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Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template
Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.
385 385
Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsua, Hong-Ping Lina*, Chih-Yuan Tangb and Ching-Yen Linb "Department of Chemistry, National Cheng Kung University, Tainan, Taiwan, 701. b Department of Zoology, National Taiwan University, Taipei, Taiwan 106
Mesoporous silica of high surface area, large pore size were readily prepared by using the bio-degradable gelatin as template and sodium silicate solution as silica source. Pore size of the mesoporous silica is dependent on the pH value of the hydrothermal solution. In addition, the gelatin-phenol formaldehyde polymer blend can also be used as the template to synthesize the mesoporous silica or mesoporous carbon via proper preparation processes. 1. Introduction Since the discovery of the quaternary ammonium surfactant-templated mesoporous silicas by Yanagisawa et al. and Mobile researcher [1], the surfactant-templating method has been extensively performed to prepare various mesoporous silicas with high surface area, tunable pore dimension, and desired morphology for the applications in catalysts, adsorbents, and nanotemplates [2-4]. In the typical synthetic composition, the cationic and neutral block-copolymer surfactants of amphiphilic property have widely used as the mesostructural template [1-4]. The pore size is, thus, mainly determined by the hydrophobic chain length of the surfactants. However, the hydrophobic parts of the surfactants decompose slowly in the environment under ambient condition [5]. With recently increasing concern on the aquatic toxicity from the surfactants, using natural-friendly reagents to prepare the mesoporous silica is much desirable. According to the silica chemistry [6], the gelatin of watersoluble natural protein, which possess lots of amino (-NH2) functional groups can have a high affinity to strongly interact with silanol groups (Si-OH) on the silicate species via multiple hydrogen bonds. Therefore, the gelatin could be regarded as an alternative template to synthesize the porous silicas.
386 386
2. Experimental Section Typical synthetic procedure for the porous silicas using gelatin is as following: 1.0 g of gelatin was dissolved in 25.0 g of water to form a clear solution. To prepare a silicate stock solution, a mixture of 4.0 g of sodium silicate (SiO2: 27 wt.%, NaOH: 14 wt.%, Aldrich) and a 25.0 g of water was added into a 25.0 ml 0.1 M H2SO4, and then the pH value was adjusted to about 5.0 at 40°C. Then, the gelatin solution was poured directly into the silicate stock solution under stirring and light-yellow precipitate was generated within seconds. After stirring for 30 min, the pH value of the gel solution was adjusted to 6.0-3.0. Fin ally, the gel solution was transferred into an autoclave, and hydrothermally treated at 100°C for 1 d. Filtration, washing, drying and calcination at 550°C gave the mesoporous silica. Silica recovery is about 95%. To synthesize the mesoporous carbon, 1.0 g of gelatin and 1.0 g of phenol formaldehyde (denoted as PF) polymer was dissolved in 5.0 g ethanol, then that solution was added into 25.0 g of water. Combining with the silicate stock solution, a PF-gelatin-silica composite was generated. After drying at 100°C, pyrolysis at 1000°C and silica removal by 6.0 wt.% HF, the mesoporous carbon was obtained. To prepare the mesoporous silica, the gelatin-PF-silica composite was hydrothermally treated at 100°C for 1 d and calcined at 550°C [7]. 3. Results and Discussion Figure 1A shows the TGA curves of the gelatin-silica composite before and after hydrothermal reaction. The high gelatin content (~ 40 wt.%) in the composite is due to that the gelatin with lots of amine groups (-NH2) can bind strongly with the silicate species through multiple hydrogen-bonds at pH « 5.0. After hydrothermal treatment, the gelatin content decrease to ~20 wt.%. This decrease indicates that some gelatins leave form the gelatin-silica composite during hydrothermal reaction. Analyzing the N2 adsorption-desorption isotherms of the calcined silicas before and after hydrothermal treatment (Figure IB), one can clearly see that the microporous silica with a type I isotherm was obtained before hydrothermal treatment, and a mesoporous silica with a type IV isotherm was prepared after hydrothermal treatment. The mesoporous silica has an apparent capillary condensation at P/Po around 0.85, and the average pore size calculated by BJH method is about 12.5 nm. It is reasonable to suppose that the pore size expansion results from further silica condensation and gelatin's leaving during hydrothermal reaction. To identify the mesostructure, the TEM image of the mesoporous silica reveals the disordered mesostructure and the pore size is about 10.0 nm (Figure 1C). When pH value of the hydrothermal solution was decreased, the pore size of the mesoporous silica decreases (Figure ID). Combining with a simple hydrothermal treatment, the mesoporous silica of tunable pore size and large
387
105
Weight loss / %
95
After hydrothermal treatment Before hydrothermal treatment
A
3 -1
100
Volume adsorbed/cm g , STP
surface area (>300 m2g"') can be synthesized with the nature-friendly gelatin and cheap sodium silicate.
90 85 80 75 70 65 60 55
700
After hydrotheraml treatment before hydrothermal treatment
hydrotheraml treatment B —— t• —— After before hydrothermal treatment
600 500 400 300 200 100 0
100
200
300
400 0
500
600
0.0
0.2
0.4
Temperature /C Temperature/°C
P/P0
0.6
0.8
D
800
— . — ppH=6.0 H=6.0 —»— pH=5.0 pH=3.0 — • —pH=3.0
700
1.0
.
dV/dD
3 -1
C
Volume adsorbed/cm g , STP
900
1
600 500 400
5
10 20 25 30 10 15 I&tffi-Hs 30
Pore Diameter(nm)
300
/
/
/
/
200 100 0 0.0
0.2
0.4 4 O
0.6
- P/P P / P0 0 - 6
0.8
1.0
Figure 1. A. The TGA curves of the gelatin-silica before and after hydrothermal treatment at 100°C. B. N2 adsorption-desorption isotherms of the calcined porous silicas. C. TEM image of the calcined mesoporous silica after hydrothermal treatment. D. N2 adsorption-desorption isotherms of the calcined mesoporous silicas hydrothermally treated in solutions of different pH values. The inset is the pore size distributions calculated by BJH method.
Owing to the gelatin is one kind of natural polymers, it thus can blend with other polymers through proper intermolecular interactions. It is well known that the thermal-setting PF polymer, a carbon source widely used in industry, has many -CH2OH and phenol groups. Therefore, the gelatin and PF polymer can form a homogenous blend through multiple hydrogen-bonding interaction. When combinding the gelatin-PF polymer blend with the silicate solution at pH « 5.0, a PF-gelatin-silica composite was readily synthesized. Because the PFgelatin-silica composite contains the carbonizable PF polymer, the mesoporous carbon was obtained from pyrolysis under N2 atmosphere and silica removal. The TEM image of the resulting mesoporous carbon reveals the disordered mesostructure and the meso-voids («few nanometers, Figure 2A). In parallel, the mesoporous carbon exhibits a type-IV N2 adsorption-desorption isotherm (Figure 2B). Analyzing the adsorption isotherm, the BET surface area is about 1200 m2g"] and pore size is around 2.5 nm. The mesoporous carbon shows the apparent vibrational band around 1580 cm"1 (G-band, interplane sp2 C-C stretching) in the Raman spectrum that reflects a high graphitized degree.
388
Alternatively, the mesoporous silica can be obtained from hydrothermal treatment and calcination of the PF-gelatin-silica composite (Figure 2C). 800
A
Volume adsorbed/cm g , STP
700
B
C
3 -1
600 500
dP/dD
400 D-band
200 100
2
3
4
5
6
7
G-band
Intensity (a.u.)
300
8
Pore Diameter/nm
0 0.00
0.2
0.4
0.6
P/P 0
0.8
1.0 1.0
50 50 nm nm
1200
1300
1400
1500
1600 -1
Wavelength/cm
1700
1800
100 nm
Figure 2. (A). N2 adsorption-desorption isotherms of the mesoporous carbon prepared with a template of the PF—gelatin blend. The inset exhibits the pore size distribution analyzed by BJH method. (B). TEM image of the mesoporous carbon. The inset shows the Raman spectrum. (C). TEM image of the mesoporous silica templated by the PF-gelatin blend.
4. Conclusion In conclusion, we performed the environment-friendly gelatin and gelatin-PF polymer blend as new templates to prepare the mesoporous silicas and mesoporous carbons with high surface areas and tunable pore size. With the textural properties of the porous silica and carbons can be feasibly controlled, potential applications in catalyst, absorption for large molecules, solar absorber, hard-template for metal oxides and electrode materials can be further explored. 5. References [1] (a). T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 63, (1990) 988. (b). C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S. Beck, Nature, 359,(1992)710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [3] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 57. [4] L. Pei, K. Kurumada, M. Tanigaki,; M. Hiro and K. Susa, J. Coll. Int. Sci., 284 (2005) 222. [5] K. Holmberg, B. Jonsson, B. Kronberg and B. Lindman, "Surfactant and Polymers in Aqueous Solution" 2nd ed, England, John Wiley & Sons (2003). [6] R. K. Her, "The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry," Wiley, New York (1979). [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin, and C. Y. Tang, Chem. Lett., 33 (2004) 1574. (b) H. P. Lin, C. Y. Chang-Chien, C. Y. Tang and C. Y. Lin, Microporous and Mesoporous Mater., 93 (2006) 344.
385 385
Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsua, Hong-Ping Lina*, Chih-Yuan Tangb and Ching-Yen Linb "Department of Chemistry, National Cheng Kung University, Tainan, Taiwan, 701. b Department of Zoology, National Taiwan University, Taipei, Taiwan 106
Mesoporous silica of high surface area, large pore size were readily prepared by using the bio-degradable gelatin as template and sodium silicate solution as silica source. Pore size of the mesoporous silica is dependent on the pH value of the hydrothermal solution. In addition, the gelatin-phenol formaldehyde polymer blend can also be used as the template to synthesize the mesoporous silica or mesoporous carbon via proper preparation processes. 1. Introduction Since the discovery of the quaternary ammonium surfactant-templated mesoporous silicas by Yanagisawa et al. and Mobile researcher [1], the surfactant-templating method has been extensively performed to prepare various mesoporous silicas with high surface area, tunable pore dimension, and desired morphology for the applications in catalysts, adsorbents, and nanotemplates [2-4]. In the typical synthetic composition, the cationic and neutral block-copolymer surfactants of amphiphilic property have widely used as the mesostructural template [1-4]. The pore size is, thus, mainly determined by the hydrophobic chain length of the surfactants. However, the hydrophobic parts of the surfactants decompose slowly in the environment under ambient condition [5]. With recently increasing concern on the aquatic toxicity from the surfactants, using natural-friendly reagents to prepare the mesoporous silica is much desirable. According to the silica chemistry [6], the gelatin of watersoluble natural protein, which possess lots of amino (-NH2) functional groups can have a high affinity to strongly interact with silanol groups (Si-OH) on the silicate species via multiple hydrogen bonds. Therefore, the gelatin could be regarded as an alternative template to synthesize the porous silicas.
386 386
2. Experimental Section Typical synthetic procedure for the porous silicas using gelatin is as following: 1.0 g of gelatin was dissolved in 25.0 g of water to form a clear solution. To prepare a silicate stock solution, a mixture of 4.0 g of sodium silicate (SiO2: 27 wt.%, NaOH: 14 wt.%, Aldrich) and a 25.0 g of water was added into a 25.0 ml 0.1 M H2SO4, and then the pH value was adjusted to about 5.0 at 40°C. Then, the gelatin solution was poured directly into the silicate stock solution under stirring and light-yellow precipitate was generated within seconds. After stirring for 30 min, the pH value of the gel solution was adjusted to 6.0-3.0. Fin ally, the gel solution was transferred into an autoclave, and hydrothermally treated at 100°C for 1 d. Filtration, washing, drying and calcination at 550°C gave the mesoporous silica. Silica recovery is about 95%. To synthesize the mesoporous carbon, 1.0 g of gelatin and 1.0 g of phenol formaldehyde (denoted as PF) polymer was dissolved in 5.0 g ethanol, then that solution was added into 25.0 g of water. Combining with the silicate stock solution, a PF-gelatin-silica composite was generated. After drying at 100°C, pyrolysis at 1000°C and silica removal by 6.0 wt.% HF, the mesoporous carbon was obtained. To prepare the mesoporous silica, the gelatin-PF-silica composite was hydrothermally treated at 100°C for 1 d and calcined at 550°C [7]. 3. Results and Discussion Figure 1A shows the TGA curves of the gelatin-silica composite before and after hydrothermal reaction. The high gelatin content (~ 40 wt.%) in the composite is due to that the gelatin with lots of amine groups (-NH2) can bind strongly with the silicate species through multiple hydrogen-bonds at pH « 5.0. After hydrothermal treatment, the gelatin content decrease to ~20 wt.%. This decrease indicates that some gelatins leave form the gelatin-silica composite during hydrothermal reaction. Analyzing the N2 adsorption-desorption isotherms of the calcined silicas before and after hydrothermal treatment (Figure IB), one can clearly see that the microporous silica with a type I isotherm was obtained before hydrothermal treatment, and a mesoporous silica with a type IV isotherm was prepared after hydrothermal treatment. The mesoporous silica has an apparent capillary condensation at P/Po around 0.85, and the average pore size calculated by BJH method is about 12.5 nm. It is reasonable to suppose that the pore size expansion results from further silica condensation and gelatin's leaving during hydrothermal reaction. To identify the mesostructure, the TEM image of the mesoporous silica reveals the disordered mesostructure and the pore size is about 10.0 nm (Figure 1C). When pH value of the hydrothermal solution was decreased, the pore size of the mesoporous silica decreases (Figure ID). Combining with a simple hydrothermal treatment, the mesoporous silica of tunable pore size and large
387
105
Weight loss / %
95
After hydrothermal treatment Before hydrothermal treatment
A
3 -1
100
Volume adsorbed/cm g , STP
surface area (>300 m2g"') can be synthesized with the nature-friendly gelatin and cheap sodium silicate.
90 85 80 75 70 65 60 55
700
After hydrotheraml treatment before hydrothermal treatment
hydrotheraml treatment B —— t• —— After before hydrothermal treatment
600 500 400 300 200 100 0
100
200
300
400 0
500
600
0.0
0.2
0.4
Temperature /C Temperature/°C
P/P0
0.6
0.8
D
800
— . — ppH=6.0 H=6.0 —»— pH=5.0 pH=3.0 — • —pH=3.0
700
1.0
.
dV/dD
3 -1
C
Volume adsorbed/cm g , STP
900
1
600 500 400
5
10 20 25 30 10 15 I&tffi-Hs 30
Pore Diameter(nm)
300
/
/
/
/
200 100 0 0.0
0.2
0.4 4 O
0.6
- P/P P / P0 0 - 6
0.8
1.0
Figure 1. A. The TGA curves of the gelatin-silica before and after hydrothermal treatment at 100°C. B. N2 adsorption-desorption isotherms of the calcined porous silicas. C. TEM image of the calcined mesoporous silica after hydrothermal treatment. D. N2 adsorption-desorption isotherms of the calcined mesoporous silicas hydrothermally treated in solutions of different pH values. The inset is the pore size distributions calculated by BJH method.
Owing to the gelatin is one kind of natural polymers, it thus can blend with other polymers through proper intermolecular interactions. It is well known that the thermal-setting PF polymer, a carbon source widely used in industry, has many -CH2OH and phenol groups. Therefore, the gelatin and PF polymer can form a homogenous blend through multiple hydrogen-bonding interaction. When combinding the gelatin-PF polymer blend with the silicate solution at pH « 5.0, a PF-gelatin-silica composite was readily synthesized. Because the PFgelatin-silica composite contains the carbonizable PF polymer, the mesoporous carbon was obtained from pyrolysis under N2 atmosphere and silica removal. The TEM image of the resulting mesoporous carbon reveals the disordered mesostructure and the meso-voids («few nanometers, Figure 2A). In parallel, the mesoporous carbon exhibits a type-IV N2 adsorption-desorption isotherm (Figure 2B). Analyzing the adsorption isotherm, the BET surface area is about 1200 m2g"] and pore size is around 2.5 nm. The mesoporous carbon shows the apparent vibrational band around 1580 cm"1 (G-band, interplane sp2 C-C stretching) in the Raman spectrum that reflects a high graphitized degree.
388
Alternatively, the mesoporous silica can be obtained from hydrothermal treatment and calcination of the PF-gelatin-silica composite (Figure 2C). 800
A
Volume adsorbed/cm g , STP
700
B
C
3 -1
600 500
dP/dD
400 D-band
200 100
2
3
4
5
6
7
G-band
Intensity (a.u.)
300
8
Pore Diameter/nm
0 0.00
0.2
0.4
0.6
P/P 0
0.8
1.0 1.0
50 50 nm nm
1200
1300
1400
1500
1600 -1
Wavelength/cm
1700
1800
100 nm
Figure 2. (A). N2 adsorption-desorption isotherms of the mesoporous carbon prepared with a template of the PF—gelatin blend. The inset exhibits the pore size distribution analyzed by BJH method. (B). TEM image of the mesoporous carbon. The inset shows the Raman spectrum. (C). TEM image of the mesoporous silica templated by the PF-gelatin blend.
4. Conclusion In conclusion, we performed the environment-friendly gelatin and gelatin-PF polymer blend as new templates to prepare the mesoporous silicas and mesoporous carbons with high surface areas and tunable pore size. With the textural properties of the porous silica and carbons can be feasibly controlled, potential applications in catalyst, absorption for large molecules, solar absorber, hard-template for metal oxides and electrode materials can be further explored. 5. References [1] (a). T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 63, (1990) 988. (b). C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S. Beck, Nature, 359,(1992)710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [3] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 57. [4] L. Pei, K. Kurumada, M. Tanigaki,; M. Hiro and K. Susa, J. Coll. Int. Sci., 284 (2005) 222. [5] K. Holmberg, B. Jonsson, B. Kronberg and B. Lindman, "Surfactant and Polymers in Aqueous Solution" 2nd ed, England, John Wiley & Sons (2003). [6] R. K. Her, "The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry," Wiley, New York (1979). [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin, and C. Y. Tang, Chem. Lett., 33 (2004) 1574. (b) H. P. Lin, C. Y. Chang-Chien, C. Y. Tang and C. Y. Lin, Microporous and Mesoporous Mater., 93 (2006) 344.