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Microwave-assisted synthesis of high aspect ratio ruthenium nanorods
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Chinese Chemical Letters 21 (2010) 628–631 www.elsevier.com/locate/cclet
Microwave-assisted synthesis of high aspect ratio ruthenium nanorods Shu Ge Peng *, Xi Ping Gao, Yong Ke Guo, Yu Qing Zhang, Han Fan Liu Key Laboratory of Polymer and Nanomaterials, College of Chemical Engineering and Pharmacy, Henan University of Science and Technology, Luoyang 471003, China Received 24 August 2009
Abstract Poly (N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium nanorods with high aspect ratio by refluxing ruthenium(III) chloride in n-propanol have been successfully prepared by means of a facile and rapid microwave heating for the first time. The structure and morphology of the obtained products were characterized by transmission electron microscopy (TEM), select area electron diffraction (SAED), ultraviolet–visible spectrophotometry (UV–vis), X-ray photoelectron spectroscopy (XPS) and Fourier transform spectroscopy (FT-IR). XPS analysis reveals that the nanorods were in the metallic state. TEM images showed that ruthenium nanorods had an obvious one-dimensional structure with the aspect ratio ranged from 5 to 40 nm and length up to 600 nm. SAED patterns indicated that the nanorods were single-crystalline with a hexagonal structure. # 2010 Shu Ge Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Poly (N-vinyl-2-pyrrolidone); Ruthenium; Nanorods; Microwave
In recent years, one-dimensional nanostructures, such as nanotubes, nanowires, nanorods and nanobelts, have been attracting considerable attention from both fundamental and applied research, mainly due to their unique structural nature and electronic, magnetic, optical and/or catalytic properties, which depend highly on their size and shape [1–5]. Compared with the zero-dimensional structure, the shape anisotropy of the one-dimensional structure also provides a better model system to study the dependence of electronic, optical, catalytic and magnetic properties on size confinement and dimensionality [6]. As an important member of the group of platinum metals, ruthenium nanoclusters have been known to show very unique and interesting activities as the catalyst [7–9]. Accordingly, much emphasis has focused on developing diverse methods to obtain size controllable ruthenium colloids [10]. However, all these methods are difficult to control the morphology of ruthenium nanoclusters. While the other novel metals, such as silver, platinum and palladium nanoclusters, have colorful shapes [11–13]. Although different methods have been developed to prepare spherical nanoparticles with different sizes, the morphology control of ruthenium still remains a preparative challenge. Up to now, only a few groups have reported the special morphologies of ruthenium nanoclusters. For example, Zhang et al. reported a shuttly like ruthenium particles with the aspect ratio enlarged from 4.5 to 5.0 [14]. Harpeness et al. synthesized rodlike ruthenium nanoclusters with the aspect ratio of only 1.6 by a microwave-polyol process [15].
* Corresponding author. E-mail address: [email protected] (S.G. Peng). 1001-8417/$ – see front matter # 2010 Shu Ge Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.01.018
S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
629
Microwave irradiation method often has been widely applied to produce one-dimensional nanostructures due to its quick, uniform and energy efficient heating method. In this paper, we explored microwave heating method to prepare ruthenium nanorods with high aspect by refluxing ruthenium(III) chloride in n-propanol using PVP as capping agent. 1. Experimental The typical synthesis is as follows. First, PVP (0.1387 g, 2.5 10 2 mol, as monomeric unit) and RuCl3 (0.0327 g, 2.5 10 3 mol) were dissolved in n-propanol (50 mL) in a 250 mL round-bottomed flask at room temperature under magnetic stirring to form a dark red solution. Then the solution was irradiated to reflux by a modified domestic microwave oven (800 W, 2.45 GHz) with a refluxing apparatus. After the mixture was refluxed for a certain period of time, the color of the solution changed from dark red to deep purple. In all the experiments the microwave over is employed at 100% power. The resulting product could be collected by centrifugation and washed three times using ethanol, then dried 10 h under vacuum at 50 8C. 2. Results and discussion It is well known that UV–vis absorption spectra have been regarded as an effective method to illustrate the evolution of metal species in the preparation of colloidal metal clusters. Fig. 1 presents the UV–vis spectra of a PVPstabilized solution before and after Ru3+ ions reduction by MW irradiation at different reaction intervals. As shown in Fig. 1, there was a peak at 340 nm assigned to the Ru3+ ions in the UV–vis spectrum of the original solution (0 h). As the irradiation time was prolonged, the peak at 340 nm decreased gradually and a broad absorption centered at 509 nm attributed to the Plasmon band of Ru was detected. After about 180 min of MW irradiation, the absorption peak at 340 nm disappeared completely, which indicated that Ru3+ ions were entirely reduced to Ru(0) metal. The increasing scattering absorbance at 509 nm with time revealed the formation of ruthenium (0) colloids. Additionally, the color of the solution turned from dark red to deep purple, which also indicated ruthenium ions were reduced and the metal particles were formed. In order to further confirm the formation of metallic ruthenium nanostructures, XPS measurements were employed to determine the oxidation state of PVP-stabilized ruthenium nanostructures (spectra not shown). The binding energies of Ru 3d5/2 at 280.0 eV, Ru 3p 1/2 at 483.8 eV and Ru 3p 3/2 at 461.2 eV in the PVP-coated ruthenium nanostructures were consistent with those of ruthenium metal [16], respectively. The combination between ruthenium and PVP was investigated by spectroscopic measurement. In comparison the FT-IR spectra of PVP-stabilized ruthenium nanoclusters with pure PVP employed in the preparation, the absorption band at 2960 cm 1, 1660 cm 1, 1280 cm 1, and 1070 cm 1 were assigned to the vibration models of C–H, C–O, N–OH, and C–N, respectively, indicating PVP
Fig. 1. UV–vis absorption spectra of ruthenium colloids stabilized by PVP at different reaction stages.
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S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
Fig. 2. Typical TEM image (a), electron diffraction pattern (b), and distribution of long-axis length (c) and aspect ratio (d) of PVP-stabilized ruthenium nanorods prepared by microwave method.
had been present on the surface of ruthenium and serving as a capping agent. Furthermore, the bands were almost the same as those of pure PVP, demonstrating the coordination between PVP and ruthenium was more weakly than the other capping agent, such as carbonyl group [10]. The morphology and size of the ruthenium nanostructures were observed by TEM technique. Fig. 2(a) shows the representative TEM image of the PVP-stabilized ruthenium nanoclusters prepared by using the microwave synthesis. It appeared that the typical one-dimensional nanorod structure of ruthenium was obtained. The yield of ruthenium nanorods was high according to the TEM images at low magnification. The distributions of the long-axis length and the aspect ratio of the ruthenium nanorods are shown in Fig. 2(c) and (d). The long-axis length of the nanorods was from 100 nm to 600 nm and the mean value was 325 nm. The aspect ratio of the ruthenium nanorods ranged between 5 and 40. To investigate the crystal structure of the nanorods, the electron diffraction pattern of the representative ruthenium nanorods is also conducted, as shown in Fig. 2(b). The electron diffraction pattern of nanorods presented the ˚ and 1.36 A ˚, single crystal diffraction design. The measuring d-spacings of (1 0 0) and (1 1 0) planes are 2.34 A respectively [17]. All the other diffraction spots could be indexed as shown in Fig. 2(b) when the electron beam direction (zone axis) was [0 0 1], which was consistent well with the standard ruthenium metal data file (JCPDS Card: 06-0663). The electron diffraction result indicated that ruthenium was one of a few transition metals that crystallize only in a hexagonal compact (h c p) structure, further confirmed the reduction of Ru3+ to Ru metal. The growth mechanism of ruthenium nanorods might due to the structure-directing action of PVP [18]. 3. Conclusion In summary, PVP-stabilized ruthenium nanorods with high aspect ratio were successfully prepared by refluxing ruthenium(III) chloride in n-propanol by microwave irradiation. The obtained products showed the single-crystalline structure of h c p ruthenium metal and typical one-dimensional nanorod structure with the aspect ratio ranged from 5 to 40 and length up to 600 nm.
S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
631
Acknowledgments This work was financially supported by Science Foundation of Henan University of Science and Technology (No. 05-160) and Research Foundation of Henan Province (No. 2008A150010). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
N. Haberkorn, J.S. Gutmann, P. Theato, ACS Nano 3 (2009) 1415. Z. Liu, X. Zhang, S. Nishimoto, J. Phys. Chem. C 112 (2008) 253. Y. Cheng, P. Xiong, C.S. Yun, Nano Lett. 8 (2008) 4179. Y. Guo, Q. Tang, H. Liu, J. Am. Chem. Soc. 130 (2008) 9198. S. Kim, N. Koratkar, T. Karabacak, Appl. Phys. Lett. 88 (2006) 263106. L. Ma, L.M. Xu, W.X. Chen, Mater. Lett. 63 (2009) 1635. I. Rossetti, F. Mangiarini, L. Forni, Appl. Catal. A: Gen. 323 (2007) 219. S. Miao, Z. Liu, B. Han, Angew. Chem. 118 (2006) 272. C. Roth, N. Benker, R. Theissmann, Langmuir 24 (2008) 2191. M. Zawadzki, J. Okal, Mater. Res. Bull. 43 (2008) 3111. H. Liang, H. Yang, W. Wang, J. Am. Chem. Soc. 131 (2009) 6068. Y. Song, Y. Yang, C.J. Medforth, J. Am. Chem. Soc. 126 (2004) 635. H.P. Choo, K.Y. Liew, W.A.K. Mahmood, J. Mater. Chem. 11 (2001) 2906. Y. Zhang, J. Yu, H. Niu, J. Colloid Interface Sci. 313 (2007) 503. R. Harpeness, Z. Peng, X. Liu, J. Colloid Interface Sci. 287 (2005) 678. J.F. Moulder, W.F. Stickle, P.E. Sobol, Handbook of X-ray Photoelectron Spectroscopy, PerkinElmer Corporation, Eden Prairie, MN, USA, 1992. [17] A.N. Grace, K. Pandian, Mater. Chem. Phys. 104 (2007) 191. [18] M. Tsuji, M. Hashimoto, Y. Nishizawa, Mater. Lett. 58 (2004) 2326.
Chinese Chemical Letters 21 (2010) 628–631 www.elsevier.com/locate/cclet
Microwave-assisted synthesis of high aspect ratio ruthenium nanorods Shu Ge Peng *, Xi Ping Gao, Yong Ke Guo, Yu Qing Zhang, Han Fan Liu Key Laboratory of Polymer and Nanomaterials, College of Chemical Engineering and Pharmacy, Henan University of Science and Technology, Luoyang 471003, China Received 24 August 2009
Abstract Poly (N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium nanorods with high aspect ratio by refluxing ruthenium(III) chloride in n-propanol have been successfully prepared by means of a facile and rapid microwave heating for the first time. The structure and morphology of the obtained products were characterized by transmission electron microscopy (TEM), select area electron diffraction (SAED), ultraviolet–visible spectrophotometry (UV–vis), X-ray photoelectron spectroscopy (XPS) and Fourier transform spectroscopy (FT-IR). XPS analysis reveals that the nanorods were in the metallic state. TEM images showed that ruthenium nanorods had an obvious one-dimensional structure with the aspect ratio ranged from 5 to 40 nm and length up to 600 nm. SAED patterns indicated that the nanorods were single-crystalline with a hexagonal structure. # 2010 Shu Ge Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Poly (N-vinyl-2-pyrrolidone); Ruthenium; Nanorods; Microwave
In recent years, one-dimensional nanostructures, such as nanotubes, nanowires, nanorods and nanobelts, have been attracting considerable attention from both fundamental and applied research, mainly due to their unique structural nature and electronic, magnetic, optical and/or catalytic properties, which depend highly on their size and shape [1–5]. Compared with the zero-dimensional structure, the shape anisotropy of the one-dimensional structure also provides a better model system to study the dependence of electronic, optical, catalytic and magnetic properties on size confinement and dimensionality [6]. As an important member of the group of platinum metals, ruthenium nanoclusters have been known to show very unique and interesting activities as the catalyst [7–9]. Accordingly, much emphasis has focused on developing diverse methods to obtain size controllable ruthenium colloids [10]. However, all these methods are difficult to control the morphology of ruthenium nanoclusters. While the other novel metals, such as silver, platinum and palladium nanoclusters, have colorful shapes [11–13]. Although different methods have been developed to prepare spherical nanoparticles with different sizes, the morphology control of ruthenium still remains a preparative challenge. Up to now, only a few groups have reported the special morphologies of ruthenium nanoclusters. For example, Zhang et al. reported a shuttly like ruthenium particles with the aspect ratio enlarged from 4.5 to 5.0 [14]. Harpeness et al. synthesized rodlike ruthenium nanoclusters with the aspect ratio of only 1.6 by a microwave-polyol process [15].
* Corresponding author. E-mail address: [email protected] (S.G. Peng). 1001-8417/$ – see front matter # 2010 Shu Ge Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.01.018
S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
629
Microwave irradiation method often has been widely applied to produce one-dimensional nanostructures due to its quick, uniform and energy efficient heating method. In this paper, we explored microwave heating method to prepare ruthenium nanorods with high aspect by refluxing ruthenium(III) chloride in n-propanol using PVP as capping agent. 1. Experimental The typical synthesis is as follows. First, PVP (0.1387 g, 2.5 10 2 mol, as monomeric unit) and RuCl3 (0.0327 g, 2.5 10 3 mol) were dissolved in n-propanol (50 mL) in a 250 mL round-bottomed flask at room temperature under magnetic stirring to form a dark red solution. Then the solution was irradiated to reflux by a modified domestic microwave oven (800 W, 2.45 GHz) with a refluxing apparatus. After the mixture was refluxed for a certain period of time, the color of the solution changed from dark red to deep purple. In all the experiments the microwave over is employed at 100% power. The resulting product could be collected by centrifugation and washed three times using ethanol, then dried 10 h under vacuum at 50 8C. 2. Results and discussion It is well known that UV–vis absorption spectra have been regarded as an effective method to illustrate the evolution of metal species in the preparation of colloidal metal clusters. Fig. 1 presents the UV–vis spectra of a PVPstabilized solution before and after Ru3+ ions reduction by MW irradiation at different reaction intervals. As shown in Fig. 1, there was a peak at 340 nm assigned to the Ru3+ ions in the UV–vis spectrum of the original solution (0 h). As the irradiation time was prolonged, the peak at 340 nm decreased gradually and a broad absorption centered at 509 nm attributed to the Plasmon band of Ru was detected. After about 180 min of MW irradiation, the absorption peak at 340 nm disappeared completely, which indicated that Ru3+ ions were entirely reduced to Ru(0) metal. The increasing scattering absorbance at 509 nm with time revealed the formation of ruthenium (0) colloids. Additionally, the color of the solution turned from dark red to deep purple, which also indicated ruthenium ions were reduced and the metal particles were formed. In order to further confirm the formation of metallic ruthenium nanostructures, XPS measurements were employed to determine the oxidation state of PVP-stabilized ruthenium nanostructures (spectra not shown). The binding energies of Ru 3d5/2 at 280.0 eV, Ru 3p 1/2 at 483.8 eV and Ru 3p 3/2 at 461.2 eV in the PVP-coated ruthenium nanostructures were consistent with those of ruthenium metal [16], respectively. The combination between ruthenium and PVP was investigated by spectroscopic measurement. In comparison the FT-IR spectra of PVP-stabilized ruthenium nanoclusters with pure PVP employed in the preparation, the absorption band at 2960 cm 1, 1660 cm 1, 1280 cm 1, and 1070 cm 1 were assigned to the vibration models of C–H, C–O, N–OH, and C–N, respectively, indicating PVP
Fig. 1. UV–vis absorption spectra of ruthenium colloids stabilized by PVP at different reaction stages.
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S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
Fig. 2. Typical TEM image (a), electron diffraction pattern (b), and distribution of long-axis length (c) and aspect ratio (d) of PVP-stabilized ruthenium nanorods prepared by microwave method.
had been present on the surface of ruthenium and serving as a capping agent. Furthermore, the bands were almost the same as those of pure PVP, demonstrating the coordination between PVP and ruthenium was more weakly than the other capping agent, such as carbonyl group [10]. The morphology and size of the ruthenium nanostructures were observed by TEM technique. Fig. 2(a) shows the representative TEM image of the PVP-stabilized ruthenium nanoclusters prepared by using the microwave synthesis. It appeared that the typical one-dimensional nanorod structure of ruthenium was obtained. The yield of ruthenium nanorods was high according to the TEM images at low magnification. The distributions of the long-axis length and the aspect ratio of the ruthenium nanorods are shown in Fig. 2(c) and (d). The long-axis length of the nanorods was from 100 nm to 600 nm and the mean value was 325 nm. The aspect ratio of the ruthenium nanorods ranged between 5 and 40. To investigate the crystal structure of the nanorods, the electron diffraction pattern of the representative ruthenium nanorods is also conducted, as shown in Fig. 2(b). The electron diffraction pattern of nanorods presented the ˚ and 1.36 A ˚, single crystal diffraction design. The measuring d-spacings of (1 0 0) and (1 1 0) planes are 2.34 A respectively [17]. All the other diffraction spots could be indexed as shown in Fig. 2(b) when the electron beam direction (zone axis) was [0 0 1], which was consistent well with the standard ruthenium metal data file (JCPDS Card: 06-0663). The electron diffraction result indicated that ruthenium was one of a few transition metals that crystallize only in a hexagonal compact (h c p) structure, further confirmed the reduction of Ru3+ to Ru metal. The growth mechanism of ruthenium nanorods might due to the structure-directing action of PVP [18]. 3. Conclusion In summary, PVP-stabilized ruthenium nanorods with high aspect ratio were successfully prepared by refluxing ruthenium(III) chloride in n-propanol by microwave irradiation. The obtained products showed the single-crystalline structure of h c p ruthenium metal and typical one-dimensional nanorod structure with the aspect ratio ranged from 5 to 40 and length up to 600 nm.
S.G. Peng et al. / Chinese Chemical Letters 21 (2010) 628–631
631
Acknowledgments This work was financially supported by Science Foundation of Henan University of Science and Technology (No. 05-160) and Research Foundation of Henan Province (No. 2008A150010). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
N. Haberkorn, J.S. Gutmann, P. Theato, ACS Nano 3 (2009) 1415. Z. Liu, X. Zhang, S. Nishimoto, J. Phys. Chem. C 112 (2008) 253. Y. Cheng, P. Xiong, C.S. Yun, Nano Lett. 8 (2008) 4179. Y. Guo, Q. Tang, H. Liu, J. Am. Chem. Soc. 130 (2008) 9198. S. Kim, N. Koratkar, T. Karabacak, Appl. Phys. Lett. 88 (2006) 263106. L. Ma, L.M. Xu, W.X. Chen, Mater. Lett. 63 (2009) 1635. I. Rossetti, F. Mangiarini, L. Forni, Appl. Catal. A: Gen. 323 (2007) 219. S. Miao, Z. Liu, B. Han, Angew. Chem. 118 (2006) 272. C. Roth, N. Benker, R. Theissmann, Langmuir 24 (2008) 2191. M. Zawadzki, J. Okal, Mater. Res. Bull. 43 (2008) 3111. H. Liang, H. Yang, W. Wang, J. Am. Chem. Soc. 131 (2009) 6068. Y. Song, Y. Yang, C.J. Medforth, J. Am. Chem. Soc. 126 (2004) 635. H.P. Choo, K.Y. Liew, W.A.K. Mahmood, J. Mater. Chem. 11 (2001) 2906. Y. Zhang, J. Yu, H. Niu, J. Colloid Interface Sci. 313 (2007) 503. R. Harpeness, Z. Peng, X. Liu, J. Colloid Interface Sci. 287 (2005) 678. J.F. Moulder, W.F. Stickle, P.E. Sobol, Handbook of X-ray Photoelectron Spectroscopy, PerkinElmer Corporation, Eden Prairie, MN, USA, 1992. [17] A.N. Grace, K. Pandian, Mater. Chem. Phys. 104 (2007) 191. [18] M. Tsuji, M. Hashimoto, Y. Nishizawa, Mater. Lett. 58 (2004) 2326.