- Email: [email protected]
Rapid removal of organic template from SBA-15 with microwave assisted extraction
Materials Letters 63 (2009) 1693–1695
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Rapid removal of organic template from SBA-15 with microwave assisted extraction Teh-Long Lai a, Youn-Yuen Shu a,⁎, Ya-Chu Lin a, Wan-Ning Chen b, Chen-Bin Wang b,⁎ a b
Environmental Analysis Laboratory, Department of Chemistry, National Kaohsiung Normal University, Kaohsiung 802, Taiwan, ROC Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan, 33509, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 17 March 2009 Accepted 7 May 2009 Available online 14 May 2009 Keywords: Porosity Nanomaterials
a b s t r a c t The removal of surfactant templates from the pores of as-prepared SBA-15 was studied by means of microwave assisted extraction (MAE). Occluded surfactant molecules within SBA-15 were completely removed within 6 min by the MAE method, resulting in frameworks with higher surface area, lower structural shrinkage and richer silanol groups than that of thermocalcined samples. The MAE sample exhibited larger surface area (ca. 1000 m2·g− 1) than the sample treated by thermocalcining (ca. 560 m2·g− 1). As determined the enrichment of PAHs on MAE with calcined samples by on-line solid-phase extraction HPLC, the MAE sample possessed more enrichment and lower detection limit than the calcined sample. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Hexagonally ordered SBA-15 silica possesses high surface area, outstanding thermal stability, pore size adjustment, and tailored particle morphology [1]. The SBA-15 silica has already been applied in different fields of separation [2], catalysis [3], and advanced optical materials [4]. The most common methods used in removing the organic templates are calcination remove technique [5], extraction techniques [4–6] (by conventional solvent or by supercritical fluid), ozone treatment [7] and microwave methods [8,9] (by digestion and calcination). However, the adverse effects associated with the removal of the template mainly result from the rapid decomposition of the template because the temperature causes shrinkage of the structure [5]. The present work describes a novel procedure for removing the organic templates based on the advantages of microwave and extraction techniques. The advantages of extraction of the organic templates are without decomposition and permits reuse of solvents. Microwave technique is commonly used in numerous applications ranged from environmental technology [10–12] to foods [13]. To date, microwave techniques have been used to eliminate organic species from porous materials by acid digestion [8,9]. However, the most important requirements: (1) efficient removal of the template (2) shorter operation time (3) less organic solvent (4) ordered structure and specific framework, by any of the methods cannot be simultaneously achieved. In this preliminary study we report a new
⁎ Corresponding authors. Tel.: +886 3 389 1716; fax: +886 3 389 2494. E-mail addresses: [email protected] (Y.-Y. Shu), [email protected] (C.-B. Wang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.05.014
method to eliminate organic template by microwave assisted extraction (MAE), which shows many benefits over other methods such as lower structural shrinkage, larger surface areas and higher silanol group density. 2. Experimental The silica mesophase was prepared according to the synthesis outlined by Grieken [1]. The molar composition of the mixture for SBA-15 was 4 g of copolymer (P123) and 0.041 TEOS/0.24 HCl/6.67 H2O. The solid product (as-prepared) was recovered by filtration and air-dried at room temperature overnight. A small part of the asprepared sample was calcined in air at 550 °C for 6 h in order to compare with the sample that underwent the MAE procedure. In the MAE procedure, around 0.1 g of sample was placed on a watch glass with 20 ml ethanol/hexane (v/v, 1/1) as extract solvent, and heated for 2 min under a microwave irradiation (power: 100 W, frequency: 2450 MHz, repeat: 3 times) to remove the template. The chromatographic experiments were performed using HPLC Agilent 1100 Series equipped with diode array detector and a column oven. A 125 mm × 4 mm reverse-phase C-18 column (chrompack) was used for separation and pre-column was used for enrichment. The flow rate was 1.0 ml/min, UV detector wavelength was 230 nm and column oven temperature maintained 25 °C. 3. Results and discussion Fig. 1 shows the XRD diffraction patterns of the as-prepared, MAE and calcined SBA-15 materials. The results show that both pretreatment methods (MAE and thermocalcined) agree well with those reported for the mesoporous SBA-15 properties and structure. The 2θ position for the SBA-15 after MAE is lower than that of the calcined SBA-15, indicating a larger unit cell size for the MAE sample. In fact,
1694
T.-L. Lai et al. / Materials Letters 63 (2009) 1693–1695
Fig. 1. XRD patterns of as-prepared, MAE and calcined SBA-15 materials.
the 2θ position for the MAE sample is similar to the as-prepared sample, indicating that the shrinkage of structure does not occur during the removal of the surfactant template under MAE procedure. The narrower and intenser XRD diffraction pattern of the MAE sample may also indicate that the removal of the surfactant template possesses better crystallinity than the thermocalcined sample. Fig. 2 shows the IR absorbance spectra of the as-prepared, MAE and calcined SBA-15 materials. A broad band around 3430 cm− 1 appears for all samples, which is partially caused by the O–H stretching vibration mode of the adsorbed water molecules, whose bending vibration mode is responsible for the band recorded at 1630 cm− 1. Several absorption bands around 2865–3000 and 1375–1475 cm− 1 shown in as-prepared spectrum can be assigned to C–H stretching and bending vibrations of the template P123. After treatment (MAE and thermocalcined), the C–H vibration peaks are nearly indiscernible. This suggests the efficient removal of the surfactant template by MAE and thermocalcined methods. More importantly, the relative intensity of Si–OH bending bands around 956 cm− 1 is persistent for asprepared and MAE samples, but much weaker for the calcined sample. This demonstrates that the MAE procedure leads to the retention of a high level of silanol groups on the pore wall surface, while the thermocalcined method will unavoidably reduce their number. The number of silanol groups also can be indirectly proven by the thermogravimetry (TG) analysis. The TG (not shown) curve for the MAE sample shows more weight loss (7.8%) than the calcined sample (4.7%). The MAE sample seems to exhibit a higher Si–OH group density than the calcined sample. The nitrogen adsorption–desorption isotherms of SBA-15 materials at 77 K are shown in Fig. 3, which exhibits a typical IV shape for both
Fig. 2. IR spectra of as-prepared, MAE and calcined SBA-15 materials.
Fig. 3. N2 adsoption–desorption isotherms of (i) MAE sample: (●) adsorption, (○) desorption, and (ii) calcined sample: (■) adsorption, (□) desorption.
the MAE (circles) and calcined (squares) samples. The isotherms with clear H1-type hysteresis loops at high relative pressure (P/P0), indicating the presence of large pores and a narrow pore size
Fig. 4. TEM images of (a). MAE sample, (b) Calcined sample.
T.-L. Lai et al. / Materials Letters 63 (2009) 1693–1695
1695
MAE method can use the end-capping process to modify the SBA-15 surface and increase the separation efficiency for HPLC. 4. Conclusion Microwave assisted extraction is effective in extracting the surfactant template from the pores of as-prepared SBA-15. The MAE method leads to fast and complete removal of the template, which is reflected by larger surface area, lower structural shrinkage and the abundant silanol groups on the surface than the sample treated by thermocalcined. Acknowledgement Fig. 5. Enrichment of PAHs on MAE and calcined samples by on-line SPE HPLC: Naphthalene (1); Biphenyl (2); Phenanthrene (3); and Pyrene (4).
distributions. The BET surface area is 1064 m2·g− 1 for the MAE sample, which is higher than the calcined sample (ca. 567 m2·g− 1). Apparently, the MAE sample has a lower structural shrinkage and better structural quality than the thermocalcined sample. The transmission electron microscopy (TEM) image of MAE sample [Fig. 4(a)] shows well-ordered arrays of mesoporous in large domains. The morphology is wheat-like and is the same as that of typical asprepared SBA-15 and calcined SBA-15 [Fig. 4(b)]. These results further suggest that the MAE method does not induce the collapse of the structural order of the as-prepared sample. The MAE method has been considered as a potential alternative to traditional solid–liquid extraction. Some of its potential advantages over Soxhlet extraction are significant reduction of extraction time and solvent usage, improved extraction yield and provides agitation during extraction to improve the mass transfer phenomenon. In the application of SBA-15, the MAE and calcined samples was compared with on-line solid-phase extraction (SPE) in respect of sensitivity and selectivity for PAHs (Fig. 5). It shows the typical chromatograms obtained after enriching 0.5 mL/L PAHs. Apparently, the MAE sample has higher enrichment and a lower detection limit than the calcined sample. The abundant silanol groups obtained by
We are pleased to acknowledge the financial support for this study by the National Science Council of the Republic of China under contract numbers NSC 97-2811-M-017-001 and NSC 96-2113-M-606001-MY3. References [1] van Grieken Rafael, Calleja Guillermo, Stucky Galen D, Melero Juan A, García Rafael A, Iglesias Jose. Langmuir 2003;19:3966–73. [2] Doadrio AL, Sousa EMB, Doadrio JC, Pérez Pariente J, Izquierdo-Barba I, Vallet-Regi M. J Control Release 2004;97:125–32. [3] Korányi Tamás I, Vít Zdeněk, Poduval Dilip G, Ryoo Ryong, Kim Hei Seung, Hensen Emiel JM. J Catal 2008;253:119–31. [4] Scott Brian J, Wirnsberger Gernot, Stucky Galen D. Chem Mater 2001;13:3140–50. [5] Kleitz Freddy, Schmidt Wolfgang, Schüth Ferdi. Microporous Mesoporous Mater 2003;65:1–29. [6] Kawi Sibudjing, Lai MW. Chem Commun 1998;13:1407–8. [7] Keene Matthew TJ, Denoyel Renaud, Llewellyn Philip L. Chem Commun 1998;20:2203–4. [8] Tian Bozhi, Liu Xiaoying, Yu Chengzhong, Gao Feng, Luo Qian, Xie Songhai, et al. Chem Commun 2002;11:1186–7. [9] He Jing, Yang Xingbin, Evans DG, Duan Xue. Mater Chem Phys 2002;77:270–5. [10] Shu Youn Yuen, Lai Teh Long. J Chromatogr A 2001;927:131–41. [11] Shu Youn Yuen, Lai Teh Long, Lin Huann shyang, Yang Thomas C, Chang Chi-Peng. Chemosphere 2003;52:1667–78. [12] Lai Teh Long, Lee Chia Chan, Wu Kuen Shian, Shu Youn Yuen, Wang Chen Bin. Appl Catal B 2006;68:147–53. [13] Shu Youn Yuen, Ko Ming Yu, Chang Yuan Shiun. Microchem J 2003;74:131–9.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Rapid removal of organic template from SBA-15 with microwave assisted extraction Teh-Long Lai a, Youn-Yuen Shu a,⁎, Ya-Chu Lin a, Wan-Ning Chen b, Chen-Bin Wang b,⁎ a b
Environmental Analysis Laboratory, Department of Chemistry, National Kaohsiung Normal University, Kaohsiung 802, Taiwan, ROC Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan, 33509, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 17 March 2009 Accepted 7 May 2009 Available online 14 May 2009 Keywords: Porosity Nanomaterials
a b s t r a c t The removal of surfactant templates from the pores of as-prepared SBA-15 was studied by means of microwave assisted extraction (MAE). Occluded surfactant molecules within SBA-15 were completely removed within 6 min by the MAE method, resulting in frameworks with higher surface area, lower structural shrinkage and richer silanol groups than that of thermocalcined samples. The MAE sample exhibited larger surface area (ca. 1000 m2·g− 1) than the sample treated by thermocalcining (ca. 560 m2·g− 1). As determined the enrichment of PAHs on MAE with calcined samples by on-line solid-phase extraction HPLC, the MAE sample possessed more enrichment and lower detection limit than the calcined sample. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Hexagonally ordered SBA-15 silica possesses high surface area, outstanding thermal stability, pore size adjustment, and tailored particle morphology [1]. The SBA-15 silica has already been applied in different fields of separation [2], catalysis [3], and advanced optical materials [4]. The most common methods used in removing the organic templates are calcination remove technique [5], extraction techniques [4–6] (by conventional solvent or by supercritical fluid), ozone treatment [7] and microwave methods [8,9] (by digestion and calcination). However, the adverse effects associated with the removal of the template mainly result from the rapid decomposition of the template because the temperature causes shrinkage of the structure [5]. The present work describes a novel procedure for removing the organic templates based on the advantages of microwave and extraction techniques. The advantages of extraction of the organic templates are without decomposition and permits reuse of solvents. Microwave technique is commonly used in numerous applications ranged from environmental technology [10–12] to foods [13]. To date, microwave techniques have been used to eliminate organic species from porous materials by acid digestion [8,9]. However, the most important requirements: (1) efficient removal of the template (2) shorter operation time (3) less organic solvent (4) ordered structure and specific framework, by any of the methods cannot be simultaneously achieved. In this preliminary study we report a new
⁎ Corresponding authors. Tel.: +886 3 389 1716; fax: +886 3 389 2494. E-mail addresses: [email protected] (Y.-Y. Shu), [email protected] (C.-B. Wang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.05.014
method to eliminate organic template by microwave assisted extraction (MAE), which shows many benefits over other methods such as lower structural shrinkage, larger surface areas and higher silanol group density. 2. Experimental The silica mesophase was prepared according to the synthesis outlined by Grieken [1]. The molar composition of the mixture for SBA-15 was 4 g of copolymer (P123) and 0.041 TEOS/0.24 HCl/6.67 H2O. The solid product (as-prepared) was recovered by filtration and air-dried at room temperature overnight. A small part of the asprepared sample was calcined in air at 550 °C for 6 h in order to compare with the sample that underwent the MAE procedure. In the MAE procedure, around 0.1 g of sample was placed on a watch glass with 20 ml ethanol/hexane (v/v, 1/1) as extract solvent, and heated for 2 min under a microwave irradiation (power: 100 W, frequency: 2450 MHz, repeat: 3 times) to remove the template. The chromatographic experiments were performed using HPLC Agilent 1100 Series equipped with diode array detector and a column oven. A 125 mm × 4 mm reverse-phase C-18 column (chrompack) was used for separation and pre-column was used for enrichment. The flow rate was 1.0 ml/min, UV detector wavelength was 230 nm and column oven temperature maintained 25 °C. 3. Results and discussion Fig. 1 shows the XRD diffraction patterns of the as-prepared, MAE and calcined SBA-15 materials. The results show that both pretreatment methods (MAE and thermocalcined) agree well with those reported for the mesoporous SBA-15 properties and structure. The 2θ position for the SBA-15 after MAE is lower than that of the calcined SBA-15, indicating a larger unit cell size for the MAE sample. In fact,
1694
T.-L. Lai et al. / Materials Letters 63 (2009) 1693–1695
Fig. 1. XRD patterns of as-prepared, MAE and calcined SBA-15 materials.
the 2θ position for the MAE sample is similar to the as-prepared sample, indicating that the shrinkage of structure does not occur during the removal of the surfactant template under MAE procedure. The narrower and intenser XRD diffraction pattern of the MAE sample may also indicate that the removal of the surfactant template possesses better crystallinity than the thermocalcined sample. Fig. 2 shows the IR absorbance spectra of the as-prepared, MAE and calcined SBA-15 materials. A broad band around 3430 cm− 1 appears for all samples, which is partially caused by the O–H stretching vibration mode of the adsorbed water molecules, whose bending vibration mode is responsible for the band recorded at 1630 cm− 1. Several absorption bands around 2865–3000 and 1375–1475 cm− 1 shown in as-prepared spectrum can be assigned to C–H stretching and bending vibrations of the template P123. After treatment (MAE and thermocalcined), the C–H vibration peaks are nearly indiscernible. This suggests the efficient removal of the surfactant template by MAE and thermocalcined methods. More importantly, the relative intensity of Si–OH bending bands around 956 cm− 1 is persistent for asprepared and MAE samples, but much weaker for the calcined sample. This demonstrates that the MAE procedure leads to the retention of a high level of silanol groups on the pore wall surface, while the thermocalcined method will unavoidably reduce their number. The number of silanol groups also can be indirectly proven by the thermogravimetry (TG) analysis. The TG (not shown) curve for the MAE sample shows more weight loss (7.8%) than the calcined sample (4.7%). The MAE sample seems to exhibit a higher Si–OH group density than the calcined sample. The nitrogen adsorption–desorption isotherms of SBA-15 materials at 77 K are shown in Fig. 3, which exhibits a typical IV shape for both
Fig. 2. IR spectra of as-prepared, MAE and calcined SBA-15 materials.
Fig. 3. N2 adsoption–desorption isotherms of (i) MAE sample: (●) adsorption, (○) desorption, and (ii) calcined sample: (■) adsorption, (□) desorption.
the MAE (circles) and calcined (squares) samples. The isotherms with clear H1-type hysteresis loops at high relative pressure (P/P0), indicating the presence of large pores and a narrow pore size
Fig. 4. TEM images of (a). MAE sample, (b) Calcined sample.
T.-L. Lai et al. / Materials Letters 63 (2009) 1693–1695
1695
MAE method can use the end-capping process to modify the SBA-15 surface and increase the separation efficiency for HPLC. 4. Conclusion Microwave assisted extraction is effective in extracting the surfactant template from the pores of as-prepared SBA-15. The MAE method leads to fast and complete removal of the template, which is reflected by larger surface area, lower structural shrinkage and the abundant silanol groups on the surface than the sample treated by thermocalcined. Acknowledgement Fig. 5. Enrichment of PAHs on MAE and calcined samples by on-line SPE HPLC: Naphthalene (1); Biphenyl (2); Phenanthrene (3); and Pyrene (4).
distributions. The BET surface area is 1064 m2·g− 1 for the MAE sample, which is higher than the calcined sample (ca. 567 m2·g− 1). Apparently, the MAE sample has a lower structural shrinkage and better structural quality than the thermocalcined sample. The transmission electron microscopy (TEM) image of MAE sample [Fig. 4(a)] shows well-ordered arrays of mesoporous in large domains. The morphology is wheat-like and is the same as that of typical asprepared SBA-15 and calcined SBA-15 [Fig. 4(b)]. These results further suggest that the MAE method does not induce the collapse of the structural order of the as-prepared sample. The MAE method has been considered as a potential alternative to traditional solid–liquid extraction. Some of its potential advantages over Soxhlet extraction are significant reduction of extraction time and solvent usage, improved extraction yield and provides agitation during extraction to improve the mass transfer phenomenon. In the application of SBA-15, the MAE and calcined samples was compared with on-line solid-phase extraction (SPE) in respect of sensitivity and selectivity for PAHs (Fig. 5). It shows the typical chromatograms obtained after enriching 0.5 mL/L PAHs. Apparently, the MAE sample has higher enrichment and a lower detection limit than the calcined sample. The abundant silanol groups obtained by
We are pleased to acknowledge the financial support for this study by the National Science Council of the Republic of China under contract numbers NSC 97-2811-M-017-001 and NSC 96-2113-M-606001-MY3. References [1] van Grieken Rafael, Calleja Guillermo, Stucky Galen D, Melero Juan A, García Rafael A, Iglesias Jose. Langmuir 2003;19:3966–73. [2] Doadrio AL, Sousa EMB, Doadrio JC, Pérez Pariente J, Izquierdo-Barba I, Vallet-Regi M. J Control Release 2004;97:125–32. [3] Korányi Tamás I, Vít Zdeněk, Poduval Dilip G, Ryoo Ryong, Kim Hei Seung, Hensen Emiel JM. J Catal 2008;253:119–31. [4] Scott Brian J, Wirnsberger Gernot, Stucky Galen D. Chem Mater 2001;13:3140–50. [5] Kleitz Freddy, Schmidt Wolfgang, Schüth Ferdi. Microporous Mesoporous Mater 2003;65:1–29. [6] Kawi Sibudjing, Lai MW. Chem Commun 1998;13:1407–8. [7] Keene Matthew TJ, Denoyel Renaud, Llewellyn Philip L. Chem Commun 1998;20:2203–4. [8] Tian Bozhi, Liu Xiaoying, Yu Chengzhong, Gao Feng, Luo Qian, Xie Songhai, et al. Chem Commun 2002;11:1186–7. [9] He Jing, Yang Xingbin, Evans DG, Duan Xue. Mater Chem Phys 2002;77:270–5. [10] Shu Youn Yuen, Lai Teh Long. J Chromatogr A 2001;927:131–41. [11] Shu Youn Yuen, Lai Teh Long, Lin Huann shyang, Yang Thomas C, Chang Chi-Peng. Chemosphere 2003;52:1667–78. [12] Lai Teh Long, Lee Chia Chan, Wu Kuen Shian, Shu Youn Yuen, Wang Chen Bin. Appl Catal B 2006;68:147–53. [13] Shu Youn Yuen, Ko Ming Yu, Chang Yuan Shiun. Microchem J 2003;74:131–9.