In Situ Recrystallization of Silica Template for Synthesis of Novel

ARTICLE pubs.acs.org/IECR

In Situ Recrystallization of Silica Template for Synthesis of Novel Microporous ZSM-5/Hollow Mesoporous Carbon Composites Suk Bon Yoon,† Jong-Yun Kim,†,* Seung-Kyu Park,‡ Jung Ho Kim,§ Min-Sik Kim,§ and Jong-Sung Yu§,* †

The Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, Daejeon, 305-353, Korea Department of Chemical Engineering, Hoseo University, Asan, 336-795, Korea § Department of Advanced Materials Chemistry, WCU Research Team, Korea University, Jochiwon, 339-700, Korea ‡

bS Supporting Information ABSTRACT: Silica-based nanocasting synthesis of a nanostructured carbon replica inevitably involves the disposal of silica waste and toxic etchant after the time-consuming and costly etching processes for selective removal of silica template from a carbon/silica composite to produce the silica-free carbon replica, not only resulting in chemical waste, but also posing serious environmental concerns. Instead of removal of the silica template, the in situ recrystallization transformation of the silica into more useful functional nanostructured silica offers an attractive alternative to the problem of handling silica waste and toxic etchants. In this work, the novel composites composed of microporous zeolite ZSM-5 crystals and hollow core-mesoporous shell carbon (HCMSC) capsules are synthesized for the first time by such transformation process of sacrificial silica template in the carbon/solid core-mesoporous shell silica (SCMSS) composite through hydrothermal process under alkaline condition. Compared to the commercial filter materials, the zeolite/HCMSC composite (BET surface area: 532600 m2/g) possessing a wide range of pore sizes, i.e., micropores from zeolites, mesopores from the outer shells, and macropores from the hollow core of the carbon capsules reveals the outstanding adsorption capacity for the typical malodorous acetaldehyde. Therefore, the recrystallization approach will be appealing as a simple, economical, environmentally benign, and efficient direct synthesis process for the preparation of new multifunctional composite materials for many advanced applications such as removal of volatile organic compounds, separation, energy storage, and catalysis. Recrystallization transformation approach of sacrificial silica in silica/carbon composites is reported for the first time for the formation of new composite materials composed of microporous ZSM-5 zeolite and hollow mesoporous carbon capsules. That is, the silica template waste is utilized to produce a new highly desirable crystalline microporous ZSM-5 silica material by this approach. The composite demonstrated high adsorption capacity for acetaldehyde.

1. INTRODUCTION Porous materials in the range of micropore (50 nm) have been of great interest due to their many emerging applications as catalysts,13 separation systems,4,5 low dielectric constant materials,6,7 storage and delivery materials,8,9 electrode materials,1014 and photonic crystals.15,16 A wide variety of different compositions including inorganic, organic, metal, or carbon materials are now available for these porous materials. Nanoporous zeolite molecular sieves have widely been used in industry as heterogeneous catalysts, especially in oil refining and petrochemistry as solid acid catalysts,17 since they possess several unique structural features such as high surface area, adjustable pore size, hydrophilicity, acidity, and good thermal and chemical stability. However, the pores of the zeolites were less than 2 nm in diameter, which was too small to accommodate relatively bulky organic materials and inorganic organic complex molecules in a variety of applications, limiting their applications into the micropore range. The discovery of new M41S silica mesoporous families with pores larger than 2 nm in diameter in 1992 extended the applications into much wider pore ranges,18 bringing a new prosperous era in the porous material research.1921 Recently, porous carbon materials have attracted considerable attention because of their remarkable properties such as high r 2011 American Chemical Society

specific surface area, large pore volume, chemical inertness, and good mechanical stability, which propose great potentials in many areas of modern science and technology including water and air purification, gas separation, catalysis, chromatography, energy storage, and electrode for battery and fuel cell.2228 Template-directed synthesis has been extensively explored for the preparation of nanostructured carbon materials with welldefined pore structure and morphology for the past decades.2934 Formation of uniform and interconnected pores and specific morphologies in these nanostructured carbon materials is usually achieved by nanocasting of the silica inorganic porous materials as hard templates. Ordered mesoporous carbon (OMC) is the most successful example of mesostructured replicas made through the nanocasting strategy of various ordered mesoporous silica.2931 The carbon capsules with hollow core and mesoporous shell (HCMSC) synthesized from the spherical silica with solid core and mesoporous shell (SCMSS) are also a good example for such controlled synthesis of both pore structure and particle morphology found in the resulting spherical hollow Received: November 5, 2010 Accepted: May 13, 2011 Revised: May 12, 2011 Published: May 13, 2011 7998

dx.doi.org/10.1021/ie102238y | Ind. Eng. Chem. Res. 2011, 50, 7998–8005

Industrial & Engineering Chemistry Research

ARTICLE

Scheme 1. Synthesis Processes for the HCMSC Capsule or ZSM-5/HCMSC Composite from the Carbon/SCMSS Composite

carbon.3537 Most recently, ordered multimodal porous carbon with mesoporous wall has been also fabricated through inverse nanocasting of ordered hierarchical nanostructured silica composed of particulate silica gels in the wall of ordered macropore array.38,39 However, the procedure in such silica-directed synthesis of the porous carbon materials always requires the selective removal of the silica template from the silica/carbon composite by using ethanolic sodium hydroxide solution at its boiling temperature or harmful hydrofluoric acid, not only resulting in treatment of chemical waste, but also posing significant environmental concerns. Therefore, although recycling of the silica waste is of a critical concern in industrial process, the difficulty in separation of siliceous materials from the complex mixture of a silica waste, solvent and etchant solution makes it quite formidable to recycle the silica waste. Instead, the transformation of the sacrificial silica template in the silica/carbon composites into more useful silica material seems to be an attractive alternative. Since zeolite surface possesses very strong acidity good for catalysis, in situ recrystallization of the silica waste into functional zeolite molecular sieves will be very attractive in terms of environmental benefit and production of valuable functional materials for many useful applications. There have been some studies on the partial recrystallization transformation of MCM-41 and HMS silica into ZSM-5 type zeolites, which have usually been prepared by using tetrapropylammonium hydroxide (TPAOH) as a templating agent.40,41 Ostwald’s rule42 which states that a metastable silicate phase will successively transform to more stable (denser) phases until it reaches the most stable phase (quartz) implies that, in principle, the recrystallization of amorphous silica to zeolite crystal is possible. Zeolites with a variety of morphologies such as films, monoliths, hollow worm-like tubes, and hollow capsules have been generated via preformed zeolite seeds.4346 In this work, the in situ recrystallization transformation approach of the sacrificial silica in the silica/carbon composites is reported for the first time for the formation of a new composite materials composed of microporous ZSM-5 zeolite crystals and HCMSC capsules. That is, the silica template waste is utilized to

produce new functional crystalline microporous ZSM-5 silica by this approach. Thus, this method cannot only eliminate a troublesome selective etching process, which can cause costly waste treatment but also provide a novel way of creating more useful advanced materials. Interestingly, the resulting microporous zeolite/HCMSC composite revealed excellent adsorption capability for acetaldehyde, a typical example of volatile organic compounds (VOCs). Therefore, the current approach represents a simple, highly economical, environmentally benign, and efficient process for the massive production of new advanced multifunctional composite materials, minimizing chemical waste for our environments.

2. EXPERIMENTAL SECTION 2.1. Synthesis of Monodisperse Solid Core-Mesoporous Shell Silica (SCMSS) Nanospheres. Monodisperse silica spheres

were synthesized based on the modified St€ober method.47 A 40mL portion of aqueous ammonia (NH4OH, 28 wt.%) was mixed with a solution containing 1000 mL of absolute ethanol (EtOH) and 80 mL of deionized water (H2O), and the full solution was stirred for 30 min. Then, 60 mL of TEOS (98%, Aldrich) was added to the above solution and stirred for 6 h at room temperature to result in colloidal suspension solution containing monodisperse silica particles. A mixture containing 50 mL of TEOS and 20 mL of octadecyltrimethoxysilane (C18-TMS) was added into the above-synthesized colloidal silica suspension solution under vigorously stirring at room temperature, and the resulting mixture solution was further stirred for 5 h at ambient conditions to introduce mesoporous shell over the silica spheres. The resulting as-synthesized SCMSS particles were retrieved by centrifugation, dried at 343 K overnight, and then calcined at 823 K for 7 h under oxygen atmosphere to remove octadecyl organic groups as previously described.35 2.2. Synthesis of Carbon/SCMSS Composites. Aluminumimpregnated SCMSS with acid catalytic sites on the surface was used as a template for the condensation polymerization of phenol and formaldehyde inside the mesopores of SCMSS nanospheres.35

7999

dx.doi.org/10.1021/ie102238y |Ind. Eng. Chem. Res. 2011, 50, 7998–8005

Industrial & Engineering Chemistry Research Aluminum was incorporated into the silica framework via an impregnation method, i.e., SCMSS nanospheres were suspended in an aqueous solution of 3.0 102 M AlCl3 3 6H2O (Si/Al molar ratio = 10417) for 1 h, dried at 343 K for overnight, and calcined at 823 K for 7 h in air to obtain the aluminumimpregnated SCMSS nanospheres.48 Phenolic resin/SCMSS composite was prepared by adding 3.0 g of the aluminumimpregnated SCMSS particles into the mixture containing 0.94 g of phenol and 0.76 g of paraformaldehyde, slowly heating to 393 K and holding at that temperature for 5 h. Excess polymer precursor was removed by vacuum at ambient temperature. The resultant polymer/SCMSS composite was heated under N2 gas flow at a rate of 3 K/min to 1173 K in a tube furnace, and then carbonized at 1173 K for 7 h to prepare the carbon/SCMSS composite. Either tetrapropylammonium hydroxide (TPAOH) or tetrapropylammonium bromide (TPABr) was used as a templating agent for the synthesis of ZSM-5 zeolite. Two grams of the carbon/SCMSS composite was added into 10 g of 1.0 M TPAOH aqueous solution, and mixed for 30 min under vigorous stirring. In the case of using TPABr, 2 g of the carbon/SCMSS composite was added into mixture solution containing 0.22 g of NaOH, 0.32 g of TPABr, and 10 g of deionized water and mixed for 30 min under vigorous stirring. In a subsequent recrystallization process, the mixture of carbon/SCMSS composite and TPAOH solution (or TPA salt solution in alkaline condition) was placed into the stainless autoclave, heated to 373 K, and held at that temperature for 24 h. Dissolution of amorphous silica from the carbon/SCMSS composite followed by in situ recrystallization into ZSM-5 zeolite resulted in ZSM-5/HCMSC-x composites, where x = OH or Br depending on the TPAOH or TPABr used for the synthesis. As-synthesized ZSM-5/HCMSC composite was filtered, washed with excess water and ethanol, dried at 343 K for overnight, and subsequently calcined at 873 K for 7 h under N2 gas flow to remove the TPAOH or TPABr from the ZSM-5/HCMSC framework, which results in calcined ZSM5/HCMSC composite. For comparison, silica-free HCMSC capsules were obtained after the silica template was selectively removed from the above-prepared carbon/SCMSS composite by using 48% HF solution as previously described.35 Scheme 1 illustrates a synthesis process for the ZSM-5/HCMSC composite or silica-free HCMSC from the carbon/SCMSS composite. 2.3. Characterization. Powder X-ray diffraction (XRD) patterns of the samples were recorded by using a Rigaku Miniflex diffractometer with CuKR radiation (30 kV, 15 mA). The nitrogen adsorption and desorption isotherm measurements were made on a Micromeritics ASAP 2000 at 77 K. The samples were pretreated by vacuum degassing overnight at 423 K before isotherm measurements in the ASAP 2000. Specific surface area was determined by nitrogen adsorption data in the relative pressure range from 0.05 to 0.2 using the BET (Brunauer EmmettTeller) equation. Total pore volume was determined from the amount of gas adsorbed at the relative pressure of 0.99. Pore size distribution was calculated from the adsorption branch of the nitrogen isotherm by using the BJH (BarrettJoyner Halenda) method. Scanning electron microscope (SEM) pictures were collected with JEOL JSM-840A microscope. Transmission electron microscope (TEM) images were obtained by using EM 912 Omega at 120 kV. 2.4. Fixed-Bed Column Experiment. The experimental setup based on ASTM D6646 breakthrough capacity test unit was used to evaluate the acetaldehyde adsorption capacity of calcined

ARTICLE

Scheme 2. Experimental Setup of an in-House Built Analytical System Used to Test the Performance of the Unpleasant Gas Removal Based on ASTM D6646 Breakthrough Capacity Test Method

ZSM-5/HCMSC composite in a humidified air/acetaldehyde gaseous mixture at room temperature (Scheme 2). Acetaldehyde adsorption properties of a commercially available NH4-ZSM-5 type zeolite (Zeolyst CBV5524G, Zeolyst International) and granulated activated carbon (SGF100, Samchully Activated Carbon Co, Ltd., Korea) were also measured for comparison under the same experimental conditions. A 0.1-g portion of adsorbent was loaded into a tubular glass column (length 20 cm, i.d. Ten mm) with a thin layer of glass wool to retain adsorbent powders. Effluent acetaldehyde concentration was measured using gas chromatography in a humid air stream at a flow rate of 0.4 L min1. The humid feed gas stream was prepared by mixing dry acetaldehyde gas with air passing through a water bubbler at room temperature. Initial acetaldehyde gas concentration in a humid air was 25 ppm, which is within the normal concentration range found in sick house syndrome.

3. RESULTS AND DISCUSSION Scheme 1 illustrates a synthesis process for silica-free HCMSC or ZSM-5/HCMSC composite from the same starting carbon/ SCMSS composite material. The HCMSC capsule was generated through the selective dissolution of the sacrificial SCMSS template,35 whereas the ZSM-5/HCMSC composite was prepared through recrystallization transformation of the SCMSS template in the carbon/SCMSS composite material. Figure 1 shows the representative SEM image of the resulting composite composed of the HCMSC capsules and zeolite crystals, which were prepared using TPAOH, along with the corresponding TEM image of HCMSC capsules in the composite. The ZSM-5 zeolite crystals in the ZSM-5/HCMSCOH composite (prepared with TPAOH) exhibited typical pseudohexagonal plate-like shape with twin intergrowths as reported.49 The HCMSC existing as an individual capsule has a bimodal pore structure consisting of a spherical macroscopic hollow core (ca. 150 nm in diameter) and a mesoporous shell (ca. 30 nm in shell thickness). Disordered mesopores can be clearly seen in the magnified TEM image of the shell of HCMSC in Figure 1c. During the selective dissolution and recrystallization of the amorphous silica template from the carbon/SCMSS composite, most of the HCMSC capsules retain their spherical morphology although some broken spheres are occasionally seen in the electron microscope images. Eventually, the ZSM-5/HCMSC composites reveal multimodal porosity spanning from micropores to meso- and macropores in the framework. The ZSM-5 crystals in ZSM-5/HCMSC-Br composites synthesized by using TPABr instead of TPAOH as an organic template for the formation of ZSM-5 with Si/Al molar ratios = 8000



ARTICLE

Figure 1. (a) SEM image of as-synthesized ZSM-5/HCMSCOH composite prepared using TPAOH as a template agent for ZSM-5 with Si/Al = 30, (b) corresponding TEM image of the HCMSC in the composite, and (c) high-magnification TEM image of the HCMSC.

Figure 2. SEM images of as-synthesized ZSM-5/HCMSC-Br composites prepared using TPABr as a template agent for ZSM-5 with (a) Si/Al = 417 and (b) Si/Al = 35, respectively.

417 and 35 show crystal morphologies different from those in the ZSM-5/HCMSCOH composite as evident in Figure 2. Interestingly, the ZSM-5 crystals in the ZSM-5/HCMSC-Br composites also exhibited the morphology transition from the stackedplate to rectangular column with decreasing Si/Al ratio from 417 to 35. It was found that the spherical HCMSC capsules were uniformly distributed between the ZSM-5 crystals throughout the sample. The mesoporous carbon capsules largely maintained the spherical shape after calcination as shown in SEM and TEM images of the calcined composites. (see Figures S1 and S2 of the Supporting Information, SI) Since the amorphous silica “hard templates” are dissolved out of the carbon framework and recrystallized into the crystalline zeolite particles in the vicinity of the carbon, the resultant composites provide an excellent homogeneous mixture of mesoporous carbon and microporous zeolite. Mixtures prepared through physical mixing of corresponding powders often reveal microscopic phase separation of ZSM-5 crystals and HCMSC capsules, where only either ZSM-5 crystals or HCMSC capsules are locally predominant, indicating that the homogeneous mixing of different nanoparticles particularly with different densities and hydrophilicity is in fact difficult by the simple physical mixing. The current recrystallization method offers additional advantage of having better homogeneous composite materials. Figure 3 presents the powder XRD patterns of the assynthesized and calcined ZSM-5/HCMSCOH composites measured to identify the crystal structure of the zeolite in the composites. All of the diffraction patterns of the resulting zeolite/ carbon composites prepared at different Si/Al molar ratios = ¥, 40 and 30 in this work agreed well with that of typical ZSM-5 zeolite as previously reported.50 Two XRD peaks observed at 2θ ≈ 38 and 44 are assigned to an aluminum sample holder for

Figure 3. XRD patterns of ZSM-5/HCMSCOH composites prepared with different molar ratios of Si to Al (a) in the as-synthesized state and (b) in the calcined state.

powder XRD measurements. The increase of two peaks at 2θ ≈ 7.510.0 after calcination corresponds to the removal of the organic template trapped in the micropores of the ZSM-5 zeolite. The ZSM-5 crystalline structure starts to decrease when the Si/ Al ratio in the synthesis medium decreases to 20, and completely disappears at Si/Al = 10, indicating that the Si/Al ratio is an important factor for the generation of the ZSM-5 crystals as well as their morphological shape as seen in SEM images in Figure 2. There were not significant differences in XRD patterns between the ZSM-5/HCMSCOH and ZSM-5/HCMSCBr. Figure 4a shows N2 sorption isotherms of as-synthesized and calcined ZSM-5/HCMSCOH composites prepared at Si/Al = 30 as a representative example. As shown in the isotherm curves, the volume adsorbed for the calcined ZSM-5/HCMSCOH at low pressures (P/Po < 0.05) was much higher than that for the 8001



ARTICLE

from N2 sorption isotherms of all the samples are summarized in Table 1. Gas adsorption capacity of the calcined ZSM-5/HCMSC composite was compared to those of the commercial products. Acetaldehyde gas is chosen in the present work because it is a well-known VOC and very difficult to remove from the atmosphere at ambient temperature. Although there have been various types of adsorbents developed for the removal of acetaldehyde,5358 activated carbon and NH4-ZSM-5 type zeolite are the most effective adsorbent for the removal of acetaldehyde.59 To evaluate the gas adsorption capacity, the humidified air/acetaldehyde gaseous mixtures passed through the breakthrough capacity test unit (see Scheme 2) based on ASTM D6646 at room temperature. Figure 5 shows the breakthrough curves of a normalized relative concentration of effluent gas vs contact time between acetaldehyde gas and adsorbents. The normalized relative concentration of effluent gas is obtained by the following equation. C ¼

Figure 4. N2 adsorption/desorption isotherms for the as-synthesized and calcined ZSM-5/HCMSCOH with Si/Al molar ratio = 30 (top). Pore size distribution curves calculated from the adsorption branch of N2 isotherms (bottom).

as-synthesized ZSM-5/HCMSCOH, which indicates a significant increase of micropores in the calcined ZSM-5/ HCMSCOH due to removal of organic template molecules from the as-synthesized ZSM-5. The high-magnification TEM image in Figure 1c and the high surface area are clear evidence of the presence of mesopores in the shell of HCMS carbon in addition to the textural mesopores between HCMS carbon particles. Interestingly, there is no clear capillary condensation step in the adsorption branch. The mesopore diameter of the HCMSC capsules exhibited a bit broad pore size distribution for both as-synthesized and calcined ZSM-5/HCMSCOH composites as evident from the pore size distribution curves in Figure 4b. The hysteresis loops with an abrupt decrease in gas volume at around p/p0 = 0.5 of desorption isotherm for both the as-synthesized and calcined ZSM-5/HCMSCOH may be attributed to the textural mesopores between HCMSC particles as well as the cavitation effect observed for macroporous hollow core surrounded by the mesoporous shell of the HCMSC.51 Because the composite possesses micropores and macropores as well as mesopores, and the size of the mesopores are just at the lower limit of the mesopores (∼2 nm), the N2 isotherm curve may show mixed isotherm shape accommodating type I, type II, and type IV, reflecting all of the pore sizes available in the composite.52 Structural properties such as BET surface area, total pore volume, and pore size obtained

Ct Ci Cf Ci

ð1Þ

where C* is a normalized relative concentration of effluent gas, Ci is an initial effluent gas concentration (t = 0 min), Cf is a final effluent gas concentration (t = 18 min), and Ct is an effluent gas concentration at a certain time t. A final effluent gas concentration (Cf) at 18 min of activated carbon and NH4-ZSM-5 type zeolite was 17 ppm and 10 ppm, respectively, while Cf of calcined ZSM-5/HCMSCOH composite was 6 ppm under the same experimental conditions. This indicates that the ZSM-5/ HCMSCOH composite shows the best adsorption capacity for acetaldehyde. The shape of the breakthrough curve is dependent on many parameters such as initial inlet concentration, flow rate, temperature, relative humidity, particle size of the adsorbents, pretreatment conditions, and column dimensions.59,60 Probably due to the severe experimental conditions in terms of inlet concentration and flow rate in our present work, two commercial products tested in the present work revealed a steep rise with no appreciable breakthrough time as shown in Figure 5. However, the calcined ZSM-5/HCMSCOH composite showed a distinct breakthrough point at around 12 min, beyond which a relative effluent acetaldehyde concentration gradually increased with time, whereas the activated carbon and NH4ZSM-5 showed an immediate increase with time. Although NH4-ZSM-5 and activated carbon show no appreciable breakthrough time, they also indeed possess adsorption capacity on acetaldehyde. Adsorption capability can be expressed in loading amount of adsorbed gas per unit mass of adsorbent. The loading for acetaldehyde in ZSM-5/HCMSC composite up to 12 min is calculated as 1.92 mg 3 g1, while the loading for NH4-ZSM-5 and activated carbon are 1.69 mg 3 g1 and 1.42 mg 3 g1, respectively. After all, the performance of our ZSM-5/HCMSC composite material is overwhelming under our experimental conditions compared with those of other commercial adsorbents, NH4ZSM-5 and activated carbon in terms of the breakthrough time. The structural properties of the materials tested in our present work do not contribute significantly to the difference in performance of the acetaldehyde adsorption since the pore volume and surface area of the activated carbon are comparable or even better to those of the ZSM-5/HCMSC composites as shown in Table 1. The better performance of ZSM-5/HCMSC composite is rather 8002



ARTICLE

Table 1. Structural Properties for the SCMSS Particles, HCMSC Capsules, As-Synthesized and Calcined ZSM-5/HCMSC-x Composites, Commercial NH4-ZSM5 (CBV5524G) and Activated Carbon (SGF-100) BET surface area (m2/g) sample ZSM-5/HCMSCOH

ZSM-5/HCMSC-Br

Si/Al ratio

calcined

as-syn.

calcined

as-syn.

calcined

30

140

569

0.17

0.44

1.6

2.2

40

238

532

0.23

0.44

1.5

2.2

¥ 35

119 235

486 600

0.13 0.20

0.35 0.41

1.6 2.0

2.5 2.7

417

178

591

0.17

0.39

2.4

520

HCMSC activated carbon

pore diameter (nm)

as-syn.

SCMSS NH4-ZSM5

total pore volume (cc/g)

26

2.8

0.48

3.5

1,370

1.28

3.0

378

0.24

1,200

0.50

1.7

Thus, the recrystallization transformation approach can be attractive as a simple, highly economical, environmentally benign, and efficient synthesis process for new types of composite materials with advanced synergistic functions, which are not possible for a single component. In addition, MCM- and SBAtype mesoporous silicas have also been used as templates for nanocasting synthesis of ordered mesoporous carbons (OMCs). The silica template waste can be also recrystallized into other valuable zeolite forms as well as ZSM-5 to generate new forms of functional zeolite-OMC composites. Further work in this direction is currently underway.

’ ASSOCIATED CONTENT Figure 5. Breakthrough curves for acetaldehyde at an inlet gas concentration of Co= 25 ppm with flow rate of 0.4 L min1: (0) commercial activated carbon, (O) NH4-ZSM-5, and (Δ) calcined ZSM-5/ HCMSCOH composite (Si/Al = 30). A solid line is a guide for eye, and an arrow indicates the breakthrough point of calcined ZSM-5/ HCMSCOH composite.

ascribed to synergistic effect originating from their close interaction between zeolite and carbon capsules, since the ZSM-5/ HCMSC composite is an excellent homogeneous mixture of mesoporous carbon and microporous zeolite as shown in Figures 2 and S2 of the SI. On the contrary, such a homogeneous mixture is hardly obtainable by an ordinary physical mixing between carbon and zeolite due to the difference in density and strong attractive interactions between hydrophobic carbon materials, where the attractive interaction among hydrophobic substances (carboncarbon) is much higher than that between hydrophobic and hydrophilic substances (carbon-zeolite).

4. CONCLUSIONS The novel composites of microporous zeolite ZSM-5 crystals and meso/macroporous HCMSC capsules have been synthesized for the first time by the recrystallization transformation process of amorphous silica template in the carbon/SCMSS composite. The resulting ZSM-5/HCMSC composites possess a wide range of pore sizes, i.e., micropores from zeolites, mesopores, and macropores from mesoporous shell and hollow core in the HCMSC, respectively, and demonstrated excellent adsorption capacity for acetaldehyde due to unique structural properties.

bS

Supporting Information. TEM images of calcined ZSM5/HCMSCOH composite and of the HCMSC in the calcined composite. SEM images of calcined ZSM-5/HCMSC-Br composite and corresponding TEM images of HCMSC in the calcined composite. This information is available free of charge via the Internet at http://pubs.acs.org

’ AUTHOR INFORMATION Corresponding Author

*Tel.:þ82-41-860-1494. Fax: þ82-41-867-5396. E-mail: jsyu212@ korea.ac.kr(J.-S.Y). Tel.: þ82-42-868-4736. Fax: þ82-42-8688148. E-mail: [email protected] (J.-Y.K).

’ ACKNOWLEDGMENT This work was supported by the WCU (No. R31-2008-00010035-0) Research Program, the NRF grant funded by the Korean Government (MEST:2009-0077413), the Nuclear R&D Program of the Ministry of Education, Science and Technology and Center for Ultra-Microchemical Process Systems through the Korea Science and Engineering Foundation, and Korea Research Foundation, and Hoseo University. We would also like to thank KBSI at Chuncheon, Jeonju, and Daejeon for TEM, SEM, and XRD measurements. ’ REFERENCES (1) Yu, J.-S.; Kang, S.; Yoon, S. B.; Chai, G. Fabrication of Ordered Uniform Porous Carbon Networks and their Application to a Catalyst Supporter. J. Am. Chem. Soc. 2002, 124, 9382. 8003


Industrial & Engineering Chemistry Research (2) Lytle, J. C.; Stein, A. Annual Reviews of Nano Research; Cao, G., Brinker, C. J., Eds.; World Scientific Publishing Co.: River Edge, NJ; Chapter 1, 1, 2006. (3) Vinu, A.; Sawant, D. P.; Ariga, K.; Hartmann, M.; Halligudi, S. B. Benzylation of Benzene and other Aromatics by Benzyl Chloride over Mesoporous AlSBA-15 Catalysts. Microporous Mesoporous Mater. 2005, 80, 195. (4) Ariga, K.; Vinu, A.; Miyahara, M.; Hill, J. P.; Mori, T. One-Pot Separation of Tea Components through Selective Adsorption on PoreEngineered Nanocarbon, Carbon Nanocage. J. Am. Chem. Soc. 2007, 129, 11022. (5) Ji, Q.; Yoon, S. B.; Hill, J. P.; Vinu, A.; Yu, J.-S.; Ariga, K. Layer-by-Layer Films of Dual-Pore Carbon Capsules with Designable Delectivity of Gas Adsorption. J. Am. Chem. Soc. 2009, 131, 4220. (6) Hermans, T. M.; Choi, J.; Lohmeijer, B. G. G.; Dubois, G.; Pratt, R. C.; Kim, H.-C.; Waymouth, R. M.; Hedrick, J. L. Application of Solvent-Directed Assembly of Block Copolymers to the Synthesis of Nanostructured Materials with Low Dielectric Constants. Angew. Chem., Int. Ed. 2006, 45, 6648. (7) Mitra, A.; Cao, T. G.; Wang, H. T.; Wang, Z. B.; Huang, L.; Li, S.; Li, Z. J.; Yan, Y. S. Synthesis and Evaluation of Pure-Silica-Zeolite BEA as Low Dielectric Constant Material for Microprocessors. Ind. Eng. Chem. Res. 2004, 43, 2946. (8) Ji, Q.; Miyahara, M.; Hill, J. P.; Acharya, S.; Vinu, A.; Yoon, S. B.; Yu, J.-S.; Sakamoto, K.; Ariga, K. Stimuli-Free Auto-Modulated Material Release from Mesoporous Nanocompartment Films. J. Am. Chem. Soc. 2008, 130, 2376. (9) Fang, B.; Kim, M.; Kim, J. H.; Yu, J.-S. Controllable Synthesis of Herarchical Nnostructured Hollow Core/Mesopore Shell Carbon for Electrochemical Hydrogen Storage. Langmuir 2008, 24, 12068. (10) Zhang, S.; Liu, M. Dual-Scale Porous Electrodes for Solid Oxide Fuel Cells from Polymer Foams. Adv. Mater. 2005, 17, 487. (11) Ito, S.; Takeuchi, T.; Katayama, T.; Sugiyama, M.; Matsuda, M.; Kitamura, T.; Wada, Y.; Yanagida, S. Conductive and Transparent Multilayer Films for Low-Temperature-Sintered Mesoporous TiO2 Electrodes of Dye-Sensitized Solar Cells. Chem. Mater. 2003, 15, 2824. (12) Kim, M.; Hwang, S.; Yu, J.-S. Novel Ordered Nanoporous Graphitic C3N4 as a Support for Pt-Ru Anode Catalyst in Direct Methanol Fuel Cell. J. Mater. Chem. 2007, 17, 1656. (13) Fang, B.; Kim, J. H.; Yu, J.-S. Colloid-Imprinted Carbon with Superb Nanostructure as an Efficient Cathode Electrocatalyst Support in Proton Exchange Membrane Fuel Cell. Electrochem. Commun. 2008, 10, 659. (14) Chai, G. S.; Yoon, S. B.; Yu, J.-S.; Choi, J.-H.; Sung, Y.-E. Ordered Porous Carbons with Tunable Pore Sizes as Catalyst Supports in Direct Methanol Fuel Cell. J. Phys. Chem. B 2004, 108, 7074. (15) Wijnhoven, J. E. G. J.; Bechger, L.; Vos, W. L. Fabrication and Characterization of Large Macroporous Photonic Crystals in Titania. Chem. Mater. 2001, 13, 4486. (16) Kubo, S.; Gu, Z.-Z.; Takahashi, K.; Fujishima, A.; Segawa, H.; Sato, O. Tunable Photonic Band Gap Crystals Based on a Liquid CrystalInfiltrated Inverse Opal Structure. J. Am. Chem. Soc. 2004, 126, 8314. (17) Corma, A. From Microporous to Mesoporous Molecular Sieve Materials and Their Use in Catalysis. Chem. Rev. 1997, 97, 2373. (18) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Ordered Mesoporous Molecular Sieves Synthesized by a LiquidCrystal Template Mechanism. Nature 1992, 359, 710. (19) Tanev, P. T.; Pinnavaia, T. J. A Neutral Templating Route to Mesoporous Molecular Sieves. Science 1995, 267, 865. (20) Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredirckson, G. H.; Chemlka, B. F.; Stucky, G. D. Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores. Science 1998, 279, 548. (21) Sayari, A.; Kruk, M.; Jaroniec, M.; Moudrakovski, I. L. New Approaches to Pore Size Engineering of Mesoporous Silicates. Adv. Mater. 1998, 10, 1376. (22) Fang, B.; Chaudhari, N. K.; Kim, M.-S.; H. Kim, J.; Yu, J -S. Homogeneous Deposition of Platinum Nanoparticles on Carbon Black

ARTICLE

for Proton Exchange Membrane Fuel Cell. J. Am. Chem. Soc. 2009, 131, 15330. (23) Rodriguez-Reinoso, F. Introduction in Carbon Technology; Marsh, H., Heintz, E. A., Rodriguez-Reinoso, F., Eds.; Universidad de Alicante, Secretariado de publications: Alicante, 35, 1997. (24) Patrick, J. W. Porosity in Carbons: Characterization and Applications; Edward Arnold: London, 1995. (25) Kim, J. H.; Fang, B.; Yoon, S. B.; Yu, J.-S. Hollow Core/ Mesoporous Shell Carbon Capsule as an Unique Cathode Catalyst Support in Direct Methanol Fuel Cell. Appl. Catal. B: Environ. 2009, 88, 368. (26) Fang, B.; Fan, S.-Q.; Kim, J. H.; Kim, M.-S.; Kim, M.; Chaudhari, N. K.; Ko, J.; Yu, J.-S. Incorporating Hierarchical Nanostructured Carbon Counter Electrode Into Metal-Free Organic DyeSensitized Solar Cell. Langmuir 2010, 26, 11238. (27) Fang, B.; Lim, S.; Kim, M.-S.; Kim, J. H.; Yang, D.; Yu, J.-S. Ordered Multimodal Porous Carbon with Hierarchical Nanostructure for High Li Storage Capacity and Good Cycling Performance. J. Mater. Chem. 2010, 20, 10253. (28) Fang, B.; Kim, M.; Yu, J.-S. Hollow Core/Mesoporous Shell Carbon as a Highly Efficient Catalyst Support in Direct Formic Acid Fuel Cell. Appl. Catal. B: Environ. 2008, 84, 100. (29) Lu, A. H.; Sch€uth, F. Nanocasting: A Versatile Strategy for Creating Nanostructured Porous Materials. Adv. Mater. 2006, 18, 1793. (30) Yoon, S. B.; Kim, J. Y.; Yu, J.-S. Synthesis of Highly Ordered Nanoporous Carbon Molecular Sieves from Silylated MCM-48 Using Divinylbenzene as Precursor. Chem. Commun. 2001, 559. (31) Yoon, S. B.; Kim, J. Y.; Kooli, F.; Lee, C. W.; Yu, J.-S. Synthetic Control of Ordered and Disordered arrays of Carbon Nanofibers from SBA-15 Silica Templates. Chem. Commun. 2003, 1740. (32) Su, F.; Zhao, X. S.; Wang, Y.; Zeng, J.; Zhou, Z.; Lee, J. Y. Synthesis of Graphitic Ordered Macroporous Carbon with a ThreeDimensional Interconnected Pore Structure for Electrochemical Applications. J. Phys. Chem. B 2005, 109, 20200. (33) Yoon, S. B.; Chai, G. S.; Kang, S.; Yu, J.-S.; Gierszal, K. P.; Jaroniec, M. Graphitized Pitch-Based Carbons with Ordered Nanopores Synthesized by Using Colloidal Crystals as Templates. J. Am. Chem. Soc. 2005, 127, 4188. (34) Fang, B.; Kim, M.; Hwang, S.; Yu, J.-S. Colloid-Imprinted Carbon with Tailored Nanostructure as an Unique Anode Electrocatalyst Support for Formic Acid Oxidation. Carbon 2008, 46, 876. (35) Yoon, S. B.; Sohn, K.; Kim, J. Y; Yu, J.-S.; Hyeon, T. Fabrication of Carbon Capsules with Hollow Macroporous Core/Mesoporous Shell Structures. Adv. Mater. 2002, 14, 19. (36) Yoon, S. B.; Kim, J.-Y.; Kim, J. H.; Park, Y. J.; Yoon, K. R.; Park, S.-K.; Yu, J.-S. Synthesis of Monodisperse Spherical Silica Particles with Solid Core and Mesoporous Shell: Mesopore Channels Perpendicular to the Surface. J. Mater. Chem. 2007, 17, 1758. (37) Kim, J. H.; Yu, J.-S. Erythrocyte-like Hollow Carbon Capsules and Their Application in Proton Exchange Membrane Fuel Cell. Phys. Chem. Chem. Phys. 2010, 12, 15301. (38) Chai, G. S.; Shin, I. S.; Yu, J.-S. Synthesis of Ordered Uniform Macroporous Carbons with Mesoporous Walls Templated by Aggregates of Polystyrene Spheres and Silica Particles for Use as Catalyst Supports in Direct Methanol Fuel Cell. Adv. Mater. 2004, 16, 2057. (39) Fang, B.; Kim, J. H.; Kim, M.-S.; Yu, J.-S. Ordered Hierarchical Nanostructured Carbon as a Highly Efficient Cathode Catalyst Support in Proton Exchange Membrane Fuel Cell. Chem. Mater. 2009, 21, 789. (40) Kloetstra, K. R.; van Bekkum, H.; Jansen, J. C. Mesoporous Material Containing Framework Tectosilicate by Pore-Wall Recrystallization. Chem. Commun. 1997, 2281. (41) Verhoef, M. J.; Kooyman, P. J.; van der Waal, J. C.; Rigutto, M. S.; Peters, J. A.; van Bekkum, H. Partial Transformation of MCM-41 Material into Zeolites:Formation of Nananosized MFI Type Crystallites. Chem. Mater. 2001, 13, 683. (42) Barrer, R. M. Hydrothermal Cchemistry of Zeolites; Academic Press: London, 174, 1982. 8004



ARTICLE

(43) Song, W.; Kanthasamy, R.; Grassian, V. H.; Larsen, S. C. Hexagonal, Hollow, Aluminium-Containing ZSM-5 Tubes Prepared from Mesoporous Silica Templates. Chem. Commun. 2004, 1920. (44) Mintova, S.; H€olzl, M.; Valtchev, V.; Mihailova, B.; Bouizi, Y.; Bein, T. Closely Packed Zeolite Nanocrystals Obtained via Transformation of Porous Amorphous Silica. Chem. Mater. 2004, 16, 5452. (45) Dong, A.; Ren, N.; Yang, W.; Wang, Y.; Zhang, Y.; Wang, D.; Hu, J.; Gao, Z.; Tang, Y. Preparation of Hollow Zeolite Spheres and Three-Dimensionally Ordered Macroporous Zeolite Monoliths with Functionalized Interiors. Adv. Funct. Mater. 2003, 13, 943. (46) Cho, S. I.; Choi, S. D.; Kim, J.-H.; Kim, G.-J. Synthesis of ZSM-5 Films and Monoliths with Bimodal micro/Mesoscopic Structures. Adv. Funct. Mater. 2004, 14, 49. (47) St€ober, W.; Fink, A.; Bohn, E. Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range. J. Colloid Interface Sci. 1968, 26, 62. (48) Kim, J.-Y.; Lee, S.-J.; Yu, J.-S. Post-Synthetic Incorporation of Ga into Mesoporous Siliceous MCM-41. Bull. Korean Chem. Soc. 2000, 21, 544. (49) Bonilla, G.; Díaz, I.; Tsapatsis, M.; Jeong, H.-K.; Lee, Y.; Vlachos, D. G. Zeolite (MFI) Crystal Morphology Control Using Organic Structure-Directing Agents. Chem. Mater. 2004, 16, 5697. (50) Meier, W. M.; Olson, D. H. Atlas of Zeolite Structure, 2nd revised ed.; Butterworth: Cambridge, 1987. (51) Haffer, S.; Tiemann, M.; Froba, M. Periodic Mesoporous Organosilica Materials with Uniform Spherical Core-Shell Structure. Chem.—Eur. J. 2010, 16, 10447. (52) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscow, L.; Pierotti, R. A.; Rouquerol, T.; Siemienewska, T. Reporting Physisorption Data for Gas/Solid Systems - with Special Reference to the Determination of Surface Area and Porosity. Pure Appl. Chem. 1985, 57, 603. (53) Sugiura, M.; Fukumoto, K. Removal of Acetaldehyde by Sepiolite-2-Aminobenzoic Acid Complex from Ambient Air. Clay Sci. 1992, 8, 257. (54) Noda, T.; Suzuki, M. Study on Development of Adsorbent of Acetaldehyde. Kagaku Kogaku Ronbunshu 1998, 24, 646. (55) Noda, T. Adsorvent of Acetaldehyde Made of Sepiolite. Adsorpt. News 1999, 13, 16. (56) Noda, T.; Tomura, S.; Sakoda, A. Acetaldehyde Adsorption Characteristics of Adsorbent Made of Sepiolite Impregnated with Amino Compound. Nendo Kagaku 2001, 41, 75. (57) El-Sayed, Y.; Bandosz, T. J. Acetaldehyde Adsorption on Nitrogen-Containing Activated Carbons. Langmuir 2002, 18, 3213. (58) Kumagai, S.; Sasaki, K.; Shimizu, Y.; Takeda, K. Formaldehyde and Acetaldehyde Adsorption Properties of Heat-Treated Rice Husks. Sep. Purif. Technol. 2008, 61, 398. (59) Hayashi, T.; Kumita, M.; Otani, A. Removal of Acetaldehyde Vapor with Impregnated Activated Carbons:Effects of Steric Structure on Impregnant and Acidity. Environ. Sci. Technol. 2005, 39, 5436. (60) Yori, J. C.; D’Ippolito, S. A.; Pieck, C. L.; Vera, C. R. Deglycerolization of Biodiesel Streams by Adsorption over Silica Beds. Energy Fuels 2007, 21, 347.

8005


In Situ Recrystallization of Silica Template for Synthesis of Novel

Recommend Documents