Journal of Colloid and Interface Science 365 (2012) 137–142

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Synthesis of ultra-large-pore FDU-12 silica using ethylbenzene as micelle expander

Liang Huang, Michal Kruk ⇑Center for Engineered Polymeric Materials, Department of Chemistry, College of Staten Island and Graduate Center, City University of New York, 2800 Victory Boulevard,Staten Island, NY 10314, United States

a r t i c l e i n f o

Article history:Received 18 July 2011Accepted 16 September 2011Available online 24 September 2011

Keywords:Ordered mesoporous silicaFDU-12Cage-like mesoporeMicelle expanderClosed-pore silica

0021-9797/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.jcis.2011.09.044

⇑ Corresponding author.E-mail address: michal.kruk@csi.cuny.edu (M. Kru

a b s t r a c t

Ultra-large-pore FDU-12 (ULP-FDU-12) silica with face-centered cubic structure (Fm3m type) of sphericalmesopores was synthesized using Pluronic F127 triblock copolymer (EO106PO70EO106) and ethylbenzeneas a new micelle expander at initial temperature of 14 �C. Ethylbenzene was identified on the basis of itsreported extent of solubilization in poly(ethylene oxide)–poly(propylene oxide)-type surfactant micelles,which was similar to that of xylene, the latter having been shown earlier to afford ULP-FDU-12. The unit-cell parameter of as-synthesized ULP-FDU-12 was 55 nm, which is similar to the highest value reportedwhen xylenes (mixture of isomers) were used and larger than that achieved with trimethylbenzene. Theunit-cell parameter of calcined ULP-FDU-12 reached 52 nm. For the obtained materials, the nominal porecage diameter calculated from nitrogen adsorption reached 32 nm, whereas the actual pore cage diame-ter calculated using the geometrical relation was 36 nm. The pore entrance size was below 5 nm beforethe acid treatment, but was greatly enlarged as a result of the treatment. The sample prepared withouthydrothermal treatment was converted to ordered closed-pore silica at as low as 400–450 �C. Our studyconfirms the ability to select micelle expanders on the basis of data on solubilization of compounds inmicelle solutions.

� 2011 Elsevier Inc. All rights reserved.

1. Introduction

The pore size adjustability is one of the most profound signa-tures of ordered mesoporous materials synthesized through themicelle-templating approach [1,2]. The inherent feature of themicelle templating is that the pore size adjustment can be achievedthrough a selection of a surfactant of a suitable molecular size [1,2]and thus the one forming micelles of a particular size. An alterna-tive inherent pore size adjustment pathway involves the use of amicelle swelling agent (micelle expander) [1,2] that is solubilizedin the micelles, thereby increasing their size. In addition to thetwo inherent pore size adjustment mechanisms related to theproperties of the micelles, there is an additional factor related tothe shrinkage of the framework upon removal of the surfactanttemplate, which may reduce the size of void spaces (pores) inthe framework that were once filled with the surfactant [3–5].While the removal of the surfactant by the extraction or micro-wave digestion typically results in low shrinkage in the case of por-ous silicas [3], the removal of the surfactant through calcinationmay result in a substantial shrinkage [4,5]. The latter is signifi-cantly dependent on the synthesis temperature, and for instance,it can be large for silicas synthesized at 0–40 �C and small for mate-rials hydrothermally treated at 100 �C or higher for extended

ll rights reserved.

k).

periods of time [4,5]. For block-copolymer-templated silicas wherethe poly(ethylene oxide) blocks of the template tend to be embed-ded in the silica framework, the hydrothermal treatment is alsolikely to enlarge the size of the surfactant-filled void [2,6] as a re-sult of the shift of the region occupied by the silica framework out-ward from the micelle core [7].

The application of micelle expanders opens an avenue for a con-venient adjustment of the pore size. While in many cases, one cantune the pore diameter through the adjustment of the relativeamount of the swelling agent added [1,2], this approach oftenresults in the loss of structural ordering before any major pore sizeenlargement is attained (see for instance [8,9]). Over the last6 years, another opportunity emerged, in which one uses a largeexcess of a swelling agent and the pore diameter depends on theextent of solubilization of particular swelling agent in the surfac-tant micelles [4,10–15]. This approach was first demonstrated tobe successful in the case of large-pore SBA-15 (LP-SBA-15) silica[10,11]. Later, it was noted that this synthesis did not appear toinvolve any major uptake of the swelling agent [4]. It was alsorealized that the major enlargement of pore diameter in the sub-ambient temperature approach reported for FDU-12 silica [16–18] with face-centered cubic structure of spherical mesopores[19], and leading to large-pore FDU-12 (LP-FDU-12), did not appearto involve any major increase in the uptake of the swelling agent[5]. It was hypothesized that the success of the syntheses of LP-SBA-15 and LP-FDU-12 was related to the rather limited swelling

138 L. Huang, M. Kruk / Journal of Colloid and Interface Science 365 (2012) 137–142

of the surfactant micelles [4,5], which did not lead to disorganiza-tion of the structure of the templated material, unlike in so manycases involving the swelling agents [8,9]. Later, it was postulatedthat in cases where the use of the swelling agent does not leadto disruption of the structure of the material, it might be possibleto enhance the swelling and thus increase the pore size, if a swell-ing agent of a higher extent of solubilization in the surfactant tem-plate can be identified [12]. It was also outlined that potentiallysuperior swelling agent candidates can be identified on the basisof the data on the extent of solubilization of these substances inmicelles of particular surfactants [12]. For instance, in the seriesof benzene derivatives, their uptake in Pluronic block copolymermicelles was reported to decrease as the size and number of alkylsubstituents on the benzene ring increased [20,21], which can beused to identify suitable swelling agent candidates [12]. On thebasis of the above reasoning, 1,3,5-triisopropylbenzene (TIPB)and cyclohexane were identified [12] and shown to be superior mi-celle expanders for Pluronic-P123-templated synthesis of 2-D hex-agonal materials with cylindrical mesopores, including SBA-15silica [12] and periodic mesoporous organosilicas (PMOs) [15]. Inthis case, swelling agents expected to exhibit quite low solubiliza-tion in Pluronics were selected, because Pluronic P123 (EO20-

PO70EO20) has a high proportion of the hydrophobic block(�70 wt.%) and exhibits quite high uptake of aromatics, when com-pared to Pluronics with lower fraction of the hydrophobic block[21].

The surfactant-templated synthesis of silicas with very largespherical mesopores required a different micelle expander[13,16], because suitable block copolymer surfactants, such as Plu-ronic F127 (EO106PO70EO106), exhibit a much lower fraction of thehydrophobic block (�30 wt.% for F127). Indeed, Pluronic F127(EO106PO70EO106) was shown to afford LP-FDU-12 silicas withhighly ordered face-centered cubic structures of large mesopores(�25 nm), when 1,3,5-trimethylbenzene (TMB) was used as aswelling agent [16]. Later, it was hypothesized that the use of a mi-celle expander that is solubilized in Pluronics to a more significantextent may bring further gains in the unit-cell dimensions andpore size [13]. On the basis of the solubilization behavior of aro-matics (outlined above), xylene (dimethylbenzene) and toluene(methylbenzene) were selected as swelling agent candidates andindeed shown to be superior to TMB [13,14] in the silica[13,16,22] and organosilica [14,23] synthesis. In particular, xylenes(mixture of xylene isomers, which may contain some ethylben-zene) was found to afford FDU-12 (denoted ultra-large-pore FDU-12, ULP-FDU-12) with particularly large unit-cell parameter, whichreached 56 nm for as-synthesized samples and 53 nm for calcinedmaterials [13]. The pore diameter reached 36 nm and was tunablethrough adjustment of hydrothermal treatment and acid treatmentconditions [13].

Our aim is to enhance the ability to successfully predict swell-ing agent candidates and to extend the library of the swellingagents with superior performance [12–15]. This effort is particu-larly timely, as recent reports revealed major improvements in per-formance for catalytically active species supported on large-poreordered mesoporous materials, including LP-SBA-15 and LP-FDU-12 [22,24]. On the basis of the literature data, we postulated thatthe solubilization of benzene derivatives in Pluronics can be tunedthrough the number and size of the alkyl substituents on the ben-zene ring [12]. However, the influence of the number versus thesize of the substituents was not addressed. An appealing case forfurther investigation was the xylene and ethylbenzene pair, inwhich there are either two substituents with one carbon atom eachor one substituent with two carbon atoms. The data on solubiliza-tion of xylene and ethylbenzene in poly(ethylene oxide)–poly(pro-pylene oxide)-type surfactant micelles indicated their similarextent of solubilization [20,21]. While experimental study of one

of the considered block copolymers showed that ethylbenzenewas solubilized to a greater extent than xylene [20], predictionsfor Pluronics indicated otherwise [21], which suggested similarperformance of both compounds. Xylenes (mixture of xylene iso-mers, possibly containing some ethylbenzene) was already shownto be an excellent swelling agent for the synthesis of ULP-FDU-12,as discussed above. Therefore, in this study, the suitability of eth-ylbenzene as a swelling agent for the synthesis of ULP-FDU-12was investigated along with the evaluation of individual xyleneisomers (ortho, meta and para). It was shown that ethylbenzeneis indeed an excellent swelling agent, being comparable to the xy-lenes (mixture of isomers). It was also observed that the perfor-mance of individual xylene isomers as swelling agents wassimilar, but they appeared to afford slightly lower unit-cell sizethan ethylbenzene or the mixture of xylene isomers.

2. Experimental

2.1. Materials

Pluronic F127 was received as a research sample from BASF.Ethylbenzene (99.8%) and m-xylene (99+ %) were acquired fromFisher, o-xylene (99%) and p-xylene (99%) were from Alfa Aesarand tetraethyl orthosilicate was from Acros. The synthesis wassimilar to that developed earlier for xylenes [13], but either ethyl-benzene or one of xylene isomers (o-xylene, m-xylene andp-xylene) was used. In a typical synthesis procedure, 1.00 g of Plu-ronic F127 and 2.50 g of KCl were dissolved at 14.0 �C in 60 mL of2.0 M HCl in a glass container with magnetic stirring. Then 5.2 g(6.0 mL) ethylbenzene was added and the mixture was stirred at350 rpm at 14.0 �C for 1 day in a container covered with parafilm.It should be noted that the proportion of the swelling agent was se-lected to match the proportion of xylenes that allowed to achievethe highest unit-cell size in our earlier study [13]. Next, 4.5 g(4.8 mL) of TEOS was added. The reaction mixture was stirred at14.0 �C in a covered container for another day, and then transferredto a polypropylene bottle and maintained at 100 �C for 1 day. Theproduct was filtered, and dried in a vacuum oven at 60 �C. Theresulting as-synthesized material was calcined at 550 �C (heatingramp 2 �C/min) under air for 5 h to remove the surfactant tem-plate. A part of the dried as-synthesized sample was subjected toan acid treatment [5,13,16,25,26], in which 0.5 g of the samplewas placed in 30 mL of 2.0 M HCl solution and heated at 130 �Cin a Teflon-lined autoclave for 4 days. The resulting sample was fil-tered, dried and calcined at 550 �C. The synthesis was also per-formed without any hydrothermal treatment or acid treatment,that is, the sample was filtered out after 1 day of stirring at lowtemperature. After drying at 60 �C in a vacuum oven, the as-syn-thesized material was calcined at different temperatures in therange 300–650 �C under air for 5 h (heating ramp 2 �C/min).

2.2. Measurements

Small-angle X-ray scattering (SAXS) patterns were acquiredusing a Bruker Nanostar U SAXS/WAXS instrument with a rotat-ing anode X-ray source (Cu Ka radiation) and Vantec-2000two-dimensional detector. Nitrogen adsorption isotherms weremeasured at �196 �C on a Micromeritics ASAP 2020 volumetricadsorption analyzer. Before the analysis, the samples were out-gassed under vacuum at 200 �C for 2 h in the port of the adsorp-tion analyzer. Transmission electron microscopy (TEM) imageswere acquired on a FEI Tecnai G2 Twin microscope operated at120 kV. Before taking the images, the sample was dispersed inethanol using sonication, and then deposited on carbon-coatedcopper grid.

L. Huang, M. Kruk / Journal of Colloid and Interface Science 365 (2012) 137–142 139

2.3. Calculations

The BET specific surface area, SBET, was calculated from data inthe relative pressure range 0.04–0.20 [27]. The total pore volume,Vt, was estimated from the uptake of nitrogen at a relative pressureof �0.99 [27]. The micropore volume, Vmi, was evaluated using theas plot method with a macroporous silica gel as a reference adsor-bent [13,28]. The pore size distribution was estimated using theBJH method [29] with the KJS correction derived for cylindricalmesopores [30]. The statistical film thickness curve establishedfor a macroporous silica gel was used in these calculations [28].The BJH–KJS calculations were not calibrated for spherical mesop-ores considered in the current study, and in the case of large spher-ical mesopores, they are known to result in underestimation of thepore diameter by 2–6 nm [5,13]. Therefore, the pore diameter, wd,was also estimated using a relation proposed for a face-centeredcubic arrangement of spherical mesopores [31]:

wd ¼ a6pv

Vpq1þ Vpqþ Vmiq

� �13

ð1Þ

where the unit-cell parameter, a, was calculated from the positionof (111) peak on the SAXS pattern, q is the density of silica frame-work, which was assumed to be 2.2 g cm�3, and v equal to 4 is thenumber of spherical pores in the unit cell. The primary mesoporevolume, Vp, was estimated as a difference between the total porevolume and the micropore volume, because there was no evidenceof any appreciable secondary mesopore volume and the occurrenceof the capillary condensation at a relative pressure close to the sat-uration vapor pressure precluded the use of as plot analysis in cal-culations of Vp.

3. Results and discussion

SAXS patterns for as-synthesized and calcined samples synthe-sized using ethylbenzene and xylene isomers (o-xylene, m-xylene

2θ (degree)0.3 0.6 0.9 1.2 1.5

ln (i

nten

sity

)

Ethylbenzene

p-Xylene

m-Xylene

o-Xylene

Xylenes

Ethylbenzene (AT)

111

311

422444111

311

422 440 444

111

311

422 440 444111

311

422444

111

311

422444111

311331

220

(a)

Fig. 1. SAXS patterns for: (a) as-synthesized and (b) calcined ULP-FDU-12 samples. The sathe sample prepared with xylenes were reported elsewhere, wherein the sample was d

and p-xylene) as swelling agents are shown in Fig. 1a and b. Thesesamples were synthesized at low temperature (14 �C) and hydro-thermally treated at 100 �C for 1 day. Patterns for a sample synthe-sized as described earlier [13] with the same relative proportion ofxylenes (mixture of isomers, which may contain some ethylben-zene) were included for comparison. All the SAXS patterns weresimilar and can be identified as those of the face-centered cubicstructure of Fm3m symmetry. The unit-cell parameter for the as-synthesized material prepared in the presence of ethylbenzenereached 55.6 nm, which is comparable to the highest value ob-served when xylenes were employed as a swelling agent [13]. Thisvalue is also comparable to the unit-cell size attained for face-cen-tered cubic silica templated by poly(ethylene oxide)–polystyreneblock copolymer (56.7 nm) [32]. The unit-cell parameters foras-synthesized samples synthesized in the presence of o-xylene,m-xylene and p-xylene were 50.6, 51.9 and 51.9 nm, being 7–9%lower than those for the ethylbenzene and the xylenes mixture.After calcination at 550 �C, the unit-cell parameter of the samplesynthesized with ethylbenzene decreased significantly (to45.0 nm), following the trend observed in the synthesis with xy-lenes [13]. When the as-synthesized material was additionally sub-jected to the acid treatment at 130 �C for 4 days, the shrinkageupon calcination was largely suppressed and the unit-cell parame-ter of the surfactant-free material reached 52.3 nm (down from53.7 nm before the calcination), being nearly the same as the high-est value achieved with xylenes for the calcined material (53.5 nm)[13]. The unit-cell parameter of 52.3 nm exceeds that attained forsurfactant-free LP-FDU-12 synthesized using TMB as a swellingagent (up to 50.5 nm) [16,22], even though in the latter cases, amicrowave digestion, which is known to lead to small shrinkage[3], was used to remove the surfactant. It should be noted thatthe relative peak intensity on SAXS patterns changed dramaticallyas a result of the acid treatment, which was already seen in thecase of syntheses of FDU-12 with TMB and xylenes [5,13].

Shown in Fig. 2 are TEM images of the calcined ULP-FDU-12sample prepared in the presence of ethylbenzene (without the acid

2θ (degree)

ln (i

nten

sity

)

Ethylbenzene

p-Xylene

m-Xylene

o-Xylene

Xylenes

Ethylbenzene (AT)

111

311

422444

111

311

422444

111

311

422444

111

311

422444

111

311

422444

111

311331

220

(b)

620533622

220

220

440

0.3 0.6 0.9 1.2 1.5

mple denoted (AT) was subjected to acid treatment at 130 �C for 4 days. The data forenoted EH5 [13].

Fig. 2. Transmission electron microscopy images of ULP-FDU-12 showing: (a)[100] projection, and (b) [110] projection.

2θ (degree)0.5 1.0 1.5 2.0 2.5 3.0

ln (i

nten

sity

)

as-synthesized

350 oC

400 oC

450 oC

650 oC

111

311400331

440

111

311

400440

111

311111

311

111

311

440

300 oC

551711640

444,551,711,640

400 440422 444,551,

711,640

400440422 444,551,

711,640

111

311

440444,551,711,640

Fig. 4. SAXS patterns for ULP-FDU-12 sample synthesized at 14 �C withoutsubsequent hydrothermal treatment, which was as-synthesized and calcined atdifferent temperatures.

140 L. Huang, M. Kruk / Journal of Colloid and Interface Science 365 (2012) 137–142

treatment), which show [100] and [110] projections for the face-centered cubic structure. While stacking sequences characteristicof face centered cubic and 3-D hexagonal structures are seen in

Relative Pressure0.0 0.2 0.4 0.6 0.8 1.0

Amou

nt A

dsor

bed

(cm

3 STP

g-1

)

0

200

400

600

800

14C1d+100C1d+A130C4d

14C1d+100C1d

(a)

Fig. 3. (a) Nitrogen adsorption isotherms and (b) pore size distributions for ULP-FDU-12

many closed-packed structures with spherical mesopores [33], noclear evidence of 3-D hexagonal intergrowth was seen in the pres-ent case.

Fig. 3a shows nitrogen adsorption isotherms for calcined silicasprepared in the presence of ethylbenzene, one being for the sampleprepared without the acid treatment, and the other one with the

Pore Diameter (nm)10 20 30 40 50

Pore

Siz

e D

istri

butio

n (c

m3 g

-1 n

m-1

)

0.00

0.02

0.04

0.06

14C1d+100C1d

14C1d+100C1d+A130C4d

(b)

. The isotherm for the acid treated sample was offset vertically by 200 cm3 STP g�1.

Pore Diameter (nm)5 10 15 20 25 30Po

re S

ize

Dis

tribu

tion

(cm

3 g-1

nm

-1)

0.000

0.005

0.010

0.015

0.020

0.025

350 oC 300 oC

(b)(a)

Fig. 5. (a) Nitrogen adsorption isotherms and (b) pore size distributions for ULP-FDU-12 sample synthesized at 14 �C without subsequent hydrothermal treatment, which wascalcined at different temperatures.

L. Huang, M. Kruk / Journal of Colloid and Interface Science 365 (2012) 137–142 141

acid treatment at 130 �C for 4 days. The former sample showed asteep step of capillary condensation at a relative pressure of�0.915 and a capillary evaporation delayed to the lower limit ofadsorption–desorption hysteresis (in this case, the relative pres-sure of �0.49) [34]. This behavior shows that the material had anarrow size distribution of large mesopores (see pore size distribu-tion in Fig. 3b) and the entrances to the mesopores were below5 nm in diameter [34]. The specific surface area of this materialwas 213 m2 g�1, the total pore volume was 0.33 cm3 g�1 and themicropore volume was 0.07 cm3 g�1. The low surface area and totalpore volume can be attributed to the large shrinkage upon calcina-tion (see above). The maximum on the pore size distribution was at23 nm. The sample obtained after the acid treatment exhibited asteep capillary condensation step at a higher relative pressure (p/p0 = �0.937) and a relatively narrow hysteresis loop with the cap-illary evaporation at p/p0 = �0.8, which indicates a significant porecage diameter enlargement (see Fig. 3b) and a dramatic increase inthe pore entrance size, which is likely to be close to the pore cagediameter [13]. The BET specific surface area was 251 m2 g�1, thetotal pore volume was 0.91 cm3 g�1, and there was no microporos-ity detectable using the as plot method. The maximum on the poresize distribution was at 32 nm (see Fig. 3b). The pore diameter wasalso calculated using Eq. (1) and reached 35.7 nm for the acid-treated material. The adsorption isotherms for the silicas preparedin the presence of ethylbenzene and the structural parametersderived from them were similar to those reported for the largest-pore ULP-FDU-12 silicas synthesized using xylenes as a swellingagent [13]. This demonstrates that ethylbenzene is another optionfor the synthesis of FDU-12 silicas with the highest attainable unit-cell sizes and pore diameters. The availability of several superiorswelling agents for a particular surfactant has already been dem-onstrated to be useful in the surfactant-templated synthesis of por-ous materials. Namely, an earlier study of organosilicas with 2-Dhexagonal structures of very large cylindrical mesopores showedthat although cyclohexane was suitable as a micelle expander forPluronic P123 for several framework compositions, it did not workwell for one important framework composition (phenylene-bridged organosilica) and its substitution with TIPB was crucialin obtaining well-defined products [15]. Moreover, unlike xylenes,which is a mixture of isomers without fully specified composition,ethylbenzene is a single compound available with high purity,

which may potentially have an impact on the reproducibility ofthe synthesis. Our synthesis with xylenes was very well reproduc-ible [13], but other composition of the isomer mixture may poten-tially afford slightly different results. To this end, TMB isomerswere shown to yield somewhat different results in alkylammoni-um-templated synthesis [35].

Shown in Fig. 4 are SAXS patterns for FDU-12 silica prepared inthe presence of ethylbenzene at low temperature only. The pat-terns correspond to as-synthesized sample and the samplesderived from it through calcination at different temperatures in300–650 �C range. All the SAXS patterns featured multiple peaksthat are characteristic of a face-centered cubic structure, showingthat the material retained its periodic structure over the entiretemperature range. The unit-cell parameter for the as-synthesizedsample was 52.3 nm (which is somewhat smaller than that for thehydrothermally treated as-synthesized material), and it decreasedto 45.0, 42.8, 42.5, 41.6 and 40.3 after calcination at 300, 350, 400,450 and 650 �C, respectively. As seen in Fig. 5, the material calcinedat 300 and 350 �C exhibited adsorption isotherms characteristic ofa large-pore material with spherical mesopores, the total pore vol-ume of 0.32 and 0.29 cm3 g�1, respectively, the BET specific surfacearea of 300 and 265 m2 g�1, respectively, and the pore diameterwas 22.2 and 21.4 nm, respectively. On the other hand, a lowuptake of nitrogen was observed after calcination at a temperatureof 400 �C or higher, thus showing the pore closing [13,36] aroundthis temperature. The other ULP-FDU-12 sample prepared in thesame manner exhibited the pore closing in 400–450 �C range (datanot shown). The pore closing for the present samples happens to besomewhat lower than the temperature of 450 �C reported earlierfor the pore closing of ULP-FDU-12 prepared using xylenes as aswelling agent [13]. The present pore closing temperatureapproaches the temperature that was sufficient to derive closed-pore silicas from periodic mesoporous organosilicas with Fm3mstructure (400 �C) [14], but in the latter case, mesopore volumeswere typically low and they would be further reduced as a resultof shrinkage that leads to thermally-induced pore closing. Conse-quently, ULP-FDU-12 appears to be a better precursor to closed-pore silicas with appreciable mesopore volume. It should be notedthat this volume cannot be directly assessed by gas adsorption, butcan in some cases be obtained through extrapolation of data foropen-pore materials [13,37]. It is also noteworthy that the periodic

142 L. Huang, M. Kruk / Journal of Colloid and Interface Science 365 (2012) 137–142

structure persisted at temperature of 650 �C, which is 250 �C abovethe pore closing temperature, showing that the loss of the poreconnectivity is not a prelude to the sintering of the material.

4. Conclusions

Ethylbenzene was predicted to be a powerful swelling agent forthe synthesis of ordered mesoporous silicas with spherical mesop-ores on the basis of its reported extent of solubilization in poly(eth-ylene oxide)–poly(propylene oxide)-based copolymer surfactantsand of the known swelling agent performance of other alkyl-substituted benzenes. The application of ethylbenzene in thelow-temperature synthesis involving Pluronic F127 block copoly-mer, which was similar to that originally developed for LP-FDU-12 using TMB and later improved through the use of xylenes,afforded ultra-large-pore FDU-12 silicas with unit-cell sizes andpore diameters matching those attained earlier for xylenes. Conse-quently, ethylbenzene-based synthesis was established as an alter-native avenue to face-centered cubic silicas that exhibit the highestreported unit-cell sizes and diameters of spherical mesopores. ULP-FDU-12 prepared at low temperature only exhibited thethermally-induced pore closing at 400–450 �C, which is very low.The suitability of individual xylene isomers as swelling agentswas investigated and appeared to approach that of xylenes mixtureand ethylbenzene. These results show that the performance of thealkyl-substituted benzenes as swelling agents primarily dependson the total number of carbon atoms in the alkyl substituentsrather than on the details of the molecular structure.

Acknowledgments

NSF is acknowledged for partial support of this research (awardDMR-0907487) and for funding the SAXS/WAXS system throughaward CHE-0723028. Acknowledgment is made to the Donors ofthe American Chemical Society Petroleum Research Fund for partialsupport of this research (Award PRF #49093-DNI5). The ImagingFacility at CSI is acknowledged for providing access to TEM. BASFis acknowledged for the donation of the F127 block copolymer.

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