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Synthesis of silica nanocubes by sol–gel method
Materials Letters 59 (2005) 4013 – 4015 www.elsevier.com/locate/matlet
Synthesis of silica nanocubes by sol–gel method Kaifeng Yu, Yupeng Guo, Xuefeng Ding, Jingzhe Zhao, Zichen Wang * College of Chemistry, Jilin University, Changchun, 130023, China Received 27 March 2005; accepted 21 July 2005 Available online 8 September 2005
Abstract A novel approach was employed in the fabrication of silica nanocubes with controlled size and shape. The silica nanocubes were highly dispersed with width of about 30 nm and product with high purity. A small amount of tartaric acid was introduced in the TEOS hydrolysis process. In this work tartaric acid as the organic template, was formed on the surface of hydrous silica colloidal particles. The organic template ordered by carboxyl, led to the self-assembly of amorphous silica sol encapsulated into cubic matrixes, and the organic template was packed into 3D structure. D 2005 Elsevier B.V. All rights reserved. Keywords: Silica; Nanocubes; TEOS; Sol – gel method
1. Introduction
2. Experimental
Over the past decade, inorganic nanoparticles of uniform size and shape are of special interest from both theoretical and practical perspectives [1,2]. Fields would greatly benefit from advance in the synthesis of nanostructural materials include photonics, nanoelectronics, information storage, catalysis, and biosensors [3 –12]. In particular, several nanocubes materials such as manganese sulfide [13], cobalt oxide [14], Silver [15], cobalt hexacyanoferrate [16], cobalt ferrite [17], cuprous oxide [18,19], chromium [20], silver sulfide [21] have been investigated extensively, but silica nanocubes have not been reported. Here, we report the preparation of silica nanocubes by sol – gel method at room temperature. In this paper, therefore, we report our recent effort in morphological control of silica. In particular, monodispersed nanocubes of silica have been achieved for the first time. To achieve controlled fabrication of nanomaterials by precipitation methods, fundamental aspects on synthetic conditions and process parameters need to be investigated, which includes precipitation mode (e.g., either heterogeneous or homogeneous), reaction temperature and time, concentrations of starting reagents, etc.
2.1. Materials
* Corresponding author. Tel./fax: +86 431 8499134. E-mail address: [email protected] (Z. Wang). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.07.055
Tetraethyl orthosilicate (TEOS) was purchased from Shanghai chemical company. Ethanol, ammonia and tartaric acid were from Beijing chemical company. All other reagents were of analytical grade and used without further purification. The distilled water was used throughout. 2.2. Preparation of silica nanocubes Here, we present a relatively easy synthesis procedure for silica nanocubes by sol –gel method. The synthesis of silica nanocubes involved the following steps. These silica nanocubes were synthesized by hydrolyzing tetraethyl orthosilicate (TEOS) in a mixture of ethanol, ammonia, water, and tartaric acid. The reaction was carried out as follows: 7.3 g (0.035 mol) of TEOS was dissolved in 50 ml of absolute ethanol containing 0.2 g (0.00133 mol) of tartaric acid and 0.6 g of water. The solution was permitted to stand for 30 min to form SiO2 sol, and finally 20 ml of ammonium hydroxide solution (28% NH3 solution) was added. After 15 –20 min, the reaction was observed to be completed. Then, the reaction products were washed with a large amount of water. Finally, the products were dried in an oven at 100 -C.
4014
K. Yu et al. / Materials Letters 59 (2005) 4013 – 4015
2.3. Characterization Morphologies and structures of the as-synthesized samples as well as their calcined samples were investigated using an H-800EM transmission electron microscope (TEM) with a LaB6 electron gun and an electron kinetic energy of 200 kV. For specimen preparation, 3 mg of dry samples were dispersed into approximately 15 mL of acetone, and the resultant mixture was then treated with
(a)
Fig. 2. IR of silica samples prepared by novel sol-gel procedure.
100nm
(b)
ultrasound radiation for 1 h. A few drops of ultrasonicated mixture were then spread onto a commercial copper grid coated with amorphous carbon layers and Formvar film, followed by a drying treatment at 60 -C. Various chemical bonding information on silicon – oxygen hydroxyl were studied with Fourier transform infrared spectroscopy (FTIR) using a potassium bromide (KBr) pellet technique. Each FTIR spectrum was collected from 400 to 4000 cm 1. Thermal behavior of samples was analyzed using thermogravimetric method (TGA) in a SHIMADZU TGA-60H. About 10 –11 mg of the samples was heated with an air flow of 100 mL min 1 and at a heating rate of 50 -C min 1 from room temperature to 800 -C. The crystallographic information of prepared samples was analyzed by powder X-ray diffraction (XRD) method using an SHIMADZU XRD˚ ) at 6000 diffractometer with Cu Ka radiation (k = 1.5406 A a scanning rate of 1 min 1.
3. Results and discussion 50nm
The reaction products are silica nanocubes (Fig. 1). Typically, the nanocubes are 30 nm in length, 30 nm in width. IR spectra (Fig.
(c)
50nm
Fig. 1. TEM images of (a) final product, (b) and (c) high magnification of (a).
Fig. 3. TG-DTA of silica nanocubes.
K. Yu et al. / Materials Letters 59 (2005) 4013 – 4015
4015
and 30 – 60 min for H2O / TEOS molar ratio and time of standing, respectively. In contrast, prolonged TEOS hydrolysis for 1 day, of after 30 min when the H2O / TEOS molar ratio was increased to 4, gave only a gel phase of aggregated silica particles several micrometers in size. Likewise, no nanocubes were formed when the TEOS solution was used immediately after preparation, presumably due to the absence of condensed silicates during crystallization of the organic matrixes, which subsequently coalesce into polycrystalline aggregates.
4. Conclusion 20
30
40
50
60
70
2θ Fig. 4. XRD of silica nanocubes.
2) of silica nanocubes have a 946 cm 1 signal assigned to the Si – OH vibration and an 1102 cm 1 signal assigned to the Si – O stretching vibration. Thermal analysis shows a distinct weight loss between 150 and 250 -C for the control crystals of ammonium tartrate (Fig. 3). The amount of ammonium tartrate in the assynthesized silica material is estimated be less than 18 wt.%. XRD pattern (Fig. 4) of silica nanocubes indicates that the silica nanocubes are amorphous silica. When freshly distilled TEOS dissolved in absolute ethanol containing tartaric acid was added immediately to ammonium hydroxide solution, silica nanocubes did not form. The products were instead spherical particles and aggregates. The fact that tartaric acid is the only isomer showing this effect may be linked to the unique nature of the H-bonding in this case, and this is thought to play an important role in the reaction mechanism. The reaction mechanism of formation of the silica nanocubes is still unknown. In the usual hydrolysis reaction of TEOS using NH3 as catalyst, the products are nonporous spherical silica particles of uniform size [22]. In this reaction, it is considered that SiO2 sol particles were the starting point for the formation of silica nanocubes, and the silica nanocubes are formed in the tartaric acid matrixes. The essential conditions for the formation of silica nanocubes, therefore, are the presence of SiO2 sol and tartaric acid, and the diameter of the silica nanocubes depends on the size of SiO2 sol particles. We propose, therefore, that the addition of aqueous NH4OH plays a dual role in the mechanism of silica nanocubes formation: first as a source of OH ions for the base catalysis of TEOS condensation, and second as an initiator of ammonium tartaric acid crystallization, which in turn is responsible for the templated growth of individual silica nanocubes. These processes need to be chemically coupled with good fidelity. Moreover, interactions between the hydrolysis products and the incipient organic crystal are likely to be synergistic. The kinetics of these processes is also important: for example, synthesis of the silica nanocubes was highly dependent on the extent of silica condensation present at the onset of ammonium tartrate crystal growth. The latter occurred immediately on addition of NH4OH, whereas the former was dependent on the H2O / TEOS molar ratio and the amount of time the TEOS solution was allowed to stand prior to base catalysis; optimum conditions for our experiments were in the range of 0 – 1,
We have described the synthesis and characterization of silica nanocubes. Silica nanocubes can be synthesized by sol – gel method. The incipient crystallization of forms of ammonium tartrate can be used for the surface-specific templating of sol –gel reactions to produce silica nanocubes. By judicious control of both the crystallization and condensation processes, silica nanocubes can be produced. The development of this method for the synthesis of functionalized silicas, as well as other metal oxide materials is currently in progress. This work was supported by the National Nature Science Foundation of China.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
M.A. El-Sayed, Chem. Res. 34 (2001) 257. A.P. Alivisatos, Science 271 (1996) 933. P. Jiang, J.F. Bertone, V.L. Colvin, Science 291 (2001) 453. Y. Huang, X. Duan, Y. Cui, L. Lauhon, K. Kim, C.M. Lieber, Science 294 (2001) 1313. X. Duan, Y. Huang, C.M. Lieber, Nano Lett. 2 (2002) 487. M. Valden, X. Lai, D.W. Goodman, Science 281 (1998) 1647. V.F. Puntes, K.M. Krishnan, A.P. Alivisatos, Science 291 (2001) 2115. S. Sun, C.B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000) 1989. R. Jin, Y.W. Cao, C.A. Mirkin, K.L. Kelly, G.C. Schatz, J.G. Zheng, Science 294 (2001) 1901. M.P. Bruchez, M. Moronne, P. Gin, S. Weiss, A.P. Alivisatos, Science 281 (1998) 2013. W.C.W. Chan, S. Nie, Science 281 (1998) 2016. C.J. Murphy, N.R. Jana, AdV. Mater. 14 (2002) 80. Young-wool Jun, Yoon-young Jung, Jinwoo Cheon, J. Am. Chem. Soc. 124 (2002) 615. Rong Xu, Huachun Zeng, J. Phys. Chem., B 107 (2003) 926. Yugang Sun, Younan Xia, J. Am. Chem. Soc. 126 (2004) 3892. Sebastien Vaucher, John Fielden, Stephen Mann, Nano Lett. 2 (2002) 225. Qing Song, Z. John Zhang, J. Am. Chem. Soc. 126 (19) (2004) 6164. Run Liu, Fumiyasu Oba, A. Jay, Chem. Mater. 15 (2003) 4882. Linfeng Guo, Catherine J. Murphy, Nano Lett. 3 (2003) 231. J.C. Rao, X.X. Zhang, B. Qin, K.K. Fung, Ultramicroscopy 98 (2004) 231. Mengdong Wu, Xinxin Pan, Xuefeng Qian, Inorg. Chem. Commun. 7 (2004) 359. W. Sto¨ber, A. Fink, E.J. Bohn, J. Colloid Interface Sci. 26 (1968) 62.
Synthesis of silica nanocubes by sol–gel method Kaifeng Yu, Yupeng Guo, Xuefeng Ding, Jingzhe Zhao, Zichen Wang * College of Chemistry, Jilin University, Changchun, 130023, China Received 27 March 2005; accepted 21 July 2005 Available online 8 September 2005
Abstract A novel approach was employed in the fabrication of silica nanocubes with controlled size and shape. The silica nanocubes were highly dispersed with width of about 30 nm and product with high purity. A small amount of tartaric acid was introduced in the TEOS hydrolysis process. In this work tartaric acid as the organic template, was formed on the surface of hydrous silica colloidal particles. The organic template ordered by carboxyl, led to the self-assembly of amorphous silica sol encapsulated into cubic matrixes, and the organic template was packed into 3D structure. D 2005 Elsevier B.V. All rights reserved. Keywords: Silica; Nanocubes; TEOS; Sol – gel method
1. Introduction
2. Experimental
Over the past decade, inorganic nanoparticles of uniform size and shape are of special interest from both theoretical and practical perspectives [1,2]. Fields would greatly benefit from advance in the synthesis of nanostructural materials include photonics, nanoelectronics, information storage, catalysis, and biosensors [3 –12]. In particular, several nanocubes materials such as manganese sulfide [13], cobalt oxide [14], Silver [15], cobalt hexacyanoferrate [16], cobalt ferrite [17], cuprous oxide [18,19], chromium [20], silver sulfide [21] have been investigated extensively, but silica nanocubes have not been reported. Here, we report the preparation of silica nanocubes by sol – gel method at room temperature. In this paper, therefore, we report our recent effort in morphological control of silica. In particular, monodispersed nanocubes of silica have been achieved for the first time. To achieve controlled fabrication of nanomaterials by precipitation methods, fundamental aspects on synthetic conditions and process parameters need to be investigated, which includes precipitation mode (e.g., either heterogeneous or homogeneous), reaction temperature and time, concentrations of starting reagents, etc.
2.1. Materials
* Corresponding author. Tel./fax: +86 431 8499134. E-mail address: [email protected] (Z. Wang). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.07.055
Tetraethyl orthosilicate (TEOS) was purchased from Shanghai chemical company. Ethanol, ammonia and tartaric acid were from Beijing chemical company. All other reagents were of analytical grade and used without further purification. The distilled water was used throughout. 2.2. Preparation of silica nanocubes Here, we present a relatively easy synthesis procedure for silica nanocubes by sol –gel method. The synthesis of silica nanocubes involved the following steps. These silica nanocubes were synthesized by hydrolyzing tetraethyl orthosilicate (TEOS) in a mixture of ethanol, ammonia, water, and tartaric acid. The reaction was carried out as follows: 7.3 g (0.035 mol) of TEOS was dissolved in 50 ml of absolute ethanol containing 0.2 g (0.00133 mol) of tartaric acid and 0.6 g of water. The solution was permitted to stand for 30 min to form SiO2 sol, and finally 20 ml of ammonium hydroxide solution (28% NH3 solution) was added. After 15 –20 min, the reaction was observed to be completed. Then, the reaction products were washed with a large amount of water. Finally, the products were dried in an oven at 100 -C.
4014
K. Yu et al. / Materials Letters 59 (2005) 4013 – 4015
2.3. Characterization Morphologies and structures of the as-synthesized samples as well as their calcined samples were investigated using an H-800EM transmission electron microscope (TEM) with a LaB6 electron gun and an electron kinetic energy of 200 kV. For specimen preparation, 3 mg of dry samples were dispersed into approximately 15 mL of acetone, and the resultant mixture was then treated with
(a)
Fig. 2. IR of silica samples prepared by novel sol-gel procedure.
100nm
(b)
ultrasound radiation for 1 h. A few drops of ultrasonicated mixture were then spread onto a commercial copper grid coated with amorphous carbon layers and Formvar film, followed by a drying treatment at 60 -C. Various chemical bonding information on silicon – oxygen hydroxyl were studied with Fourier transform infrared spectroscopy (FTIR) using a potassium bromide (KBr) pellet technique. Each FTIR spectrum was collected from 400 to 4000 cm 1. Thermal behavior of samples was analyzed using thermogravimetric method (TGA) in a SHIMADZU TGA-60H. About 10 –11 mg of the samples was heated with an air flow of 100 mL min 1 and at a heating rate of 50 -C min 1 from room temperature to 800 -C. The crystallographic information of prepared samples was analyzed by powder X-ray diffraction (XRD) method using an SHIMADZU XRD˚ ) at 6000 diffractometer with Cu Ka radiation (k = 1.5406 A a scanning rate of 1 min 1.
3. Results and discussion 50nm
The reaction products are silica nanocubes (Fig. 1). Typically, the nanocubes are 30 nm in length, 30 nm in width. IR spectra (Fig.
(c)
50nm
Fig. 1. TEM images of (a) final product, (b) and (c) high magnification of (a).
Fig. 3. TG-DTA of silica nanocubes.
K. Yu et al. / Materials Letters 59 (2005) 4013 – 4015
4015
and 30 – 60 min for H2O / TEOS molar ratio and time of standing, respectively. In contrast, prolonged TEOS hydrolysis for 1 day, of after 30 min when the H2O / TEOS molar ratio was increased to 4, gave only a gel phase of aggregated silica particles several micrometers in size. Likewise, no nanocubes were formed when the TEOS solution was used immediately after preparation, presumably due to the absence of condensed silicates during crystallization of the organic matrixes, which subsequently coalesce into polycrystalline aggregates.
4. Conclusion 20
30
40
50
60
70
2θ Fig. 4. XRD of silica nanocubes.
2) of silica nanocubes have a 946 cm 1 signal assigned to the Si – OH vibration and an 1102 cm 1 signal assigned to the Si – O stretching vibration. Thermal analysis shows a distinct weight loss between 150 and 250 -C for the control crystals of ammonium tartrate (Fig. 3). The amount of ammonium tartrate in the assynthesized silica material is estimated be less than 18 wt.%. XRD pattern (Fig. 4) of silica nanocubes indicates that the silica nanocubes are amorphous silica. When freshly distilled TEOS dissolved in absolute ethanol containing tartaric acid was added immediately to ammonium hydroxide solution, silica nanocubes did not form. The products were instead spherical particles and aggregates. The fact that tartaric acid is the only isomer showing this effect may be linked to the unique nature of the H-bonding in this case, and this is thought to play an important role in the reaction mechanism. The reaction mechanism of formation of the silica nanocubes is still unknown. In the usual hydrolysis reaction of TEOS using NH3 as catalyst, the products are nonporous spherical silica particles of uniform size [22]. In this reaction, it is considered that SiO2 sol particles were the starting point for the formation of silica nanocubes, and the silica nanocubes are formed in the tartaric acid matrixes. The essential conditions for the formation of silica nanocubes, therefore, are the presence of SiO2 sol and tartaric acid, and the diameter of the silica nanocubes depends on the size of SiO2 sol particles. We propose, therefore, that the addition of aqueous NH4OH plays a dual role in the mechanism of silica nanocubes formation: first as a source of OH ions for the base catalysis of TEOS condensation, and second as an initiator of ammonium tartaric acid crystallization, which in turn is responsible for the templated growth of individual silica nanocubes. These processes need to be chemically coupled with good fidelity. Moreover, interactions between the hydrolysis products and the incipient organic crystal are likely to be synergistic. The kinetics of these processes is also important: for example, synthesis of the silica nanocubes was highly dependent on the extent of silica condensation present at the onset of ammonium tartrate crystal growth. The latter occurred immediately on addition of NH4OH, whereas the former was dependent on the H2O / TEOS molar ratio and the amount of time the TEOS solution was allowed to stand prior to base catalysis; optimum conditions for our experiments were in the range of 0 – 1,
We have described the synthesis and characterization of silica nanocubes. Silica nanocubes can be synthesized by sol – gel method. The incipient crystallization of forms of ammonium tartrate can be used for the surface-specific templating of sol –gel reactions to produce silica nanocubes. By judicious control of both the crystallization and condensation processes, silica nanocubes can be produced. The development of this method for the synthesis of functionalized silicas, as well as other metal oxide materials is currently in progress. This work was supported by the National Nature Science Foundation of China.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
M.A. El-Sayed, Chem. Res. 34 (2001) 257. A.P. Alivisatos, Science 271 (1996) 933. P. Jiang, J.F. Bertone, V.L. Colvin, Science 291 (2001) 453. Y. Huang, X. Duan, Y. Cui, L. Lauhon, K. Kim, C.M. Lieber, Science 294 (2001) 1313. X. Duan, Y. Huang, C.M. Lieber, Nano Lett. 2 (2002) 487. M. Valden, X. Lai, D.W. Goodman, Science 281 (1998) 1647. V.F. Puntes, K.M. Krishnan, A.P. Alivisatos, Science 291 (2001) 2115. S. Sun, C.B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000) 1989. R. Jin, Y.W. Cao, C.A. Mirkin, K.L. Kelly, G.C. Schatz, J.G. Zheng, Science 294 (2001) 1901. M.P. Bruchez, M. Moronne, P. Gin, S. Weiss, A.P. Alivisatos, Science 281 (1998) 2013. W.C.W. Chan, S. Nie, Science 281 (1998) 2016. C.J. Murphy, N.R. Jana, AdV. Mater. 14 (2002) 80. Young-wool Jun, Yoon-young Jung, Jinwoo Cheon, J. Am. Chem. Soc. 124 (2002) 615. Rong Xu, Huachun Zeng, J. Phys. Chem., B 107 (2003) 926. Yugang Sun, Younan Xia, J. Am. Chem. Soc. 126 (2004) 3892. Sebastien Vaucher, John Fielden, Stephen Mann, Nano Lett. 2 (2002) 225. Qing Song, Z. John Zhang, J. Am. Chem. Soc. 126 (19) (2004) 6164. Run Liu, Fumiyasu Oba, A. Jay, Chem. Mater. 15 (2003) 4882. Linfeng Guo, Catherine J. Murphy, Nano Lett. 3 (2003) 231. J.C. Rao, X.X. Zhang, B. Qin, K.K. Fung, Ultramicroscopy 98 (2004) 231. Mengdong Wu, Xinxin Pan, Xuefeng Qian, Inorg. Chem. Commun. 7 (2004) 359. W. Sto¨ber, A. Fink, E.J. Bohn, J. Colloid Interface Sci. 26 (1968) 62.