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Microwave assisted-direct synthesis of highly ordered large pore functionalized mesoporous SBA
Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.
511 511
Microwave assisted-direct synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park* Lab. ofNano-Green Catalysis, Nano Center for Fine Chemicals Fusion Technology, Dep't of Chemistry, Inha University, Incheon 402-751, Korea
Microwave sysnthesis has been successfully applied for the direct synthesis of organo-functionalized SBA-15 and 16 mesoporous materials through the cocondensations of organosilanes with sodium metasilicate in the presence of triblock copolymers as structure directing agents. The obtained materials have large pores, long range order of cubic and hexagonal mesostructures, and the loading of organo groups up to 10% of the silica frameworks. 1. Introduction Recently, microwave sysnthesis has been applied to the rapid and economical synthesis route of various nanoporous materials which normally required several days to prepare under traditional hydrothermal conditions. The microwave synthesis also offers potential advantages over hydrothermal synthesis, such as rapid and homogeneous heating throughout the reaction vessel, homogeneous nucleation and rapid crystallization, phase selectivity, and facile particle size and morphological control, etc. This method has been successfully applied to the synthesis of various kind of nanoporous materials, namely zeolite A, Y, Beta, ZMS-5, MCM-41, SBA-15, and SBA-16 [1-5]. Recently, Kormaneni and co-worker have applied microwave synthesis method in the direct synthesis of transition metal substituted SBA-15 under acidic condition.6"7 It rapid heating and fast supersaturation were believed to facilitate the co-condensation processes during the synthesis [6]. However, to the best of our knowledge, there has been no report on the microwave synthesis of organofunctionalized SBA-15 and 16 through the co-condensation of organosilanes and silica source. The organo-functionalization has been known to play important role in expanding the applications of mesoporous silica in catalysis, separation, and sensor design [8]. Herein, we report the synthesis of large pore
512
organo-functionalized SBA-15 and 16 mesoporous silica through cocondensation reactions between organosilanes and sodium metalicate in the acidic condition under microwave irradiation. 2. Experimental Section The organo-functionalized SBA-15 and 16 mesoporous materials were synthesized according to the same procedure by co-condensations of organosilanes (chloropropyltriethoxysilane/CPTES, cyanopropyltriethoxysilane/ CNPTES, propylanilinetriethoxysilane/PATES, and aminopropyltriethoxysilane/APTES) with a sodium metasilicate in the presence of a triblock copolymer as a structure directing agent under microwave irradiation. Preparation of chloropropyl-functionalized SBA-15 is given as an example. In a typical synthesis, 16 g of 10% (w/w) aqueous solution of PI23 was poured into 26.6 g distilled water and then 0.016-(0.016 x x%) mole of sodium metasilicate was added to the solutions. To the vigorously stirred solutions, 13 g of concentrated hydrochloric acid (37.6%) was quickly added followed by 0.016 x x% mole ofCPTES (x = 5, 7.5, and 10). The final gel mixtures were stirred for 1 hour at 313 K before subjected to the microwave digestion system (CEM Corporation, MARS-5) of which condition was set at 373 K for 2 h at operated power of 300 W (100%). The crystallized products were filtered, washed with warm distilled water and finally dried at 333 K. The surfactant was then selectively removed by Soxhlet extraction over ethano} for 24 h. For the synthesis of the organo-functionalized SBA-16, a triblock copolymer F127 was used as the structure directing agent. 3. Results and Discussion Surfactant-free SBA-15 and SBA-16 functionalized with different organic functional groups prepared by the microwave assisted-direct synthesis showed XRD patterns (not shown) with a very intense diffraction peak in the range of 0.8-1.0° 20 and two or more additional peaks at higher degree within 1.2-2.0° 20. The XRD patterns indicated the long range ordered and excellent textural uniformity of the organo-functionalized SBA-15 and SBA-16 mesoporous materials with hexagonal and cubic mesostructures obtained from triblock copolymers as structure-directing agents [9]. The N2 adsorption and desorption isotherms (not shown) of all the surfactant-free samples showed the defined type IV behavior with hysteresis loops, which are characteristic for mesoporous materials with narrow distribution of pore size that facilitate the condensation of N2 [9]. Table 1. provides the textural properties of the organo-functionalized mesoporous materials synthesized from the microwave assisted-direct synthesis. These results show that well ordered mesoporous materials could be synthesized at organo functionalization levels corresponding to x values of at
513
(f) (f)
Intensity (a.u.)
(e)
(d)
(c) (b)
(a) 1
2
3
2 theta (degree) (degree)
Fig. 1. XRD patterns of Clpr-SBA-16: (a)x=10, (b)*=7.5, (c)*=5 andClprSBA-15: (d)x=10, (e)jt=7.5, (f)*=5
4
least 10% organic group to silica molar ratio regardless the nature of the organosilanes added into the synthesis gel. In all cases the mean pore sizes were large than 5 nm for SBA-15 and 3 nm for SBA-16, respectively. In general, the pore sizes were not affected by the amounts of organosilanes added to the synthesis gels. The successful functionalizations were proven by near infrared and mid infrared spectra which showed the vibration bands for the organic moieties. Addition of different amounts of CPTES into the initial gel mixtures during the synthesis seems to give effect to the mesostructure of the SBA15 materials. At CPTES to silica molar ratio = 5 and 7.5%, the XRD patterns (Fig. le and If) could be indexed as a hexagonal mesostructure of SBA-15 mesoporous materials, respectively.
However, at molar ratio = 10%, the XRD pattern showed the characteristic for mesoporous material with cubic structure of laid symmetry.10 The mesophase transformation due to the presence of CPTES during the synthesis were clearly shown by the TEM image (Fig. 3d). The XRD patterns of Clpr-SBA-16 synthesized from the co-condensation of CPTES and sodium metasilicate in the presence of F127 surfactant were characteristic for the expected SBA-16 mesoporous material with Im3m symmetry, with very intense main diffraction peaks of 110 plane and additional diffraction peaks at higher 20 of 200, 211, and 220 planes. Further evidences were provided scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images (Fig. 3a and 3b). The SEM and TEM images showed the typical dodecahedron morphology and cage-type Im3m cubic structure of SBA-16, respectively.4 (a)
(b)
(c)
(d)
50 nm
Fig. 2. SEM and TEM images of Clpr-SBA-16 and Clpr-SBA-15. (a) and (b) SEM and TEM images of Clpr-SBA-16 (x = 10); (c) and (d) SEM and TEM images of Clpr-SBA-15 (* = 10).
514 Table 1. Textural properties of organo-functionalized SBA-15 and 16 Resulted material P123 5 Clpr-SBA-15 CPTES P123 7.5 Clpr-SBA-15 CPTES P123 10 CPTES Clpr-SBA-15 F127 5 CPTES Clpr-SBA-16 F127 7.5 CPTES Clpr-SBA-16 F127 10 CPTES Clpr-SBA-16 P123 5 CNpr-SBA-15 CNPTES P123 10 CNPTES CNpr-SBA-15 PATES P123 5 ANpr-SBA-15 PATES P123 10 ANpr-SBA-15 APTES P123 5 NH2pr-SBA-15 P123 7.5 APTES NH2pr-SBA-15 P123 10 NH2pr-SBA-15 APTES *Calculated from desorption branch of the full isotherm Organosilane
SDA
X
Framework d/nm structure Hexagonal/P6m/« 8.9 Hexagonal//'(5/n/n 9.7 Cvtb\dla3d 8.7 Cub\c/Im3m 10.4 Cubic/Im3m 10.0 Cubic/Im3m 9.7 HexsLgonai/P6mm 8.8 Hexagona\/P6mm 8.5 Hexagonal/P6mm 10.2 Hexagonal/.P<5/?im 10.2 Hexagonal/P6/nm 9.9 Hexagonal/.P6mm 9.8 Hexagonal/P6mm 11.2 by using a BJH method.
Pore size/nm* 5.1 5.0 4.3 3.3 3.4 3.2 7.7 7.2 7.9 7.1 7.1 7.7 7.8
4. Conclusion Microwave assisted-direct synthesis has been used to synthesize organofunctionalized SBA-15 and 16 with highly ordered mesostructures, large pore size and high loading of organic group. It was proven to be an effective and convenient method for the organic functionalization on mesoporous silica. 5. Acknowledgement This work was supported by Brain Korea 21 (BK21) Program. 6. References [1] S. A. Galema, Chem. Soc. Rev. 26 (1997) 233. [2] C. S. Cundy, Collect. Czech. Chem. Commun. 63 (1998) 1699. [3] S-E. Park, J.-S. Chang, Y. K. Hwang, D. S. Kim, S. H. Jhung and J. S. Hwang, Catal. Surv. Asia 8 (2004) 91. [4] Y. K. Hwang, J.-S. Chang, Y.-U. Kwon and S.-E. Park, Micro. Meso. Mater. 68 (2004) 21. [5] Y. K. Hwang, J.-S Chang, S.-E. Park, D. S. Kim, Y.-U. Kwon, S. H. Jhung, J.-S. Hwang and M. S. Park, Angew. Chem. Int. Ed. 44 (2005) 556. [6] B. L. Newalkar, J. Olanrewaju and S. Komarneni, Chem. Mater. 13 (2001) 552. [7] B. L. Newalkar, J. Olanrewaju and S. Komarneni, J. Phys. Chem. B 105 ( 2001) 8356. [8] R. J. P. Corriu, A. Mehdi and C. Reye", J. Mater. Chem. 15 (2005) 4285. [9] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [10] T.-W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601.
511 511
Microwave assisted-direct synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park* Lab. ofNano-Green Catalysis, Nano Center for Fine Chemicals Fusion Technology, Dep't of Chemistry, Inha University, Incheon 402-751, Korea
Microwave sysnthesis has been successfully applied for the direct synthesis of organo-functionalized SBA-15 and 16 mesoporous materials through the cocondensations of organosilanes with sodium metasilicate in the presence of triblock copolymers as structure directing agents. The obtained materials have large pores, long range order of cubic and hexagonal mesostructures, and the loading of organo groups up to 10% of the silica frameworks. 1. Introduction Recently, microwave sysnthesis has been applied to the rapid and economical synthesis route of various nanoporous materials which normally required several days to prepare under traditional hydrothermal conditions. The microwave synthesis also offers potential advantages over hydrothermal synthesis, such as rapid and homogeneous heating throughout the reaction vessel, homogeneous nucleation and rapid crystallization, phase selectivity, and facile particle size and morphological control, etc. This method has been successfully applied to the synthesis of various kind of nanoporous materials, namely zeolite A, Y, Beta, ZMS-5, MCM-41, SBA-15, and SBA-16 [1-5]. Recently, Kormaneni and co-worker have applied microwave synthesis method in the direct synthesis of transition metal substituted SBA-15 under acidic condition.6"7 It rapid heating and fast supersaturation were believed to facilitate the co-condensation processes during the synthesis [6]. However, to the best of our knowledge, there has been no report on the microwave synthesis of organofunctionalized SBA-15 and 16 through the co-condensation of organosilanes and silica source. The organo-functionalization has been known to play important role in expanding the applications of mesoporous silica in catalysis, separation, and sensor design [8]. Herein, we report the synthesis of large pore
512
organo-functionalized SBA-15 and 16 mesoporous silica through cocondensation reactions between organosilanes and sodium metalicate in the acidic condition under microwave irradiation. 2. Experimental Section The organo-functionalized SBA-15 and 16 mesoporous materials were synthesized according to the same procedure by co-condensations of organosilanes (chloropropyltriethoxysilane/CPTES, cyanopropyltriethoxysilane/ CNPTES, propylanilinetriethoxysilane/PATES, and aminopropyltriethoxysilane/APTES) with a sodium metasilicate in the presence of a triblock copolymer as a structure directing agent under microwave irradiation. Preparation of chloropropyl-functionalized SBA-15 is given as an example. In a typical synthesis, 16 g of 10% (w/w) aqueous solution of PI23 was poured into 26.6 g distilled water and then 0.016-(0.016 x x%) mole of sodium metasilicate was added to the solutions. To the vigorously stirred solutions, 13 g of concentrated hydrochloric acid (37.6%) was quickly added followed by 0.016 x x% mole ofCPTES (x = 5, 7.5, and 10). The final gel mixtures were stirred for 1 hour at 313 K before subjected to the microwave digestion system (CEM Corporation, MARS-5) of which condition was set at 373 K for 2 h at operated power of 300 W (100%). The crystallized products were filtered, washed with warm distilled water and finally dried at 333 K. The surfactant was then selectively removed by Soxhlet extraction over ethano} for 24 h. For the synthesis of the organo-functionalized SBA-16, a triblock copolymer F127 was used as the structure directing agent. 3. Results and Discussion Surfactant-free SBA-15 and SBA-16 functionalized with different organic functional groups prepared by the microwave assisted-direct synthesis showed XRD patterns (not shown) with a very intense diffraction peak in the range of 0.8-1.0° 20 and two or more additional peaks at higher degree within 1.2-2.0° 20. The XRD patterns indicated the long range ordered and excellent textural uniformity of the organo-functionalized SBA-15 and SBA-16 mesoporous materials with hexagonal and cubic mesostructures obtained from triblock copolymers as structure-directing agents [9]. The N2 adsorption and desorption isotherms (not shown) of all the surfactant-free samples showed the defined type IV behavior with hysteresis loops, which are characteristic for mesoporous materials with narrow distribution of pore size that facilitate the condensation of N2 [9]. Table 1. provides the textural properties of the organo-functionalized mesoporous materials synthesized from the microwave assisted-direct synthesis. These results show that well ordered mesoporous materials could be synthesized at organo functionalization levels corresponding to x values of at
513
(f) (f)
Intensity (a.u.)
(e)
(d)
(c) (b)
(a) 1
2
3
2 theta (degree) (degree)
Fig. 1. XRD patterns of Clpr-SBA-16: (a)x=10, (b)*=7.5, (c)*=5 andClprSBA-15: (d)x=10, (e)jt=7.5, (f)*=5
4
least 10% organic group to silica molar ratio regardless the nature of the organosilanes added into the synthesis gel. In all cases the mean pore sizes were large than 5 nm for SBA-15 and 3 nm for SBA-16, respectively. In general, the pore sizes were not affected by the amounts of organosilanes added to the synthesis gels. The successful functionalizations were proven by near infrared and mid infrared spectra which showed the vibration bands for the organic moieties. Addition of different amounts of CPTES into the initial gel mixtures during the synthesis seems to give effect to the mesostructure of the SBA15 materials. At CPTES to silica molar ratio = 5 and 7.5%, the XRD patterns (Fig. le and If) could be indexed as a hexagonal mesostructure of SBA-15 mesoporous materials, respectively.
However, at molar ratio = 10%, the XRD pattern showed the characteristic for mesoporous material with cubic structure of laid symmetry.10 The mesophase transformation due to the presence of CPTES during the synthesis were clearly shown by the TEM image (Fig. 3d). The XRD patterns of Clpr-SBA-16 synthesized from the co-condensation of CPTES and sodium metasilicate in the presence of F127 surfactant were characteristic for the expected SBA-16 mesoporous material with Im3m symmetry, with very intense main diffraction peaks of 110 plane and additional diffraction peaks at higher 20 of 200, 211, and 220 planes. Further evidences were provided scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images (Fig. 3a and 3b). The SEM and TEM images showed the typical dodecahedron morphology and cage-type Im3m cubic structure of SBA-16, respectively.4 (a)
(b)
(c)
(d)
50 nm
Fig. 2. SEM and TEM images of Clpr-SBA-16 and Clpr-SBA-15. (a) and (b) SEM and TEM images of Clpr-SBA-16 (x = 10); (c) and (d) SEM and TEM images of Clpr-SBA-15 (* = 10).
514 Table 1. Textural properties of organo-functionalized SBA-15 and 16 Resulted material P123 5 Clpr-SBA-15 CPTES P123 7.5 Clpr-SBA-15 CPTES P123 10 CPTES Clpr-SBA-15 F127 5 CPTES Clpr-SBA-16 F127 7.5 CPTES Clpr-SBA-16 F127 10 CPTES Clpr-SBA-16 P123 5 CNpr-SBA-15 CNPTES P123 10 CNPTES CNpr-SBA-15 PATES P123 5 ANpr-SBA-15 PATES P123 10 ANpr-SBA-15 APTES P123 5 NH2pr-SBA-15 P123 7.5 APTES NH2pr-SBA-15 P123 10 NH2pr-SBA-15 APTES *Calculated from desorption branch of the full isotherm Organosilane
SDA
X
Framework d/nm structure Hexagonal/P6m/« 8.9 Hexagonal//'(5/n/n 9.7 Cvtb\dla3d 8.7 Cub\c/Im3m 10.4 Cubic/Im3m 10.0 Cubic/Im3m 9.7 HexsLgonai/P6mm 8.8 Hexagona\/P6mm 8.5 Hexagonal/P6mm 10.2 Hexagonal/.P<5/?im 10.2 Hexagonal/P6/nm 9.9 Hexagonal/.P6mm 9.8 Hexagonal/P6mm 11.2 by using a BJH method.
Pore size/nm* 5.1 5.0 4.3 3.3 3.4 3.2 7.7 7.2 7.9 7.1 7.1 7.7 7.8
4. Conclusion Microwave assisted-direct synthesis has been used to synthesize organofunctionalized SBA-15 and 16 with highly ordered mesostructures, large pore size and high loading of organic group. It was proven to be an effective and convenient method for the organic functionalization on mesoporous silica. 5. Acknowledgement This work was supported by Brain Korea 21 (BK21) Program. 6. References [1] S. A. Galema, Chem. Soc. Rev. 26 (1997) 233. [2] C. S. Cundy, Collect. Czech. Chem. Commun. 63 (1998) 1699. [3] S-E. Park, J.-S. Chang, Y. K. Hwang, D. S. Kim, S. H. Jhung and J. S. Hwang, Catal. Surv. Asia 8 (2004) 91. [4] Y. K. Hwang, J.-S. Chang, Y.-U. Kwon and S.-E. Park, Micro. Meso. Mater. 68 (2004) 21. [5] Y. K. Hwang, J.-S Chang, S.-E. Park, D. S. Kim, Y.-U. Kwon, S. H. Jhung, J.-S. Hwang and M. S. Park, Angew. Chem. Int. Ed. 44 (2005) 556. [6] B. L. Newalkar, J. Olanrewaju and S. Komarneni, Chem. Mater. 13 (2001) 552. [7] B. L. Newalkar, J. Olanrewaju and S. Komarneni, J. Phys. Chem. B 105 ( 2001) 8356. [8] R. J. P. Corriu, A. Mehdi and C. Reye", J. Mater. Chem. 15 (2005) 4285. [9] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [10] T.-W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601.