Materials Letters 65 (2011) 3519–3521

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Materials Letters

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Blending effect of sucrose and surfactant templating agents on silica mesostructure

Dong-Wook Lee, Jong-Soo Bae, Se Joon Park, Ho Won Ra, Jai-Chang Hong, Young-Chan Choi ⁎Clean Fossil Energy Research Center, Climate Change Technology Research Division, Korea Institute of Energy Research (KIER), 71-2, Jang-dong, Yuseong, Daejeon 305-343, Republic of Korea

⁎ Corresponding author. Tel.: +82 42 860 3784; fax:E-mail address: youngchan@kier.re.kr (Y.-C. Choi).

0167-577X/$ – see front matter © 2011 Elsevier B.V. Adoi:10.1016/j.matlet.2011.07.089

a b s t r a c t

a r t i c l e i n f o

Article history:Received 18 April 2011Accepted 27 July 2011Available online 31 July 2011

Keywords:Porous materialsSol–gel preparation

We report the blending effect of surfactant and sucrose as a nonsurfactant templating agent on the silicamesostructure. The CTAB/sucrose-templated mesoporous silica (SCS) was compared with CTAB-templatedMCM-41. The MCM-41 showed spherical morphology with a particle diameter of 1.1–1.5 μm, and gave abimodal size distribution, centered at 2.1 nm and 8.9 nm, which is assigned to hexagonally-arrayed cylindricalpores and interparticle-pores between small MCM-41 clusters, respectively. SCS gave unique andextraordinary morphology in which two different mesostructures have grown with both of them facingeach other. The ordered MCM-41 pore structure clung to silica nanosphere-framed wormlike mesostructure,resulting in a bimodal pore size distribution centered at 2.1 nm and 7.0 nm. It was revealed that both of CTABand sucrose act independently as a surfactant and a nonsurfactant template.

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1. Introduction

Since the first synthesis of MCM-41 in 1992 [1,2], there hasbeen intense research activity in synthesizing various mesoporousmaterials using supramolecular assembly of surfactant moleculesas a template. Recently, Wei and coworkers first reported a novel,versatile, low-cost, and nontoxic synthetic method of mesoporoussilica by using D-glucose, dibenzoyl-L-tartaric acid (DBTA), D-maltoseas a nonsurfactant template [3]. Since that publication, some researchgroups have synthesized nonsurfactant-templated mesoporous silicaby using polymeric silica or silica nanospheres as a silica source, andemploying hydroxy-carboxylic acid compounds, polysaccharide oramine-functionalized noble metal precursor as a nonsurfactanttemplate, respectively [4–9]. For a comprehensive understanding oftheir various mesostructures, many of the research groups have beendedicated to the study on both of surfactant and nonsurfactant-derived mesoporous materials. However, to the best of our knowl-edge, there have been no publications on blending of surfactant andnonsurfactant templating agents for synthesis of mesoporous silica.Here we report the blending effect of surfactant and nonsurfactanttemplating agents on the texture of mesoporous silica. The blending ofcitric acid or sucrose as a nonsurfactant template with cetyltrimethy-lammonium bromide (CTAB) as a surfactant template was attemptedto investigate the transformation of secondary particle morphologyand pore properties.

2. Experimental

2.1. Synthesis of MCM-41

MCM-41 was synthesized by the preparation method reported byN. Xiao and coworkers [10]. In a typical synthesis of MCM-41, 0.8 g ofCTAB was added into 25 mL of distilled water, followed by vigorousstirring at 80 °C for 10 min. Subsequently, 12 mL of NH3 (Junsei,28 wt.%) was added into the CTAB solution dropwise. After that,addition of 4.5 mL tetraethyl orthosilicate (TEOS, 98 wt.% Aldrich)wascarried out, and the final solution was stirred vigorously for 2 h. Byusing a blower, the final solutionwas dried for 24 h on an alumina trayat room temperature, and the dried silica-CTAB composites were agedin an oven at 100 °C for 20 h. After the calcination of aged compositesat 550 °C for 8 h, MCM-41 was synthesized.

2.2. Synthesis of mesoporous silica through blending surfactant andnonsurfactant templates

The mixture of distilled water, CTAB and NH3 was prepared by thesame manner as MCM-41. 1.0 g of either sucrose or citric acid as anonsurfactant template was added into the mixture of distilled water,CTAB and NH3, followed by vigorous stirring at room temperature for10 min. Subsequently, 4.5 mL of TEOS was added into the CTABsolution. After stirring the solution vigorously at room temperaturefor 2 h, drying of the solution was conducted with a blower at roomtemperature for 24 h, and then the dried samples were aged at 100 °Cfor 20 h. After calcination at 550 °C for 8 h, mesoporous silica wasprepared. The citric acid/CTAB-templated silica materials are desig-nated as CCS, and the sucrose/CTAB-templated silica materials aredenoted as SCS.

Fig. 1. Pore size distributions of MCM-41, CCS and SCS samples.

Table 1Pore properties of mesoporous silica materials.

Sample S.A.BET Vtot Da Dpp Dps

(m2/g)a (cm3/g)b (nm)c (nm)d (nm)e

MCM-41 770 0.65 3.2 2.1 8.9CCS 740 0.59 2.5 2.4 –

SCS 750 0.67 3.0 2.1 7.0

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 Peak pore diameter of primary pore size distribution.e Peak pore diameter of secondary pore size distribution.

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3. Results and discussion

Fig. 1 and Table 1 present thepore size distribution and various poreproperties of MCM-41, CCS and SCS, calculated from the desorptionbranches of isotherms by using the Barrett–Joyner–Halenda (BJH)method. MCM-41 gives a bimodal pore size distribution, centered at2.1 nm and 8.9 nm, and its specific surface area and pore volume are

Fig. 2. TEM images of a) MCM-41, b) CCS, c) MCM-41 phase of SCS, and d) wormlike-mesostr100 nm. The inset of d) is a small angle XRD pattern of SCS.

770 m2/g and 0.65 cm3/g, respectively. The primary pore size isattributed to capillary condensation in channels of MCM-41 structure,and the secondary pore size seemsderived from the interpores betweenMCM-41 nanoparticles [11]. CCS shows monomodal pore size distribu-tion centered at 2.4 nm. The specific surface area and total pore volumeforCCSare740 m2/gand0.59 cm3/g. In the caseof SCS, the shapeof poresize distribution is very analogous to that ofMCM-41. SCS has 2.1 nm ofprimary mesopore size and 7.0 nm of secondarymesopore size, smallerthan that ofMCM-41. The specific surface area and total pore volume forSCS are 750 m2/g and 0.67 cm3/g, respectively.

Fig. 2 exhibits TEM images of MCM-41, CCS and SCS. The secondaryparticles of MCM-41 showed spherical morphology with a particlediameter of 1.1–1.5 μm. In contrast to MCM-41, the secondary particlesof CCS samples gave an irregular shape having a particle diameter in therange of 0.3–0.7 μm, and the irregular shaped particles were agglomer-ated. In contrast, SCShasuniqueandextraordinarymorphology inwhichthe regular MCM-41 pore structure clung to the silica nanosphere-framed wormlike mesostructure (Fig. 2c). As shown in Fig. 2d, the silicananosphere-framed wormlike mesostructure clinging to MCM-41structure was almost consistent with sucrose-templated wormlikemesostructure reported in the previous publication [9], which indicatesthat SCS possesses properties both of a surfactant-derived orderedstructure and a non-surfactant-derived wormlike mesostructure TheTEM image in Fig. 2c allows one to estimate the pore size of 2.4 nm andthe pore wall thickness of 1.9 nm forMCM-41 structure. The pore size isin good agreement with the primary mesopore size shown in Fig. 1 andTable 1. The opposite side of the MCM-41 structure has 3D-inter-connected mesostructures with silica nanospheres of 7.7 nm as aframework. The inset of Fig. 2d exhibits a small angle XRD pattern ofSCS. SCS samples exhibit showed typical diffraction peaks of 2Dhexagonal pore arrangement at 2.5°, 4.3°, and 5.0° of 2θ, which canbe indexed to (100), (110) and (200) reflections. Moreover, the SCSsamples exhibits another broad diffraction peak at 2θ=0.63°, corre-sponding to a pore–pore correlation distance of 14 nm [12]. The porewall thickness can be calculated by subtracting the secondary peak porediameter from the pore–pore correlation distance. The calculated porewall thickness is 7 nm, which is nearly consistent with thickness of thesilica-nanosphere framework shown in Fig. 2d. Accordingly, it wasrevealed that the broad diffraction peak at 2θ=0.63° is ascribed to thewormlikemesostructures clung to theMCM-41 structure. Therefore, we

ucture phase of SCS; the scale bar of a) and b) is 500 nm, and the scale bar of c) and d) is

3521D.-W. Lee et al. / Materials Letters 65 (2011) 3519–3521

deduce thatblending of CTAB andsucrose templates lead to theMCM-41structure formed on the sucrose-derived wormlike mesostructure.Presumably, it is suggested that the irregular agglomeratedmorphologyof CCS andnoeffects of citric acid as a pore formingagent are attributed aneutralization reaction of the citric acid and the ammonia catalyst. Inaddition, it is presumed that the heterogeneous mesostructure of SCS isderived from a pseudomorphic transformation of as-formed colloidalsilica-sucrose nanocomposites into a MCM-41 structure during anaging procedure. The hydrogen bonding interaction between sucroseand colloidal silica particles is suggested to to be the reason why thewormlike mesostructure derived from colloidal silica–sucrose nano-composites is partially maintained despite the pseudomorphic transfor-mation to MCM-41 during an aging procedure. In order to verify theproposedmechanism, various analyses and further studyonCCS andSCSare underway and will be published in the near future.

4. Conclusions

CCS and SCS were synthesized in order to observe the variationof MCM-41 mesostructures by blending of citric acid and sucrosewith CTAB. The blending of citric acid with CTAB transformed themicrosphere texture of MCM-41 into irregular agglomerated mor-phology, and nonsurfactant-derived pore formation by citric acidwas not observed in a CTAB-citric acid mixture system. However, SCSgave a unique and extraordinary morphology in which the sucrose-

templated wormlike mesostructure clung to the MCM-41 structure,indicating that sucrose plays an important role as a nonsurfactanttemplate.

Acknowledgments

This work was supported by the Korea Institute of Energy TechnologyEvaluation and Planning (KETEP) grant funded by the Ministry ofKnowledge Economy (MKE), and a primary project of the Korea Instituteof Energy Research (KIER).

References

[1] Kresge CT, Leonowicz ME, Roth WJ, Vartuli JC, Beck JS. Nature 1992;359:710–2.[2] Beck JS, Vartuli JC, RothWJ, Leonowicz ME, Kresge CT, Schmitt KD, et al. J Am Chem

Soc 1992;114:10834–43.[3] Wei Y, Jin D, Ding T, Shin WH, Liu X, Cheng SZD, et al. Adv Mater 1998;10:313–6.[4] Pang JB, Qiu KY, Wei Y. Microporous Mesoporous Mater 2000;40:299–304.[5] Pang JB, Qiu KY, Wei Y. Chem Mater 2001;13:2361–5.[6] Takahashi R, Sato S, Sodesawa T, Kawakita M, Ogura K. J Phys Chem B 2000;104:

12184–91.[7] Lee DW, Ihm SK, Lee KH. Chem Mater 2005;17:4461–7.[8] Lee DW, Yu CY, Lee KH. J Phys Chem C 2008;112:5136–40.[9] Lee DW, Yu CY, Lee KH. J Mater Chem 2009;19:299–304.[10] Xiao N, Wang L, Liu S, Zou Y, Wang C, Ji Y, et al. J Mater Chem 2009;19:661–5.[11] Galarneau A, Iapichella J, Bonhomme K, Renzo FD, Kooyman P, Terasaki O, et al.

Adv Funct Mater 2006;16:1657–67.[12] Kim SS, Pauly TR, Pinnavaia TJ. Chem Commun 2000:835–6.