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Evaporizing-deposition to synthesize micro- and nanoscale spherical anatase TiO2 film
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Materials Letters 62 (2008) 2036 – 2038 www.elsevier.com/locate/matlet
Evaporizing-deposition to synthesize micro- and nanoscale spherical anatase TiO2 film Daoai Wang a,b , Bo Yu a , Jingcheng Hao a , Weimin Liu a,⁎ a
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China Received 22 September 2007; accepted 5 November 2007 Available online 12 November 2007
Abstract Micro-and nanoscale spherical anatase TiO2 films have been successfully prepared via evaporizing–deposition route. The morphology and the crystalline structure of the samples were characterized in more detail with field emission scanning electron microscopy (FE–SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The TiO2 films with micro-and nanoscale surface structures can be constructed by simply adjusting the evaporation condition of TiCl4 in the air after being annealed. These surfaces can be turned from superhydrophilic to super-hydrophobic after modification with a thin layer of hydrophobic silicone, mainly depending on the surface morphology. © 2007 Published by Elsevier B.V. Keywords: Anatase; TiO2; Evaporizing-deposition; TiCl4; Wettability
1. Introduction Titanium dioxide (TiO2), as a predominant semiconductor, has been proven to be one of the most suitable materials for wideranging environmental applications, photocatalysts, photoelectronics, sensors, energy-storage, and conversion technologies [1–4]. In recent years, TiO2 materials such as nanoparticles, nanowires, nanotubes, and nanorods have been successively synthesized through sol-gel technology, electrochemical approach, templated synthesis, layer-by-layer assembly strategy and hydrothermal synthesis etc [5–11]. A challenge to prepare TiO2 films is wide-ranging applications in different fields. Compact TiO2 films with low surface areas are usually prepared by sol-gel method, and preparing other morphology TiO2 films usually needs special technologies and equipments [12–14]. The low product and high cost also restrict the applications of these materials. Novel simple method to prepare TiO2 films with large area is still the target of chemists and materials scientists. TiO2 as a self-cleaning material, the wettability will affect its applications [15–17]. The wettability, a very important aspect of ⁎ Corresponding author. Tel.: +86 931 4968166; fax: +86 931 8277088. E-mail address: [email protected] (W. Liu). 0167-577X/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.matlet.2007.11.009
materials, is becoming an interesting area of the studies which is governed by both the surface chemical composition and geometric structure. It may be an effective route that first a rough TiO2 surface with micro-and nanoscale structures (like
Fig. 1. XRD pattern of the prepared sample scraped from the substrate after being calcined at 400 °C for 2 h.
D. Wang et al. / Materials Letters 62 (2008) 2036–2038
2037
interface energy was used to modify the TiO2 surface for obtaining super-hydrophobic surfaces with a contact angle of about 156 ± 1°. This functional surface can be applied in various industrial fields such as anti-fogging, self-cleansing, and anticorrosion etc. 2. Experimental
Fig. 2. The XPS analysis of the as-prepared anatase TiO2 film before and after being modified with PDMSVT. The inset is the XPS analysis of Ti2p region after modification.
the lotus leaf surface) is formed and then the surface is modified with low surface free energy agent to create super-hydrophobic TiO2 surface [18]. In this study, we used a simple evaporizingdeposition route to successfully prepare anatase TiO2 films with micro-and nanoscale spherical structures on different substrates. Poly(dimethylsiloxane) vinyl terminated (PDMSVT) with low
Anatase TiO2 films were produced using evaporation and deposition synthesis with successive heat treatment. Twenty milliliters volatile TiCl4 was filled in a flask with a tubelet to flow argon, and maintained it at about 80 °C in an oil bath. The washed substrates, such as glass slide, silicon substrate, conductive glass substrate and titanium plate, were placed on the top of the flask without completely covering the beaker for the evaporation of TiCl4 till a white film formed owing to the hydrolyzation of TiCl4 in the air. The films were then immediately transferred into a 120 °C drying oven for 30 min and annealed at 400 °C for 2 h. To simplify the expression for chemical reactions, we can see that: hydrolyzation
400- C
TiCl4 þ H2 O Y TiðOHÞ4 Y TiO2 ðanataseÞ The PDMSVT films were obtained by spin-coating at a rate of 3000 rpm for 30 s and annealed in a vacuum oven at 120 °C for 2 h. The phase identification of the sample was conducted with
Fig. 3. FESEM images of the sample prepared on conductive glass substrates. The inset is the photograph of a few water droplets on the resulting surface before (a) and after (b) modification with PDMSVT with the water contact angle of about 0° (a) 156 ± 1° (b).
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D. Wang et al. / Materials Letters 62 (2008) 2036–2038
powder X-ray diffraction (XRD) (Philips Corp, X'Pert-MRD). The morphologies and composition of samples were observed on field emission scanning electron microscopy (FESEM) (SEM6701F) and PHI-5702 X-ray photoelectron spectroscopy (XPS).
regardless of the surface free energy. Summary, the micro-and nanoscale spherical anatase TiO2 films could be used as functional surfaces applied in various industrial fields such as anti-fogging, self-cleansing and anti-corrosion etc.
3. Results and discussion
4. Conclusions
The power X-ray diffraction (XRD) pattern recorded from the asprepared surface after annealed at 400 °C for about 2 h is shown in Fig. 1. The crystal of the product is very fine. All the peaks can be indexed to anatase TiO2 with crystalline cell constants of a = 3.785 and c = 9.513 Å, which are basically in agreement with the reported values Joint Committee on Powder Diffraction Standards (JCPDS) card No. 21-1272, and no impurities are detected. Fig. 2 shows the X-ray photoelectron spectroscopy (XPS) spectra of the anatase TiO2 film before and after treatment with PDMSVT. The binding energies obtained in the XPS analysis are corrected for specimen charging by referencing the C 1s to 284.8 eV. The wide-scan spectrum of the sample before modified is dominated by signals attributable to titanium, oxygen and carbon (coming from the test system). No other signal was detected for samples, indicating that the samples are very pure. After modifying with PDMSVT, the sharp signal of silicon can be detected. The signal of carbon of the modification agent is obviously strengthened. The signal of titanium is very low, as shown in the inset of Fig. 2, demonstrating the TiO2 surface is sufficiently covered by the modification agent which can lead to a new surface performance. Fig. 3 shows FE–SEM images of the sample on conductive glass substrates before (a, c) and after (b) modification. One can see that a large amount of TiO2 particles covered the surface of the substrate forming rough structure. More detailed information of the surface structure from Fig. 3c demonstrated that the particles covered on the surface are spheres with the size from several hundred nanometers to one micrometer, which the larger spheres consist of small particles with the size of about tens nanometers. So this method can prepare spherical anatase TiO2 with micro-and nanoscale surface structures. These TiO2 surfaces with large surface area can be very useful in wideranging fields such as in photocatalysts, photoelectronics, dye-sensitized solar cells. The applied researches are being done. The wetting properties of the samples before and after modified with PDMSVT were tested for opening the applications of micro-and nanoscale spherical anatase TiO2 films. As we know, a drop of water spreads extensively on the surface with a contact angle of less than 10° or larger than 150°, indicating that the surface is super-hydrophilic or super-hydrophobic [19,20]. The results show that the micro-and nanoscale spherical anatase TiO2 surfaces are super-hydrophilic with a contact angle of about 0°, as inserted in Fig. 3a. The super-hydrophilic surfaces could be due to the intrinsic character of TiO2 and the capillary effect. After modified with PDMSVT, the surface morphology was not changed but the surfaces could be turned from super-hydrophilicity to super-hydrophobicity, as shown in the inset of Fig. 3b, the water contact angle is about 156 ± 1°. To test the effect of morphology to its wettability, some comparative tests with the same treatment were done. The TiO2 compact film showed a contact angle of about 90° after the same modification. We presume that the micro-and nanoscale surface structures play a very important role for the super-hydrophobic surface,
Anatase TiO2 films were successfully prepared by means of a simple evaporizing-deposition route with successive heat treatment. These TiO2 films with micro-and nanoscale surface structures can be successively turned from super-hydrophilic to superhydrophobic after modification with the hydrophobic silicone, mainly depending on the surface morphology. This preparation method could be an exciting addition to the fast growth family of synthesis film material which can be applied in different fields. Acknowledgment The authors gratefully acknowledge the Innovation Group Foundation from NSFC (50421502) and the National 973 Project (2007CB607601). References [1] K. Sunada, Y. Kikuchi, K. Hashimoto, A. Fujishima, Environ. Sci. Technol. 32 (1998) 726. [2] B. O'Regan, M. Grätzel, Nature 353 (1991) 737. [3] E. Topoglidis, A.E.G. Cass, B. O'Regan, J.R. Durrant, J. Electroanal. Chem. 517 (2001) 20. [4] S.H. Lim, J. Luo, Z. Zhong, W. Ji, J. Lin, Inorg. Chem. 44 (2005) 4124. [5] S. Liu, K. Huang, Sol. Energ. Mater. Sol. Cells 85 (2005) 125. [6] M. Zukalova, A. Zukal, L. Kavan, M. Nazeeruddin, K.P. Liska, M. Gratzel, Nano Lett. 5 (2005) 1789. [7] C.W. Wu, T. Ohsuna, M. Kuwabara, K. Kuroda, J. Am. Chem. Soc. 128 (2006) 4544. [8] J.M. Mack, H. Tsuchiya, P. Schmuki, Angew. Chem., Int. Ed. Engl. 44 (2005) 2100. [9] Y. Guo, J. Hu, H. Liang, L. Wan, C. Bai, Adv. Funct. Mater. 15 (2005) 196. [10] M. Tournoux, R. Marchand, L. Brohan, Prog. Solid State Chem. 17 (1986) 33. [11] T.P. Feist, P.K. Davies, J. Solid State Chem. 101 (1992) 275. [12] G.K. Mor, K. Shankar, M. Paulose, O.K. Varghese, C.A. Grimes, Nano Lett. 6 (2006) 215. [13] Z.R. Tian, J.A. Voigt, J. Liu, B. Mckenzie, H. Xu, J. Am. Chem. Soc. 125 (2003) 12384. [14] B. Chi, T. Jin, Cryst. Growth Des. 7 (2007) 815. [15] A. Fujishima, K. Honda, Nature 238 (1972) 37. [16] R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431. [17] X. Zhang, M. Jin, Z. Liu, S. Nishimoto, H. Saito, T. Murakami, A. Fujishima, Langmuir 22 (2006) 9477. [18] Z. Guo, F. Zhou, J. Hao, W. Liu, J. Am. Chem. Soc. 127 (2005) 15670. [19] L. Feng, S. Li, Y. Li, H. Li, L. Zhang, J. Zhai, B. Liu, L. Jiang, D. Zhu, Adv. Mater. 14 (2002) 1857. [20] R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kijima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431.
Materials Letters 62 (2008) 2036 – 2038 www.elsevier.com/locate/matlet
Evaporizing-deposition to synthesize micro- and nanoscale spherical anatase TiO2 film Daoai Wang a,b , Bo Yu a , Jingcheng Hao a , Weimin Liu a,⁎ a
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China Received 22 September 2007; accepted 5 November 2007 Available online 12 November 2007
Abstract Micro-and nanoscale spherical anatase TiO2 films have been successfully prepared via evaporizing–deposition route. The morphology and the crystalline structure of the samples were characterized in more detail with field emission scanning electron microscopy (FE–SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The TiO2 films with micro-and nanoscale surface structures can be constructed by simply adjusting the evaporation condition of TiCl4 in the air after being annealed. These surfaces can be turned from superhydrophilic to super-hydrophobic after modification with a thin layer of hydrophobic silicone, mainly depending on the surface morphology. © 2007 Published by Elsevier B.V. Keywords: Anatase; TiO2; Evaporizing-deposition; TiCl4; Wettability
1. Introduction Titanium dioxide (TiO2), as a predominant semiconductor, has been proven to be one of the most suitable materials for wideranging environmental applications, photocatalysts, photoelectronics, sensors, energy-storage, and conversion technologies [1–4]. In recent years, TiO2 materials such as nanoparticles, nanowires, nanotubes, and nanorods have been successively synthesized through sol-gel technology, electrochemical approach, templated synthesis, layer-by-layer assembly strategy and hydrothermal synthesis etc [5–11]. A challenge to prepare TiO2 films is wide-ranging applications in different fields. Compact TiO2 films with low surface areas are usually prepared by sol-gel method, and preparing other morphology TiO2 films usually needs special technologies and equipments [12–14]. The low product and high cost also restrict the applications of these materials. Novel simple method to prepare TiO2 films with large area is still the target of chemists and materials scientists. TiO2 as a self-cleaning material, the wettability will affect its applications [15–17]. The wettability, a very important aspect of ⁎ Corresponding author. Tel.: +86 931 4968166; fax: +86 931 8277088. E-mail address: [email protected] (W. Liu). 0167-577X/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.matlet.2007.11.009
materials, is becoming an interesting area of the studies which is governed by both the surface chemical composition and geometric structure. It may be an effective route that first a rough TiO2 surface with micro-and nanoscale structures (like
Fig. 1. XRD pattern of the prepared sample scraped from the substrate after being calcined at 400 °C for 2 h.
D. Wang et al. / Materials Letters 62 (2008) 2036–2038
2037
interface energy was used to modify the TiO2 surface for obtaining super-hydrophobic surfaces with a contact angle of about 156 ± 1°. This functional surface can be applied in various industrial fields such as anti-fogging, self-cleansing, and anticorrosion etc. 2. Experimental
Fig. 2. The XPS analysis of the as-prepared anatase TiO2 film before and after being modified with PDMSVT. The inset is the XPS analysis of Ti2p region after modification.
the lotus leaf surface) is formed and then the surface is modified with low surface free energy agent to create super-hydrophobic TiO2 surface [18]. In this study, we used a simple evaporizingdeposition route to successfully prepare anatase TiO2 films with micro-and nanoscale spherical structures on different substrates. Poly(dimethylsiloxane) vinyl terminated (PDMSVT) with low
Anatase TiO2 films were produced using evaporation and deposition synthesis with successive heat treatment. Twenty milliliters volatile TiCl4 was filled in a flask with a tubelet to flow argon, and maintained it at about 80 °C in an oil bath. The washed substrates, such as glass slide, silicon substrate, conductive glass substrate and titanium plate, were placed on the top of the flask without completely covering the beaker for the evaporation of TiCl4 till a white film formed owing to the hydrolyzation of TiCl4 in the air. The films were then immediately transferred into a 120 °C drying oven for 30 min and annealed at 400 °C for 2 h. To simplify the expression for chemical reactions, we can see that: hydrolyzation
400- C
TiCl4 þ H2 O Y TiðOHÞ4 Y TiO2 ðanataseÞ The PDMSVT films were obtained by spin-coating at a rate of 3000 rpm for 30 s and annealed in a vacuum oven at 120 °C for 2 h. The phase identification of the sample was conducted with
Fig. 3. FESEM images of the sample prepared on conductive glass substrates. The inset is the photograph of a few water droplets on the resulting surface before (a) and after (b) modification with PDMSVT with the water contact angle of about 0° (a) 156 ± 1° (b).
2038
D. Wang et al. / Materials Letters 62 (2008) 2036–2038
powder X-ray diffraction (XRD) (Philips Corp, X'Pert-MRD). The morphologies and composition of samples were observed on field emission scanning electron microscopy (FESEM) (SEM6701F) and PHI-5702 X-ray photoelectron spectroscopy (XPS).
regardless of the surface free energy. Summary, the micro-and nanoscale spherical anatase TiO2 films could be used as functional surfaces applied in various industrial fields such as anti-fogging, self-cleansing and anti-corrosion etc.
3. Results and discussion
4. Conclusions
The power X-ray diffraction (XRD) pattern recorded from the asprepared surface after annealed at 400 °C for about 2 h is shown in Fig. 1. The crystal of the product is very fine. All the peaks can be indexed to anatase TiO2 with crystalline cell constants of a = 3.785 and c = 9.513 Å, which are basically in agreement with the reported values Joint Committee on Powder Diffraction Standards (JCPDS) card No. 21-1272, and no impurities are detected. Fig. 2 shows the X-ray photoelectron spectroscopy (XPS) spectra of the anatase TiO2 film before and after treatment with PDMSVT. The binding energies obtained in the XPS analysis are corrected for specimen charging by referencing the C 1s to 284.8 eV. The wide-scan spectrum of the sample before modified is dominated by signals attributable to titanium, oxygen and carbon (coming from the test system). No other signal was detected for samples, indicating that the samples are very pure. After modifying with PDMSVT, the sharp signal of silicon can be detected. The signal of carbon of the modification agent is obviously strengthened. The signal of titanium is very low, as shown in the inset of Fig. 2, demonstrating the TiO2 surface is sufficiently covered by the modification agent which can lead to a new surface performance. Fig. 3 shows FE–SEM images of the sample on conductive glass substrates before (a, c) and after (b) modification. One can see that a large amount of TiO2 particles covered the surface of the substrate forming rough structure. More detailed information of the surface structure from Fig. 3c demonstrated that the particles covered on the surface are spheres with the size from several hundred nanometers to one micrometer, which the larger spheres consist of small particles with the size of about tens nanometers. So this method can prepare spherical anatase TiO2 with micro-and nanoscale surface structures. These TiO2 surfaces with large surface area can be very useful in wideranging fields such as in photocatalysts, photoelectronics, dye-sensitized solar cells. The applied researches are being done. The wetting properties of the samples before and after modified with PDMSVT were tested for opening the applications of micro-and nanoscale spherical anatase TiO2 films. As we know, a drop of water spreads extensively on the surface with a contact angle of less than 10° or larger than 150°, indicating that the surface is super-hydrophilic or super-hydrophobic [19,20]. The results show that the micro-and nanoscale spherical anatase TiO2 surfaces are super-hydrophilic with a contact angle of about 0°, as inserted in Fig. 3a. The super-hydrophilic surfaces could be due to the intrinsic character of TiO2 and the capillary effect. After modified with PDMSVT, the surface morphology was not changed but the surfaces could be turned from super-hydrophilicity to super-hydrophobicity, as shown in the inset of Fig. 3b, the water contact angle is about 156 ± 1°. To test the effect of morphology to its wettability, some comparative tests with the same treatment were done. The TiO2 compact film showed a contact angle of about 90° after the same modification. We presume that the micro-and nanoscale surface structures play a very important role for the super-hydrophobic surface,
Anatase TiO2 films were successfully prepared by means of a simple evaporizing-deposition route with successive heat treatment. These TiO2 films with micro-and nanoscale surface structures can be successively turned from super-hydrophilic to superhydrophobic after modification with the hydrophobic silicone, mainly depending on the surface morphology. This preparation method could be an exciting addition to the fast growth family of synthesis film material which can be applied in different fields. Acknowledgment The authors gratefully acknowledge the Innovation Group Foundation from NSFC (50421502) and the National 973 Project (2007CB607601). References [1] K. Sunada, Y. Kikuchi, K. Hashimoto, A. Fujishima, Environ. Sci. Technol. 32 (1998) 726. [2] B. O'Regan, M. Grätzel, Nature 353 (1991) 737. [3] E. Topoglidis, A.E.G. Cass, B. O'Regan, J.R. Durrant, J. Electroanal. Chem. 517 (2001) 20. [4] S.H. Lim, J. Luo, Z. Zhong, W. Ji, J. Lin, Inorg. Chem. 44 (2005) 4124. [5] S. Liu, K. Huang, Sol. Energ. Mater. Sol. Cells 85 (2005) 125. [6] M. Zukalova, A. Zukal, L. Kavan, M. Nazeeruddin, K.P. Liska, M. Gratzel, Nano Lett. 5 (2005) 1789. [7] C.W. Wu, T. Ohsuna, M. Kuwabara, K. Kuroda, J. Am. Chem. Soc. 128 (2006) 4544. [8] J.M. Mack, H. Tsuchiya, P. Schmuki, Angew. Chem., Int. Ed. Engl. 44 (2005) 2100. [9] Y. Guo, J. Hu, H. Liang, L. Wan, C. Bai, Adv. Funct. Mater. 15 (2005) 196. [10] M. Tournoux, R. Marchand, L. Brohan, Prog. Solid State Chem. 17 (1986) 33. [11] T.P. Feist, P.K. Davies, J. Solid State Chem. 101 (1992) 275. [12] G.K. Mor, K. Shankar, M. Paulose, O.K. Varghese, C.A. Grimes, Nano Lett. 6 (2006) 215. [13] Z.R. Tian, J.A. Voigt, J. Liu, B. Mckenzie, H. Xu, J. Am. Chem. Soc. 125 (2003) 12384. [14] B. Chi, T. Jin, Cryst. Growth Des. 7 (2007) 815. [15] A. Fujishima, K. Honda, Nature 238 (1972) 37. [16] R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431. [17] X. Zhang, M. Jin, Z. Liu, S. Nishimoto, H. Saito, T. Murakami, A. Fujishima, Langmuir 22 (2006) 9477. [18] Z. Guo, F. Zhou, J. Hao, W. Liu, J. Am. Chem. Soc. 127 (2005) 15670. [19] L. Feng, S. Li, Y. Li, H. Li, L. Zhang, J. Zhai, B. Liu, L. Jiang, D. Zhu, Adv. Mater. 14 (2002) 1857. [20] R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kijima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431.