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Hydrothermal synthesis of zinc oxide powders with different morphologies
SSC 5008
PERGAMON
Solid State Communications 113 (2000) 363–366 www.elsevier.com/locate/ssc
Hydrothermal synthesis of zinc oxide powders with different morphologies Dairong Chen*, Xiuling Jiao, Gang Cheng Department of Chemistry, Shandong University, Jinan 250100, People’s Republic of China Received 25 June 1999; received in revised form 15 September 1999; accepted 30 September 1999 by F.J. DiSalvo
Abstract Zinc oxide powders have been successfully prepared via hydrothermal process. The effects of reaction temperature and organic additives on the particulate properties such as the particle morphology and size are discussed. The result reveals that high temperature leads to a similar growth speed of different crystallographic planes and several templates result in the formation of particles with different morphologies and sizes. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Semiconductors; B. Chemical synthesis; C. Scanning and transmission electron microscopy
1. Introduction Zinc oxide is intensively used in a variety of applications such as varistors, semiconductors and so on [1]. On the contrary, zinc oxide powders with ultrafine particles are applicable to various materials such as photo-catalysts and nonlinear optical materials. Zinc oxide powders are generally obtained by the thermal decomposition technique or co-precipitation method [2–5]. As a method for preparing high-quality ceramic powders, the hydrothermal synthetic route has advantages to obtain high crystallized powders with narrow grain size-distribution and high purity without treatment at high temperature. The particle properties such as morphology and size can be controlled via the hydrothermal process by adjusting the reaction temperature, time and additives [6,7]. Several oxides such as g-Fe2O3, ZrO2 and PZT [8–10] have been successfully prepared by this method and the hydrothermal technique has attracted great interest for it is one of the most promising methods for controlling particle size, morphology and size distribution. However, there is little information on the synthesis of zinc oxide powders using the hydrothermal method except the hydrothermal preparation of ZnO powders from different precursors [11] and hydrothermal ZnO crystal growth [12]. * Corresponding author. E-mail address: [email protected] (D. Chen)
The present investigation focuses on the hydrothermal synthesis of zinc oxide powders and the effects of reaction temperature and template are also discussed. This paper considered the hydrothermal synthesis of zinc oxide powders has four advantages: (1) the reaction is carried out under moderate conditions; (2) powders with nanometer-size can be obtained by this method; (3) powders with different morphologies form by adjusting the reaction conditions; and (4) the as-prepared powders might have different properties from those obtained at high temperature.
2. Experimental All the reagents are of analytical grade and without further purification before utilization. The synthesis procedure is as follows: ZnCl2 and NaOH with molar ratio of 1:2 are dissolved in deionized water, and the white Zn(OH)2 precipitate forms. After filtration and washing with deionized water, the white precipitate is dispersed in deionized water and the pH value is adjusted to 5–8 by HCl. After stirring for about 3 h, the homogeneous sol is poured into a teflon-lined autoclave and hydrothermally heated at the designed temperature for a planned period. Then, the autoclave is cooled to room temperature and the product is filtered and washed with deionized water and then dried at room temperature. The X-ray powder diffraction data are recorded on a
0038-1098/00/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00472-X
364
D. Chen et al. / Solid State Communications 113 (2000) 363–366
Table 1 Reaction conditions and particle properties of title compound without additives No.
1 2 3 4 5 a
Particle properties a
Reaction conditions
FWHM of 002 reflection (degrees)
Temperature (8C)
Time (h)
Morphology
Size (nm)
100 160 180 200 220
10 6 6 6 5
Bullet-like Rod-like Sheet Polyhedron Crushed stone-like
100–200 100–200 50–200 200–400 50–200
0.51 0.45 0.40 0.32 0.45
Observed from the TEM graphs.
Rigaku D/MAX-III diffractometer with CuKa radiation ˚ ) and Ni filter and collected over the range (l 1.5418 A 20 , 2u , 60 at room temperature. The mean size and morphologies of zinc oxide particles are observed by transmission electron microscopy (TEM, JEM-100CXII). The IR spectrum of the as-prepared sample is recorded on a Nicolet 5DX FT-IR instrument using the KBr pellet technique. The IR result indicates that the product has hydroxyls, which is different from the reported electrochemically grown ZnO quantum dots [13].
without additives. Pure zinc oxide powder is formed only after hydrothermal heating at 1008C for about 10 h and the reaction time is obviously reduced with the reaction temperature increasing from 100 to 2208C. Compared to other method for synthesizing zinc oxide powders, the reaction condition is considerably moderate. The reaction temperature is also much lower than the reported hydrothermal process for preparing pure ZnO powders [11]. In the precipitation and hydrothermal process, the ZnO powders form via two reactions: ZnCl2 1 2NaOH ! Zn OH2 # 12Na1 1 2Cl2
1
3. Results and discussion Zn OH2
3.1. Effect of reaction temperature Table 1 lists the synthesis conditions and the particle properties as well as the full width on half maximum of the 002 diffraction reflection of the as-prepared zinc oxide
hydrothermal conditions
!
2 H2 O
ZnO
2
The above results indicate that the Zn(OH)2 precipitate can lose water at 1008C under the hydrothermal conditions.
Table 2 Powder particle properties with different additives (reaction temperature—1608C, reaction time—6 h) No.
6 7 8 9 10 11 12 13 14 15 16 17 18 19
Additives
Tributylamine Triethylamine Triethanolamie Diisopropylamine Ammonium phosphate 1, 6-Hexadianol Triethyldiethylnol Isopropylamine Cyclohexylamine n-Butylamine Ammonium chloride Hexamethylenetetramine Ethylene glycol Ethanolamine
Particle properties Morphology
Size (nm)
Rod-like Rod-like Spindle-like Rod-like Rod-like Rod-like Rod-like Rod or sheet-like Sheet-like Sheet-like Sheet Snow-flake like Ellipse Polyhedron
200–300 100–300 100–300 200–400 200–500 300–700 100–300 – 300–500 200–400 50–200 20–50 40–100 50–200
Fig. 1. XRD patterns of as-prepared ZnO powder. (a), (b), (c), (d) correspond to No. 1, 11, 17, 19 in Tables 1 and 2, respectively.
D. Chen et al. / Solid State Communications 113 (2000) 363–366
365
Fig. 2. TEM graphs of as-prepared ZnO with different templating agents. (a), (b), (c), (d) correspond to No. 1, 11, 17, 19 in Tables 1 and 2, respectively.
Table 1 also shows that the reaction temperature greatly influences the particle morphology of as-prepared ZnO powders. Increasing the reaction temperature from 100 to 2208C, the particle morphology changes from bullet-like and rod-like to crush stone-like shape. This is due to the change of growth speed between the different crystallographic planes. The growth speed of the different crystal faces tends to be similar at high temperature, and the particle morphologies change from 1D rod-like shape to 2D sheetlike and then to 3D crush stone-like shape while the reaction temperature is raised from 100 to 2208C. The particle size calculated from FWHM is similar to that from TEM graphs, which reveals that as-prepared ZnO powders have low polymerization. 3.2. Effect of the template To investigate the effect of the template on particulate properties, a variety of templates are added to the reaction mixture while the temperature is held at 1608C. Table 2 lists the reaction conditions and the corresponding particle morphologies of as-prepared powders. Fig. 1 gives the XRD patterns of the typical samples and Fig. 2 shows the corresponding TEM graphs. No significant orientation can be seen from the XRD patterns due to the random arrangement of different small crystals. Table 2 reveals di- and tri-organic amines as well as 1,6hexadianol and triethyldiethylnol which has a long 1D chain and two end-hydroxyls are favorable to form 1D
morphology crystals, such as rod-like shape. As a comparison, sheet-like morphology particles were formed using nand cyclo-organic amine as additives. While ethanolamine, ethylene glycol and ammonium phosphate is used as morphology template, 3D morphology crystals are obtained. On the contrary, additives play an important effect on the particle size. Using different templates, the particle size changes from 20 nm to 2 mm. While hexamethylenetetramine and ethylene glycol are used as crystal morphology templates, ZnO powders with nanometer particles (20– 100 nm) can be obtained. This is because of the relative change between nucleation and crystal growth speed. Large amounts of nuclei are formed using hexamethylenetetramine and ethylene glycol as additives, which result in the formation of small size particles. While other additives lead to rapid crystal growth and then the formation of large size particles. The results reveal that the additives greatly influence the crystal nucleation and grain growth, and the particle morphology and size can be effectively controlled by adjusting the template. 4. Conclusions The main conclusions of the present study are as follows: 1. Zinc oxide powders with different particle morphologies and sizes have been obtained via the hydrothermal process using different organic compounds as template agents.
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D. Chen et al. / Solid State Communications 113 (2000) 363–366
2. The reaction temperature significantly influences the particle morphology. Increasing the temperature, the particle morphologies change from rod-like to polyhedra. 3. Particles with different morphologies and sizes can be obtained by adjusting the template agents.
Acknowledgements This work is supported by the Key Lab. of Inorganic Synthesis and Preparation of the Jilin University.
[4] [5] [6] [7]
[8] [9] [10] [11] [12]
References [1] J.C.M. Brentano, C. Goldberg, Phys. Rev. 94 (1954) 56. [2] T. Tsuchida, S. Kitajima, Chem. Lett. (1990) 1769. [3] S.M. Haile, D.W. Johnson Jr., J. Am. Ceram. Soc. 72 (1989) 2004.
[13]
E. Matijevic, Acc. Chem. Res. 14 (1981) 22. Q.P. Zhong, E. Matijevic, J. Mater. Chem. 6 (3) (1996) 443. E. Matijevic, J. Eur. Ceram. Soc. 18 (9) (1998) 1357. J.H. Adair, T. Li, T. Kido, K. Havey, J. Moon, J. Mecholsky, A. Morrone, D.R. Talham, M.H. Ludwig, L. Wang, Mater. Sci. Engng R-Reports 23 (4–5) (1998) 139. D. Chen, R. Xu, J. Solid State Chem. 137 (1998) 185. D. Chen, X. Jiao, R. Xu, J. Mater. Sci. Lett. 17 (1998) 53. A.T. Chien, J.S. Speck, F.F. Lange, J. Mater. Res. 12 (5) (1997) 1176. W. Li, E. Shi, B. Wang, C. Xia, W. Zhong, J. Inorg. Mater. 13 (1) (1998) 27, in Chinese. M. Suscavage, M. Harris, D. Bliss, P. Yip, S.Q. Wang, D. Schwall, L. Bouthillette, J. Bailey, M. Callahan, D.C. Look, D.C. Reynolds, R.L. Jones, C.W. Litton, MRS Internet J. Nitride Semiconductor Res. 4 (1999) 294. S. Mahamuni, K. Borgohain, B.S. Bendre, J. Appl. Phys. 85 (5) (1999) 2861.
PERGAMON
Solid State Communications 113 (2000) 363–366 www.elsevier.com/locate/ssc
Hydrothermal synthesis of zinc oxide powders with different morphologies Dairong Chen*, Xiuling Jiao, Gang Cheng Department of Chemistry, Shandong University, Jinan 250100, People’s Republic of China Received 25 June 1999; received in revised form 15 September 1999; accepted 30 September 1999 by F.J. DiSalvo
Abstract Zinc oxide powders have been successfully prepared via hydrothermal process. The effects of reaction temperature and organic additives on the particulate properties such as the particle morphology and size are discussed. The result reveals that high temperature leads to a similar growth speed of different crystallographic planes and several templates result in the formation of particles with different morphologies and sizes. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Semiconductors; B. Chemical synthesis; C. Scanning and transmission electron microscopy
1. Introduction Zinc oxide is intensively used in a variety of applications such as varistors, semiconductors and so on [1]. On the contrary, zinc oxide powders with ultrafine particles are applicable to various materials such as photo-catalysts and nonlinear optical materials. Zinc oxide powders are generally obtained by the thermal decomposition technique or co-precipitation method [2–5]. As a method for preparing high-quality ceramic powders, the hydrothermal synthetic route has advantages to obtain high crystallized powders with narrow grain size-distribution and high purity without treatment at high temperature. The particle properties such as morphology and size can be controlled via the hydrothermal process by adjusting the reaction temperature, time and additives [6,7]. Several oxides such as g-Fe2O3, ZrO2 and PZT [8–10] have been successfully prepared by this method and the hydrothermal technique has attracted great interest for it is one of the most promising methods for controlling particle size, morphology and size distribution. However, there is little information on the synthesis of zinc oxide powders using the hydrothermal method except the hydrothermal preparation of ZnO powders from different precursors [11] and hydrothermal ZnO crystal growth [12]. * Corresponding author. E-mail address: [email protected] (D. Chen)
The present investigation focuses on the hydrothermal synthesis of zinc oxide powders and the effects of reaction temperature and template are also discussed. This paper considered the hydrothermal synthesis of zinc oxide powders has four advantages: (1) the reaction is carried out under moderate conditions; (2) powders with nanometer-size can be obtained by this method; (3) powders with different morphologies form by adjusting the reaction conditions; and (4) the as-prepared powders might have different properties from those obtained at high temperature.
2. Experimental All the reagents are of analytical grade and without further purification before utilization. The synthesis procedure is as follows: ZnCl2 and NaOH with molar ratio of 1:2 are dissolved in deionized water, and the white Zn(OH)2 precipitate forms. After filtration and washing with deionized water, the white precipitate is dispersed in deionized water and the pH value is adjusted to 5–8 by HCl. After stirring for about 3 h, the homogeneous sol is poured into a teflon-lined autoclave and hydrothermally heated at the designed temperature for a planned period. Then, the autoclave is cooled to room temperature and the product is filtered and washed with deionized water and then dried at room temperature. The X-ray powder diffraction data are recorded on a
0038-1098/00/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00472-X
364
D. Chen et al. / Solid State Communications 113 (2000) 363–366
Table 1 Reaction conditions and particle properties of title compound without additives No.
1 2 3 4 5 a
Particle properties a
Reaction conditions
FWHM of 002 reflection (degrees)
Temperature (8C)
Time (h)
Morphology
Size (nm)
100 160 180 200 220
10 6 6 6 5
Bullet-like Rod-like Sheet Polyhedron Crushed stone-like
100–200 100–200 50–200 200–400 50–200
0.51 0.45 0.40 0.32 0.45
Observed from the TEM graphs.
Rigaku D/MAX-III diffractometer with CuKa radiation ˚ ) and Ni filter and collected over the range (l 1.5418 A 20 , 2u , 60 at room temperature. The mean size and morphologies of zinc oxide particles are observed by transmission electron microscopy (TEM, JEM-100CXII). The IR spectrum of the as-prepared sample is recorded on a Nicolet 5DX FT-IR instrument using the KBr pellet technique. The IR result indicates that the product has hydroxyls, which is different from the reported electrochemically grown ZnO quantum dots [13].
without additives. Pure zinc oxide powder is formed only after hydrothermal heating at 1008C for about 10 h and the reaction time is obviously reduced with the reaction temperature increasing from 100 to 2208C. Compared to other method for synthesizing zinc oxide powders, the reaction condition is considerably moderate. The reaction temperature is also much lower than the reported hydrothermal process for preparing pure ZnO powders [11]. In the precipitation and hydrothermal process, the ZnO powders form via two reactions: ZnCl2 1 2NaOH ! Zn OH2 # 12Na1 1 2Cl2
1
3. Results and discussion Zn OH2
3.1. Effect of reaction temperature Table 1 lists the synthesis conditions and the particle properties as well as the full width on half maximum of the 002 diffraction reflection of the as-prepared zinc oxide
hydrothermal conditions
!
2 H2 O
ZnO
2
The above results indicate that the Zn(OH)2 precipitate can lose water at 1008C under the hydrothermal conditions.
Table 2 Powder particle properties with different additives (reaction temperature—1608C, reaction time—6 h) No.
6 7 8 9 10 11 12 13 14 15 16 17 18 19
Additives
Tributylamine Triethylamine Triethanolamie Diisopropylamine Ammonium phosphate 1, 6-Hexadianol Triethyldiethylnol Isopropylamine Cyclohexylamine n-Butylamine Ammonium chloride Hexamethylenetetramine Ethylene glycol Ethanolamine
Particle properties Morphology
Size (nm)
Rod-like Rod-like Spindle-like Rod-like Rod-like Rod-like Rod-like Rod or sheet-like Sheet-like Sheet-like Sheet Snow-flake like Ellipse Polyhedron
200–300 100–300 100–300 200–400 200–500 300–700 100–300 – 300–500 200–400 50–200 20–50 40–100 50–200
Fig. 1. XRD patterns of as-prepared ZnO powder. (a), (b), (c), (d) correspond to No. 1, 11, 17, 19 in Tables 1 and 2, respectively.
D. Chen et al. / Solid State Communications 113 (2000) 363–366
365
Fig. 2. TEM graphs of as-prepared ZnO with different templating agents. (a), (b), (c), (d) correspond to No. 1, 11, 17, 19 in Tables 1 and 2, respectively.
Table 1 also shows that the reaction temperature greatly influences the particle morphology of as-prepared ZnO powders. Increasing the reaction temperature from 100 to 2208C, the particle morphology changes from bullet-like and rod-like to crush stone-like shape. This is due to the change of growth speed between the different crystallographic planes. The growth speed of the different crystal faces tends to be similar at high temperature, and the particle morphologies change from 1D rod-like shape to 2D sheetlike and then to 3D crush stone-like shape while the reaction temperature is raised from 100 to 2208C. The particle size calculated from FWHM is similar to that from TEM graphs, which reveals that as-prepared ZnO powders have low polymerization. 3.2. Effect of the template To investigate the effect of the template on particulate properties, a variety of templates are added to the reaction mixture while the temperature is held at 1608C. Table 2 lists the reaction conditions and the corresponding particle morphologies of as-prepared powders. Fig. 1 gives the XRD patterns of the typical samples and Fig. 2 shows the corresponding TEM graphs. No significant orientation can be seen from the XRD patterns due to the random arrangement of different small crystals. Table 2 reveals di- and tri-organic amines as well as 1,6hexadianol and triethyldiethylnol which has a long 1D chain and two end-hydroxyls are favorable to form 1D
morphology crystals, such as rod-like shape. As a comparison, sheet-like morphology particles were formed using nand cyclo-organic amine as additives. While ethanolamine, ethylene glycol and ammonium phosphate is used as morphology template, 3D morphology crystals are obtained. On the contrary, additives play an important effect on the particle size. Using different templates, the particle size changes from 20 nm to 2 mm. While hexamethylenetetramine and ethylene glycol are used as crystal morphology templates, ZnO powders with nanometer particles (20– 100 nm) can be obtained. This is because of the relative change between nucleation and crystal growth speed. Large amounts of nuclei are formed using hexamethylenetetramine and ethylene glycol as additives, which result in the formation of small size particles. While other additives lead to rapid crystal growth and then the formation of large size particles. The results reveal that the additives greatly influence the crystal nucleation and grain growth, and the particle morphology and size can be effectively controlled by adjusting the template. 4. Conclusions The main conclusions of the present study are as follows: 1. Zinc oxide powders with different particle morphologies and sizes have been obtained via the hydrothermal process using different organic compounds as template agents.
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D. Chen et al. / Solid State Communications 113 (2000) 363–366
2. The reaction temperature significantly influences the particle morphology. Increasing the temperature, the particle morphologies change from rod-like to polyhedra. 3. Particles with different morphologies and sizes can be obtained by adjusting the template agents.
Acknowledgements This work is supported by the Key Lab. of Inorganic Synthesis and Preparation of the Jilin University.
[4] [5] [6] [7]
[8] [9] [10] [11] [12]
References [1] J.C.M. Brentano, C. Goldberg, Phys. Rev. 94 (1954) 56. [2] T. Tsuchida, S. Kitajima, Chem. Lett. (1990) 1769. [3] S.M. Haile, D.W. Johnson Jr., J. Am. Ceram. Soc. 72 (1989) 2004.
[13]
E. Matijevic, Acc. Chem. Res. 14 (1981) 22. Q.P. Zhong, E. Matijevic, J. Mater. Chem. 6 (3) (1996) 443. E. Matijevic, J. Eur. Ceram. Soc. 18 (9) (1998) 1357. J.H. Adair, T. Li, T. Kido, K. Havey, J. Moon, J. Mecholsky, A. Morrone, D.R. Talham, M.H. Ludwig, L. Wang, Mater. Sci. Engng R-Reports 23 (4–5) (1998) 139. D. Chen, R. Xu, J. Solid State Chem. 137 (1998) 185. D. Chen, X. Jiao, R. Xu, J. Mater. Sci. Lett. 17 (1998) 53. A.T. Chien, J.S. Speck, F.F. Lange, J. Mater. Res. 12 (5) (1997) 1176. W. Li, E. Shi, B. Wang, C. Xia, W. Zhong, J. Inorg. Mater. 13 (1) (1998) 27, in Chinese. M. Suscavage, M. Harris, D. Bliss, P. Yip, S.Q. Wang, D. Schwall, L. Bouthillette, J. Bailey, M. Callahan, D.C. Look, D.C. Reynolds, R.L. Jones, C.W. Litton, MRS Internet J. Nitride Semiconductor Res. 4 (1999) 294. S. Mahamuni, K. Borgohain, B.S. Bendre, J. Appl. Phys. 85 (5) (1999) 2861.