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Ag bimetallic nanorattle with Au core
Scripta Materialia 54 (2006) 159–162 www.actamat-journals.com
Synthesis of Pt/Ag bimetallic nanorattle with Au core Jianhui Yang a
a,b
, Lehui Lu
a,b
, Haishui Wang a, Hongjie Zhang
a,*
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China b Graduate School of the Chinese Academy of Sciences, Beijing 100064, PR China Received 12 April 2005; received in revised form 22 August 2005; accepted 26 September 2005 Available online 26 October 2005
Abstract A straightforward combination of the seeding growth method and replacement reaction allowed for the formation of a nanorattle composed of a gold core and Pt/Ag shell. The size, structure, and composition of the Pt/Ag rattle-type nanostructure were confirmed by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectrometry. Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Seeding growth method; Template-engaged reaction; Pt/Ag nanorattle
1. Introduction Recently, considerable efforts [1–4] have been devoted to designing nanostructures with hollow interiors due to the prospective applications of such materials in drug delivery, photonic crystals, and catalysts [5–8]. As a result, a series of different procedures have been developed to fabricate these hollow materials in a variety of areas such as inorganic ceramics, organic polymers, and their hybrids [9–12]. In particular, rattle-type nanoparticles (core/shell particles with movable cores encapsulated in the shells) have been successfully synthesized with noble metal nanocores [13–15]. As shown by Koo and co-workers, metal– silica nanorattles were prepared by the pre-shell/post-core method [15]. Yin and co-workers also obtained the Pt–CoO rattle-type spheres (entitled yolk-shell nanostructures) [16]. More recently, Xia and co-workers synthesized nanorattles consisting of Au/Ag alloy cores and shells by the electroless and galvanic replacement reaction [17]. However, this method is unavailable for the synthesis of nanorattles with pure gold cores. In this communication, we report a straightforward combination of the seeding *
Corresponding author. Tel.: +86 431 5262127; fax: +86 431 5698041. E-mail address: [email protected] (H. Zhang).
growth method and replacement reaction to form nanorattles composed of gold cores with Pt/Ag shells. 2. Experimental The synthesis proceeded as follows. Hundred mL of aqueous solution containing 0.01 g HAuCl4 Æ 3H2O was heated to boiling and 3 mL of 1% sodium citrate solution was added. The solution was then kept boiling for another 40 min and was then cooled to room temperature. A gold colloid of 12 nm in diameter was obtained, according to transmission electron microscopy (TEM) measurements. Subsequently, at room temperature, five sets of aqueous solutions (A–E) containing 0.5 mL of 10 mM AgNO3, 1 mL of 100 mM ascorbic acid, and 20 mL of 50 mM cetyl trimethyl ammonium bromide (CTAB) were prepared. Afterwards, different amounts (2, 1, 0.5, 0.2, 0.1 mL) of the 12 nm seed solution were added to the A–E samples, respectively, and then 0.1 mL 1 M NaOH was added drop-by-drop to the above solutions under stirring. Within 1–10 min, depending on the seed concentration, a color change occurred from red to brown suggesting the formation of composite nanoparticles. At last, 2 mL of 0.8 M HPt2Cl6 solution were added to the above five solutions at 75 °C under vigorous stirring. The color of the five sets
1359-6462/$ - see front matter Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2005.09.055
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J. Yang et al. / Scripta Materialia 54 (2006) 159–162
of solutions changed to dark brown immediately, and the solutions were then kept in a 75 °C water bath for 40 min. The morphology of the nanoparticles was characterized by TEM (JEOL 2000-FX). The composite nanoparticles were separated from the surfactant by centrifuging at 4000 rpm for 10 min. Samples for TEM were prepared by placing a drop of the solution onto a carbon-coated copper grid, and allowing natural evaporation of the solvent. The structure and composition of the nanorattles was investigated by scanning electron microscopy (SEM) and energy disperse X-ray (EDX) using a JEOL backscattering microscope (6300F). X-ray photoelectron spectrometry (XPS) analysis was performed on a VG ESCA MKII. Samples for XPS and backscattering SEM measurement were prepared by adding several drops of condensed solution to a glass substrate and then leaving them to dry in air.
3.1. Electron microscopy measurement Fig. 1 gives a backscattered SEM image of sample B; the image shows the presence of nanorattles composed of gold encapsulated in nanoshells and a very small percentage of hollow nanorods and nanowires with gold core, because the presence of rodlike micelle CTAB promoted the silver nanorods with gold cores formation. Moreover, EDX measurements (data not shown) of sample B showed that the
3. Results and discussion Our strategies to fabricate such materials were as follows. First, the 12 nm gold seeds were prepared by the citrate-reduction procedure of Frens [18]. Next, monodispersed core–shell Au–Ag nanoparticles were obtained by the seeding growth method in micellar media [19]. Finally, core–shell Au/Ag nanoparticles reacted with aqueous HPt2Cl6 solution to form the nanorattle composed of gold encapsulated in Pt/Ag nanoshell by the templateengaged reaction [9]: PtCl2 6ðaqÞ þ 4AgðsÞ ! PtðsÞ þ 4AgClðsÞ þ 2ClðaqÞ
and partial Ag+ can be reduced to Ag by ascorbic acid [19]. At the same time, the resultant Pt atoms from the galvanic reaction were deposited on the surface of each nanoparticle to form a bimetallic shell [20]. The results reveal that the dominant surface compositions of samples are Pt and Ag bimetallic. All the reactions were confined to the vicinity of the particle surface, and our suggestion that the nanoparticles are Pt/Ag bimetallic nanorattles with Au cores is proved by the following experiments.
Fig. 1. Backscattering SEM image of sample B.
Fig. 2. TEM images of Pt/Ag@Au nanorattles: (a) sample B and (b) sample A.
J. Yang et al. / Scripta Materialia 54 (2006) 159–162
as-prepared sample consisted of Au, Pt and Ag atoms. To further confirm such a structure, we also examined the asprepared samples using TEM. The TEM images corresponding to sample B and A are presented in Fig. 2(a) and (b), respectively. As observed from Fig. 2, the as-prepared sample consists of nanorattles and some gold cores are not located in the centers of these nanorattles. Because the inner diameter of the shell was larger than the size of the core, it is believed that the Au core encapsulated in each shell was potentially movable when the system is in a liquid medium. As is evident from this figure, the average size of the gold core is 12 nm and the average diameters of the hollow nanostructure for samples A and B were 30 nm and 40 nm, respectively. The diameters of the nanoparticles increase from A to B as the seed concentration is decreased, which is consistent with our previous results
Pt4f5/2
Intensity (a.u)
Pt4f7/2
66
68
(a)
70
72
74
76
78
80
Binding Energy (eV) Ag3d5/2
Intensity (a.u)
Ag3d 3/2
161
[19]. All as-prepared samples were similar in structure and the diameters increased from A to E. Each of the nanostructures had a gold core, which suggested that the Au/Ag nanoparticles have a core–shell structure. The shell of the nanostructure seemed to be an incomplete structure and primarily composed of discrete nanoparticles because both HAuCl4 and AgCl can continuously diffuse across this layer. This could be attributed to the fact that the Ostwald ripening process for Pt nanoparticles might require a relatively higher temperature due to the higher melting point of this metal [3]. As a result, the walls of the nanorattle could not be effectively reconstructed to form a highly crystalline structure at 75 °C in an aqueous medium. 3.2. X-ray photoelectron spectroscopy analysis XPS is valuable for detecting the surface composition of samples. XPS can report detailed information on the nearsurface elemental compositions, and can also provide strong evidence for the formation of core–shell structure [21,22]. As for all samples, XPS measurement showed a significant Pt 4f signal (Fig. 3(a)), corresponding to the binding energy of metal Pt, and Ag 3d signal (Fig. 3(b)), corresponding to the binding energy of metal Ag. However, no Au signal (Fig. 3(c) a) corresponding to Au seed was detected. When we further etched the samples for different times the Au signal (Fig. 3(c) b) could be detected. We explain this result as follows: it is known that depending on the experimental setup and the elements present, the XPS technique has a detectable depth of 2–10 nm [23]. Therefore, when the Au seed has been encapsulated by the Pt/Ag nanoshell, the Au signal corresponding to an Au seed cannot be detected directly by the XPS technique, which is further evidence for our claim that nanorattles composed of gold encapsulated in Pt/Ag nanoshell have been formed in the present work. 4. Conclusions
365
370
375
Binding Energy (eV)
(b)
a: before etching b: after etching
Au4f 5/2
Au4f7/2
Intensity (a.u)
b
In summary, the combination of the seeding growth method and replacement reaction was employed to prepare nanorattles composed of gold encapsulated in Pt/Ag nanoshells. The void space of such nanostructure could be simply controlled by changing the amounts of the Au seeds. Importantly, with this procedure, other types of composite metallic nanorattles can be prepared by rational combination of experimental conditions. Acknowledgements
a
80
(c)
82
84
86
88
90
Binding Energy (eV)
Fig. 3. XPS spectra of Pt/Ag@Au nanorattles: (a) Pt 4f orbital, (b) Ag 3d orbital and (c) Au 4f orbital.
This work was financially supported by the National Natural Science Foundation of China (Nos. 20171043, 20131010), the National Natural Science Foundation of China-Special for Instruments (No. 20121701) and the ‘‘863’’ National Foundation for High Technology Development and Programming (No. 2002AA302105, 2002AA324080).
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J. Yang et al. / Scripta Materialia 54 (2006) 159–162
References [1] Caruso F. Adv Mater 2001;13:11. [2] Cushing BL, Kolesnichenko VL, OConner CJ. Chem Rev 2004;104:3839. [3] Sun Y, Mayers B, Xia Y. Adv Mater 2003;15:641. [4] Lu LH, Sun GY, Xi SQ, Wang HS, Zhang HJ, Wang TD, et al. Langmuir 2003;19:3074. [5] Gill I, Ballesteros A. J Am Chem Soc 1998;120:8587. [6] Prodan E, Radloff C, Halas NJ, Nordlander P. Science 2003;302:419. [7] Schierhorn M, Liz-Marza´n LM. Nano Lett 2002;2:13. [8] Kim S, Kim M, Lee WY, Hyeon T. J Am Chem Soc 2002;124:7642. [9] Sun Y, Mayers B, Xia Y. Nano Lett 2002;2:481. [10] Caruso F, Caruso RA, Mo¨hwald H. Science 1998;282:1111. [11] Oldenburg SJ, Averitt RD, Westcott SL, Halas NJ. Chem Phys Lett 1998;288:243.
[12] Liang H, Zhang H, Hu J, Guo Y, Wan L, Bai C. Angew Chem Int Ed 2004;43:1540. [13] Kim M, Sohn K, Na HB, Hyeon T. Nano Lett 2002;2:1383. [14] Kamata K, Lu Y, Xia Y. J Am Chem Soc 2003;125:2384. [15] Hah HH, Um JI, Han SH, Koo SK. Chem Commun 2004:1012. [16] Yin Y, Rioux RM, Erdonmez CK, Hughes S, Somorjai GA, Alivisatos AP. Science 2004;304:711. [17] Sun Y, Willey B, Li Z, Xia Y. J Am Chem Soc 2004;126:9399. [18] Frens G. Nature 1973;241:20. [19] Lu LH, Wang HS, Zhou YH, Xi SQ, Zhang HJ, Hu JW, et al. Chem Commun 2002:144. [20] Damle C, Kumar A, Sastry M. J Phys Chem B 2002;106:297. [21] Remita H, Etcheberry A, Belloni J. J Phys Chem B 2003;107:31. [22] Yonezawa T, Toshima N. J Chem Soc Faraday Trans 1995;95:4111. [23] Briggs D, Seath MP. Practical surface analysis. 2nd ed. Chichester: Wiley; 1990.
Synthesis of Pt/Ag bimetallic nanorattle with Au core Jianhui Yang a
a,b
, Lehui Lu
a,b
, Haishui Wang a, Hongjie Zhang
a,*
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China b Graduate School of the Chinese Academy of Sciences, Beijing 100064, PR China Received 12 April 2005; received in revised form 22 August 2005; accepted 26 September 2005 Available online 26 October 2005
Abstract A straightforward combination of the seeding growth method and replacement reaction allowed for the formation of a nanorattle composed of a gold core and Pt/Ag shell. The size, structure, and composition of the Pt/Ag rattle-type nanostructure were confirmed by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectrometry. Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Seeding growth method; Template-engaged reaction; Pt/Ag nanorattle
1. Introduction Recently, considerable efforts [1–4] have been devoted to designing nanostructures with hollow interiors due to the prospective applications of such materials in drug delivery, photonic crystals, and catalysts [5–8]. As a result, a series of different procedures have been developed to fabricate these hollow materials in a variety of areas such as inorganic ceramics, organic polymers, and their hybrids [9–12]. In particular, rattle-type nanoparticles (core/shell particles with movable cores encapsulated in the shells) have been successfully synthesized with noble metal nanocores [13–15]. As shown by Koo and co-workers, metal– silica nanorattles were prepared by the pre-shell/post-core method [15]. Yin and co-workers also obtained the Pt–CoO rattle-type spheres (entitled yolk-shell nanostructures) [16]. More recently, Xia and co-workers synthesized nanorattles consisting of Au/Ag alloy cores and shells by the electroless and galvanic replacement reaction [17]. However, this method is unavailable for the synthesis of nanorattles with pure gold cores. In this communication, we report a straightforward combination of the seeding *
Corresponding author. Tel.: +86 431 5262127; fax: +86 431 5698041. E-mail address: [email protected] (H. Zhang).
growth method and replacement reaction to form nanorattles composed of gold cores with Pt/Ag shells. 2. Experimental The synthesis proceeded as follows. Hundred mL of aqueous solution containing 0.01 g HAuCl4 Æ 3H2O was heated to boiling and 3 mL of 1% sodium citrate solution was added. The solution was then kept boiling for another 40 min and was then cooled to room temperature. A gold colloid of 12 nm in diameter was obtained, according to transmission electron microscopy (TEM) measurements. Subsequently, at room temperature, five sets of aqueous solutions (A–E) containing 0.5 mL of 10 mM AgNO3, 1 mL of 100 mM ascorbic acid, and 20 mL of 50 mM cetyl trimethyl ammonium bromide (CTAB) were prepared. Afterwards, different amounts (2, 1, 0.5, 0.2, 0.1 mL) of the 12 nm seed solution were added to the A–E samples, respectively, and then 0.1 mL 1 M NaOH was added drop-by-drop to the above solutions under stirring. Within 1–10 min, depending on the seed concentration, a color change occurred from red to brown suggesting the formation of composite nanoparticles. At last, 2 mL of 0.8 M HPt2Cl6 solution were added to the above five solutions at 75 °C under vigorous stirring. The color of the five sets
1359-6462/$ - see front matter Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2005.09.055
160
J. Yang et al. / Scripta Materialia 54 (2006) 159–162
of solutions changed to dark brown immediately, and the solutions were then kept in a 75 °C water bath for 40 min. The morphology of the nanoparticles was characterized by TEM (JEOL 2000-FX). The composite nanoparticles were separated from the surfactant by centrifuging at 4000 rpm for 10 min. Samples for TEM were prepared by placing a drop of the solution onto a carbon-coated copper grid, and allowing natural evaporation of the solvent. The structure and composition of the nanorattles was investigated by scanning electron microscopy (SEM) and energy disperse X-ray (EDX) using a JEOL backscattering microscope (6300F). X-ray photoelectron spectrometry (XPS) analysis was performed on a VG ESCA MKII. Samples for XPS and backscattering SEM measurement were prepared by adding several drops of condensed solution to a glass substrate and then leaving them to dry in air.
3.1. Electron microscopy measurement Fig. 1 gives a backscattered SEM image of sample B; the image shows the presence of nanorattles composed of gold encapsulated in nanoshells and a very small percentage of hollow nanorods and nanowires with gold core, because the presence of rodlike micelle CTAB promoted the silver nanorods with gold cores formation. Moreover, EDX measurements (data not shown) of sample B showed that the
3. Results and discussion Our strategies to fabricate such materials were as follows. First, the 12 nm gold seeds were prepared by the citrate-reduction procedure of Frens [18]. Next, monodispersed core–shell Au–Ag nanoparticles were obtained by the seeding growth method in micellar media [19]. Finally, core–shell Au/Ag nanoparticles reacted with aqueous HPt2Cl6 solution to form the nanorattle composed of gold encapsulated in Pt/Ag nanoshell by the templateengaged reaction [9]: PtCl2 6ðaqÞ þ 4AgðsÞ ! PtðsÞ þ 4AgClðsÞ þ 2ClðaqÞ
and partial Ag+ can be reduced to Ag by ascorbic acid [19]. At the same time, the resultant Pt atoms from the galvanic reaction were deposited on the surface of each nanoparticle to form a bimetallic shell [20]. The results reveal that the dominant surface compositions of samples are Pt and Ag bimetallic. All the reactions were confined to the vicinity of the particle surface, and our suggestion that the nanoparticles are Pt/Ag bimetallic nanorattles with Au cores is proved by the following experiments.
Fig. 1. Backscattering SEM image of sample B.
Fig. 2. TEM images of Pt/Ag@Au nanorattles: (a) sample B and (b) sample A.
J. Yang et al. / Scripta Materialia 54 (2006) 159–162
as-prepared sample consisted of Au, Pt and Ag atoms. To further confirm such a structure, we also examined the asprepared samples using TEM. The TEM images corresponding to sample B and A are presented in Fig. 2(a) and (b), respectively. As observed from Fig. 2, the as-prepared sample consists of nanorattles and some gold cores are not located in the centers of these nanorattles. Because the inner diameter of the shell was larger than the size of the core, it is believed that the Au core encapsulated in each shell was potentially movable when the system is in a liquid medium. As is evident from this figure, the average size of the gold core is 12 nm and the average diameters of the hollow nanostructure for samples A and B were 30 nm and 40 nm, respectively. The diameters of the nanoparticles increase from A to B as the seed concentration is decreased, which is consistent with our previous results
Pt4f5/2
Intensity (a.u)
Pt4f7/2
66
68
(a)
70
72
74
76
78
80
Binding Energy (eV) Ag3d5/2
Intensity (a.u)
Ag3d 3/2
161
[19]. All as-prepared samples were similar in structure and the diameters increased from A to E. Each of the nanostructures had a gold core, which suggested that the Au/Ag nanoparticles have a core–shell structure. The shell of the nanostructure seemed to be an incomplete structure and primarily composed of discrete nanoparticles because both HAuCl4 and AgCl can continuously diffuse across this layer. This could be attributed to the fact that the Ostwald ripening process for Pt nanoparticles might require a relatively higher temperature due to the higher melting point of this metal [3]. As a result, the walls of the nanorattle could not be effectively reconstructed to form a highly crystalline structure at 75 °C in an aqueous medium. 3.2. X-ray photoelectron spectroscopy analysis XPS is valuable for detecting the surface composition of samples. XPS can report detailed information on the nearsurface elemental compositions, and can also provide strong evidence for the formation of core–shell structure [21,22]. As for all samples, XPS measurement showed a significant Pt 4f signal (Fig. 3(a)), corresponding to the binding energy of metal Pt, and Ag 3d signal (Fig. 3(b)), corresponding to the binding energy of metal Ag. However, no Au signal (Fig. 3(c) a) corresponding to Au seed was detected. When we further etched the samples for different times the Au signal (Fig. 3(c) b) could be detected. We explain this result as follows: it is known that depending on the experimental setup and the elements present, the XPS technique has a detectable depth of 2–10 nm [23]. Therefore, when the Au seed has been encapsulated by the Pt/Ag nanoshell, the Au signal corresponding to an Au seed cannot be detected directly by the XPS technique, which is further evidence for our claim that nanorattles composed of gold encapsulated in Pt/Ag nanoshell have been formed in the present work. 4. Conclusions
365
370
375
Binding Energy (eV)
(b)
a: before etching b: after etching
Au4f 5/2
Au4f7/2
Intensity (a.u)
b
In summary, the combination of the seeding growth method and replacement reaction was employed to prepare nanorattles composed of gold encapsulated in Pt/Ag nanoshells. The void space of such nanostructure could be simply controlled by changing the amounts of the Au seeds. Importantly, with this procedure, other types of composite metallic nanorattles can be prepared by rational combination of experimental conditions. Acknowledgements
a
80
(c)
82
84
86
88
90
Binding Energy (eV)
Fig. 3. XPS spectra of Pt/Ag@Au nanorattles: (a) Pt 4f orbital, (b) Ag 3d orbital and (c) Au 4f orbital.
This work was financially supported by the National Natural Science Foundation of China (Nos. 20171043, 20131010), the National Natural Science Foundation of China-Special for Instruments (No. 20121701) and the ‘‘863’’ National Foundation for High Technology Development and Programming (No. 2002AA302105, 2002AA324080).
162
J. Yang et al. / Scripta Materialia 54 (2006) 159–162
References [1] Caruso F. Adv Mater 2001;13:11. [2] Cushing BL, Kolesnichenko VL, OConner CJ. Chem Rev 2004;104:3839. [3] Sun Y, Mayers B, Xia Y. Adv Mater 2003;15:641. [4] Lu LH, Sun GY, Xi SQ, Wang HS, Zhang HJ, Wang TD, et al. Langmuir 2003;19:3074. [5] Gill I, Ballesteros A. J Am Chem Soc 1998;120:8587. [6] Prodan E, Radloff C, Halas NJ, Nordlander P. Science 2003;302:419. [7] Schierhorn M, Liz-Marza´n LM. Nano Lett 2002;2:13. [8] Kim S, Kim M, Lee WY, Hyeon T. J Am Chem Soc 2002;124:7642. [9] Sun Y, Mayers B, Xia Y. Nano Lett 2002;2:481. [10] Caruso F, Caruso RA, Mo¨hwald H. Science 1998;282:1111. [11] Oldenburg SJ, Averitt RD, Westcott SL, Halas NJ. Chem Phys Lett 1998;288:243.
[12] Liang H, Zhang H, Hu J, Guo Y, Wan L, Bai C. Angew Chem Int Ed 2004;43:1540. [13] Kim M, Sohn K, Na HB, Hyeon T. Nano Lett 2002;2:1383. [14] Kamata K, Lu Y, Xia Y. J Am Chem Soc 2003;125:2384. [15] Hah HH, Um JI, Han SH, Koo SK. Chem Commun 2004:1012. [16] Yin Y, Rioux RM, Erdonmez CK, Hughes S, Somorjai GA, Alivisatos AP. Science 2004;304:711. [17] Sun Y, Willey B, Li Z, Xia Y. J Am Chem Soc 2004;126:9399. [18] Frens G. Nature 1973;241:20. [19] Lu LH, Wang HS, Zhou YH, Xi SQ, Zhang HJ, Hu JW, et al. Chem Commun 2002:144. [20] Damle C, Kumar A, Sastry M. J Phys Chem B 2002;106:297. [21] Remita H, Etcheberry A, Belloni J. J Phys Chem B 2003;107:31. [22] Yonezawa T, Toshima N. J Chem Soc Faraday Trans 1995;95:4111. [23] Briggs D, Seath MP. Practical surface analysis. 2nd ed. Chichester: Wiley; 1990.