Preparation and Adsorption Properties of Thiol-Functionalized

Dec 17, 2008 - Mesoporous silica microspheres (MSM) approximately 1.0 μm in diameter were prepared by the hydrolysis and condensation of ...
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Ind. Eng. Chem. Res. 2009, 48, 938–943

Preparation and Adsorption Properties of Thiol-Functionalized Mesoporous Silica Microspheres Yoshikazu Miyake,* Masanori Yosuke, Eiichi Azechi, Sadao Araki, and Shunsuke Tanaka Department of Chemical Engineering and High Technology Research Center, Kansai UniVersity, 3-3-35, Yamate-cho, Suita, Osaka 564-8680, Japan

Mesoporous silica microspheres (MSM) approximately 1.0 µm in diameter were prepared by the hydrolysis and condensation of tetraethoxysilane (TEOS) under the presence of dodecylamine (DDA) as a molecular template and catalyst in ethanol-water solution. Isolated MSM were obtained in a narrow range of experimental conditions, which were experimentally correlated by the linear relationship between the molar ratio of ethanol and TEOS and that of DDA and TEOS. Isolated MSM modified with thiol groups were also prepared under similar experimental conditions, by co-condensation of TEOS and 3-mercaptopropyltrimethoxysilane (MPTMS). The thiol-functionalized MSM (SH-MSM) adsorbed silver ions from an aqueous solution. Asymmetrical polystyrene film, in which the SH-MSM were self-assembled on the surface of the water phase side of the film, was obtained by spreading and polymerizing of styrene monomer with dispersed SH-MSM on the water surface. The polymer film containing SH-MSM also effectively adsorbed silver ions. Introduction Since 1992, when Mobil researchers published an excellent method for the preparation of mesoporous materials using surfactant as a templating agent,1 many papers have been published on the preparation methods and applications of mesoporous silica.2–10 Prepared mesoporous silica has two advantages over previous mesoporous materials: a higher specific surface area of more than 1000 m2/g made up of uniform mesopores about twice the length of the surfactant, and regular arrangement of the mesopores in silica due to the higher order assembly of surfactants. Up to now, characteristics of the regular arrangements of mesopores have not been used in functional materials in nanotechnology. However, materials with high specific surface areas and uniform mesopores can be used as adsorbents and catalyst carriers. When mesoporous silica is used as an adsorbent or catalyst carrier, the spherical morphology of silica is very useful. For example, if mesoporous silica is used as an adsorbent in a packed column, the spherical morphology helps to decrease the pressure drop.11 Some methods for preparing mesoporous silica spheres have been developed. These are mainly classified into two categories: (1) two-phase systems composed of organic and water phases and (2) analogies of the well-known Sto¨ber method12 in the homogeneous phase. A two-phase system was first reported by Huo et al.,13 in which hydrophobic tetrabutoxysilane as a silica source was mechanically dispersed in the aqueous solution of a dissolved surfactant. Spherical mesoporous silica about 500 µm in diameter was obtained. The formation mechanism has been studied by Miyake et al.,14 and they found that the surfactants in the aqueous phase were extracted together with water molecules into the hydrophobic phase of tetrabutoxysilane, and that hydrolysis and condensation of tetrabutoxysilane proceeded in the water-in-oil microemulsions. As the hydrophobic phases were dispersed in the aqueous phase, spherical mesoporous silica with a large diameter was obtained. Recently, in another two-phase system composed of water and paraffin phases, spherical mesoporous silica several tens of micrometers in diameter was prepared.15 * To whom correspondence should be addressed. Tel.: +81-6-63680950. Fax: +81-6-6388-8869. E-mail: [email protected].

For the other type of method, i.e., the modified Sto¨ber method, two reaction systems have been reported to date.16–28 One reaction system used a quaternary ammonium salt such as dodecyltrimethylamine chloride as a templating agent and NH3 or NaOH for catalysis of the hydrolysis and condensation of tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS) as a silica source.16–23 The solvents used were a mixture of ethanol or methanol and water. Micro- and submicrometer sized spherical mesoporous silica were prepared. Mesoporous silica microspheres (MSM) were obtained in an isolated state and/or as aggregated particles. The state of the MSM may be dependent on the concentrations of alcohol, surfactant, and silicon alkoxides. Recently, Yano et al. have discussed the preparation conditions of MSM under the presence of alkyl quaternary ammonium salt in the methanol solution of TMOS and NaOH or NH3. The isolated MSM were obtained under slower precipitation rates.21–23 The other reaction system is composed of a primary amine such as a dodecylamine (DDA) and a TEOS as the silica source.24–28 For this system, DDA is bifunctional as the templating agent and the catalyst for hydrolysis and condensation of TEOS. A mixture of ethanol and water was also used as the solvent for this reaction system. Mesoporous silica about one micrometer in diameter was obtained by this method. Shiratori et al.25 have reported the experimental conditions required for obtaining isolated MSM under the equal volume fraction of ethanol and water. They have obtained the relationship between [EtOH]/[TEOS] and [DDA]/[TEOS] for the formation of isolated MSM. There is another system to prepare the spherical silica particles as known MSU-1,29,30 in which the nonionic surfactant or block copolymer was used as a template in the presence of NaF. In this study, first, in order to confirm Shiratori’s relationship between [EtOH]/[TEOS] and [DDA]/[TEOS] under wide experimental conditions, we researched the experimental conditions to obtain the isolated MSM, especially the effects of EtOH and DDA concentrations at constant concentration of TEOS. We also obtained a linear relationship between the molar ratios [EtOH]/[TEOS] and [DDA]/[TEOS]. Next, thiol-functionalized MSM (SH-MSM) were prepared by co-condensation of TEOS and 3-mercaptopropyltrimethox-

10.1021/ie800614c CCC: $40.75  2009 American Chemical Society Published on Web 12/17/2008

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ysilane (MPTMS) in the ethanol-water solvent containing dissolved DDA. Isolated SH-MSM were also obtained under a narrow range of experimental conditions. The SH-MSM are expected as an adsorbent for a soft acid such as Ag+, Hg2+ and Pd2+, because the thiol group is a soft base.30 In order to elucidate the adsorption properties of the SH-MSM and to recover silver ions in the photograph industry and the plating industry, the adsorption behavior for Ag+ with the SH-MSM was studied by a batch operation. Furthermore, after adsorption, to avoid separating the isolated SH-MSM from the aqueous phase, the isolated SH-MSM were fixed in a polystyrene film, which was prepared by the spreading and polymerizing of styrene monomers with dispersed SH-MSM on the surface of the water phase. The adsorption of silver ions from the aqueous phase by a composite material consisting of SH-MSM and polystyrene film was also evaluated. Experimental Section Preparation of MSM. TEOS was poured into a 50 cm3 vial containing 30 cm3 of an ethanol-water mixture with dissolved DDA as the templating agent, accompanied by vigorous stirring with a magnetic stirrer. After stirring for 15 s, the vial was placed in a water bath held at 298 K without stirring. The reaction time was 3 h. The effect of agitation was also studied by varying the magnetic stirrer speed from 100 to 900 rpm. The precipitates obtained from the resultant solutions were separated by centrifuge. The DDA was removed by Soxhlet extraction with ethanol for 24 h. After DDA removal, the precipitates were dried for 24 h at 333 K. The silica precipitates were characterized by SEM (JSM5410, JEOL), N2 adsorption (BELSOAP mini, Bel Japan), and XRD (JDX-3530, JEOL). We investigated experimental conditions such as the ethanol, DDA, and TEOS concentrations required to form isolated MSM. Preparation of Thiol-Functionalized MSM. Using the preparation conditions for obtaining isolated MSM, SH-MSM was prepared by co-condensation of MPTMS and TEOS. The molar fraction of MPTMS to total silica was changed from 0 to 50%. After 3 h without stirring, the SH-MSM was separated from the solutions by centrifugation. The surfactants were removed from the resulting materials by Soxhlet extraction with ethanol for 24 h and dried in air at room temperature. Silver Ion Adsorption by Thiol-Functionalized MSM. SHMSM (50 mg) was added to 25 mL of a 10 mM solution of silver nitrate in a 50 cm3 vial and kept for 24 h in a water bath at 298 K. After the adsorption equilibrium had been reached, the SH-MSM was separated by centrifugation. The concentration of silver ions in the aqueous solution was measured by inductively coupled plasma (ICP) spectrometry (ICPS-1000III, Shimadzu Corp.). The adsorption quantity, q (mmol/g), of silver ions was evaluated using the following equation q)

([Ag]0 - [Ag]e)VAq WMSM

(1)

where [Ag]0 and [Ag]e are the concentrations of silver (mM) in the initial and equilibrium states, respectively, and VAq (dm3) and WMSM (g) are the initial volume of silver nitrate solution and the weight of SH-MSM, respectively. Preparation of Thiol-Functionalized MSM Dispersed in Polystyrene Film. Styrene monomer was used after removing the stabilizer with NaOH solution. 25 mg of SH-MSM after removal of DDA with Soxhlet extraction was dispersed by stirring for 24 h in 10 cm3 of styrene monomer solution. 1 cm3 of styrene monomer solution was spread on the surface of

Figure 1. Map of states of mesoporous silica. SEM images of silica: (a) isolated MSM, (b) aggregated MSM, and (c) nonspherical state. [TEOS] ) 175 mM.

distilled water in a laboratory dish. The monomer solution was then irradiated with UV light by using a high voltage Hg lamp for 24 h. A circular polystyrene film about 20 mm in diameter was obtained. The structure of the film was observed by SEM. Adsorption of silver ions was investigated by immersing this polystyrene film into 50 cm3 of an aqueous silver nitrate solution. Results and Discussion Preparation Conditions for Isolated MSM. We prepared the MSM in a 50 cm3 vial, from 175 mM TEOS in an ethanol and water mixture containing dissolved DDA as the molecular template. After a reaction time of 3 h without stirring, the states of silica separated from the solution by centrifuge were classified into four categories, i.e., (1) isolated MSM, (2) aggregated MSM, (3) no spherical state, and (4) no precipitate. The SEM images for three of these categories are shown in Figure 1. The diameters of isolated MSM were in the range from 1.0 to 1.3 µm, irrespective of the ethanol and DDA concentrations. The Sto¨ber method is well-known for the preparation of monodispersed silica spheres.12 In the Sto¨ber method, silica spheres are prepared from an ethanol-water mixture in the presence of ammonia as catalyst. In this system, it is suggested that DDA acts as a catalyst and molecular template.24 Under a constant TEOS concentration of 175 mM, the states of silica particles obtained at several different ethanol and DDA concentrations were mapped, as shown in Figure 1. The preparation conditions required to form isolated MSM occurred over a narrow band of ethanol concentrations in the range from 50 to 75 vol%, with the concentration required increasing with an increase in the DDA concentration. Above the upper region of the narrow band, because the reaction rate of hydrolysis and condensation of TEOS is very low, the silica particles were not obtained. However, as the reaction rate is very fast below the lower region of the narrow band, the spherical silica particles were aggregated with each other. We measured the time, tF, when the solutions become clouded, by visual observation. The relationships between tF and ethanol or DDA concentrations are shown in Figure 2. The value of tF is an indicator for evaluating the overall reaction rates of TEOS hydrolysis and condensation in the reaction

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Figure 2. Effects of DDA and ethanol concentrations on the time, tF, for the formation of precipitates. Circle and square symbols show the effects of DDA and EtOH concentrations on tF value, respectively. Solid and open symbols correspond to the isolated MSM and aggregated MSM, respectively.

Figure 3. Correlation between [EtOH]/[TEOS] and [DDA]/[TEOS] for preparation of the isolated MSM. Closed circles, this study; open squares, ref 25; open triangles, ref 28. The dotted-broken line is Shiratori’s linear relationship.25

system. Under a constant [DDA] ) 40 mM, the tF value increased linearly with the ethanol concentration. Above 60 vol %, isolated MSM (denoted by solid squares) were obtained. On the other hand, at lower than 55 vol %, the silica microspheres were aggregated with each other (denoted by open squares). The value of tF slowly decreased with increase in the DDA concentration under [EtOH] ) 62.5 vol %. At a DDA concentration above 60 mM, aggregated silica was obtained (open circles). Isolated MSM were obtained at DDA concentrations below 55 mM (solid circles). These results suggest that there is a minimum tF value, in this case 300 s, required for obtaining the isolated MSM, because spherical silica were aggregated at lower tF values, which is the fast condensation rate. In order to obtain isolated MSM, there are optimum conditions for the reaction rate of hydrolysis and condensation of TEOS. The conditions for the preparation of isolated MSM were correlated by the linear relationship between [EtOH]/[TEOS] and [DDA]/[TEOS], as shown in Figure 3. The data shown by solid circles in Figure 3 were obtained using experimental conditions of [DDA] ) 20-100 mM and [TEOS] ) 87.5-438 mM under a constant ethanol concentration of 62.5 vol %, in addition to the data already presented in Figure 1. The data of Shiratori et al.25 and Yu et al.28 are also shown in Figure 3, using open squares and open triangles, respectively. These experimental data for preparing isolated MSM can be correlated by a linear relationship, which can be expressed by the following experimental equation without theoretical base [DDA] [EtOH] ) 165 + 25((15) (2) [TEOS] [TEOS] The two dotted lines in Figure 3 were calculated by using intercept values of +40 and +10, respectively. The data for

Figure 4. XRD patterns of isolated SH-MSM after removal of DDA. [EtOH] ) 62.5 vol %, [DDA] ) 40 mM, [TEOS] + [MPTMS] ) 175 mM.

Figure 5. Effect of DDA concentration on the nitrogen adsorption at 77 K for silica after removal of DDA. [EtOH] ) 62.5 vol %, [TEOS] ) 175 mM.

[DDA]/[TEOS] values lower than 0.4 fell within these lines, but at higher [DDA]/[TEOS] values there were some deviations. The dotted-broken line in Figure 3 shows Shiratori’s linear relationship.25 We also examined the effect of stirring on the preparation of isolated MSM under the conditions [DDA] ) 40 mM, [TEOS] ) 175 mM, and [EtOH] ) 62.5 vol %. At stirring speeds of 100, 300, and 500 rpm, isolated MSM were obtained, but at speeds of 700 and 900 rpm, aggregated MSM were obtained. It is difficult to elucidate the effect of stirring on the formation of isolated MSM, but one of the reasons may be that the frequency of collisions between silica particles increased with increased stirring speed. As a result, with no stirring, sharper monodispersion of isolated MSM was obtained. The XRD patterns of the MSM after removal of DDA were measured and are shown in Figure 4. The first peak for isolated MSM was observed near 2θ ≈ 2.8, but higher order peaks were not observed. This result means that no discernible long-range order in the pore arrangement exists in the MSM. The nanostructure may be a wormhole-like pore structure.28 The nitrogen adsorption isotherm for MSM after DDA removal was measured at 77 K, and the results are shown in Figure 5. The adsorbed volume of nitrogen increased with an increasing DDA concentration in the initial reaction mixture. On the other hand, the micropore volume, which corresponds to the adsorbed volume at a low relative pressure in Figure 5, was almost constant irrespective of the DDA concentration. The pore properties are summarized in Table 1. The BET specific surface area was more than 1000 m2/g. The BET specific surface area and the specific pore volume were increased with increasing the feed concentration of DDA, due to the increase in the incorporated quantity of DDA in isolated or aggregated MSM. The average pore diameter was in the range of 2.0-2.5 nm, which was larger than the data of Yu et al.28 but smaller than

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Table 1. Pore Characteristics of MSM

[DDA] BET specific specific pore average pore (mM) surface area, SBET (m2/g) volume, VP (cm3/g) diameter, dP (nm)b 40c 40 60 80

980 1080 1410 1560

0.53 0.58 0.80 0.77

a [TEOS] ) 175 mM, [EtOH] ) 62.5 vol %. Dollimore-Heal method. c Agitation at 300 rpm.

2.1 2.5 2.2 2.0 b

Calculated by the

Figure 8. Effect of MPTMS molar fraction on the nitrogen adsorption at 77 K for isolated SH-MSM after removal of DDA. Offset of ordinate are +500 (for 0%), +400 (5%), +300 (10%), +200 (15%), +100 (20%), and +0 (25%). [EtOH] ) 62.5 vol %, [DDA] ) 40 mM, [TEOS] + [MPTMS] ) 175 mM. Table 2. Pore Characteristics of Thiol-Fuctionalized MSMa

Figure 6. SEM images of SH-MSM for several MPTMS molar fractions in feed solution: (a) 5, (b) 15, (c) 25, and (d) 35 mol %. [EtOH] ) 62.5 vol %, [DDA] ) 40 mM, [TEOS] + [MPTMS] ) 175 mM.

Figure 7. FT-IR spectra for SH-MSM: (a) before and (b) after removal of DDA with Soxhlet extraction. [EtOH] ) 62.5 vol %, [DDA] ) 40 mM, [TEOS] + [MPTMS] ) 175 mM, [MPTMS] ) 10%.

that of Shiratori et al.25 The difference may be due to the removal method of DDA, i.e., extraction or calcinations.25,28 Preparation and Characteristics of Thiol-Functionalized MSM. SH-MSM were prepared by using a mixture of TEOS and MPTMS under a constant [EtOH] ) 62.5 vol % and [DDA] ) 40 mM. The molar fraction of MPTMS was varied from 5 to 50% under a total TEOS and MPTMS concentration of 175 mM. SEM images of the obtained silica are shown in Figure 6. At MPTMS molar fractions from 5 to 25 mol %, isolated MSM were obtained. However, above 30 mol % MPTMS, aggregated MSM were obtained, as shown in Figure 6d. The diameter of isolated MSM, about 1.0 µm, was almost independent of the MPTMS molar fraction. The FT-IR spectra of the isolated MSM obtained before and after Soxhlet extraction of the isolated SH-MSM are shown in Figure 7. The peaks of NH2, CH2, and CH3 groups of spectra b due to DDA had disappeared from spectra a, but a peak due to an SH group did not appear near 2500-2600 cm-1. This result shows that the DDA used as a template was removed by Soxhlet

[MPTMS]/([MPTMS] + [TEOS]) (mol %)

BET specific surface area, SBET (m2/g)

specific pore volume, VP (cm3/g)

average pore diameter, dP (nm)b

0 5 10 15 20 25

1080 970 960 940 750 590

0.58 0.48 0.47 0.45 0.35 0.29

2.5 2.4 2.4 2.6 2.7 2.6

a [DDA] ) 40 mM, [TEOS] + [MPTMS] ) 175 mM, [EtOH ]) 62.5 vol %. b Calculated by the Dollimore-Heal method.

extraction. Figure 4 shows the XRD patterns obtained after Soxhlet extraction. The position of the first peak of the XRD patterns was not shifted in the presence of MPTMS. The peaks in the XRD patterns became sharp after the removal of DDA, but the first peak of the XRD patterns became broader with an increase in the MPTMS molar fraction. The behavior means that the quantity of DDA trapped in MSM decreased with the MPTMS concentration. Figure 8 shows the adsorbed volume of nitrogen at 77 K for isolated SH-MSM. The adsorbed volume decreased with increasing MPTMS molar fraction, but the micropore volume, which corresponds to the adsorbed volume at a low relative pressure in Figure 8, was almost constant irrespective of the MPTMS concentration. The pore characteristics of these MSM are summarized in Table 2. The average pore diameter increased slightly with an increase in the MPTMS concentration. The specific pore volume and BET surface area were almost independent of the MPTMS molar fraction up to 15 mol %. However, above 20 mol % MPTMS, these values decreased linearly with increasing MPTMS molar fraction. In order to clarify the formation mechanism of the isolated SH-MSM, the residual DDA, MPTMS, and TEOS in the mixed solvent need to be analyzed. This will be discussed in future studies. Adsorption of Silver Ions by Isolated Thiol-Functionalized MSM. The adsorption quantity of silver ions was obtained from eq 1, using the silver ion concentrations in the feed and equilibrium solutions. The relationship between the adsorption quantity of silver ions, q(Ag+), and the MPTMS molar fraction is shown by solid circles in Figure 9. The broken linear line as shown in Figure 9 was calculated by the least-squares method using these five data points. The adsorption quantity of silver ions can be linearly correlated with the MPTMS molar fraction. There are some reports30,31 in the literature about the absorption of Hg2+ with the SH-MSM, but there are few reports on the absorption of Ag+. Therefore, it is assumed that an ion of silver strongly interacts with one site of SH group in the MSM and that all SH groups in the MSM effectively act as

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Figure 9. Relationship between adsorption quantity of silver ions and molar fraction of MPTMS in feed solution. Solid circles, isolated SHMSM; open circles, polystyrene film dispersed SH-MSM; solid squares, data for Hg(II)30 The broken line was calculated by the least-squares method using the five data points of the solid circles. The solid line was calculated by eq 3.

adsorbent sites. Then, the maximum adsorption quantity of silver ion is equal to the molar quantity of SH group per unit weight, m(SH), with units mmol/g, which can be estimated as follows. If the SH-MSM was composed of SiO2 (molecular weight 60 g/mol) produced from TEOS and SiO1.5C3H6SH (molecular weight 127 g/mol) produced from MPTMS, the molar quantity of MPTMS per 1 g of the SH-MSM, m(SH), is expressed as

Figure 10. SEM images of polystyrene film: (a) cross section, (b) and (c) water side, and (d) air side.

m(SH) ) 175[MPTMS] (3) 127 × 0.175[MPTMS] + 60(0.175 - 0.175[MPTMS]) where [MPTMS] is the molar fraction of MPTMS in the TEOS and MPTMS mixture. The first and second terms in the denominator are the weight of SiO1.5C3H6SH and SiO2, respectively. The numerator is millimoles of MPTMS. It is noted that the total concentration of TEOS and MPTMS was 175 mM. The results calculated by eq 3 are shown by the solid line in Figure 9. However, the experimental data were greater than the solid line calculated by eq 3. The difference became larger for the higher MPTMS contents. The adsorption behavior of mercury(II) ion with SH-MSM prepared by MSU-1 method is shown by the solid square symbols for the data of Bibbly and Mercier.30 They concluded that an ion of Hg2+ adsorbs on one site of SH group and the complex of SHg+ is formed. It is also deduced for silver ion that the 1:1 complex of Ag+ and SH group is formed. But the experimental results mean that a part of adsorbed silver ion was incorporated into the mesopores of SH-MSM. It may be caused by the interaction of Ag+ and OH group on the MSM. However, because the silver ion and mercury ion30 were not practically adsorbed with isolated MSM (0% [MPTMS]), further detailed data are required to resolve this contradiction.31 Preparation and Characteristics of Polystyrene Film Containing Dispersed Thiol-Functionalized MSM. An asymmetrical film about 2 cm in diameter was obtained. Figure 10 shows SEM images of the polystyrene film containing dispersed SHMSM. A cross section of the polystyrene film is shown in Figure 10a. The film thickness was about 100 µm. Figures 10b and 10c are SEM images taken on the water surface of the polystyrene film. The SH-MSM were self-assembled on the water surface of the film. In contrast, there are no MSM on the air surface of the film, as shown in Figure 10d. The formation process of the asymmetrical film is shown in Figure 11. During polymerization of the styrene monomer, the SH-MSM dispersed in the styrene monomer solution self-assembled at the interface between the styrene monomer solution and the water phase, due to gravitation and/or the hydrophilicity of the SH-MSM.

Figure 11. Illustration of formation process of polystyrene film on the water phase.

The prepared polystyrene film was immersed in an aqueous solution containing dissolved silver ions. The adsorbed quantity was obtained by eq 1, where the weight of SH-MSM used was 2.5 mg. The value was equal to the weight of SH-MSM contained in 1.0 cm3 of styrene monomer solution, because it is assumed that the MSM were homogeneously dispersed in styrene monomer solution. These values are plotted against the MPTMS molar fraction, using open circles, in Figure 9. The adsorption quantity with the film dispersed SH-MSM was slightly smaller than that with the isolated SH-MSM, which may be a result of some errors in the weight of the MSM in polymer film. This result suggests that most SH-MSM dispersed in polymer film acted as adsorption sites, because the MSM were assembled at one side of the polystyrene film. The polystyrene film can be used as a new type of separation film, in which the functionalized MSM have self-assembled. Conclusion The isolated MSM and SH-MSM were prepared by use of the primary amine, DDA, and the characaterization and adsorption behavior of silver ion with SH-MSM were evaluated, and the following conclusions were obtained. (1) The isolated MSM were obtained in a narrow range of experimental conditions. The regions were described by a linear experimental equation between the molar ratio of [EtOH]/ [TEOS] and that of [DDA]/[TEOS]. (2) The isolated SH-MSM were also prepared using TEOS and MPTMS. The BET specific surface area and specific pore volume were almost independent of the MPTMS molar fraction

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up to 15 %, but above 20 % MPTMS, these values decreased linearly with increasing MPTMS molar fraction. (3) The SH-MSM effectively adsorbed silver ions from aqueous solution. The adsorption quantity of silver ion linearly increased with MPTMS molar fraction. The values were over the maximum theoretical values calculated by eq 3, which is derived by assuming a 1:1 complex formation between SH group and silver ion. As the results could not be reasonably interpreted, further analyses have to be undertaken. (4) An asymmetric polystyrene film, with the SH-MSM assembled on one side of the film, was prepared. This film can be also used to separate silver ions from an aqueous phase. Literature Cited (1) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. A New Family of Mesoporous Molecular-Sieves Prepared with Liquid-Crystal Templates. J. Am. Chem. Soc. 1992, 114, 10834. (2) Bagshaw, S. A.; Prouzet, E.; Pinnavaia, T. J. Templating of Mesoporous Molecular-Sieves by Nonionic Polyethylene Oxide Surfactants. Science 1995, 269, 1242. (3) Feng, X.; Fryxell, G. F.; Wang, L. Q.; Kim, A. Y.; Liu, J.; Kemner, K. M. Functionalized Monolayers on Ordered Mesoporous Supports. Science 1997, 276, 923. (4) Lu, Y. F.; Ganguli, R.; Drewien, C. A.; Anderson, C. J.; Brinker, C. J.; Gong, W. L.; Guo, Y. X.; Soyez, H.; Dunn, B.; Huang, H.; Zink, J. I. Continuous Formation of Supported Cubic and Hexagonal Mesoporous Films by Sol Gel Dip-Coating. Nature 1997, 389, 364. (5) Zhao, D.; Fend, H.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores. Science 1998, 279, 548. (6) Brinker, C. J.; Lu, Y. F.; Sellinger, A.; Fan, H. Y. EvapolationInduced Self-Assembly. AdV. Mater. 1999, 11, 579. (7) Margolese, D.; Melero, J. A.; Christiansen, S. C.; Chmelka, B. F.; Stucky, G. D. Direct Syntheses of Ordered SBA-15 Mesoporous Silica Containing Sulfonic Acid Groups. Chem. Mater. 2000, 12, 2448. (8) Huang, M. H.; Choudrey, A.; Yang, P. D. Ag Nanowire Formation within Mesoporous Silica. Chem. Commun. 2000, 1063. (9) Jung, J. H.; Ono, Y.; Hanabusa, K.; Shinkai, S. Creation of Both Right-Handed and Left-Handed Silica Structures by Sol-Gel Trancription of Organogel Fibers Comprised of Chiral Diaminocyclohexane Derivatives. J. Am. Chem. Soc. 2000, 122, 5008. (10) Inagaki, S.; Guan, S.; Ohsuna, T.; Terasaki, O. An Ordered Mesoporous Organosilica Hybrid Material with a Crystal-Like Wall Structure. Nature 2002, 416, 304. (11) Miyake, Y.; Hanaeda, M.; Asada, M. Separation of Organic Compounds by Spherical Mesoporous Silica Prepared from W/O Microemulsions of Tetrabutoxysilane. Ind. Eng. Chem. Res. 2007, 46, 8152. (12) Sto¨ber, W.; Fink, A.; Bohn, E. J. Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range. J. Colloid Interface Sci. 1968, 26, 62. (13) Huo, Q.; Feng, J.; Schuth, F.; Stucky, G. D. Preparation of Hard Mesoporous Silica Spheres. Chem. Mater. 1997, 9, 14. (14) Miyake, Y.; Kato, T. The Formation Process of Spherical Mesoporous Silica with Reverse Nanostructure of MCM41 in a Two-Phase System. J. Chem. Eng. Jpn. 2005, 38, 60.

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ReceiVed for reView April 16, 2008 ReVised manuscript receiVed October 20, 2008 Accepted November 4, 2008 IE800614C