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Hydrothermal preparation of selenium nanorods
Materials Chemistry and Physics 98 (2006) 191–194
Hydrothermal preparation of selenium nanorods Yuan-tao Chen ∗ , Wei Zhang, Yan-qing Fan, Xiao-qing Xu, Zhong-xin Zhang Department of Chemistry, Qinghai Normal University, Xining 810008, PR China Received 6 February 2004; accepted 11 May 2005
Abstract Trigonal selenium nanorods have successfully been synthesized through a simple and convenient hydrothermal route. The effect of hydrothermal temperature on the morphology of products was investigated. It was found that excess hydrazine might act as catalyst in the formation of selenium rods. © 2006 Published by Elsevier B.V. Keywords: Nanostructures; Semiconductors; Crystal growth; Electron microscopy
1. Introduction One-dimensional nanoscale materials, such as nanowires, rods, or tubes, have stimulated great interest recently due to their unique electronic, optical and mechanical properties and their potential applications in fabricating nanodevices [1,2]. As one of the most important photoelectric and semiconductor materials, selenium nanocrystals have critical applications, such as in rectifiers, solar cells, photographic exposure meters and xenography [3]. Selenium also has a high reactivity towards a wealth of chemicals that can be potentially exploited to converted selenium into other functional materials, such as Ag2 Se, CdSe [4,5]. Selenium exists in a number of crystalline structures, the principal ones being trigonal, consisting of helica chains, and less stable monoclinic, consisting of Se8 rings, and amorphous selenium consisting of a mixture of disordered chains. The transformation energy from amorphous to trigonal crystal phase is 6.63 kJ mol−1 . Recently, there have been some reports on the synthesis of selenium nanoparticles [3,6–10]. For example, Qian and co-workers used ␥-radiation method to prepare trigonal selenium nanocrystals [6]. Johnson et al. synthesized selenium nanoparticles in microemulsion by a reverse micelle method [3]. Gao et al. synthesized the hollow selenium nanospheres by using an in situ template–interface reaction [7]. Abdelouas et al. reported their work on using protein cytochrome ∗
Corresponding author.
0254-0584/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.matchemphys.2005.05.051
c3 reducing selenate to make selenium nanowires [8]. Of very late, Gates et al. reported the preparation of nanowires by aging amorphous selenium in the dark [9,10], the synthetic process involved anisotropic 1D growth on seeds of trigonal selenium that were generated in the same reaction solution through homogeneous nucleation, and the growth selenium continuously resulted from the slow dissolution of amorphous colloidal selenium. All above-mentioned methods were very useful and were of widespread importance, but there were some limitations to their practical applications. For example, some methods needed relatively elongated synthetic time, some methods used cost reagent. Here, a simple hydrothermal route was developed to synthesize trigonal selenium nanorods, based on aging amorphous selenium. In fact, the hydrothermal route is one of the most powerful strategies employed in the preparation of one-dimensional materials, and many products with control of the shape and size have been synthesized by careful consideration of the reaction condition and reactants by this technique [11]. In this paper, the effect of synthetic temperature on the morphology of products was also investigated.
2. Experimental All the reagents are commercially available and analytical grades used without further purification. In a typical procedure, 1 ml of hydrazine (N2 H4 , 50%, v/v) and 0.128 g
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Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
of selenious acid were put into a Teflon-lined autoclave (50 ml capacity). The autoclave was then filled with distilled water to 80% of the total volume, sealed and maintained at 110–180 ◦ C for 2–12 h, and then cooled to room temperature naturally. The black product was filtered off and washed with distilled water and absolute alcohol, finally dried in air before further characterization. The crystal structure and composition of the final sample were analyzed by X-ray diffraction on a Japan Rigaku D/MAX-2400 X-ray diffractometer with Cu K␣ radiation ˚ at a scanning rate of 0.02◦ s−1 in the 2θ range (λ = 1.54178 A), ◦ of 20–70 . The morphology and size were characterized by a JSM-5600LV scanning electron microscopy.
3. Results and discussions All the samples obtained by hydrothermal route in this paper could be indexed as trigonal phase (JCPDS card no. 06-362). Fig. 1 shows a typical XRD pattern of as obtained trigonal selenium nanorods prepared at 110 ◦ C for 2 h. The SEM images of selenium rods prepared by different synthetic temperature were shown in Fig. 2. Rods with average diameter of 400 nm and length of 1 m could be obtained at 110 ◦ C for 2 h. Rods with average diameter of 500 nm and length of 2.5 m could been at 120 ◦ C for 2 h. Rods with average diameter of 2 m and length of 5 m could be obtained at 130 ◦ C for 2 h. The interconnected melting selenium rods could be obtained at 180 ◦ C for 12 h, due to relative low melting point (217 ◦ C). Intensive and careful observation would find that the deviation of rod size was becoming larger, and rods have more faceted characteristic when the reaction temperature was increased from 110 to 130 ◦ C. In short, the high reaction temperature led to wide distribution. To some degree, the result is similar to what Peng et al. found in the shape control synthesis of CdSe nanocrystals [12]. It was found that the smaller particles grew faster than the larges ones at high
Fig. 2. SEM images of selenium rods prepared at (A) 110 ◦ C, 2 h; (B) 120 ◦ C, 2 h; (C) 130 ◦ C, 2 h; (D) 180 ◦ C, 12 h.
Fig. 1. XRD pattern of selenium rods prepared at temperature 110 ◦ C for 2 h.
monomer concentration, and as a result, the size distribution can be focused down to one that is nearly monodisperse. If the monomer concentration drops below a critical threshold, small nonocrystals were depleted as larger ones grew and the distribution broadened. In this communication, it was believed that the higher reaction temperature with same reaction time causes the monomer selenium concentration quick
Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
drop. The formation of the monodisperse nanorods as Fig. 2A shown was case of the former. It was achieved by stopping the reaction while the monomer concentration of selenium in solution was still high. The rods, as shown in Fig. 2B and C,
193
might result from stopping the reaction when the monomer concentration of selenium dropped far below its critical value. In order to understand the mechanism of selenium rods formation, the pure amorphous seeds, prepared by hydrazine reducing selenious acid with excess hydrazine removal, were crystallized by hydrothermal route at 130 ◦ C for 2h. The final sample displayed nearly spherical morphology as shown in Fig. 3B and C. We also prepared selenium particles by hydrothermal treating aqueous solution containing of ascorbic acid and selenious acid, the final sample also revealed spherical shape. Thus, it was supposed that the excess hydrazine might play a critical role in the selenium nanorod formation in this paper. In fact, it was found that amine (including compound having amino-group such as hydrazine) could facilitate the crystal phase transformation from amorphous to trigonal selenium by activating amorphous selenium ring [13]. That is to say, excess hydrazine may act as catalyst in the formation of selenium rods in this paper. Though the intrinsic anisotropic growth character of trigonal selenium determines the resultant crystal shape, in a way, only if the growth rate is fast enough, the result is rod-like shape; if the overall growth rate is very slow, a nearly spherical shape that minimizes surface area is favored. We observed the similar results in our previous work [14].
4. Conclusions In summary, a relatively simple and convenient hydrothermal route was developed to synthesize trigonal selenium rods. The size distribution of rods is becoming larger, and selenium rods have more faceted characteristic with increasing temperature. Excess hydrazine might act as catalyst in the formation of selenium rods.
Acknowledgement This work is financially supported by ‘Light of West China’ and ‘Project of Chunhui’. The authors are indebted to Yu Jiang of Qinghai Normal University for instructive discussion.
References
Fig. 3. SEM images of (A) the amorphous selenium before hydrothermal crystallization; (B and C) the selenium crystallines prepared by hydrothermal crystallizing pure amorphous selenium at 130 ◦ C, for 2 or 6 h; (D) selenium spheres prepared by hydrothermal crystallizing selenious acid and ascorbic acid at 130 ◦ C for 2 h.
[1] A.P. Alivisatos, Science 271 (1996) 933. [2] L.E. Brus, J. Phys. Chem. 90 (1986) 2555. [3] J.A. Johnson, N.L. Ssaboungi, P. Thyagarajan, R. Csencsits, D. Meisel, J. Phys. Chem. B 103 (1999) 59. [4] Z. Adam Peng, X.G. Peng, J. Am. Chem. Soc. 123 (2001) 183. [5] B. Gates, Y. Wu, Y. Yin, P. Yang, Y. Xia, J. Am. Chem. Soc. 123 (2001) 11500. [6] Y. Zhu, Y. Qian, H. Huang, M. Zhang, Mater. Lett. 18 (1996) 119.
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Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
[7] X. Gao, J.S. Zhang, L.D. Zhang, Adv. Mater. 14 (2002) 290. [8] A. Abdelouas, W.L. Gong, W. Lutze, J.A. Shelnutt, R. Franco, I. Moura, Chem. Mater. 12 (2000) 1510. [9] B. Gates, Y. Yin, Y. Xia, J. Am. Chem. Soc. 122 (2000) 12582. [10] B. Gates, B. Mayers, B. Cattle, Y. Xia, Adv. Funct. Mater. 12 (2002) 219.
[11] M. Niederberger, H.J. Muhr, F. Krumeich, F. Bieri, D.G. Nther, R. Nesper, Chem. Mater. 12 (2000) 1995. [12] X.G. Peng, L. Manna, W.D. Yang, J. Wickham, E. Scher, A. Kadavanich, A.P. Alivisatos, Nature 404 (2000) 59. [13] M.D. Gui, Inorganic Chemistry, vol. 5, second ed., Scientific Press, Beijing, 1998, p. 320. [14] Y.T. Chen, Y. Guo, H.L. Li, Chem. Lett. 2 (2002) 252.
Hydrothermal preparation of selenium nanorods Yuan-tao Chen ∗ , Wei Zhang, Yan-qing Fan, Xiao-qing Xu, Zhong-xin Zhang Department of Chemistry, Qinghai Normal University, Xining 810008, PR China Received 6 February 2004; accepted 11 May 2005
Abstract Trigonal selenium nanorods have successfully been synthesized through a simple and convenient hydrothermal route. The effect of hydrothermal temperature on the morphology of products was investigated. It was found that excess hydrazine might act as catalyst in the formation of selenium rods. © 2006 Published by Elsevier B.V. Keywords: Nanostructures; Semiconductors; Crystal growth; Electron microscopy
1. Introduction One-dimensional nanoscale materials, such as nanowires, rods, or tubes, have stimulated great interest recently due to their unique electronic, optical and mechanical properties and their potential applications in fabricating nanodevices [1,2]. As one of the most important photoelectric and semiconductor materials, selenium nanocrystals have critical applications, such as in rectifiers, solar cells, photographic exposure meters and xenography [3]. Selenium also has a high reactivity towards a wealth of chemicals that can be potentially exploited to converted selenium into other functional materials, such as Ag2 Se, CdSe [4,5]. Selenium exists in a number of crystalline structures, the principal ones being trigonal, consisting of helica chains, and less stable monoclinic, consisting of Se8 rings, and amorphous selenium consisting of a mixture of disordered chains. The transformation energy from amorphous to trigonal crystal phase is 6.63 kJ mol−1 . Recently, there have been some reports on the synthesis of selenium nanoparticles [3,6–10]. For example, Qian and co-workers used ␥-radiation method to prepare trigonal selenium nanocrystals [6]. Johnson et al. synthesized selenium nanoparticles in microemulsion by a reverse micelle method [3]. Gao et al. synthesized the hollow selenium nanospheres by using an in situ template–interface reaction [7]. Abdelouas et al. reported their work on using protein cytochrome ∗
Corresponding author.
0254-0584/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.matchemphys.2005.05.051
c3 reducing selenate to make selenium nanowires [8]. Of very late, Gates et al. reported the preparation of nanowires by aging amorphous selenium in the dark [9,10], the synthetic process involved anisotropic 1D growth on seeds of trigonal selenium that were generated in the same reaction solution through homogeneous nucleation, and the growth selenium continuously resulted from the slow dissolution of amorphous colloidal selenium. All above-mentioned methods were very useful and were of widespread importance, but there were some limitations to their practical applications. For example, some methods needed relatively elongated synthetic time, some methods used cost reagent. Here, a simple hydrothermal route was developed to synthesize trigonal selenium nanorods, based on aging amorphous selenium. In fact, the hydrothermal route is one of the most powerful strategies employed in the preparation of one-dimensional materials, and many products with control of the shape and size have been synthesized by careful consideration of the reaction condition and reactants by this technique [11]. In this paper, the effect of synthetic temperature on the morphology of products was also investigated.
2. Experimental All the reagents are commercially available and analytical grades used without further purification. In a typical procedure, 1 ml of hydrazine (N2 H4 , 50%, v/v) and 0.128 g
192
Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
of selenious acid were put into a Teflon-lined autoclave (50 ml capacity). The autoclave was then filled with distilled water to 80% of the total volume, sealed and maintained at 110–180 ◦ C for 2–12 h, and then cooled to room temperature naturally. The black product was filtered off and washed with distilled water and absolute alcohol, finally dried in air before further characterization. The crystal structure and composition of the final sample were analyzed by X-ray diffraction on a Japan Rigaku D/MAX-2400 X-ray diffractometer with Cu K␣ radiation ˚ at a scanning rate of 0.02◦ s−1 in the 2θ range (λ = 1.54178 A), ◦ of 20–70 . The morphology and size were characterized by a JSM-5600LV scanning electron microscopy.
3. Results and discussions All the samples obtained by hydrothermal route in this paper could be indexed as trigonal phase (JCPDS card no. 06-362). Fig. 1 shows a typical XRD pattern of as obtained trigonal selenium nanorods prepared at 110 ◦ C for 2 h. The SEM images of selenium rods prepared by different synthetic temperature were shown in Fig. 2. Rods with average diameter of 400 nm and length of 1 m could be obtained at 110 ◦ C for 2 h. Rods with average diameter of 500 nm and length of 2.5 m could been at 120 ◦ C for 2 h. Rods with average diameter of 2 m and length of 5 m could be obtained at 130 ◦ C for 2 h. The interconnected melting selenium rods could be obtained at 180 ◦ C for 12 h, due to relative low melting point (217 ◦ C). Intensive and careful observation would find that the deviation of rod size was becoming larger, and rods have more faceted characteristic when the reaction temperature was increased from 110 to 130 ◦ C. In short, the high reaction temperature led to wide distribution. To some degree, the result is similar to what Peng et al. found in the shape control synthesis of CdSe nanocrystals [12]. It was found that the smaller particles grew faster than the larges ones at high
Fig. 2. SEM images of selenium rods prepared at (A) 110 ◦ C, 2 h; (B) 120 ◦ C, 2 h; (C) 130 ◦ C, 2 h; (D) 180 ◦ C, 12 h.
Fig. 1. XRD pattern of selenium rods prepared at temperature 110 ◦ C for 2 h.
monomer concentration, and as a result, the size distribution can be focused down to one that is nearly monodisperse. If the monomer concentration drops below a critical threshold, small nonocrystals were depleted as larger ones grew and the distribution broadened. In this communication, it was believed that the higher reaction temperature with same reaction time causes the monomer selenium concentration quick
Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
drop. The formation of the monodisperse nanorods as Fig. 2A shown was case of the former. It was achieved by stopping the reaction while the monomer concentration of selenium in solution was still high. The rods, as shown in Fig. 2B and C,
193
might result from stopping the reaction when the monomer concentration of selenium dropped far below its critical value. In order to understand the mechanism of selenium rods formation, the pure amorphous seeds, prepared by hydrazine reducing selenious acid with excess hydrazine removal, were crystallized by hydrothermal route at 130 ◦ C for 2h. The final sample displayed nearly spherical morphology as shown in Fig. 3B and C. We also prepared selenium particles by hydrothermal treating aqueous solution containing of ascorbic acid and selenious acid, the final sample also revealed spherical shape. Thus, it was supposed that the excess hydrazine might play a critical role in the selenium nanorod formation in this paper. In fact, it was found that amine (including compound having amino-group such as hydrazine) could facilitate the crystal phase transformation from amorphous to trigonal selenium by activating amorphous selenium ring [13]. That is to say, excess hydrazine may act as catalyst in the formation of selenium rods in this paper. Though the intrinsic anisotropic growth character of trigonal selenium determines the resultant crystal shape, in a way, only if the growth rate is fast enough, the result is rod-like shape; if the overall growth rate is very slow, a nearly spherical shape that minimizes surface area is favored. We observed the similar results in our previous work [14].
4. Conclusions In summary, a relatively simple and convenient hydrothermal route was developed to synthesize trigonal selenium rods. The size distribution of rods is becoming larger, and selenium rods have more faceted characteristic with increasing temperature. Excess hydrazine might act as catalyst in the formation of selenium rods.
Acknowledgement This work is financially supported by ‘Light of West China’ and ‘Project of Chunhui’. The authors are indebted to Yu Jiang of Qinghai Normal University for instructive discussion.
References
Fig. 3. SEM images of (A) the amorphous selenium before hydrothermal crystallization; (B and C) the selenium crystallines prepared by hydrothermal crystallizing pure amorphous selenium at 130 ◦ C, for 2 or 6 h; (D) selenium spheres prepared by hydrothermal crystallizing selenious acid and ascorbic acid at 130 ◦ C for 2 h.
[1] A.P. Alivisatos, Science 271 (1996) 933. [2] L.E. Brus, J. Phys. Chem. 90 (1986) 2555. [3] J.A. Johnson, N.L. Ssaboungi, P. Thyagarajan, R. Csencsits, D. Meisel, J. Phys. Chem. B 103 (1999) 59. [4] Z. Adam Peng, X.G. Peng, J. Am. Chem. Soc. 123 (2001) 183. [5] B. Gates, Y. Wu, Y. Yin, P. Yang, Y. Xia, J. Am. Chem. Soc. 123 (2001) 11500. [6] Y. Zhu, Y. Qian, H. Huang, M. Zhang, Mater. Lett. 18 (1996) 119.
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Y.-t. Chen et al. / Materials Chemistry and Physics 98 (2006) 191–194
[7] X. Gao, J.S. Zhang, L.D. Zhang, Adv. Mater. 14 (2002) 290. [8] A. Abdelouas, W.L. Gong, W. Lutze, J.A. Shelnutt, R. Franco, I. Moura, Chem. Mater. 12 (2000) 1510. [9] B. Gates, Y. Yin, Y. Xia, J. Am. Chem. Soc. 122 (2000) 12582. [10] B. Gates, B. Mayers, B. Cattle, Y. Xia, Adv. Funct. Mater. 12 (2002) 219.
[11] M. Niederberger, H.J. Muhr, F. Krumeich, F. Bieri, D.G. Nther, R. Nesper, Chem. Mater. 12 (2000) 1995. [12] X.G. Peng, L. Manna, W.D. Yang, J. Wickham, E. Scher, A. Kadavanich, A.P. Alivisatos, Nature 404 (2000) 59. [13] M.D. Gui, Inorganic Chemistry, vol. 5, second ed., Scientific Press, Beijing, 1998, p. 320. [14] Y.T. Chen, Y. Guo, H.L. Li, Chem. Lett. 2 (2002) 252.