KlingshirnSHR J. Mater Chem 5174 2005

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Ionic liquids as solvent and solvent additives for the synthesis of solgelmaterials

Marc A. Klingshirn,b Scott K. Spear,a John D. Holbreyc and Robin D. Rogers*a

Received 27th June 2005, Accepted 6th October 2005

First published as an Advance Article on the web 27th October 2005DOI: 10.1039/b508927a

The ionic liquid (IL) 1-butyl-3-methylimidazolium chloride was used as a drying control

chemical additive in the synthesis of silica solgel materials with and without methanol as

a co-solvent. The resulting gels were characterized by using thermogravimetric analysis,

differential scanning calorimetry, infrared spectroscopy and water sorption kinetics. Calcined

gels were analyzed using scanning electron microscopy and nitrogen adsorption isotherms for

surface area and pore volume determination. Non-calcined gels were monolithic and showed

general cloudiness with lesser degrees observed at higher IL volumes. Calcinations resulted

in the formation of powders with increased available surface area as the amount of IL

volume was increased. This is consistent with an increase in respective pore volume but a

general decrease in average pore size. The resulting materials exhibited conventional

structural microdomains, in contrast to periodicity reported when other ionic liquids were

used as templates.

Introduction

The use of ionic liquids (ILs) in various areas of chemistry has

increased tremendously over the past few years, for example, in

catalysis, separation science, and in electrochemical applica-

tions, among others.111 Their advantageous properties often

include negligible vapor pressure and variation in liquid

characteristics from hydrophilic to hydrophobic salts. These

tunable properties make them suitable for many applications,

yet despite their increasing popularity, ILs have only recently

begun to see use in the area of structural materials science.

Recent studies have been conducted using them as templating

agents in the synthesis of mesoporous and microporous

materials, and as solvents for the preparation of aerogels and

functionalized solgels.1218 Due to the generally negligible

vapor pressure of ILs, it has been suggested that ILs could

be used as non-volatile drying control chemical additives

(DCCAs) during the synthesis of silica solgels, resulting in

reduced shrinkage and subsequent matrix collapse during

formation of the gels. It is anticipated that the use of ILs as

co-solvents for silica solgel formation would allow control

over the structural properties of the resultant gels, particularly

with respect to pore size, structure and distribution, taking

advantage of the readily modifiable and controllable solvent

and physical characteristics of ILs.

Solgels are of interest in areas such as optics, sensors,

catalysis, and separations.1922 Control over the morphology is

of specific interest for separation science applications if pore

dimensions can be tailored to meet specific separations needs.

While many different solvents have been used for the forma-

tion of solgels, the introduction of DCCAs such as glycerol,

dimethylformamide, and oxalic acid have proven to be the

most effective methodology for influencing the formation and

properties of solgels.2326 DCCAs help to control the rate of

hydrolysis, condensation of hydroxyl groups, pore liquid

vapor pressure, and drying stresses during solvent removal.

Volatile components, generally the co-solvent and water, from

the matrix can be easily evaporated leaving the DCCA behind,which can then be removed and decomposed at higher

temperatures, or recovered using other techniques such as

supercritical drying. The resulting materials generally have

more uniform pore size, distributions and are more permeable

due to limited pore contraction which increases constriction.27

Common DCCAs (Table 1) generally have low vapor

pressures and moderately high boiling points. In comparison,

the IL 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]) has

no detectable vapor pressure and decomposes above 200 uC

without boiling.28 In this study, we show that [C4mim][Cl]

can serve as a DCCA with similar structure controlling

characteristics to more common additives, thus allowing

preparation of solgel glasses with high porosities and internalsurface areas.

aDepartment of Chemistry and Center for Green Manufacturing TheUniversity of Alabama, Box 870336, Tuscaloosa, AL, 35487-0336, USA.E-mail: [email protected]; Fax: (205) 348-0823;Tel: (205) 348-4323bChemistry Department, St. Olaf College, 1520 St. Olaf Avenue,Northfield, MN 55057, USAcQUILL, Queens University of Belfast, Belfast, Northern Ireland, UKBT9 5AG

Table 1 Physical properties of three common DCCAs, glycerol,dimethylformamide and oxalic acid

DCCAMeltingpoint/uC

Boilingpoint/uC

Vapor pressure@ 20 uC/mm Hg

Glycerol 17.8 290 ,1.0DMF 261 153 2.6Oxalic acid 101.5 149160a ,0.01[C4mim][Cl] 66 254

b c

a Sublimation occurs thereafter. b Upper liquid limit (decompositionthereafter).28 c Not measurable.

PAPER www.rsc.org/materials | Journal of Materials Chemistry

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Experimental

Materials

The ionic liquid [C4mim][Cl] was synthesized following litera-

ture procedures28 using chemicals as received from Aldrich

(Milwaukee, WI). Tetramethyl orthosilicate (TMOS) and

methanol were used as received from Aldrich (Milwaukee,WI). Deionized water (18 MV cm21) was purified using a

Barnstead Nanopure system (Dubuque, IA) and used for all

experiments.

Synthesis of gels

Silica gels were formed following Scheme 1 with a molar ratio

of silica monomer to water of 1 : 4. Gels were produced by

dissolving molten [C4mim][Cl] (heated to y70 uC in a hot

water bath until melted) in deionized water in a small glass

scintillation vial or beaker. This was allowed to cool to room

temperature where methanol was then added (if used) and

mixed. TMOS monomer was added and the mixture vortexed

until a monophasic solution was obtained. If a monophasic

solution was not readily obtained, the biphasic mixtures were

placed on a rotating wheel to insure adequate mixing. The gel

formulations are given in Table 2.

Gels were stored in covered vials with punched pin-holes for

a one week period to allow slow evaporation of the volatile

components. The resulting gels which contained methanol

were cloudy and opaque in appearance. The level of

transparency increased as both the volume of IL and methanol

in the reaction mixture were increased. When methanol

was omitted from the reaction, gels formed were generally

cloudy in appearance regardless of the volume of IL that was

incorporated.

Gels were loosely ground inside the synthesis vial with

a spatula and characterized by TGA and DSC prior to

calcination. Calcination was performed to remove the IL fromthe matrix. This was performed by placement of the gels in

clean glass vials followed by ramping at 5 uC min21 to 500 uC.

The calcined materials were then powdered with an electric

grinder for additional characterization. All gels were then

stored in capped vials.

Characterization of gels

Thermogravimetric analyses (TGA) of the air-dried gels were

performed on a TA Instruments 2950 Thermogravimetric

Analyzer (New Castle, DE). Samples were heated under a

nitrogen atmosphere from room temperature to 500 uC at

5 uC min21 followed by a 5 min isotherm. Differential scan-

ning calorimetry (DSC) experiments were carried out on a TA

Instruments DSC 2920 Modulated DSC calorimeter (New

Castle, DE). Original air-dried gels, prior to calcination, were

analyzed in aluminum pans (TA Instruments pt. # 900793.901)

with lids containing a pin-hole (TA Instruments pt. #

900860.901), by heating to 350 uC with ramping at 5 uC min21.

The calcined gels were characterized using scanning electron

microscopy (SEM) (Hitachi S-2500), infrared spectroscopy

(IR) (BioRad FTS40), and BET nitrogen adsorption analysis

(Nova 1200e Surface Area and Pore Size Analyzer) to

determine available surface area and pore volume. BET

analysis gave total specific area in addition to micropore,

macro/mesopore area, and pore volumes. The average poresize for the calcined gels was calculated using the pore volume

and surface area obtained from BET analysis, applying the

cylindrical model.

Results and discussion

Glycerol, a commonly used DCCA, has been found to reduce

cracking and increase transparency of silica solgels.29 The

Scheme 1 Formation of silica solgels using tetramethyl orthosilicate

and the IL [C4mim][Cl].

Table 2 Silica solgel formulationsa

Gel [C4mim][Cl]/mL DI water/mL Methanol/mL TMOS/mL Original gel size/cm3 Degree of cloudiness Rate of gelation

(a) 0.25 1.20 0.25 2.50 3.9(b) 0.75 1.20 0.75 2.50 4.9(c) 1.00 1.20 1.00 2.50 5.4(d) 1.25 1.20 1.25 2.50 5.4

(e) 0.50 1.20 0.00 2.50 3.9(f) 1.50 1.20 0.00 2.50 4.9(g) 2.00 1.20 0.00 2.50 5.4(h) 2.50 1.20 0.00 2.50 5.4

Control 0.00 1.20 2.50 2.50 5.4 a Order of mixing follows from left to right. Densities of reactants: [C4mim][Cl]: 1.080 g mL

21;28 DI water: 1.000 g mL21; methanol:0.791 g mL21; TMOS 1.023 g mL21. Arrows point in direction of increased cloudiness and increased rate of gelation.

This journal is The Royal Society of Chemistry 2005 J. Mater. Chem., 2005, 15, 51745180 | 5175


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molecular structure of glycerol favors hydrogen bonding

with the silica framework, thus allowing for the formation

of a film on the surface. The formed film changes the capillary

pressures by reducing the contact angle of the solvent

and matrix.21 The low vapor pressure of glycerol is also useful

since it is retained within the smallest pores of the gel, in

turn forcing pores to be formed when it is removed during

calcination.ILs with long alkyl chains have been found to preferentially

assemble in a so-called tail-to-tail fashion with the head

representing the imidazole moiety and the tail representing

the alkyl chain.30 This aggregation is similar to traditional

surfactants such as cetyltrimethylammonium bromide com-

monly used for the preparation of ordered solgel materials.

The hydrogen bonding abilities of the imidazole head group

makes it a strong candidate for interaction with the silica

matrix, thus allowing for film or monolayer formation within

the matrix, and such interactions have been the basis of IL

applications in gas chromatographic systems.9,31 Many ILs, as

with glycerol, have negligible vapor pressures; however, the IL

can be decomposed with little to no residue remaining. Theremoval of all residue is clearly evident since ash material

would appear in the SEM images of the calcined materials.

The lack of residue is in contrast to glycerol, which favors

decomposition into carbonates upon calcination at high

temperatures.32 The clean removal of the IL is made possible

by the decomposition pathway which follows a nucleophilic

attack of the anion on the imidazolium cation thus giving rise

to starting materials which are then easily volatilized at high

temperatures.33

Non-calcined gels

In our studies, monolithic gels were generally cloudy inappearance when first formed. The degree of cloudiness

decreased as the amount of [C4mim][Cl] was increased. In

addition, the rate of gelation decreased as the amount of

[C4mim][Cl] was increased, a result of the blocking of methoxy

groups, essentially diluting the monomer within the system.

Upon drying under ambient conditions, the gels shrank due to

loss of methanol and pore volume and subsequent contraction

of the silica matrix. As expected, the degree of shrinkage was

lower when only [C4mim][Cl] IL was incorporated.

Air-dried non-calcined gels were analyzed using differential

scanning calorimetry (DSC). Fig. 1 shows a typical DSC

thermogram that exhibits three distinct endotherms. These gels

were not fully dried, and the presence of methanol and water isstill evident. A broad endotherm occurring at 60 uC corres-

ponds to the removal of water and methanol from the gel

pores. The second endotherm at y130 uC is attributed to the

loss of bound water, trapped water within exclusive pores, and/

or the condensation of free or blocked hydroxyl groups. The

traditional decomposition endotherm for the IL is observed

starting at y225 uC.

If the small endotherms at y130 uC are integrated, and the

heat flow associated with this transition plotted against the

total volume of IL and methanol (Fig. 2), there is a direct

correlation between the heat flow and the overall micro-

porosity of the gel. A larger amount of heat is needed to

remove water from the micropores. This overall decrease in

pore size is supported further by the SEM imaging.

Thermogravimetric (TGA) traces of the air-dried gels are

shown in Fig. 3, with two major weight losses observed. The

first event, indicative of water loss, occurs at very low

temperatures. The second weight loss, which starts around

225 uC, coincides with the decomposition of the IL within the

matrix. These temperatures correspond to the endotherms

observed by DSC. The remaining mass after heating is the pure

silica material with no IL or methanol remaining.

Fig. 1 DSC thermograms of silica solgels synthesized in the IL

[C4mim][Cl] and methanol: (a) 0.25 mL IL/0.25 mL methanol; (b)

0.75 mL IL/0.75 mL methanol; (c) 1.0 mL IL/1.0 mL methanol; (d)

1.25 mL IL/1.25 mL methanol.

Fig. 2 Relationship of heat flow, microporosity, and residual

hydroxy groups within the silica matrix.

Fig. 3 TGA traces of silica solgels synthesized in pure [C4mim][Cl].

Gel formulations correspond to gels e through h of Table 2.



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Fig. 4 shows the uptake of water from the atmosphere by the

[C4mim][Cl] solgels as a function of time. The non-calcined

IL-gels, prior to these experiments, were dried in a 120 uC

oven for 17 h to remove water from the gels. The gels werethen allowed to sit open to the atmosphere (y65% relative

humidity) on the lab bench, with masses determined at allotted

times. As expected, the rate of water uptake increases as the

amount of IL is increased. Noticeably though, there appear to

be stages in which the gel hydrates itself. Inflection points

are observed which correspond to further increases in water

uptake. Final saturation, relative to the lab environment, is

reached after about 4 h.

Fig. 5 represents the difference, in mass percent, between

each time interval plotted as a function of time. The small

plateaux observed, indicate that the hydration takes place in

peaks or stages. Monitoring up to 4 h showed three distinct

stages in the hydration of the gels, corresponding to thediffusion of water into the macropores, mesopores, and micro-

pores, which are filled with IL. As expected, the degree of

porosity is the smallest when smaller amounts of IL are

incorporated. As the volume is increased, the porosity also

increases, but the formation of smaller pores becomes more

dominant. This is further corroborated by SEM and surface

area measurements that are discussed later. The literature

indicates that gels synthesized with formamide and oxalic acid

as DCCAs show a narrower pore size distribution.27 The

narrower distribution will become evident in the work

described here, and is discussed later.

Experiments to determine the behavior of the IL in the solmatrix were carried out by drying a solgel synthesized with

only IL at 120 uC for 3.5 h followed by DSC characterization.

The DSC trace (Fig. 6) shows a glass transition at ca. 290 uC

with melting at ca. 60 uC. Residual water is lost at ca. 100 uC.

A large endotherm starting at 200 uC corresponds to the

decomposition of the IL. Usually the neat IL will crystallize34

and exhibit a corresponding exothermic peak; however, crystal-

lization is not found to occur within the silica framework.

Infrared spectroscopy of the non-calcined gels (Fig. 7)

showed small peaks at ca 2900 cm21, corresponding to the

imidazolium cation alkyl groups and any residual methoxy

groups of the silica monomer. If the hydrolysis of the methoxy

groups and subsequent hydrolysis proceeded to completion, nocontribution from residual methoxy groups would be seen.

This suggests that the IL is blocking the complete reaction of

the monomer. These peaks are present in all non-calcined gels

regardless of the amount of IL used.

Zhou et al.13 synthesized monolithic silica using

[C4mim][BF4] and observed peaks at 1700 cm21 which were

assigned to the stacking of the imidazolium rings of the IL.

This pp stacking of the imidazolium rings was reported to

lead to a worm-hole effect (ordered periodicity) and the

Fig. 4 Water vapor sorption kinetics of pure [C4mim][Cl] solgels.

Gel formulations correspond to gels e through h of Table 2. The

experiments were performed simultaneously.

Fig. 5 Change in mass as a function of time when the [C 4mim][Cl]

solgels are exposed to air.

Fig. 6 DSC thermogram of a typical [C4mim][Cl] silica solgel after

drying for 3.5 h at 120 uC: (a) freezing of IL/water; (b) glass transition

of [C4mim][Cl]; (c) melting of [C4mim][Cl]; (d) vaporization of residual

water; (e) decomposition of [C4mim][Cl].

Fig. 7 IR spectra of silica solgels: (a) Controlgel; (b) non-calcined

IL silica solgel; (c) calcined solgel synthesized with IL.



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formation of long channels. They also attributed the observed

worm-hole formation to hydrogen bonding between the

tetrafluoroborate anion and the hydroxyl groups of the silica.

The gels made using [C4mim][Cl] lack these peaks at 1700 cm21

associated with the imidazolium ring stacking, which is

consistent with the lack of long channels within the materials

made here, and instead the presence of microdomains. The

SEM images, to be discussed later, also emphasize the lack of

ordered periodicity. It is to be noted that the crystal structures

of the [C4mim][Cl] polymorphs show hydrogen bonding of the

chloride anion with nearly every hydrogen associated with

the imidazolium ring and those on the alkyl groups.34 Such

hydrogen bonding would help disrupt any ring stacking such

as that suggested by Zhou et al.13 The tetrafluoroborate anion

used by Zhou is a much poorer hydrogen bond acceptor than

chloride thus allowing for preferential stacking.

Calcined gels

After slow drying of the gels at room temperature for several

weeks until no further shrinkage was observed, the gels were

calcined at 500 uC to decompose and remove the IL from the

matrix. The gels were then ground and subjected to BET

analysis. Larger pieces of the calcined gels were analyzed by

SEM. For these studies, the IL was used as a DCCA in a

traditional manner where half the solvent, methanol in this

instance, was substituted with the IL. The second set of

materials was synthesized using only IL, without the addition

of methanol, with the hypothesis that the absence of methanol

would create larger pores due to larger IL volumes and less

contraction during drying and calcination due to the ILs

negligible vapor pressure.

SEMs of the gels revealed a marked effect as the volume of

IL was increased. When small amounts of IL were incorpo-

rated, a highly porous solid with large pores, was formed

(Fig. 8). As the amount of IL was increased, the macroporosity

appeared to decrease with a more uniform topography

observed. At low magnifications, the surfaces look relatively

smooth, however higher magnification shows that the gels are

indeed porous, but with much smaller pores and a smaller pore

size distribution. (A more uniform pore size distribution is one

reason that DCCAs are used in solgel synthesis.)

The surface morphology of silica solgels when synthesized

in various amounts of [C4mim][Cl] without methanol are

shown in Fig. 9. In each case the molten ionic liquid was

dissolved in water followed by addition of the silica monomer.

The silica to water ratio was 1 : 4 so there was enough water

to allow for complete hydrolysis of the monomer. As the

concentration of IL was increased, the morphology of the

resulting gels changed dramatically. While the gels were

generally more porous when lower amounts of IL were

incorporated, a more ordered, highly porous material was

observed at higher volumes. The gels with the lower volumes

of IL incorporated were more opaque, white, in appearance,

while at higher volumes they become more transparent. In

addition, the gels were more brittle when smaller volumes of

Fig. 8 SEM images of silica solgels synthesized in 1 : 1 [C4mim][Cl]methanol: (a) 0.25 mL IL/0.25 mL methanol; (b) 0.75 mL IL/0.75 mL

methanol; (c) 1.0 mL IL/1.0 mL methanol; (d) 1.25 mL IL/1.25 mL methanol.

Fig. 9 SEM images of silica solgels synthesized in [C4mim][Cl]: (a) 0.5 mL IL; (b) 1.5 mL IL; (c) 2.0 mL IL; (d) 2.5 mL IL.



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[C4mim][Cl] were added. When these topographies are com-

pared to those when methanol was used, distinct differences

are seen. The use of pure ILs in the synthesis produced more

highly porous materials with higher pore size distributions.

Available surface areas and pore volumes were determinedby BET analysis (Table 3). The use of only ILs in the synthesis

of solgels produced a more open framework (higher available

surface area) as compared to when the IL was used with

methanol. As expected, the overall available surface areas are

less than when ILs with longer alkyl chains are incorporated.

In addition, the calculated average pore size decreases as the

amount of IL is increased.

Conclusions

The silica solgels synthesized in the presence of [C4mim][Cl]

showed an increase in available surface area as the amount of

IL volume was increased. Pore volumes were also found toincrease, however in both instances, no dramatic increase was

seen when a total volume greater than 1.5 mL of solvent was

used. The resulting materials did not exhibit periodicity (as

seen with other published reports) which can be attributed to

the nature of the IL and its physical properties. The highly

coordinating nature of the chloride anion and its strong

hydrogen bonding capabilities leads to the formation of micro-

domains rather than long channels. SEM imaging indicates

the formation of a more uniform surface and a narrower pore

size distribution as the amount of IL is increased, in common

with more traditional DCCAs. The materials prepared here

have an overall lower surface area compared to when ILs with

longer alkyl chains are used; however, the ability to controlthe pore size distribution and overall morphology may lead to

the generation of new materials with applications to sensors

and catalysis.

Acknowledgements

This research has been supported by the U.S. Environmental

Protection Agencys STAR program through grant number

RD-83143201. Although the research described in this article

has been funded in part by EPA, it has not been subjected to

the Agencys required peer and policy review and therefore

does not necessarily reflect the views of the Agency and no

official endorsement should be inferred. The authors would

also like to thank Ms. Jolanta Nunley (The University of

Alabama Electron Microscope Facility) for assistance in

obtaining the SEM images and Dr. Ramana G. Reddy (The

University of Alabama Department of Metallurgical andMaterials Engineering) for assistance with surface area

measurements.

References

1 M. A. Klingshirn, S. K. Spear, R. Subramanian, J. D. Holbrey,J. G. Huddleston and R. D. Rogers, Chem. Mater., 2004, 16,30913097.

2 R. A. Silva, G. G. Silva, R. L. Moreira and M. A. Pimenta, Phys.Chem. Chem. Phys., 2003, 5, 24242428.

3 B. D. Ghosh, K. F. Lott and J. E. Ritchie, Chem. Mater., 2005, 17,661669.

4 M. Mizutani, H. Takase, N. Adachi, T. Ota, K. Daimon andY. Hikichi, Sci. Technol. Adv. Mater., 2005, 6, 7683.

5 W. Song, D. M. Marcus, S. M. Abubakar, E. Jani and J. F. Haw,J. Am. Chem. Soc., 2003, 125, 1396413965.

6 T. Y. Park and G. F. Froment, Ind. Eng. Chem. Res., 2004, 43,682689.

7 J. Dupont, R. F. de Souza and P. A. Z. Suarez, Chem. Rev., 2002,102, 36673692.

8 T. Welton, Coord. Chem. Rev., 2004, 248, 24592477.9 D. W. Armstrong, L. He and Y-S. Liu, Anal. Chem., 1999, 71,

38733876.10 K. Shimojo and M. Goto, Anal. Chem., 2004, 76, 50395044.11 P. Bonhote, A-P. Dias, M. Armand, N. Papageorgiou,

K. Kalyanasundaram and M. Gratzel, Inorg. Chem., 1996, 35,11681178.

12 C. J. Adams, A. E. Bradley and K. R. Seddon, Aust. J. Chem.,2001, 54, 679681.

13 Y. Zhou, J. H. Shattka and M. Antonietti, Nano Lett., 2004, 4,

477481.14 Y. Zhou and M. Antonietti, Chem. Mater., 2004, 16, 544550.15 C. Y. Yuan, S. Dai, Y. Wei; Y. W. Chen-Yang and R. D. Rogers,

Ionic Liquids; Industrial-Applications for Green Chemistry, ed.K. R. Seddon, ACS Symposium Series 818, American ChemicalSociety, Washington DC, 2002, pp. 106113.

16 S. Dai, Y. H. Ju, H. J. Gau, J. S. Lin, S. J. Pennycook andC. E. Barnes, Chem. Commun., 2000, 3, 243244.

17 B. Lee, H. Luo, C. Y. Yuan, J. S. Lin and S. Dai, Chem. Commun.,2004, 2, 240241.

18 Y. Liu, M. Wang, Z. Li, H. Liu, P. He and J. Li, Langmuir, 2005,21, 16181622.

19 F. Chaumel, H. Jiang and A. Kakkar, Chem. Rev., 2001, 13,33893395.

20 S. Marx, A. Zaltsman, I. Turyan and D. Mandler, Anal. Chem.,2004, 76, 120126.

Table 3 Surface areas and calculated pore volumes of calcined silica gels synthesized in the presence of [C4mim][Cl] and methanol

Gel IL : MeOH/mLSurfacearea/m2 g21

Microporearea/m2 g21

External area(meso+macro)/m2 g21

Porevolum/mL g21

Average poresize/nm

(a) 0.25 : 0.25 283 54 229 0.6 8.5(b) 0.75 : 0.75 322 42 280 1.0 12.4(c) 1.00 : 1.00 395 80 315 0.9 9.1(d) 1.25 : 1.25 456 92 364 1.1 9.6(e) 0.50 : 0.00 320 31 289 0.6 7.5(f) 1.50 : 0.00 451 90 361 0.9 8.0(g) 2.00 : 0.00 586 141 445 1.1 7.5(h) 2.50 : 0.00 605 132 473 1.0 6.6Control 0.00 : 2.50 5 5 0 0.0 0.0C14

a 1314b C16

a 1340b C18

a 1382b a Cn corresponds to the alkyl chain length of the ionic liquid ([Cnmim][Cl]) incorporated;

b Data from ref. 14.



7/7

21 R. Ciriminna, J. Blum, D. Avnir and M. Pagliaro, Chem.Commun., 2000, 14411442.

22 Y-K. Lu and X-P. Yan, Anal. Chem., 2004, 76, 453457.23 A. V. Rao and M. M. Kulkarni, Mater. Chem. Phys., 2002, 77,

819825.24 A. V. Rao, H. M. Sakhare, A. K. Tamhankar, M. L. Shinde,

D. B. Gadave and P. B. Wagh, Mater. Chem. Phys., 1999, 60, 268273.25 L. Nikolic and L. Radnojic, Ceram. Int., 1994, 20, 309313.26 R. F. S. Lenza and W. L. Vasconcelos, J. Non-Cryst. Solids, 2003,

330, 216225.

27 L. Hench, Science of Ceramic Chemical Processing, ed. L. L. Henchand D. R. Ulrich, John Wiley & Sons, New York, 1986.

28 J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer,G. A. Broker and R. D. Rogers, Green Chem., 2001, 3, 156164.

29 A. V. Rao and M. M. Kulkarni, Mater. Chem. Phys., 2002, 77,819825.

30 T. L. Merrigan, E. D. Bates, S. C. Dorman and J. H. Davis, Jr,Chem. Commun., 2000, 20, 20512052.

31 J. Ding, T. Welton and D. W. Armstrong, Anal. Chem., 2004, 76,68196822.

32 C. J. Brinker and G. W. Scherer, SolGel Science: The Physics andChemistry of Sol-Gel Processing, Harcourt Brace Jovanovich,Boston, 1990.

33 B. K. M. Chan, N-H. Chan and M. R. Grimmett, Aust. J. Chem.,

1977, 30, 20052013.34 J. D. Holbrey, W. M. Reichert, M. Nieuwenhuyzen, S. Johnson,

K. R. Seddon and R. D. Rogers, Chem. Commun., 2003, 14,16361637.


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KlingshirnSHR J. Mater Chem 5174 2005