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Synthesis of TiO2 nanoparticles with mesoporous spherical morphology by a wet chemical method
Materials Letters 82 (2012) 208–210
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of TiO2 nanoparticles with mesoporous spherical morphology by a wet chemical method T. Prakash a, M. Navaneethan b, J. Archana b, S. Ponnusamy a,⁎, C. Muthamizhchelvan a, Y. Hayakawa b a b
Center for Materials Science and Nano Devices, Department of Physics, SRM University, Kattankulathur, Kancheepuram 603203, Tamil Nadu, India Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka‐432-8011, Japan
a r t i c l e
i n f o
Article history: Received 17 April 2012 Accepted 17 May 2012 Available online 25 May 2012 Keywords: Semiconductors Nanoparticles Chemical synthesis X-ray diffraction Optical properties
a b s t r a c t Mesoporous TiO2 microspheres are successfully synthesized via a simple wet chemical method using a mixture of ethanol, titanium isopropoxide and 2-chloroaniline. The structural, optical, vibrational and morphological properties of the TiO2 microspheres are characterized. Dominant anatase phase formation is observed in the structural analysis. A significant shift is observed for the band gap energy of the synthesized products with respect to that of bulk TiO2 because of the quantum confinement effect. The synthesis parameters are investigated in detail by a series of control experiments. Well defined mesoporous TiO2 microsphere morphology is acquired by microscopy techniques. It is found that the 2-chloroaniline influences the formation and optical properties of mesoporous TiO2 microspheres. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Materials and method
TiO2 semiconductors have attracted significant attention because their physical properties are suitable for many applications including catalysts, solar cells and gas sensors [1–4]. The crystalline phase, dimensions and morphology of TiO2 semiconductors are important factors affecting their application [5,6]. In recent years, much effort has been devoted to the fabrication of TiO2 nanostructures with different morphologies [7–10]. In particular, TiO2 microspheres exhibit excellent performance as catalysts and gas sensors because of their high specific surface area and low rate of charge carrier recombination [11]. Various chemical and physicochemical methods have been developed recently to prepare TiO2 spheres [12]. Among these techniques, a general approach to effectively prepare TiO2 spheres is to use templates based on various organic or inorganic species including polystyrene [13], carbon spheres and spheres of bacteria. Because of the facile removal of carbonaceous materials fabricated by hydrothermal carbonization, carbonaceous spheres have been used as sacrificial templates to fabricate spheres that can be applied in catalysis, sensing, chemical/biological separation, and lithium ion batteries [14–22]. In the present work, TiO2 spheres are synthesized using a simple wet chemical method without any templating agent, and their properties are investigated by a range of typical characterization techniques.
2.1. Synthesis of TiO2 spheres
⁎ Corresponding author at: Department of Physics, SRM University, Kattankulathur‐ 603 203, Kancheepuram (D.t), Tamil Nadu, India. Tel.: + 91 44 27452818; fax: + 91 44 27456255. E-mail address: [email protected] (S. Ponnusamy). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.05.064
Spherical anatase TiO2 nanostructures were prepared by fixing the ratio of titanium isopropoxide and ethanol and varying the concentration of 2-chloroaniline using a wet chemical method. In a typical process, a mixture of 2-chloroaniline and ethanol with a ratio of 1:40 was stirred. After 10 min, titanium isopropoxide (4 mL) was added to give a ratio of titanium isopropoxide, 2-chloroaniline and ethanol of 4:1:40 (sample E1), causing immediate precipitation of a brown powder. The mixture was stirred for 10 h at room temperature. The product was isolated by filtration and then dried at 100 °C in an oven under an air atmosphere. The same procedure was followed to prepare samples E2, E3 and E4, using 2, 3 and 4 mL of 2-chloroaniline, respectively.
2.2. Characterization The structural properties of the synthesized products were characterized by X-ray diffraction (XRD) using X'Pert pro (PANalytical B V, Holland) powder XRD (λ = 1.5418 Å). The morphologies and crystallite size of the resulting TiO2 nanoparticles were observed by high resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F, Japan) and scanning electron microscopy (SEM, JEOL JSM-6700F, Japan). Fourier transform infrared (FTIR) spectra were recorded by an ALPHA-T FTIR spectrometer using KBr pellet technique. UV–vis absorption spectra were recorded on a UV–vis spectrophotometer (LABINDIA/ UV3000+) in the wavelength range 200–1000 nm using ethanol as a dispersion medium.
209
Transmittance (a.u.)
(215)
(116)
(204)
(200)
(101) (004)
E1
(105)
Intensity (a.u.)
(101) (110)
T. Prakash et al. / Materials Letters 82 (2012) 208–210
E2 E3
E1
E2 E3
E4
E4 20
30
40
50
60
70
80
3500
3000
2500
2 (degree)
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 1. XRD patterns of TiO2 microsphere samples E1–4.
Fig. 3. FTIR spectra of TiO2 microsphere samples E1–4.
E4, respectively. The band gaps are blue shifted compared with that of bulk TiO2 (3.2 eV) because of the quantum confinement effect.
3. Results and discussion 3.1. XRD analysis
3.3. FTIR analysis XRD patterns of samples E1–4 are shown in Fig. 1. The samples all contain a mixture of anatase and rutile phases. The dominant peaks at 2θ = 25.3, 37.8, 48.0, 54.3, 62.7, 69.2 and 75.2° were consistent with the anatase phase of TiO2 pattern and well matched to standard JCPDS data (Card no. 78–2486), while diffraction peaks at 27 and 35.3° indicated the presence of the rutile phase. The reflection peaks were broad, indicating that the size of the crystals was in the nanoscale range. The average crystallite size was determined using the most intense XRD peak (101) using the Scherrer formula, and was found to be 5, 8, 15 and 20 nm for samples E1, E2, E3 and E4, respectively.
FTIR spectra for the samples in the range 3500–500 cm − 1 are shown in Fig. 3. The broad peak from 3000 to 3500 cm − 1 is assigned to the O–H stretching vibration of adsorbed water [23], while that at around 2856 cm − 1 is assigned to C–H stretching vibration [24]. Peaks corresponding to the O–Ti–O lattice appeared at 621 and 573 cm − 1, while the band at 1477 cm − 1 is attributed to N–H stretching of 2-chloroaniline [25–27]. The presence of functional groups in the synthesized samples confirms the strong interaction of 2-chloroaniline with TiO2.
3.4. SEM and TEM analysis 3.2. UV–vis analysis
Absorbance (a.u.)
UV–vis absorption spectra for samples E1–4 are presented in Fig. 2. The absorption edges of the samples change with the concentration of 2-chloroaniline, with absorption edges observed at 344, 348, 320 and 322 nm for samples E1, E2, E3 and E4, respectively. The band gaps were determined using these values, and were calculated to be 3.60, 3.56, 3.87 and 3.85 eV for samples E1, E2, E3 and
E4
E2
4. Conclusion E1 E3
200
The morphologies of samples E1–4 were analyzed by FESEM and are shown in Fig. 4(a), (b), (c) and (d), respectively. Low molar concentration of 2-chloroaniline yields the agglomerated morphology of TiO2 as shown in Fig. 4(a). Samples E2, E3 and E4 are composed of mesoporous microspheres. The TiO2 spheres possess very smooth surfaces and diameters of 200 to 500 nm. Fig. 4(e) shows the TEM image of sample E2. Formation of microspheres with well defined shape was clearly seen. The formation of regular TiO2 spheres appeared to inhibit their agglomeration to some extent, as observed in the HRTEM image shown in Fig. 4(f)–(h) at various locations of sample E2. Ratio of 2-chloroaniline influences the morphology of the TiO2 spheres. Fig. 4(f) and (g) shows that the spheres were composed of nanoparticles and they were interlinked by the crystal fringes and results in the formation of mesoporous spheres. The HRTEM image shown in Fig. 4(h) was obtained from a mesoporous sphere and indicates that the nanoparticles are highly crystalline.
400
600
800
Wavelength (nm) Fig. 2. UV spectra of TiO2 microsphere samples E1–4.
1000
Mesoporous TiO2 microspheres were synthesized by a simple wet chemical route, and their structural, optical and morphological properties were studied. The concentration of 2-chloroaniline added during formation affected the morphology of the mesoporous TiO2 microspheres. The average diameter of the microspheres ranged from 200 to 500 nm. Such mesoporous TiO2 microspheres may be useful for application in dye-sensitized solar cells.
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T. Prakash et al. / Materials Letters 82 (2012) 208–210
Fig. 4. (a), (b), (c) and (d) FESEM images samples E1–4, (e) TEM image of sample E2, (f), (g), (h) HRTEM images of sample E2.
Acknowledgments T. Prakash thanks SRM University for providing a research fellowship. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Hoffmann MR, Martin ST, Choi W. Chem Rev 1995;95:69–96. Linsebigler AL, Lu GQ, Yates JT. Chem Rev 1995;95:735–58. Fujishima A, Zhang XT, Tryk DA. Surf Sci Rep 2008;63:515–82. Ruiz A, Sakai G, Cornet A, Shimanoe K, Morante JR, Yamazoe N. Sens Actuators B 2003;93:509–18. Grela MA, Colussi AJ. J Phys Chem 1996;100:18214–21. Murakami N, Kurihara Y, Tsubota T, Ohno T. J Phys Chem C 2009;113:3062–9. Zhang YH, Yang YN, Xiao P, Zhang XN, Lu L, Li L. Mater Lett 2009;63:2429–31. Wang WZ, Ao L. Mater Lett 2010;64:912. Zeng W, Liu TM. Physica B 2010;405:1345. Yu QZ, Wang M, Chen HZ. Mater Lett 2010;64:428–30. Gopal K, Mor GK, Shankar K, Paulose M, Varghese OK, Grimes CA. Nano Lett 2006;6:215.
[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
Chu MQ, Liu GJ. Mater Lett 2006;60:11–4. Shen WH, Zhu YF, Dong XP, Gu JL, Shi JL. Chem Lett 2005;34:840–1. Sun XM, Li YD. Angew Chem Int Ed 2004;43:597–601. Wang CH, Chu XF, Wu MM. Sens Actuators B 2007;120:508–13. Q. Wang, H. Li, L.Q. Chen, X.J. Huang, 2001;39:2211–2214. Titirici MM, Antonietti M, Baccile N. Green Chem 2008;10:1204–12. Titirici M, Antonietti MM, Thomas A. Chem Mater 2006;18:3808–12. Sun XM, Liu JF, Li YD. Chem Eur J 2006;12:2039–47. Qian HS, Lin GF, Zhang YX, Wan PG, Xu R. Nanotechnology 2007;18:355602. Trung T, Ha CS. Mater Sci Eng C 2004;24:19. H.P. Klug, L.E. Alexander, John Wiley and Sons, New York, 1959. Ryu YB, Lee MS, Jeong ED, Kim HG, Jung WY, Baek SH, et al. Catal Today 2007;124: 88–93. Wei Q, Nie Z, Hao Y, Liu L, Chen Z, Zou J. J Sol–Gel Sci Technol 2006;39:103–9. Wang YM, Liu SW, Xiu Z, Jiao XB, Cui XP, Pan J. Mater Lett 2006;60:974–8. Zhou L, Yan S, Tian B, Zhang J, Anpo M. Mater Lett 2006;60:396–9. Zhu P, Teranishi M, Xiang J, Masuda Y, Seo W, Koumoto K. Thin Solid Films 2005;473:351–6.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of TiO2 nanoparticles with mesoporous spherical morphology by a wet chemical method T. Prakash a, M. Navaneethan b, J. Archana b, S. Ponnusamy a,⁎, C. Muthamizhchelvan a, Y. Hayakawa b a b
Center for Materials Science and Nano Devices, Department of Physics, SRM University, Kattankulathur, Kancheepuram 603203, Tamil Nadu, India Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka‐432-8011, Japan
a r t i c l e
i n f o
Article history: Received 17 April 2012 Accepted 17 May 2012 Available online 25 May 2012 Keywords: Semiconductors Nanoparticles Chemical synthesis X-ray diffraction Optical properties
a b s t r a c t Mesoporous TiO2 microspheres are successfully synthesized via a simple wet chemical method using a mixture of ethanol, titanium isopropoxide and 2-chloroaniline. The structural, optical, vibrational and morphological properties of the TiO2 microspheres are characterized. Dominant anatase phase formation is observed in the structural analysis. A significant shift is observed for the band gap energy of the synthesized products with respect to that of bulk TiO2 because of the quantum confinement effect. The synthesis parameters are investigated in detail by a series of control experiments. Well defined mesoporous TiO2 microsphere morphology is acquired by microscopy techniques. It is found that the 2-chloroaniline influences the formation and optical properties of mesoporous TiO2 microspheres. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Materials and method
TiO2 semiconductors have attracted significant attention because their physical properties are suitable for many applications including catalysts, solar cells and gas sensors [1–4]. The crystalline phase, dimensions and morphology of TiO2 semiconductors are important factors affecting their application [5,6]. In recent years, much effort has been devoted to the fabrication of TiO2 nanostructures with different morphologies [7–10]. In particular, TiO2 microspheres exhibit excellent performance as catalysts and gas sensors because of their high specific surface area and low rate of charge carrier recombination [11]. Various chemical and physicochemical methods have been developed recently to prepare TiO2 spheres [12]. Among these techniques, a general approach to effectively prepare TiO2 spheres is to use templates based on various organic or inorganic species including polystyrene [13], carbon spheres and spheres of bacteria. Because of the facile removal of carbonaceous materials fabricated by hydrothermal carbonization, carbonaceous spheres have been used as sacrificial templates to fabricate spheres that can be applied in catalysis, sensing, chemical/biological separation, and lithium ion batteries [14–22]. In the present work, TiO2 spheres are synthesized using a simple wet chemical method without any templating agent, and their properties are investigated by a range of typical characterization techniques.
2.1. Synthesis of TiO2 spheres
⁎ Corresponding author at: Department of Physics, SRM University, Kattankulathur‐ 603 203, Kancheepuram (D.t), Tamil Nadu, India. Tel.: + 91 44 27452818; fax: + 91 44 27456255. E-mail address: [email protected] (S. Ponnusamy). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.05.064
Spherical anatase TiO2 nanostructures were prepared by fixing the ratio of titanium isopropoxide and ethanol and varying the concentration of 2-chloroaniline using a wet chemical method. In a typical process, a mixture of 2-chloroaniline and ethanol with a ratio of 1:40 was stirred. After 10 min, titanium isopropoxide (4 mL) was added to give a ratio of titanium isopropoxide, 2-chloroaniline and ethanol of 4:1:40 (sample E1), causing immediate precipitation of a brown powder. The mixture was stirred for 10 h at room temperature. The product was isolated by filtration and then dried at 100 °C in an oven under an air atmosphere. The same procedure was followed to prepare samples E2, E3 and E4, using 2, 3 and 4 mL of 2-chloroaniline, respectively.
2.2. Characterization The structural properties of the synthesized products were characterized by X-ray diffraction (XRD) using X'Pert pro (PANalytical B V, Holland) powder XRD (λ = 1.5418 Å). The morphologies and crystallite size of the resulting TiO2 nanoparticles were observed by high resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F, Japan) and scanning electron microscopy (SEM, JEOL JSM-6700F, Japan). Fourier transform infrared (FTIR) spectra were recorded by an ALPHA-T FTIR spectrometer using KBr pellet technique. UV–vis absorption spectra were recorded on a UV–vis spectrophotometer (LABINDIA/ UV3000+) in the wavelength range 200–1000 nm using ethanol as a dispersion medium.
209
Transmittance (a.u.)
(215)
(116)
(204)
(200)
(101) (004)
E1
(105)
Intensity (a.u.)
(101) (110)
T. Prakash et al. / Materials Letters 82 (2012) 208–210
E2 E3
E1
E2 E3
E4
E4 20
30
40
50
60
70
80
3500
3000
2500
2 (degree)
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 1. XRD patterns of TiO2 microsphere samples E1–4.
Fig. 3. FTIR spectra of TiO2 microsphere samples E1–4.
E4, respectively. The band gaps are blue shifted compared with that of bulk TiO2 (3.2 eV) because of the quantum confinement effect.
3. Results and discussion 3.1. XRD analysis
3.3. FTIR analysis XRD patterns of samples E1–4 are shown in Fig. 1. The samples all contain a mixture of anatase and rutile phases. The dominant peaks at 2θ = 25.3, 37.8, 48.0, 54.3, 62.7, 69.2 and 75.2° were consistent with the anatase phase of TiO2 pattern and well matched to standard JCPDS data (Card no. 78–2486), while diffraction peaks at 27 and 35.3° indicated the presence of the rutile phase. The reflection peaks were broad, indicating that the size of the crystals was in the nanoscale range. The average crystallite size was determined using the most intense XRD peak (101) using the Scherrer formula, and was found to be 5, 8, 15 and 20 nm for samples E1, E2, E3 and E4, respectively.
FTIR spectra for the samples in the range 3500–500 cm − 1 are shown in Fig. 3. The broad peak from 3000 to 3500 cm − 1 is assigned to the O–H stretching vibration of adsorbed water [23], while that at around 2856 cm − 1 is assigned to C–H stretching vibration [24]. Peaks corresponding to the O–Ti–O lattice appeared at 621 and 573 cm − 1, while the band at 1477 cm − 1 is attributed to N–H stretching of 2-chloroaniline [25–27]. The presence of functional groups in the synthesized samples confirms the strong interaction of 2-chloroaniline with TiO2.
3.4. SEM and TEM analysis 3.2. UV–vis analysis
Absorbance (a.u.)
UV–vis absorption spectra for samples E1–4 are presented in Fig. 2. The absorption edges of the samples change with the concentration of 2-chloroaniline, with absorption edges observed at 344, 348, 320 and 322 nm for samples E1, E2, E3 and E4, respectively. The band gaps were determined using these values, and were calculated to be 3.60, 3.56, 3.87 and 3.85 eV for samples E1, E2, E3 and
E4
E2
4. Conclusion E1 E3
200
The morphologies of samples E1–4 were analyzed by FESEM and are shown in Fig. 4(a), (b), (c) and (d), respectively. Low molar concentration of 2-chloroaniline yields the agglomerated morphology of TiO2 as shown in Fig. 4(a). Samples E2, E3 and E4 are composed of mesoporous microspheres. The TiO2 spheres possess very smooth surfaces and diameters of 200 to 500 nm. Fig. 4(e) shows the TEM image of sample E2. Formation of microspheres with well defined shape was clearly seen. The formation of regular TiO2 spheres appeared to inhibit their agglomeration to some extent, as observed in the HRTEM image shown in Fig. 4(f)–(h) at various locations of sample E2. Ratio of 2-chloroaniline influences the morphology of the TiO2 spheres. Fig. 4(f) and (g) shows that the spheres were composed of nanoparticles and they were interlinked by the crystal fringes and results in the formation of mesoporous spheres. The HRTEM image shown in Fig. 4(h) was obtained from a mesoporous sphere and indicates that the nanoparticles are highly crystalline.
400
600
800
Wavelength (nm) Fig. 2. UV spectra of TiO2 microsphere samples E1–4.
1000
Mesoporous TiO2 microspheres were synthesized by a simple wet chemical route, and their structural, optical and morphological properties were studied. The concentration of 2-chloroaniline added during formation affected the morphology of the mesoporous TiO2 microspheres. The average diameter of the microspheres ranged from 200 to 500 nm. Such mesoporous TiO2 microspheres may be useful for application in dye-sensitized solar cells.
210
T. Prakash et al. / Materials Letters 82 (2012) 208–210
Fig. 4. (a), (b), (c) and (d) FESEM images samples E1–4, (e) TEM image of sample E2, (f), (g), (h) HRTEM images of sample E2.
Acknowledgments T. Prakash thanks SRM University for providing a research fellowship. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Hoffmann MR, Martin ST, Choi W. Chem Rev 1995;95:69–96. Linsebigler AL, Lu GQ, Yates JT. Chem Rev 1995;95:735–58. Fujishima A, Zhang XT, Tryk DA. Surf Sci Rep 2008;63:515–82. Ruiz A, Sakai G, Cornet A, Shimanoe K, Morante JR, Yamazoe N. Sens Actuators B 2003;93:509–18. Grela MA, Colussi AJ. J Phys Chem 1996;100:18214–21. Murakami N, Kurihara Y, Tsubota T, Ohno T. J Phys Chem C 2009;113:3062–9. Zhang YH, Yang YN, Xiao P, Zhang XN, Lu L, Li L. Mater Lett 2009;63:2429–31. Wang WZ, Ao L. Mater Lett 2010;64:912. Zeng W, Liu TM. Physica B 2010;405:1345. Yu QZ, Wang M, Chen HZ. Mater Lett 2010;64:428–30. Gopal K, Mor GK, Shankar K, Paulose M, Varghese OK, Grimes CA. Nano Lett 2006;6:215.
[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
Chu MQ, Liu GJ. Mater Lett 2006;60:11–4. Shen WH, Zhu YF, Dong XP, Gu JL, Shi JL. Chem Lett 2005;34:840–1. Sun XM, Li YD. Angew Chem Int Ed 2004;43:597–601. Wang CH, Chu XF, Wu MM. Sens Actuators B 2007;120:508–13. Q. Wang, H. Li, L.Q. Chen, X.J. Huang, 2001;39:2211–2214. Titirici MM, Antonietti M, Baccile N. Green Chem 2008;10:1204–12. Titirici M, Antonietti MM, Thomas A. Chem Mater 2006;18:3808–12. Sun XM, Liu JF, Li YD. Chem Eur J 2006;12:2039–47. Qian HS, Lin GF, Zhang YX, Wan PG, Xu R. Nanotechnology 2007;18:355602. Trung T, Ha CS. Mater Sci Eng C 2004;24:19. H.P. Klug, L.E. Alexander, John Wiley and Sons, New York, 1959. Ryu YB, Lee MS, Jeong ED, Kim HG, Jung WY, Baek SH, et al. Catal Today 2007;124: 88–93. Wei Q, Nie Z, Hao Y, Liu L, Chen Z, Zou J. J Sol–Gel Sci Technol 2006;39:103–9. Wang YM, Liu SW, Xiu Z, Jiao XB, Cui XP, Pan J. Mater Lett 2006;60:974–8. Zhou L, Yan S, Tian B, Zhang J, Anpo M. Mater Lett 2006;60:396–9. Zhu P, Teranishi M, Xiang J, Masuda Y, Seo W, Koumoto K. Thin Solid Films 2005;473:351–6.