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Synthesis of tin-doped indium oxide nanoparticles by an ion-exchange and hydrothermal process
Materials Letters 60 (2006) 983 – 985 www.elsevier.com/locate/matlet
Synthesis of tin-doped indium oxide nanoparticles by an ion-exchange and hydrothermal process Hua-Rui Xu a,⁎, Huaiying Zhou a , Guisheng Zhu a , Jinzhong Chen b , Chuntu Liao b a
Department of Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China b Liuzhou China-tin Group Company Ltd., Liuzhou 545006, China Received 24 August 2005; accepted 21 October 2005 Available online 10 November 2005
Abstract ITO nanopowder with uniform size was successfully prepared by an ion-exchange treatment followed by hydrothermal process. Ion-exchange treatment of the indium–tin chloride led to the formation of the homogeneous In–Sn hydroxide sol. Then, hydrothermal (240 °C for 7 h) followed by calcination (500 °C for 2 h) led to preparation of the cubic C-type rare-earth structured ITO nanopowders with a very narrow size distribution (97 ± 5 nm). Using the regenerated resin to ion-exchange, the yield of ITO could be above 99%. © 2005 Elsevier B.V. All rights reserved. Keywords: ITO; Ion-exchange; Hydrothermal
1. Introduction Tin-doped indium oxide (or ITO) is an advanced ceramic material with many electronic and optical applications due to its high electrical conductivity (up to 104 Ω− 1 cm− 1) and transparency to light [1]. ITO thin films are used in transparent electrodes for display devices, transparent coatings for solar energy heat mirrors, and window films in n–p heterojunction solar cells, etc. ITO thin films are commonly prepared by magnetron sputtering, which utilizes dense ITO targets. To optimize the sputtering efficiency, the targets, which are normally formed by sintering ITO powders, should be as dense as possible. The characteristics of the starting ITO powder strongly influence the properties of the final ITO target and the resultant ITO thin film. In practice, the target density can be improved by properly controlling the size distribution of the mixture composed of several narrowly sized nanoparticles [2]. ITO nanoparticles have been prepared by a variety of methods, including thermal hydrolysis, thermal decomposition, sol-gel technique, microemulsion and spray pyrolysis
⁎ Corresponding author. Tel.: +86 773 5605159; fax: +86 773 5603075. E-mail address: [email protected] (H.-R. Xu). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.062
[3–7]. But with each of these methods, nanosized ITO powder is difficult to obtain and often has a high degree of agglomeration. Recently, hydrothermal method was applied to the preparation of ITO powders with good dispersion [8]. However, the as-prepared particles have a wide and uncontrollable size distribution, which is not desirable. This is because heterogeneous indium and tin hydroxide powders or sols formed from direct precipitation of metal salt with sodium hydroxide or ammonia are wide size distribution and used as the hydrothermal precursor. According to the dissolution–precipitation mechanism during the hydrothermal process, the uniform-sized ITO nanopowders may be prepared but the hydrothermal process must be at a higher temperature and for a longer period. Therefore, there is a need to develop a new method to overcome this problem to obtain the homogenous precipitate with controllable particle size and narrow size distribution, which used as the hydrothermal precursor. In the present study, the possibilities of obtaining ITO powders with the uniform particle size from an aqueous solution of InCl3 and SnCl4 by an ion-exchange and hydrothermal process was examined; the InCl3 and SnCl4 solution was mixed with an anion-exchange resin converted into homogeneous In–Sn hydroxide sol in advance. This method is a modification of the basification method, but may be more advantageous because
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H.-R. Xu et al. / Materials Letters 60 (2006) 983–985
tion. Particle morphology and size was characterized by scanning electron microscopy (SEM; Philips XL30 and DX-4I) and transmission electron microscopy (TEM; Hitachi H-800). The impurities in the powders, such as Cl−, were confirmed by chemical analysis and inductively coupled plasma atomic emission spectrometer (ICP–AES; Optima 3000). 3. Results and discussion
Fig. 1. SEM and XRD of the ITO powders prepared by ion-exchange and hydrothermal process.
the nucleation is more homogeneous and no chloride salt is left in the products. 2. Experimental A commercial anion-exchange resin (Diaion SA 10A, Mitsubishi Chemical Co.) was immersed in a basic solution (NaOH) for 1 h to convert it from Cl− type to OH− type. After washing with distilled water five times to make the pH close to 7, the resin was transferred to a plastic container and stirred slightly. The indium tin solution was prepared by dissolving indium and tin metal in HCl. The quantity of metal in the solution was adjusted as final oxide composition: 90:10 weight ratio of In2O3/SnO2. The aqueous solution with the concentration of about 4 mol/L was poured down to the container to mix with the stirred resin (volume ratio of resin and In–Sn chloride solution = 75:25) and to obtain the sol. After stirring for 3 h, the colloidal sol was then separated from the resin using a 0.1mm filter. Washing the resin several times, the final sol was transferred to a 50-ml Teflon-lined stainless steel vessel. The sealed vessel was heated at 240 °C for 7 h. After cooling down to room temperature, the precipitate was centrifuged and finally dried at 80 °C for 12 h in a vacuum oven. Then the powders were calcined at 500 °C for 2 h in air in order to obtain the ITO powders. ITO powders were examined by powder X-ray diffraction (XRD; Rigaku Geigerflex D/Max 2200) using CuKα radia-
Fig. 1 showed the SEM photograph and XRD patterns of the ITO nanoparticles prepared by the ion-exchange and hydrothermal process. The particles exhibited a good dispersion, and a narrow size distribution (97 ± 5 nm) and a single phase, similar to the cubic C-type rareearth structured In2O3 (JCPDS 6-0416). ICP and chemical analysis of the powders had been showed the In2O3/SnO2 ratio of 90 : 10 same as the precursor ratio and also proven no traces of Cl− ion (less than 30 ppm). Clearly, with ion-exchange resin introduced for homogeneous precipitation, the hydrothermal method could be used to synthesize ITO nanoparticles with narrow size distribution. Yield of ITO was 95% based on starting raw materials; that is, 5% In–Sn hydroxide particles was stored in the inner pores of the resin. However, using the regenerated resin to mix with In–Sn chloride again, yield of ITO could be above 99%. By the traditional hydrothermal process, In3+ and Sn4+ cations combined with OH− to form In(OH)3 and Sn(OH)4 and formed hydrous gel-type precipitates. It is well known that controlling the precipitate condition, making the homogeneous nucleation easily appear, is too difficult. Therefore, a heterogeneous gel with a wide and uncontrollable size distribution was usually formed by the traditional coprecipitation method, hence ITO powders had a wide size distribution, even at a higher hydrothermal temperature for a longer period [8]. In the present work, the ion-exchange method is a modification of basification method; however, the precipitate can only be formed slowly because the rate of the adsorption is very slow. The as-prepared sol was dried up and characterized by TEM and XRD. The sample showed very poor crystallinity (same as the traditional coprecipitated gel powders) and soft conglomeration but with a narrow particle size (see Fig. 2). The uniform particles could be grown by the dissolution– precipitation process in the hydrothermal environment with the higher pressure and temperature [8].
Fig. 2. TEM of the In–Sn hydroxide powders prepared by ion-exchange.
H.-R. Xu et al. / Materials Letters 60 (2006) 983–985
985
4. Summary
References
ITO nanopowder with uniform size (97 ± 5 nm) was successfully prepared by an ion-exchange treatment followed by hydrothermal process. Moreover, using the regenerated resin to ion-exchange, the yield of ITO could be above 99%. Therefore, the ion-exchange treatment and hydrothermal process offers a simple and effective way for producing uniform ITO nanoparticles in the materials industry.
[1] J.G. Nam, H. Choi, S.H. Kim, K.H. Song, S.C. Park, Scr. Mater. 44 (2001) 2047. [2] A.B. Yu, N. Standish, Ind. Eng. Chem. Res. 30 (1991) 1372. [3] K.Y. Kim, S.B. Park, Mater. Chem. Phys. 86 (2004) 210. [4] S. Chen, C. Li, W. Xiong, L. Liu, H. Wang, Mater. Lett. 58 (2004) 294. [5] C. Yan, M. Zharnikov, A. Golzhauser, M. Grunze, Langmuir 16 (2000) 6208. [6] T. Kayukawa, H. Shigetani, M. Senna, J. Mater. Sci. Lett. 14 (1995) 252. [7] S. Tang, J. Yao, J. Chen, J. Luo, J. Mater. Process. Technol. 137 (2003) 82. [8] K. Yanagisawa, C.P. Udawatte, S. Nasu, J. Mater. Res. 15 (2000) 1404.
Acknowledgment This work is sponsored by the Hi-Tech Research and Development Program of China (No. 2003AA32X140).
Synthesis of tin-doped indium oxide nanoparticles by an ion-exchange and hydrothermal process Hua-Rui Xu a,⁎, Huaiying Zhou a , Guisheng Zhu a , Jinzhong Chen b , Chuntu Liao b a
Department of Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China b Liuzhou China-tin Group Company Ltd., Liuzhou 545006, China Received 24 August 2005; accepted 21 October 2005 Available online 10 November 2005
Abstract ITO nanopowder with uniform size was successfully prepared by an ion-exchange treatment followed by hydrothermal process. Ion-exchange treatment of the indium–tin chloride led to the formation of the homogeneous In–Sn hydroxide sol. Then, hydrothermal (240 °C for 7 h) followed by calcination (500 °C for 2 h) led to preparation of the cubic C-type rare-earth structured ITO nanopowders with a very narrow size distribution (97 ± 5 nm). Using the regenerated resin to ion-exchange, the yield of ITO could be above 99%. © 2005 Elsevier B.V. All rights reserved. Keywords: ITO; Ion-exchange; Hydrothermal
1. Introduction Tin-doped indium oxide (or ITO) is an advanced ceramic material with many electronic and optical applications due to its high electrical conductivity (up to 104 Ω− 1 cm− 1) and transparency to light [1]. ITO thin films are used in transparent electrodes for display devices, transparent coatings for solar energy heat mirrors, and window films in n–p heterojunction solar cells, etc. ITO thin films are commonly prepared by magnetron sputtering, which utilizes dense ITO targets. To optimize the sputtering efficiency, the targets, which are normally formed by sintering ITO powders, should be as dense as possible. The characteristics of the starting ITO powder strongly influence the properties of the final ITO target and the resultant ITO thin film. In practice, the target density can be improved by properly controlling the size distribution of the mixture composed of several narrowly sized nanoparticles [2]. ITO nanoparticles have been prepared by a variety of methods, including thermal hydrolysis, thermal decomposition, sol-gel technique, microemulsion and spray pyrolysis
⁎ Corresponding author. Tel.: +86 773 5605159; fax: +86 773 5603075. E-mail address: [email protected] (H.-R. Xu). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.062
[3–7]. But with each of these methods, nanosized ITO powder is difficult to obtain and often has a high degree of agglomeration. Recently, hydrothermal method was applied to the preparation of ITO powders with good dispersion [8]. However, the as-prepared particles have a wide and uncontrollable size distribution, which is not desirable. This is because heterogeneous indium and tin hydroxide powders or sols formed from direct precipitation of metal salt with sodium hydroxide or ammonia are wide size distribution and used as the hydrothermal precursor. According to the dissolution–precipitation mechanism during the hydrothermal process, the uniform-sized ITO nanopowders may be prepared but the hydrothermal process must be at a higher temperature and for a longer period. Therefore, there is a need to develop a new method to overcome this problem to obtain the homogenous precipitate with controllable particle size and narrow size distribution, which used as the hydrothermal precursor. In the present study, the possibilities of obtaining ITO powders with the uniform particle size from an aqueous solution of InCl3 and SnCl4 by an ion-exchange and hydrothermal process was examined; the InCl3 and SnCl4 solution was mixed with an anion-exchange resin converted into homogeneous In–Sn hydroxide sol in advance. This method is a modification of the basification method, but may be more advantageous because
984
H.-R. Xu et al. / Materials Letters 60 (2006) 983–985
tion. Particle morphology and size was characterized by scanning electron microscopy (SEM; Philips XL30 and DX-4I) and transmission electron microscopy (TEM; Hitachi H-800). The impurities in the powders, such as Cl−, were confirmed by chemical analysis and inductively coupled plasma atomic emission spectrometer (ICP–AES; Optima 3000). 3. Results and discussion
Fig. 1. SEM and XRD of the ITO powders prepared by ion-exchange and hydrothermal process.
the nucleation is more homogeneous and no chloride salt is left in the products. 2. Experimental A commercial anion-exchange resin (Diaion SA 10A, Mitsubishi Chemical Co.) was immersed in a basic solution (NaOH) for 1 h to convert it from Cl− type to OH− type. After washing with distilled water five times to make the pH close to 7, the resin was transferred to a plastic container and stirred slightly. The indium tin solution was prepared by dissolving indium and tin metal in HCl. The quantity of metal in the solution was adjusted as final oxide composition: 90:10 weight ratio of In2O3/SnO2. The aqueous solution with the concentration of about 4 mol/L was poured down to the container to mix with the stirred resin (volume ratio of resin and In–Sn chloride solution = 75:25) and to obtain the sol. After stirring for 3 h, the colloidal sol was then separated from the resin using a 0.1mm filter. Washing the resin several times, the final sol was transferred to a 50-ml Teflon-lined stainless steel vessel. The sealed vessel was heated at 240 °C for 7 h. After cooling down to room temperature, the precipitate was centrifuged and finally dried at 80 °C for 12 h in a vacuum oven. Then the powders were calcined at 500 °C for 2 h in air in order to obtain the ITO powders. ITO powders were examined by powder X-ray diffraction (XRD; Rigaku Geigerflex D/Max 2200) using CuKα radia-
Fig. 1 showed the SEM photograph and XRD patterns of the ITO nanoparticles prepared by the ion-exchange and hydrothermal process. The particles exhibited a good dispersion, and a narrow size distribution (97 ± 5 nm) and a single phase, similar to the cubic C-type rareearth structured In2O3 (JCPDS 6-0416). ICP and chemical analysis of the powders had been showed the In2O3/SnO2 ratio of 90 : 10 same as the precursor ratio and also proven no traces of Cl− ion (less than 30 ppm). Clearly, with ion-exchange resin introduced for homogeneous precipitation, the hydrothermal method could be used to synthesize ITO nanoparticles with narrow size distribution. Yield of ITO was 95% based on starting raw materials; that is, 5% In–Sn hydroxide particles was stored in the inner pores of the resin. However, using the regenerated resin to mix with In–Sn chloride again, yield of ITO could be above 99%. By the traditional hydrothermal process, In3+ and Sn4+ cations combined with OH− to form In(OH)3 and Sn(OH)4 and formed hydrous gel-type precipitates. It is well known that controlling the precipitate condition, making the homogeneous nucleation easily appear, is too difficult. Therefore, a heterogeneous gel with a wide and uncontrollable size distribution was usually formed by the traditional coprecipitation method, hence ITO powders had a wide size distribution, even at a higher hydrothermal temperature for a longer period [8]. In the present work, the ion-exchange method is a modification of basification method; however, the precipitate can only be formed slowly because the rate of the adsorption is very slow. The as-prepared sol was dried up and characterized by TEM and XRD. The sample showed very poor crystallinity (same as the traditional coprecipitated gel powders) and soft conglomeration but with a narrow particle size (see Fig. 2). The uniform particles could be grown by the dissolution– precipitation process in the hydrothermal environment with the higher pressure and temperature [8].
Fig. 2. TEM of the In–Sn hydroxide powders prepared by ion-exchange.
H.-R. Xu et al. / Materials Letters 60 (2006) 983–985
985
4. Summary
References
ITO nanopowder with uniform size (97 ± 5 nm) was successfully prepared by an ion-exchange treatment followed by hydrothermal process. Moreover, using the regenerated resin to ion-exchange, the yield of ITO could be above 99%. Therefore, the ion-exchange treatment and hydrothermal process offers a simple and effective way for producing uniform ITO nanoparticles in the materials industry.
[1] J.G. Nam, H. Choi, S.H. Kim, K.H. Song, S.C. Park, Scr. Mater. 44 (2001) 2047. [2] A.B. Yu, N. Standish, Ind. Eng. Chem. Res. 30 (1991) 1372. [3] K.Y. Kim, S.B. Park, Mater. Chem. Phys. 86 (2004) 210. [4] S. Chen, C. Li, W. Xiong, L. Liu, H. Wang, Mater. Lett. 58 (2004) 294. [5] C. Yan, M. Zharnikov, A. Golzhauser, M. Grunze, Langmuir 16 (2000) 6208. [6] T. Kayukawa, H. Shigetani, M. Senna, J. Mater. Sci. Lett. 14 (1995) 252. [7] S. Tang, J. Yao, J. Chen, J. Luo, J. Mater. Process. Technol. 137 (2003) 82. [8] K. Yanagisawa, C.P. Udawatte, S. Nasu, J. Mater. Res. 15 (2000) 1404.
Acknowledgment This work is sponsored by the Hi-Tech Research and Development Program of China (No. 2003AA32X140).