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A facile aqueous route tosynthesize highly ordered mesoporous carbons with open pore structures
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From Zeolites to Porous MOF Materials – the 40th Anniversary of International Zeolite Conference R. Xu, Z. Gao, J. Chen and W. Yan (Editors) © 2007 Elsevier B.V. All rights reserved.
A facile aqueous route tosynthesize highly ordered mesoporous carbons with open pore structures Fuqiang Zhang, Yan Meng, Bo Tu and Dongyuan Zhao* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, and The Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Laboratory of Advanced Materials, Fudan University, Shanghai 200433. Tel: 86-21-6564-2036; Fax: 86-21-6564-1740; Email: [email protected] ABSTRACT By employing an aqueous cooperative assembly of phenol/formaldehyde resols and triblock copolymers (Pluronic P123 and F127), highly ordered mesoporous carbons with 2-D hexagonal (p6m) and body-centered cubic (Im 3 m) structures (FDU-15, FDU-16) were synthesized with hydrocarbons such as hexadecane as a swelling agent. FDU-15 has a pore size of 3.8 nm and a BET surface area up to 1040 m2/g, and FDU-16 with cubic mesostructure has a pore diameter of 3.2 nm and a BET surface area of ~ 1030 m2/g. A variety of hydrocarbons with different chain length were used and the swelling ability was estimated in detail. 1. INTRODUCTION Ordered mesoporous carbon is a kind of materials with very promising properties in electrochemistry such as electronic double-layer capacity, solar cell, lithium ion battery, etc. Mesoporous carbon materials were firstly prepared using ordered mesoporous silica as hard templates by Ryoo and co-workers [1-3]. However, compared to the soft template method, the hard template one is very fussy and of high cost, which may limit the application of such materials. To resolve it, the soft template method has been developed based on the solvent induced self-assembly (EISA) of block copolymer and resols (phenol, resorcinol or phloroglucinol/formaldehyde) [4-8]. Although EISA is an appealing method for the preparation of films and monoliths, it is not a suitable pathway for industrial production due to the limitation of batch size and uniaxial structural distortion is always observed for the mesoporous materials derived from the EISA method. Compared to the EISA method, the aqueous route shows better reproducibility and unlimited fabrication batch-size, which can meet the demand of industrial production Moreover, the aqueous method has shown its great advantage in the morphology control, and ordered mesoporous silica with a variety of morphologies, such as spheres, rods, crystals, fibers etc, have been synthesized. Based on this consideration, recently, an aqueous cooperative route has been demonstrated to prepare highly ordered mesoporous carbon of bicontinuous cubic Ia3 d structure, which is as simple as that of mesoporous silica and considered to be much more facile and convenient compared to either the hard template
1857 nanocasting or the previous demonstrated EISA method [9-10]. In the EISA case, mesostructure is formed when most of the solvent is evaporated, while the cooperative self-assembly of amphiphilic surfactant and polymer precursor oligomer is the essential driving force for the formation of mesostructure in the aqueous one. The structure diversity is an important aspect of mesoporous materials for their applications. In this paper, we report the synthesis of ordered mesoporous carbon (FDU-16) with body-centered cubic structure by employing the assembly of F127 (EO106PO70EO106) and phenolic resins. FDU-15 of two-dimensional (2-D) hexagonal mesostructure is obtained by using P123 (EO20PO70EO20) as a template and hexadecane as a swelling agent. A variety of hydrocarbons (hexadecane, decane, heptane, 1, 3, 5-trimethylbenzene) with different chain length were used as swelling agents in the presence of P123 and the structure of the obtained mesoporous carbons were well characterized to get a better understanding of the swelling effect of different hydrocarbons. 2.EXPERIMENTAL SECTION Mesoporous carbon materials (FDU-16 and FDU-15) were synthesized by using triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymers Pluronic P123 (EO20PO70EO20, Mav = 5800) and F127 (EO106PO70EO106, Mav = 12600) as templates and phenol/formaldehyde as carbon precursors. Firstly, 2.0 g (21 mmol) of phenol and 7.0 ml of formaldehyde solution (40 wt%, 100 mmol) were dissolved in 50 ml (5 mmol) of 0.1 M NaOH solution. Then the mixture was stirred at 70oC for 30 min. A clear precursor solution (about 60 ml) was obtained. FDU-16 For a typical synthesis of mesoporous carbon FDU-16, 4.4 g of F127 (~ 0.35 mmol) was dissolved in 50 ml of water. Then 60 ml of the precursor solution was added into the above solution, and a clear solution was obtained. The solution stirred at 65oC for additional 96 h and then stirred at 70oC for another 24 h. The final product was collected by sedimentation separation and filtration, washed with water and dried in air. The obtained sample was calcined at 800oC for 3 h in nitrogen flow to obtain mesoporous carbon FDU-16. The heating rate was fixed at 1oC/min. FDU-15 For a typical synthesis of mesoporous carbon FDU-15, 1.6 g of hexadecane (7.1 mmol) or decane (11 mmol) was added to the solution of 3.2 g P123 (0.55 mmol) in 50 ml water. The mixture was stirred at 40oC for 5 h. A white mixture was obtained while 60 ml of precursor solution was added into the above mixture. The white mixture was continuously stirred at 65oC for additional 96 h and then stirred at 70oC for 24 h. The final products were collected, dried and calcined at 800oC in nitrogen flow to obtain mesoporous carbon FDU-15. 3. CHARACTERIZATION Powder X-ray diffraction (XRD) patterns were recorded with a Bruker D4 powder X-ray diffractometer using Cu KĮ radiation (40 kV, 40 mA). The small-angle X-ray scattering (SAXS) measurements were taken on a Nanostar U small-angle X-ray scattering system (Bruker, Germany) using Cu KĮ radiation (40 kV, 35 mA). Nitrogen adsorption-desorption isotherms were measured with a Micromeritics Tristar 3000 analyzer at 77 K. The
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Fig. 1. (A) SAXS patterns of as-made and calcined mesoporous carbon FDU-16 prepared by using triblock copolymer F127 as a template; (B) Nitrogen sorption isotherm curves of calcined FDU-16.
Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface areas. The pore-size distributions were derived from the adsorption branches of the isotherms using the Kruk-Jaroniec-Sayari (KJS) method [11]. The total pore volume, Vp, was estimated from the amount adsorbed at a relative pressure of 0.95. The unit cell parameters were calculated 2d110 using the formula a and a 2d10 / 3 for FDU-16 and FDU-15 respectively, where d110, and d10 represent the d-spacing values of the 110 and 10 diffractions. Transmission electron microscopy (TEM) experiments were conducted on a JEOL 2011 microscope operated at 200 kV. 4. RESULTS AND DISCUSSION 4.1. FDU-16 Mesoporous carbon FDU-16 can be synthesized by using F127 (EO106PO70EO106) as a template and phenol/formaldehyde as a carbon precursor. The SAXS pattern (Fig. 1A) of as-made FDU-16 shows three well-resolved diffraction peaks with a d-spacing ratio of 1: 1/¥2: 1/¥3, which can be indexed as 110, 200 and 211 reflections of an ordered body-centered cubic mesostructure (space group Im3 m). After calcination at 800oC in nitrogen, four diffraction peaks indexed as 110, 200, 211 and 220 reflections of Im3 m symmetry are observed (Fig. 1A), suggesting that the cubic mesostructure can be well retained. However, structure shrinkage occurs during the calcination process. It can be calculated from the SAXS patterns that the lattice parameter of mesoporous carbon FDU-16 shrank from 15.4 to 11.6 nm for about 24.8% after calcination at 800oC, which is similar to the mesoporous carbon (FDU-16) synthesized from the EISA method [6, 8]. TEM images (Fig. 2) of mesoporous carbon FDU-16 calcined at 800oC in N2 reveal very typical patterns of body-centered cubic structure viewed along the [100], [111] and [110] directions, directly indicating the highly ordered mesostructure. The nitrogen sorption isotherm of FDU-16 (Fig. 1B) shows a type-IV curve with a clear condensation step, suggesting a relative narrow pore size distribution. FDU-16 has a KJS pore size of f 3.2 nm, a BET surface area of 1030 m2/g and a pore volume of 0.50 cm3/g. The C:H:O element
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Fig. 2. TEM images of calcined mesoporous carbon FDU-16 viewed along [100] (a), [111] (b) and [110] (c) directions.
analysis shows that calcined FDU-16 has a carbon content over 90 wt%, confirming the carbon framework of FDU-16. The high surface area and 3-D mesopore structures may provide such materials with very promising properties in applications. 4.2. FDU-15 Using triblock copolymer P123 as a template and hexadecane as a swelling agent, ordered mesoporous carbon FDU-15 with 2-D hexagonal structure can be synthesized. SAXS patterns of as-made and calcined FDU-15 are shown in Fig. 3A. As-made FDU-15 shows four resolved diffraction peaks, associated with the 10, 11, 20 and 21 reflections of an ordered hexagonal mesostructure (space group of p6m). After calcined at 800oC in nitrogen flow, FDU-15 shows three-resolved diffraction peaks in SAXS patterns, indicating an ordered 2-D
Fig. 3. (A) SAXS patterns of as-made and calcined mesoporous carbon FDU-15 prepared by using P123 as a template; (B) Nitrogen sorption isotherm curves of calcined FDU-15.
hexagonal mesostructure and a good thermal stability. The structure is well preserved after the calcination process; nevertheless, very severe structure shrinkage occurred after this process. It can be calculated from the SAXS patterns that the lattice size of as-made FDU-15 shrank from 13.0 to 8.6 nm for 33.8% after calcination at 800oC. Compared to FDU-16 (24.8%), FDU-15 shows larger structural shrinkage, suggesting that the cubic mesostructure is relatively more stable than the hexagonal one. TEM images of calcined FDU-15 at 800qC in nitrogen (Fig. 4) show highly ordered hexagon and stripe morphologies in large domains along [110] and [001] directions, further
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Fig. 4. TEM images of calcined mesoporous carbon FDU-15 viewed along [110] (a) and [001] (b) directions.
confirming the ordered hexagonal p6m mesostructure. The nitrogen sorption isotherm of calcined FDU-15 (Fig. 3) shows a representative type-IV curve with clear condensation step. It can be calculated from the adsorption branches that calcined FDU-15 at 800qC has a pore size of 3.8 nm, a BET surface area of ~ 1040 m2/g and a pore volume of ~ 0.55 cm3/g. The C:H:O element analysis indicates that calcined FDU-15 has a carbon framework with C content above 90 wt%. Hexadecane plays an important role in the formation of FDU-15. Without using hexadecane, only sample of mixed phases of hexagonal p6m and bicontinuous cubic Ia3d can be obtained. To get a better understanding of the roles played by the hydrocarbon in this case. Mesoporous carbon materials were synthesized without or by adding hydrocarbons with different carbon chain length, such as hexadecane, decane, heptane, and 1, 3, 5-trimethylbenzene (TMB) as swelling agents and the obtained samples were denoted as S-P, S-C16, S-C10, S-C7, S-TMB, respectively. All the samples were calcined at 350oC in N2 to remove the templates and generate porous structure. The XRD patterns of samples S-P, S-C16, and S-C10 (Fig. 5A) show a strong diffraction peak at 2T around 1q, indicating ordered mesostructure. The three resolved diffraction peaks of sample S-C10 can be assigned to the 10, 20 and 21 reflections of an ordered hexagonal p6m mesostructure, while the intensity of the diffraction peaks of sample S-C10 is much lower than those of sample S-C16, indicating a poorer structural regularity for the latter. The diffraction peak of sample S-P is relatively broader compared to that of sample S-C16. TEM measurements show that sample S-P is a mixed phase of hexagonal p6m and cubic Ia3d. XRD patterns of samples S-C7 and S-TMB show no diffraction, indicating disordered mesostructures. The nitrogen sorption isotherms (Fig. 5B) of samples S-P, S-C16 and S-C10 show very sharp condensation steps, while those of samples S-C7 and S-TMB are much wider, suggesting a very broad pore size distribution. The result It consists well with their XRD patterns. The relative pressure range of the condensation steps, which associated with the pore diameter, of the five samples is in the following sequence: S-C7, S-TMB > S-C10 > S-C16 > S-P. It can be easily concluded that hydrocarbons with smaller chain length may have better swelling ability in this synthetic system, and this consists well with a previous report about the swelling ability of hydrocarbon molecules in pure surfactant solution [12]. Although TMB and heptane have better swelling ability, the obtained mesoporous carbon materials show lower pore volume. This phenomenon
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Fig. 5. (A) XRD patterns of samples S-P, S-C16, S-C10, S-TMB and S-C7. The patterns are offset along y-axis for clarity; (B) The nitrogen sorption isotherms of samples S-P, S-C16, S-C10, S-TMB and S-C7. For clarity, the isotherm of sample S-C10 is offset along y-axis with 50 cm3/g.
may be a result of the extremely serious shrinkage caused during the calcinations process. It can be concluded that hexadecane and decane can swell the surfactant micelles and induce the formation of ordered mesoporous carbon FDU-15 with 2-D hexagonal structure; while the hydrocarbons of shorter chain length may swell the micelles in such a large degree that only disordered structure are obtained. Moreover, the pore size of obtained mesoporous carbon FDU-15 can be tailored from 4.1 to 6.8 nm. 5. CONCLUSION We have demonstrated a facile aqueous route to synthesize mesoporous carbons with 2-D hexagonal (FDU-15, p6m) or cubic (FDU-16, Im3 m) structures. The pore size of FDU-15 can be tuned from 4.1 to 6.8 nm simply by adding hydrocarbons with different chain length (hexadecane or decane) as swelling agents. Hydrocarbon of shorter chain length may have better swelling ability and result in larger pore size. The structure diversity of the obtained materials may provide very great potential application fields to such materials. ACKNOWLEDGMENT This work was supported by the NSF of China (Grants 20421303, 20373013, and 20521140450), the State Key Basic Research Program of the PRC (2006CB202502), the Shanghai Science & Technology Committee(Grants 06DJ14006, 055207078, 05DZ22313, 04JC14087), Shanghai Nanotech Promotion Center (0652nm024), Shanghai Education Committee (02SG01), the Program for New Century Excellent Talents in University (Grant NCET-04-03), the LG Co., the Shanghai HuaYi Chemical Group, and Fudan Graduate
1862 Innovation Funds. We greatly thank Dr. Y. Chen, Dr. S. H. Xie, and Dr. L. J. Zhang for experimental and characterization assistance. REFERENCES [1] [2]
R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc. 122 (2000) 10712. [3] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature 412 (2001) 169. [4] C. D. Liang, K. L. Hong, G. A. Guiochon, J. W. Mays and S. Dai, Angew. Chem., Int. Ed. 43 (2004) 5785. [5] S. Tanaka, N. Nishiyama, Y. Egashira and K. Ueyama, Chem. Commun. (2005) 2125. [6] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, H. F.Yang, Z. Li, C. Z. Yu, B. Tu and D. Y. Zhao, Angew. Chem., Int. Ed. 44 (2005) 7053. [7] C. D. Liang and S. Dai, J. Am. Chem. Soc. 128 (2006) 5316. [8] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, L. Cheng, D. Feng, Z. X. Wu, Z. X. Chen, Y. Wan, A. Stein and D. Y. Zhao, Chem. Mater. 18 (2006) 4447. [9] F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, C. Z. Yu, B. Tu and D. Y. Zhao, J. Am. Chem. Soc. 127 (2005) 13508. [10] F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, Z. X. Chen, B. Tu and D. Y. Zhao, Chem. Mater. 18 (2006) 5279. [11] M. Kruk, M. Jaroniec and A. Sayari, Langmuir 13 (1997) 6267. [12] M. J. Schwuger, Kolloid –ZZ Polym. 240 (1970) 872.
From Zeolites to Porous MOF Materials – the 40th Anniversary of International Zeolite Conference R. Xu, Z. Gao, J. Chen and W. Yan (Editors) © 2007 Elsevier B.V. All rights reserved.
A facile aqueous route tosynthesize highly ordered mesoporous carbons with open pore structures Fuqiang Zhang, Yan Meng, Bo Tu and Dongyuan Zhao* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, and The Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Laboratory of Advanced Materials, Fudan University, Shanghai 200433. Tel: 86-21-6564-2036; Fax: 86-21-6564-1740; Email: [email protected] ABSTRACT By employing an aqueous cooperative assembly of phenol/formaldehyde resols and triblock copolymers (Pluronic P123 and F127), highly ordered mesoporous carbons with 2-D hexagonal (p6m) and body-centered cubic (Im 3 m) structures (FDU-15, FDU-16) were synthesized with hydrocarbons such as hexadecane as a swelling agent. FDU-15 has a pore size of 3.8 nm and a BET surface area up to 1040 m2/g, and FDU-16 with cubic mesostructure has a pore diameter of 3.2 nm and a BET surface area of ~ 1030 m2/g. A variety of hydrocarbons with different chain length were used and the swelling ability was estimated in detail. 1. INTRODUCTION Ordered mesoporous carbon is a kind of materials with very promising properties in electrochemistry such as electronic double-layer capacity, solar cell, lithium ion battery, etc. Mesoporous carbon materials were firstly prepared using ordered mesoporous silica as hard templates by Ryoo and co-workers [1-3]. However, compared to the soft template method, the hard template one is very fussy and of high cost, which may limit the application of such materials. To resolve it, the soft template method has been developed based on the solvent induced self-assembly (EISA) of block copolymer and resols (phenol, resorcinol or phloroglucinol/formaldehyde) [4-8]. Although EISA is an appealing method for the preparation of films and monoliths, it is not a suitable pathway for industrial production due to the limitation of batch size and uniaxial structural distortion is always observed for the mesoporous materials derived from the EISA method. Compared to the EISA method, the aqueous route shows better reproducibility and unlimited fabrication batch-size, which can meet the demand of industrial production Moreover, the aqueous method has shown its great advantage in the morphology control, and ordered mesoporous silica with a variety of morphologies, such as spheres, rods, crystals, fibers etc, have been synthesized. Based on this consideration, recently, an aqueous cooperative route has been demonstrated to prepare highly ordered mesoporous carbon of bicontinuous cubic Ia3 d structure, which is as simple as that of mesoporous silica and considered to be much more facile and convenient compared to either the hard template
1857 nanocasting or the previous demonstrated EISA method [9-10]. In the EISA case, mesostructure is formed when most of the solvent is evaporated, while the cooperative self-assembly of amphiphilic surfactant and polymer precursor oligomer is the essential driving force for the formation of mesostructure in the aqueous one. The structure diversity is an important aspect of mesoporous materials for their applications. In this paper, we report the synthesis of ordered mesoporous carbon (FDU-16) with body-centered cubic structure by employing the assembly of F127 (EO106PO70EO106) and phenolic resins. FDU-15 of two-dimensional (2-D) hexagonal mesostructure is obtained by using P123 (EO20PO70EO20) as a template and hexadecane as a swelling agent. A variety of hydrocarbons (hexadecane, decane, heptane, 1, 3, 5-trimethylbenzene) with different chain length were used as swelling agents in the presence of P123 and the structure of the obtained mesoporous carbons were well characterized to get a better understanding of the swelling effect of different hydrocarbons. 2.EXPERIMENTAL SECTION Mesoporous carbon materials (FDU-16 and FDU-15) were synthesized by using triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymers Pluronic P123 (EO20PO70EO20, Mav = 5800) and F127 (EO106PO70EO106, Mav = 12600) as templates and phenol/formaldehyde as carbon precursors. Firstly, 2.0 g (21 mmol) of phenol and 7.0 ml of formaldehyde solution (40 wt%, 100 mmol) were dissolved in 50 ml (5 mmol) of 0.1 M NaOH solution. Then the mixture was stirred at 70oC for 30 min. A clear precursor solution (about 60 ml) was obtained. FDU-16 For a typical synthesis of mesoporous carbon FDU-16, 4.4 g of F127 (~ 0.35 mmol) was dissolved in 50 ml of water. Then 60 ml of the precursor solution was added into the above solution, and a clear solution was obtained. The solution stirred at 65oC for additional 96 h and then stirred at 70oC for another 24 h. The final product was collected by sedimentation separation and filtration, washed with water and dried in air. The obtained sample was calcined at 800oC for 3 h in nitrogen flow to obtain mesoporous carbon FDU-16. The heating rate was fixed at 1oC/min. FDU-15 For a typical synthesis of mesoporous carbon FDU-15, 1.6 g of hexadecane (7.1 mmol) or decane (11 mmol) was added to the solution of 3.2 g P123 (0.55 mmol) in 50 ml water. The mixture was stirred at 40oC for 5 h. A white mixture was obtained while 60 ml of precursor solution was added into the above mixture. The white mixture was continuously stirred at 65oC for additional 96 h and then stirred at 70oC for 24 h. The final products were collected, dried and calcined at 800oC in nitrogen flow to obtain mesoporous carbon FDU-15. 3. CHARACTERIZATION Powder X-ray diffraction (XRD) patterns were recorded with a Bruker D4 powder X-ray diffractometer using Cu KĮ radiation (40 kV, 40 mA). The small-angle X-ray scattering (SAXS) measurements were taken on a Nanostar U small-angle X-ray scattering system (Bruker, Germany) using Cu KĮ radiation (40 kV, 35 mA). Nitrogen adsorption-desorption isotherms were measured with a Micromeritics Tristar 3000 analyzer at 77 K. The
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Fig. 1. (A) SAXS patterns of as-made and calcined mesoporous carbon FDU-16 prepared by using triblock copolymer F127 as a template; (B) Nitrogen sorption isotherm curves of calcined FDU-16.
Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface areas. The pore-size distributions were derived from the adsorption branches of the isotherms using the Kruk-Jaroniec-Sayari (KJS) method [11]. The total pore volume, Vp, was estimated from the amount adsorbed at a relative pressure of 0.95. The unit cell parameters were calculated 2d110 using the formula a and a 2d10 / 3 for FDU-16 and FDU-15 respectively, where d110, and d10 represent the d-spacing values of the 110 and 10 diffractions. Transmission electron microscopy (TEM) experiments were conducted on a JEOL 2011 microscope operated at 200 kV. 4. RESULTS AND DISCUSSION 4.1. FDU-16 Mesoporous carbon FDU-16 can be synthesized by using F127 (EO106PO70EO106) as a template and phenol/formaldehyde as a carbon precursor. The SAXS pattern (Fig. 1A) of as-made FDU-16 shows three well-resolved diffraction peaks with a d-spacing ratio of 1: 1/¥2: 1/¥3, which can be indexed as 110, 200 and 211 reflections of an ordered body-centered cubic mesostructure (space group Im3 m). After calcination at 800oC in nitrogen, four diffraction peaks indexed as 110, 200, 211 and 220 reflections of Im3 m symmetry are observed (Fig. 1A), suggesting that the cubic mesostructure can be well retained. However, structure shrinkage occurs during the calcination process. It can be calculated from the SAXS patterns that the lattice parameter of mesoporous carbon FDU-16 shrank from 15.4 to 11.6 nm for about 24.8% after calcination at 800oC, which is similar to the mesoporous carbon (FDU-16) synthesized from the EISA method [6, 8]. TEM images (Fig. 2) of mesoporous carbon FDU-16 calcined at 800oC in N2 reveal very typical patterns of body-centered cubic structure viewed along the [100], [111] and [110] directions, directly indicating the highly ordered mesostructure. The nitrogen sorption isotherm of FDU-16 (Fig. 1B) shows a type-IV curve with a clear condensation step, suggesting a relative narrow pore size distribution. FDU-16 has a KJS pore size of f 3.2 nm, a BET surface area of 1030 m2/g and a pore volume of 0.50 cm3/g. The C:H:O element
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Fig. 2. TEM images of calcined mesoporous carbon FDU-16 viewed along [100] (a), [111] (b) and [110] (c) directions.
analysis shows that calcined FDU-16 has a carbon content over 90 wt%, confirming the carbon framework of FDU-16. The high surface area and 3-D mesopore structures may provide such materials with very promising properties in applications. 4.2. FDU-15 Using triblock copolymer P123 as a template and hexadecane as a swelling agent, ordered mesoporous carbon FDU-15 with 2-D hexagonal structure can be synthesized. SAXS patterns of as-made and calcined FDU-15 are shown in Fig. 3A. As-made FDU-15 shows four resolved diffraction peaks, associated with the 10, 11, 20 and 21 reflections of an ordered hexagonal mesostructure (space group of p6m). After calcined at 800oC in nitrogen flow, FDU-15 shows three-resolved diffraction peaks in SAXS patterns, indicating an ordered 2-D
Fig. 3. (A) SAXS patterns of as-made and calcined mesoporous carbon FDU-15 prepared by using P123 as a template; (B) Nitrogen sorption isotherm curves of calcined FDU-15.
hexagonal mesostructure and a good thermal stability. The structure is well preserved after the calcination process; nevertheless, very severe structure shrinkage occurred after this process. It can be calculated from the SAXS patterns that the lattice size of as-made FDU-15 shrank from 13.0 to 8.6 nm for 33.8% after calcination at 800oC. Compared to FDU-16 (24.8%), FDU-15 shows larger structural shrinkage, suggesting that the cubic mesostructure is relatively more stable than the hexagonal one. TEM images of calcined FDU-15 at 800qC in nitrogen (Fig. 4) show highly ordered hexagon and stripe morphologies in large domains along [110] and [001] directions, further
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Fig. 4. TEM images of calcined mesoporous carbon FDU-15 viewed along [110] (a) and [001] (b) directions.
confirming the ordered hexagonal p6m mesostructure. The nitrogen sorption isotherm of calcined FDU-15 (Fig. 3) shows a representative type-IV curve with clear condensation step. It can be calculated from the adsorption branches that calcined FDU-15 at 800qC has a pore size of 3.8 nm, a BET surface area of ~ 1040 m2/g and a pore volume of ~ 0.55 cm3/g. The C:H:O element analysis indicates that calcined FDU-15 has a carbon framework with C content above 90 wt%. Hexadecane plays an important role in the formation of FDU-15. Without using hexadecane, only sample of mixed phases of hexagonal p6m and bicontinuous cubic Ia3d can be obtained. To get a better understanding of the roles played by the hydrocarbon in this case. Mesoporous carbon materials were synthesized without or by adding hydrocarbons with different carbon chain length, such as hexadecane, decane, heptane, and 1, 3, 5-trimethylbenzene (TMB) as swelling agents and the obtained samples were denoted as S-P, S-C16, S-C10, S-C7, S-TMB, respectively. All the samples were calcined at 350oC in N2 to remove the templates and generate porous structure. The XRD patterns of samples S-P, S-C16, and S-C10 (Fig. 5A) show a strong diffraction peak at 2T around 1q, indicating ordered mesostructure. The three resolved diffraction peaks of sample S-C10 can be assigned to the 10, 20 and 21 reflections of an ordered hexagonal p6m mesostructure, while the intensity of the diffraction peaks of sample S-C10 is much lower than those of sample S-C16, indicating a poorer structural regularity for the latter. The diffraction peak of sample S-P is relatively broader compared to that of sample S-C16. TEM measurements show that sample S-P is a mixed phase of hexagonal p6m and cubic Ia3d. XRD patterns of samples S-C7 and S-TMB show no diffraction, indicating disordered mesostructures. The nitrogen sorption isotherms (Fig. 5B) of samples S-P, S-C16 and S-C10 show very sharp condensation steps, while those of samples S-C7 and S-TMB are much wider, suggesting a very broad pore size distribution. The result It consists well with their XRD patterns. The relative pressure range of the condensation steps, which associated with the pore diameter, of the five samples is in the following sequence: S-C7, S-TMB > S-C10 > S-C16 > S-P. It can be easily concluded that hydrocarbons with smaller chain length may have better swelling ability in this synthetic system, and this consists well with a previous report about the swelling ability of hydrocarbon molecules in pure surfactant solution [12]. Although TMB and heptane have better swelling ability, the obtained mesoporous carbon materials show lower pore volume. This phenomenon
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Fig. 5. (A) XRD patterns of samples S-P, S-C16, S-C10, S-TMB and S-C7. The patterns are offset along y-axis for clarity; (B) The nitrogen sorption isotherms of samples S-P, S-C16, S-C10, S-TMB and S-C7. For clarity, the isotherm of sample S-C10 is offset along y-axis with 50 cm3/g.
may be a result of the extremely serious shrinkage caused during the calcinations process. It can be concluded that hexadecane and decane can swell the surfactant micelles and induce the formation of ordered mesoporous carbon FDU-15 with 2-D hexagonal structure; while the hydrocarbons of shorter chain length may swell the micelles in such a large degree that only disordered structure are obtained. Moreover, the pore size of obtained mesoporous carbon FDU-15 can be tailored from 4.1 to 6.8 nm. 5. CONCLUSION We have demonstrated a facile aqueous route to synthesize mesoporous carbons with 2-D hexagonal (FDU-15, p6m) or cubic (FDU-16, Im3 m) structures. The pore size of FDU-15 can be tuned from 4.1 to 6.8 nm simply by adding hydrocarbons with different chain length (hexadecane or decane) as swelling agents. Hydrocarbon of shorter chain length may have better swelling ability and result in larger pore size. The structure diversity of the obtained materials may provide very great potential application fields to such materials. ACKNOWLEDGMENT This work was supported by the NSF of China (Grants 20421303, 20373013, and 20521140450), the State Key Basic Research Program of the PRC (2006CB202502), the Shanghai Science & Technology Committee(Grants 06DJ14006, 055207078, 05DZ22313, 04JC14087), Shanghai Nanotech Promotion Center (0652nm024), Shanghai Education Committee (02SG01), the Program for New Century Excellent Talents in University (Grant NCET-04-03), the LG Co., the Shanghai HuaYi Chemical Group, and Fudan Graduate
1862 Innovation Funds. We greatly thank Dr. Y. Chen, Dr. S. H. Xie, and Dr. L. J. Zhang for experimental and characterization assistance. REFERENCES [1] [2]
R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc. 122 (2000) 10712. [3] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature 412 (2001) 169. [4] C. D. Liang, K. L. Hong, G. A. Guiochon, J. W. Mays and S. Dai, Angew. Chem., Int. Ed. 43 (2004) 5785. [5] S. Tanaka, N. Nishiyama, Y. Egashira and K. Ueyama, Chem. Commun. (2005) 2125. [6] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, H. F.Yang, Z. Li, C. Z. Yu, B. Tu and D. Y. Zhao, Angew. Chem., Int. Ed. 44 (2005) 7053. [7] C. D. Liang and S. Dai, J. Am. Chem. Soc. 128 (2006) 5316. [8] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, L. Cheng, D. Feng, Z. X. Wu, Z. X. Chen, Y. Wan, A. Stein and D. Y. Zhao, Chem. Mater. 18 (2006) 4447. [9] F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, C. Z. Yu, B. Tu and D. Y. Zhao, J. Am. Chem. Soc. 127 (2005) 13508. [10] F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, Z. X. Chen, B. Tu and D. Y. Zhao, Chem. Mater. 18 (2006) 5279. [11] M. Kruk, M. Jaroniec and A. Sayari, Langmuir 13 (1997) 6267. [12] M. J. Schwuger, Kolloid –ZZ Polym. 240 (1970) 872.