �C. Contrarily, although the pore size and surface areaincreased and decreased respectively with increasing the calcination

Fig. 4. Nitrogen sorption isotherms of the KCT-2, synthesized from TN–C nano-composites, with different pre-calcination temperature.

temperature, the mesostructure of KCT-2 was maintained up to800 �C, which was confirmed by the presence of the hysteresis loopuntil 800 �C (Fig. 5 and Table 2). Based on the comparison between

Fig. 6. XRD patterns of the KCT-2, synthesized from TN–S nanocomposites, withdifferent calcination temperature: A, anatase; R, rutile; B, brookite.

Table 3Size and ratio of titania crystalline phases for the mesoporous titania synthesized under various conditions.

Sample code Anatase size (nm)a Rutile size (nm)b Brookite size (nm)c Anatase/Rutile/Brookite weight ratio

KCT-2-f 9.6 –d 17.8 62/0/38KCT-2-c 10.1 – 10.4 66/0/34KCT-2-g 14.3 22.3 17.3 60/15/25KCT-2-h 19.8 29.5 27.7 27/65/8KCT-2-i – 36.2 – 0/100/0KCT-2-j – 43.1 – 0/100/0

KCT-2-k 17.5 20.4 21.8 76/10/14KCT-2-l 16.1 17.2 17.7 67/10/23KCT-2-m 17.5 29.7 17.0 51/34/15KCT-2-n 24.5 31.0 – 24/76/0KCT-2-o – 26.8 – 0/100/0

a Calculated from the (1 0 1) peak of anatase phase (2h = 25.3) using the Scherrer equation.b Calculated from the (1 1 0) peak of rutile phase (2h = 27.4) using the Scherrer equation.c Calculated from the (1 2 1) peak of brookite phase (2h = 30.8) using the Scherrer equation.d Crystal peaks were not detected.

102 D.-W. Lee, K.-H. Lee / Microporous and Mesoporous Materials 142 (2011) 98–103

Figs. 3 and 5, it is clearly revealed that the pre-calcination processhas a significant effect on improvement in the thermal stability ofthe KCT-2.

In general, the thermal stability of mesoporous titania is closelyrelated to the crystallization of amorphous titania, crystal growthand phase transformation. Particularly, the mesostructure collapseis mainly derived from phase transformation of anatase to rutile.Therefore, XRD analyses for the KCT-2 were conducted to investi-gate relationship between the improved thermal stability and ana-tase–rutile phase transformation. Fig. 6 shows XRD patterns of theKCT-2 synthesized from TN–S nanocomposites with different calci-nation temperature, and Table 3 presents anatase, rutile, brookitecrystal size and their weight ratio. The KCT-2-f calcined at 300 �Cgave diffraction peaks of anatase nanocrystal along with minorpeaks corresponding to brookite phase. Minor rutile peaksappeared at 500 �C of calcination temperature (KCT-2-g), indicat-ing that anatase–rutile phase transformation started. At 700 �C(KCT-2-i), the anatase crystal peaks disappeared, and intensityand FWHM (full width at half maximum) of the rutile crystal peaksincreased and decreased respectively. That is, in the case of theKCT-2 synthesized from TN–S nanocomposites, anatase crystalline

Fig. 7. XRD patterns of the KCT-2, synthesized from TN–C nanocomposites, withdifferent pre-calcination temperature: A, anatase; R, rutile; B, brookite.

framework was completely transformed to rutile phase at 700 �C,which is consistent with the temperature where the mesostructureof KCT-2 totally collapsed (KCT-2-i in Table 2). However, in thecase of the KCT-2-k, l, and m prepared from TN–C nanocomposites,although slight growth of the rutile crystal was shown with an in-crease in pre-calcination temperature up to 800 �C, intensity andFWHM of anatase crystal peaks were not significantly changed(Fig. 7). For the KCT-2-m, the weight ratio of the anatase crystalwas 51% high and 17.5 nm of small anatase nanocrystal size wasmaintained in spite of the pre-calcination at 800 �C and calcinationat 600 �C (Table 3), which contributed to the stable mesostructureshown in Fig. 4. Fig. 8 shows XRD patterns for the KCT-2-k, n, and osynthesized by varying the pre-calcination and calcination temper-ature. The anatase weight ratio decreased to 24%, and the anatasenanocrystal size was grown to 24.5 nm after the pre-calcination at700 �C and calcination at 700 �C. Eventually, anatase crystal frame-work was transformed into rutile phase by the pre-calcination at800 �C followed by calcination at 800 �C.

Fig. 8. XRD patterns of the KCT-2, synthesized from TN–C nanocomposites, withdifferent pre-calcination and calcination temperature: A, anatase; R, rutile; B,brookite.

Fig. 9. A schematic diagram for synthesis of the KCT-2 from TN–S or TN–C nanocomposites.

D.-W. Lee, K.-H. Lee / Microporous and Mesoporous Materials 142 (2011) 98–103 103

In summary, the KCT-2 synthesized from TN–S nanocompositeswithout the pre-calcination process showed anatase–rutile phasetransformation at 700 �C, whereas the KCT-2 prepared from TN–Cnanocomposites via the pre-calcination process had the anatase–rutile transformation temperature of 800 �C. Based on the results,we can deduce that the improvement in thermal stability ofKCT-2 is attributed to retardation of anatase–rutile phase transfor-mation through the pre-calcination process. Fig. 9 schematicallyillustrates the whole procedure of the KCT-2 from TN–S or TN–Cnanocomposites. The TN–S nanocomposites are easily obtainedby drying the sucrose-dissolved titania sol. The calcination ofTN–S nanocomposites in air results in mesoporous titania KCT-2with tunable pore size, being stable till 600 �C. In contrast, thepre-calcination of TN–S nanocomposites under vacuum results inTN–C nanocomposites, and the calcination of TN–C nanocompos-ites leads to the KCT-2 with improved thermal stability up to800 �C. During the pre-calcination process, formation of TN–Cnanocomposites through carbonization of sucrose occurs simulta-neously with crystallization of amorphous titania. In other words,prior to the calcination process for the carbon template removal,the titania nanocrystal framework of the KCT-2 was preformedamong rigid carbon template networks. This is a key point forthe improvement in thermal stability of KCT-2. The preformed tita-nia nanocrystal framework gives rise to mild crystal growth andslow phase transformation of anatase to rutile. Therefore, it canbe concluded that mesoporous titania with tunable pore size andhigh thermal stability can be easily and environmentally friendlysynthesized through the simple sucrose templating method. Inaddition, application of the KCT-2 to photocatalysis and energyconversion is underway.

4. Conclusions

The mesoporous titania KCT-2 was simply synthesized by usingenvironmentally friendly sucrose as a nonsurfactant template. The

TN–S nanocomposites were obtained by drying the mixture of8 nm-sized titania sol and sucrose. After calcination of the nano-composites, the KCT-2 with high surface area and controllable poresize was successfully synthesized. Its pore size was easily con-trolled by only changing the sucrose concentration in the TN–Snanocomposite sol. Moreover, we improved the thermal stabilityof the KCT-2 by conducting the pre-calcination process prior tothe calcination process. This is because the titania nanocrystalframework preformed among carbon template networks duringthe pre-calcination process gave rise to mild crystal growth duringthe calcination process in air.

References

[1] Y. Wei, D. Jin, T. Ding, W.-H. Shin, X. Liu, S.Z.D. Cheng, Q. Fu, Adv. Mater. 10(1998) 313.

[2] Y. Wei, J. Xu, H. Dong, J.H. Dong, K. Qiu, S.A. Jansen-Varnum, Chem. Mater. 11(1999) 2023.

[3] J.B. Pang, K.Y. Qiu, Y. Wei, Micropor. Mesopor. Mater. 40 (2000) 299.[4] J.B. Pang, K.Y. Qiu, Y. Wei, X.J. Lei, Z.F. Liu, Chem. Commun. (2000) 477.[5] J.B. Pang, K.Y. Qiu, Y. Wei, Chem. Mater. 13 (2001) 2361.[6] J.B. Pang, K.Y. Qiu, Y. Wei, J. Non-Cryst. Solids 283 (2001) 101.[7] R. Takahashi, S. Sato, T. Sodesawa, M. Kawakita, Chem. Lett. (1999) 1107.[8] R. Takahashi, K. Nakanishi, N. Soga, J. Sol–Gel. Sci. Technol. 17 (2000) 7.[9] R. Takahashi, S. Sato, T. Sodesawa, M. Kawakita, K. Ogura, J. Phys. Chem. B 104

(2000) 12184.[10] D.-W. Lee, S.-K. Ihm, K.-H. Lee, Micropor. Mesopor. Mater. 83 (2005) 262.[11] D.-W. Lee, S.-K. Ihm, K.-H. Lee, Chem. Mater. 17 (2005) 4461.[12] D.-W. Lee, S.-J. Park, S.-K. Ihm, K.-H. Lee, J. Phys. Chem. C 111 (2007) 7634.[13] D.-W. Lee, C.-Y. Yu, K.-H. Lee, J. Phys. Chem. C 112 (2008) 5136.[14] J.-Y. Zheng, K.-Y. Qiu, Q. Feng, J. Xu, Y. Wei, Mol. Cryst. Liq. Cryst. 354 (2000)

771.[15] J.-Y. Zheng, J.-B. Pang, K.-Y. Qiu, Y. Wei, Micropor. Mesopor. Mater. 49 (2001)

189.[16] B. Smarsly, D. Grosso, T. Brezesinski, N. Pinna, C. Boissière, M. Antonietti, C.

Sanchez, Chem. Mater. 16 (2004) 2948.[17] B.J. Aronson, C.F. Blanford, A. Stein, Chem. Mater. 9 (1997) 2842.[18] H. Yoshitake, T. Sugihara, T. Tatsumi, Chem. Mater. 14 (2002) 1023.[19] K. Cassiers, T. Linssen, M. Mathieu, Y.Q. Bai, H.Y. Zhu, P. Cool, E.F. Vansant, J.

Phys. Chem. B 108 (2004) 3713.[20] H. Zhang, J.F. Banfield, J. Phys. Chem. C 111 (2007) 6621.