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One-component solution system to prepare nanometric anatase TiO2
Materials Science and Engineering C 24 (2004) 19 – 22 www.elsevier.com/locate/msec
One-component solution system to prepare nanometric anatase TiO2 Tran Trung a,b, Chang-Sik Ha a,* a
Department of Polymer Science and Engineering, Pusan National University, Pusan 609-735, South Korea b Department of Electrochemistry, Hanoi University of Technology, Hanoi 10-000, Viet Nam
Abstract A novel one-pot synthesis route was proposed to prepare nanometric anatase TiO2 using trichloroethylene as reaction medium, which may have great advantage over multicomponent solution systems when TiO2 is used as a reinforcing filler for polymers dissolved in trichloroethylene. The anatase TiO2 nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy and small-angle X-ray scattering (SAXS). It was found that the diameters of TiO2 nanoparticles are in the range from 5 to 13 nm. D 2003 Elsevier B.V. All rights reserved. Keywords: Nanoparticles; Anatase; TiO2; Trichloroethylene
1. Introduction Titanium dioxide has attracted a lot of interest from both theoretical [1,2] and practical [3,4] point of view as an attractive material for metallic oxide semiconductors. Depending on titanium resources and the final target, some kinds of solvents have been used to prepare nanometeric TiO2 particles, such solvents including alcohols [4,5], carboxylic acids [6,7] and water [8,9]. In most cases, some foreign reagents have been used together with a solvent either as a peptizer (e.g. inorganic acids [9,10]), or as a stabilizer (e.g. acetic acid [4,6,7]), in order to monitor hydrolysis and condensation reactions. The particle size and pore distribution in membrane can be controlled using polyethylene glycol [5,11] or glycerol [12], as a gelling agent or a surfactant that is absorbed on the surface of primary nanosized particles. In our previous work [12], it was reported that a sol – gel process in the presence of glycerol as a new stabilizer in aqueous and non-aqueous media, which permits an easier preparation of pseudo-spherical TiO2 nanoparticles of very small size ranged from 4 to 10 nm, is to be accomplished. Recently, an attempt was made to find a novel stabilizerfree solvent system containing only titanium isopropoxide
* Corresponding author. Tel.: +82-51-510-2407; fax: +82-51-5144331. E-mail address: [email protected] (C.-S. Ha). 0928-4931/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2003.09.004
or other metal alkoxide in order to prepare TiO2 nanoparticles. In this study, we report for the first time the use of trichloroethylene, a volatile organic compound, as a reaction medium to prepare nanometeric anatase TiO2. Trichloroethylene known as a solvent widely used in polymer science is quite different from other solvents such as alcohols and water for preparation of TiO2 nanoparticles.
2. Experimental Two milliliters of titanium isoporopoxide was mixed with 60 ml of trichloroethylene with traces of water, under rigorous stirring, at room temperature. Then the hydrolysis and condensation reactions occurred under some conditions described in Scheme 1. The as-prepared powders were washed by ethanol and acetone for several times and dried at 100 jC in vacuum oven for 3 days, then heated at 400 jC for 10 h in air. The resulting powders were characterized with X-ray diffraction (XRD) measurements in the 2h range from 20j to 70j by using X-ray diffractometer (Rigaku model D/Max-2400). The radiation applied is CuKa, operating at 40 kW and 50 mA, in continuous scan mode with 0.01j step. The resulting powders were measured by a scanning electron microscopy with energy dispersive Xray microprobe (FE-SEM/EDX Hitachi microscope, Model S-4200). The size of the TiO2 particle was also measured using synchrotron small-angle X-ray scattering (SAXS) with a Rigaku X-ray generator operated at 40 kV
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T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
Scheme 1. The possible procedure and mechanism of hydrolysis and condensation reaction for the preparation of nanometeric anatase particles in the onecomponent solution system.
D ¼ 0:89*k=b*cosH
ð1Þ
where D = average crystal size (nm); k = X-ray wavelength (nm); b = excess line broadening (radians); H = Bragg angle (radians); B = line width and b = instrument line broadening. Visual evidence for crystal size of the obtained TiO2 nanoparticles prepared in trichloroethylene is provided by the typical SEM/EDX. The SEM micrograph shown in Fig. 2 clearly exhibits roughly spherical particles in nanoscale range from 5 to 13 nm. EDX studies on the samples showed that the composition of the surface layer of the TiO2 nanoparticles was nonstoichiometric and the atomic ratio of Ti/O was almost equal to 1.96. The nonstoichiometric atomic ratio of Ti/O implies that some defects exist in TiO2 nanoparticles, due to oxygen deficiencies. In other words, oxygen vacancies can cause the formation of crystallographic shear planes and active Ti-sites for the adsorption and chemisorptions of OH groups or other contaminants. Fig. 3 shows the SAXS profile, where the relative scattering intensity (I) vs. scattering vector (q) is plotted on a double logarithmic scale, for the sample heated at 400 jC for 10 h. The scattering vector q = ks ki (ks and ki are the scattered and incident wave vectors, respectively) is related to scattering angle H by:
b ¼ ðB2 b2 Þ1=2
ð2Þ
q ¼ ð4p=kÞ*sinðH=2Þ
and 40 mA in the Pohang Accelerator Laboratory, POSTECH, Korea. The scanning rate is 0.2j/min.
3. Results and discussion Fig. 1 illustrates the powder X-ray diffraction patterns of the samples dried at 100 jC (a) and heated at 400 jC (b). However, only the XRD pattern of sample heated at 400 jC exhibits intense reflection peaks at 2h: 25.23j, 36.88j, 37.75j, 47.78j, 53.82j, 54.99j, 62.59j and 68.62j, which shows that this sample possesses anatase TiO2 phase with tetragonal anatase structure. On the other hand, no reflection peak was observed in the XRD pattern of sample dried at 100 jC, except for a featureless diffraction pattern centered around 2h at 30j attributed to the crystal imperfection or the absence of long-range ordering and the existence of defects on the reflective planes in nanoparticles. The crystal size was estimated as 12.4 nm and listed in Table 1, using the most intense (101) peak, 2h = 25.23j, with its full line width at half of the maximum peak intensity of 0.65 (inset in Fig. 1), from the Debye – Scherrer formula [13,14] given by:
ð3Þ
T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
21
Fig. 1. XRD patterns of nanometric TiO2 powders prepared in trichloroethylene, heated at 100 jC for 3 days (a) and at 400 jC for 10 h (b). Inset is the most intense (101) peak, 2H = 25.23j, with its full line width at half of the maximum peak intensity of 0.65 to estimate the crystal size.
where k is wavelength of incident radiation [15]. The size of the scatters, which is defined by its characteristic length or the diameter of the particles, is inversely related to q. To determine whether scattering depends on the scattering vector q under the power law I(q)~q( exp), log – log graphs of I(q) vs. q were plotted. If scattering from particles obeys a power law, the graphs will be linear. Thus, we estimate the distribution of the particle size from a linear part of SAXS profile. For the obtained sample heated at 400 jC, the observed linear region (Fig. 3) extended over the q-range 0.1520 –0.3403 nm 1, and showed the diameter of TiO2 nanoparticles in the range from 5.8 to 13.2 nm. Table 1 summarizes the characterization data of the TiO2 nanoparticles prepared using trichloroethylene by various techniques. It is clearly shown that all the data match very well and the nanometric TiO2 anatase particles have been successfully prepared using a one-component solution system, trichloroethylene, without any foreign additive. The result suggests that a new solvent, trichloroethylene, plays a
role not only as a medium for dispersion of metal alkoxides, but a role of stabilizer and foreign surfactant additive. It may also an appropriate solvent to prepare binary or ternary nanoparticle systems. The one-pot process has an especially
Table 1 Characteristics of crystal structure and particle size Sample
Distribution of particle size
Crystal structure
TiO2 prepared in one-component solution, Tricholoroethylene
12.4 nm Tetragonal (XRD) anatase 5.8 – 13.2 nm (SAXS) 5.0 – 13 nm (SEM) Composition of the surface layer: atomic ratio of Ti/O = 1:1.96 (EDX) Stoichiometric ratio of Ti/O = 1:2
Fig. 2. SEM image of TiO2 powdery sample prepared in trichloroethylene heated at 400 jC for 10 h.
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T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
analysis shows that the diameters of TiO2 nanoparticles are in the range from 5.8 to 13.2 nm. It is concluded from the XRD, SEM, and SAXS analyses that diameters of TiO2 nanoparticles are in the range from 5 to 13 nm.
Acknowledgements
Fig. 3. Log – log plot of I(q) vs. q shows the distribution of nanoparticle size of TiO2 powder prepared in one-component solution system, trichloroethylene.
The work is supported by the National Research Laboratory Program, the Center for Integrated Molecular Systems, POSTECH, Korea and the Brain Korea 21 Project. Tran Trung wishes to thank the Korea Science and Engineering Foundation for the financial support for his post-doc. Fellowship. The SAXS measurement in the Pohang Accelerator Laboratory, Korea is also gratefully acknowledged.
References great advantage over multi-component solution systems when TiO2 is used as a reinforcing filler for polymers dissolved in trichloroethylene, because in multi-component solution systems, where foreign additives, required for preparation of TiO2 nanoparticles, often remain as undesirable contaminants in final products including polymer composites. Future studies will focus on polymer films using these nanoparticles as reinforcement using trichloroethylene as reaction medium as well as the exact role trichloroethylene in the one-pot synthetic process.
4. Conclusions In this work, a novel one-pot synthetic route was proposed to prepare nanometric anatase TiO2 using trichloroethylene as a reaction medium. TiO2 nanoparticles were successfully prepared using one-component solution system, trichloroethylene, without any foreign additive. The anatase structures of the TiO2 nanoparticles were determined by XRD. SEM micrograph image exhibits roughly spherical particles in nanoscale ranged from 5 to 13 nm. SAXS
[1] A. Goossens, B. van der Zanden, J. Schoonman, Chem. Phys. Lett. 331 (2000) 1. [2] S. Monticone, R. Tufeu, A.V. Kanaev, E. Scolan, C. Sanchez, Appl. Surf. Sci. 162 (2000) 565. [3] S.H. Chung, Y. Wang, L. Persi, F. Croce, S.G. Greenbaum, B. Scrosati, E. Plichta, J. Power Sources 98 (2001) 644. [4] J.C. Plenet, A. Brionde, E. Berstein, F. Lequevre, J. Dumas, J. Mugnier, Opt. Mater. 13 (2000) 411. [5] K. Kato, K. Niihara, Thin Solid Films 298 (1997) 76. [6] C. Suresh, V. Biju, P. Mukundan, K.G.K. Warrier, Polyhydron 17 (1998) 3131. [7] P.A. Venz, R.L. Frost, J.R. Bartlett, J.L. Woolfrey, J.T. Kloprogge, Thermochim. Acta 346 (2000) 73. [8] Q. Zhang, L. Gao, J. Guo, Appl. Catal., B Environ. 26 (2000) 207. [9] R. Zhang, L. Gao, Mater. Res. Bull. 36 (2001) 1957. [10] T. Nishide, F. Mizukami, Thin Solid Films 353 (1999) 67. [11] X.H. Liu, J. Wang, L. Wang, X. Yang, L. Li, X. Wang, Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 289 (2000) 241. [12] T. Trung, W.J. Cho, C.S. Ha, Mater. Lett. 57 (2003) 2746. [13] E. Bettaut, in: C.H. MacGillavary, G.D. Riecks (Eds.), International Tables for X-ray Crystallography, Reidel, Dordrecht, 1962, pp. 318 – 323. [14] A. Guinier, X-ray Diffraction in Crystals, Imperfect Crystals and Amorphous Bodies, Freeman, San Francisco, 1963. [15] P. Schmidt, in: D. Avnir (Ed.), The Fractal Approach to Heterogeneous Chemistry, Wiley, Chichester, UK, 1994, pp. 67 – 69.
One-component solution system to prepare nanometric anatase TiO2 Tran Trung a,b, Chang-Sik Ha a,* a
Department of Polymer Science and Engineering, Pusan National University, Pusan 609-735, South Korea b Department of Electrochemistry, Hanoi University of Technology, Hanoi 10-000, Viet Nam
Abstract A novel one-pot synthesis route was proposed to prepare nanometric anatase TiO2 using trichloroethylene as reaction medium, which may have great advantage over multicomponent solution systems when TiO2 is used as a reinforcing filler for polymers dissolved in trichloroethylene. The anatase TiO2 nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy and small-angle X-ray scattering (SAXS). It was found that the diameters of TiO2 nanoparticles are in the range from 5 to 13 nm. D 2003 Elsevier B.V. All rights reserved. Keywords: Nanoparticles; Anatase; TiO2; Trichloroethylene
1. Introduction Titanium dioxide has attracted a lot of interest from both theoretical [1,2] and practical [3,4] point of view as an attractive material for metallic oxide semiconductors. Depending on titanium resources and the final target, some kinds of solvents have been used to prepare nanometeric TiO2 particles, such solvents including alcohols [4,5], carboxylic acids [6,7] and water [8,9]. In most cases, some foreign reagents have been used together with a solvent either as a peptizer (e.g. inorganic acids [9,10]), or as a stabilizer (e.g. acetic acid [4,6,7]), in order to monitor hydrolysis and condensation reactions. The particle size and pore distribution in membrane can be controlled using polyethylene glycol [5,11] or glycerol [12], as a gelling agent or a surfactant that is absorbed on the surface of primary nanosized particles. In our previous work [12], it was reported that a sol – gel process in the presence of glycerol as a new stabilizer in aqueous and non-aqueous media, which permits an easier preparation of pseudo-spherical TiO2 nanoparticles of very small size ranged from 4 to 10 nm, is to be accomplished. Recently, an attempt was made to find a novel stabilizerfree solvent system containing only titanium isopropoxide
* Corresponding author. Tel.: +82-51-510-2407; fax: +82-51-5144331. E-mail address: [email protected] (C.-S. Ha). 0928-4931/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2003.09.004
or other metal alkoxide in order to prepare TiO2 nanoparticles. In this study, we report for the first time the use of trichloroethylene, a volatile organic compound, as a reaction medium to prepare nanometeric anatase TiO2. Trichloroethylene known as a solvent widely used in polymer science is quite different from other solvents such as alcohols and water for preparation of TiO2 nanoparticles.
2. Experimental Two milliliters of titanium isoporopoxide was mixed with 60 ml of trichloroethylene with traces of water, under rigorous stirring, at room temperature. Then the hydrolysis and condensation reactions occurred under some conditions described in Scheme 1. The as-prepared powders were washed by ethanol and acetone for several times and dried at 100 jC in vacuum oven for 3 days, then heated at 400 jC for 10 h in air. The resulting powders were characterized with X-ray diffraction (XRD) measurements in the 2h range from 20j to 70j by using X-ray diffractometer (Rigaku model D/Max-2400). The radiation applied is CuKa, operating at 40 kW and 50 mA, in continuous scan mode with 0.01j step. The resulting powders were measured by a scanning electron microscopy with energy dispersive Xray microprobe (FE-SEM/EDX Hitachi microscope, Model S-4200). The size of the TiO2 particle was also measured using synchrotron small-angle X-ray scattering (SAXS) with a Rigaku X-ray generator operated at 40 kV
20
T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
Scheme 1. The possible procedure and mechanism of hydrolysis and condensation reaction for the preparation of nanometeric anatase particles in the onecomponent solution system.
D ¼ 0:89*k=b*cosH
ð1Þ
where D = average crystal size (nm); k = X-ray wavelength (nm); b = excess line broadening (radians); H = Bragg angle (radians); B = line width and b = instrument line broadening. Visual evidence for crystal size of the obtained TiO2 nanoparticles prepared in trichloroethylene is provided by the typical SEM/EDX. The SEM micrograph shown in Fig. 2 clearly exhibits roughly spherical particles in nanoscale range from 5 to 13 nm. EDX studies on the samples showed that the composition of the surface layer of the TiO2 nanoparticles was nonstoichiometric and the atomic ratio of Ti/O was almost equal to 1.96. The nonstoichiometric atomic ratio of Ti/O implies that some defects exist in TiO2 nanoparticles, due to oxygen deficiencies. In other words, oxygen vacancies can cause the formation of crystallographic shear planes and active Ti-sites for the adsorption and chemisorptions of OH groups or other contaminants. Fig. 3 shows the SAXS profile, where the relative scattering intensity (I) vs. scattering vector (q) is plotted on a double logarithmic scale, for the sample heated at 400 jC for 10 h. The scattering vector q = ks ki (ks and ki are the scattered and incident wave vectors, respectively) is related to scattering angle H by:
b ¼ ðB2 b2 Þ1=2
ð2Þ
q ¼ ð4p=kÞ*sinðH=2Þ
and 40 mA in the Pohang Accelerator Laboratory, POSTECH, Korea. The scanning rate is 0.2j/min.
3. Results and discussion Fig. 1 illustrates the powder X-ray diffraction patterns of the samples dried at 100 jC (a) and heated at 400 jC (b). However, only the XRD pattern of sample heated at 400 jC exhibits intense reflection peaks at 2h: 25.23j, 36.88j, 37.75j, 47.78j, 53.82j, 54.99j, 62.59j and 68.62j, which shows that this sample possesses anatase TiO2 phase with tetragonal anatase structure. On the other hand, no reflection peak was observed in the XRD pattern of sample dried at 100 jC, except for a featureless diffraction pattern centered around 2h at 30j attributed to the crystal imperfection or the absence of long-range ordering and the existence of defects on the reflective planes in nanoparticles. The crystal size was estimated as 12.4 nm and listed in Table 1, using the most intense (101) peak, 2h = 25.23j, with its full line width at half of the maximum peak intensity of 0.65 (inset in Fig. 1), from the Debye – Scherrer formula [13,14] given by:
ð3Þ
T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
21
Fig. 1. XRD patterns of nanometric TiO2 powders prepared in trichloroethylene, heated at 100 jC for 3 days (a) and at 400 jC for 10 h (b). Inset is the most intense (101) peak, 2H = 25.23j, with its full line width at half of the maximum peak intensity of 0.65 to estimate the crystal size.
where k is wavelength of incident radiation [15]. The size of the scatters, which is defined by its characteristic length or the diameter of the particles, is inversely related to q. To determine whether scattering depends on the scattering vector q under the power law I(q)~q( exp), log – log graphs of I(q) vs. q were plotted. If scattering from particles obeys a power law, the graphs will be linear. Thus, we estimate the distribution of the particle size from a linear part of SAXS profile. For the obtained sample heated at 400 jC, the observed linear region (Fig. 3) extended over the q-range 0.1520 –0.3403 nm 1, and showed the diameter of TiO2 nanoparticles in the range from 5.8 to 13.2 nm. Table 1 summarizes the characterization data of the TiO2 nanoparticles prepared using trichloroethylene by various techniques. It is clearly shown that all the data match very well and the nanometric TiO2 anatase particles have been successfully prepared using a one-component solution system, trichloroethylene, without any foreign additive. The result suggests that a new solvent, trichloroethylene, plays a
role not only as a medium for dispersion of metal alkoxides, but a role of stabilizer and foreign surfactant additive. It may also an appropriate solvent to prepare binary or ternary nanoparticle systems. The one-pot process has an especially
Table 1 Characteristics of crystal structure and particle size Sample
Distribution of particle size
Crystal structure
TiO2 prepared in one-component solution, Tricholoroethylene
12.4 nm Tetragonal (XRD) anatase 5.8 – 13.2 nm (SAXS) 5.0 – 13 nm (SEM) Composition of the surface layer: atomic ratio of Ti/O = 1:1.96 (EDX) Stoichiometric ratio of Ti/O = 1:2
Fig. 2. SEM image of TiO2 powdery sample prepared in trichloroethylene heated at 400 jC for 10 h.
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T. Trung, C.-S. Ha / Materials Science and Engineering C 24 (2004) 19–22
analysis shows that the diameters of TiO2 nanoparticles are in the range from 5.8 to 13.2 nm. It is concluded from the XRD, SEM, and SAXS analyses that diameters of TiO2 nanoparticles are in the range from 5 to 13 nm.
Acknowledgements
Fig. 3. Log – log plot of I(q) vs. q shows the distribution of nanoparticle size of TiO2 powder prepared in one-component solution system, trichloroethylene.
The work is supported by the National Research Laboratory Program, the Center for Integrated Molecular Systems, POSTECH, Korea and the Brain Korea 21 Project. Tran Trung wishes to thank the Korea Science and Engineering Foundation for the financial support for his post-doc. Fellowship. The SAXS measurement in the Pohang Accelerator Laboratory, Korea is also gratefully acknowledged.
References great advantage over multi-component solution systems when TiO2 is used as a reinforcing filler for polymers dissolved in trichloroethylene, because in multi-component solution systems, where foreign additives, required for preparation of TiO2 nanoparticles, often remain as undesirable contaminants in final products including polymer composites. Future studies will focus on polymer films using these nanoparticles as reinforcement using trichloroethylene as reaction medium as well as the exact role trichloroethylene in the one-pot synthetic process.
4. Conclusions In this work, a novel one-pot synthetic route was proposed to prepare nanometric anatase TiO2 using trichloroethylene as a reaction medium. TiO2 nanoparticles were successfully prepared using one-component solution system, trichloroethylene, without any foreign additive. The anatase structures of the TiO2 nanoparticles were determined by XRD. SEM micrograph image exhibits roughly spherical particles in nanoscale ranged from 5 to 13 nm. SAXS
[1] A. Goossens, B. van der Zanden, J. Schoonman, Chem. Phys. Lett. 331 (2000) 1. [2] S. Monticone, R. Tufeu, A.V. Kanaev, E. Scolan, C. Sanchez, Appl. Surf. Sci. 162 (2000) 565. [3] S.H. Chung, Y. Wang, L. Persi, F. Croce, S.G. Greenbaum, B. Scrosati, E. Plichta, J. Power Sources 98 (2001) 644. [4] J.C. Plenet, A. Brionde, E. Berstein, F. Lequevre, J. Dumas, J. Mugnier, Opt. Mater. 13 (2000) 411. [5] K. Kato, K. Niihara, Thin Solid Films 298 (1997) 76. [6] C. Suresh, V. Biju, P. Mukundan, K.G.K. Warrier, Polyhydron 17 (1998) 3131. [7] P.A. Venz, R.L. Frost, J.R. Bartlett, J.L. Woolfrey, J.T. Kloprogge, Thermochim. Acta 346 (2000) 73. [8] Q. Zhang, L. Gao, J. Guo, Appl. Catal., B Environ. 26 (2000) 207. [9] R. Zhang, L. Gao, Mater. Res. Bull. 36 (2001) 1957. [10] T. Nishide, F. Mizukami, Thin Solid Films 353 (1999) 67. [11] X.H. Liu, J. Wang, L. Wang, X. Yang, L. Li, X. Wang, Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 289 (2000) 241. [12] T. Trung, W.J. Cho, C.S. Ha, Mater. Lett. 57 (2003) 2746. [13] E. Bettaut, in: C.H. MacGillavary, G.D. Riecks (Eds.), International Tables for X-ray Crystallography, Reidel, Dordrecht, 1962, pp. 318 – 323. [14] A. Guinier, X-ray Diffraction in Crystals, Imperfect Crystals and Amorphous Bodies, Freeman, San Francisco, 1963. [15] P. Schmidt, in: D. Avnir (Ed.), The Fractal Approach to Heterogeneous Chemistry, Wiley, Chichester, UK, 1994, pp. 67 – 69.