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Galvanic synthesis of three-dimensional and hollow metallic nanostructures.

Park SH, Son JG, Lee TG, Kim J, Han SY, Park HM, Song JY - Nanoscale Res Lett (2014)

Bottom Line: Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG.During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V.The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

View Article: PubMed Central - PubMed

Affiliation: Korea Research Institute of Standard and Science, Daejeon, 305-340, Republic of Korea, psh@kriss.re.kr.

ABSTRACT
We report a low-cost, facile, and template-free electrochemical method of synthesizing three-dimensional (3D) hollow metallic nanostructures. The 3D nanoporous gold (3D-NPG) nanostructures were synthesized by a galvanic replacement reaction (GRR) using the different reduction potentials of silver and gold; hemispherical silver nanoislands were electrochemically deposited on cathodic substrates by a reverse-pulse potentiodynamic method without templates and then nanoporous gold layer replicated the shape of silver islands during the GRR process in an ultra-dilute electrolyte of gold(III) chloride trihydrate. Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG. During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V. And the GRR process of silver nanoislands was also applicable to fabrication of the 3D hollow nanostructures of platinum and palladium. The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

No MeSH data available.


TEM images of the 3D-NPG nanostructure. (a) BFTEM image and (b) SAED pattern.
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Fig3: TEM images of the 3D-NPG nanostructure. (a) BFTEM image and (b) SAED pattern.

Mentions: GRR in ultra-dilute electrolyte led to the formation of uniform and ultra-thin 3D-NPG nanostructures because the low concentration of the electrolyte decreased the concentration gradient between the cathodic surface and solution and formed a thick double layer (diffusive region) leading to a slow reaction-rate of galvanic replacement [26, 29, 30]. Therefore, for the ultra-dilute electrolyte (50 μM), the GRR occurred only on the surface of the silver islands and after 24 h resulted in the formation of the isolated 3D-NPG on the substrate (see yellow dotted lines in Additional file 1: Figure S2a). With further time up to 48 h, the GRR occurred over the entire bottom surface as well as the silver nanoislands, forming the interconnected 3D-NPG (see Additional file 1: Figure S2b). However, with the further GRR time up to 72 h, the nanopores of 3D-NPG gradually disappeared, and thick gold walls with smooth surfaces were produced by oxidizing silver in the core (Additional file 1: Figures S1d and S1h). In contrast, when the electrolyte concentration was increased to 200 μM HAuCl4 · nH2O, the initial hemispherical shape was not maintained and became rough because the GRR occurred faster and severely (Additional file 1: Figure S3). In addition, AgCl precipitates substantially formed on the nanostructure surface (see the yellow arrows marked in Additional file 1: Figure S3).Figure 3 shows the typical bright field TEM (BFTEM) image and selected area electron diffraction (SAED) pattern of 3D-NPG shown in Figure 2b. The SAED shows a ring-like pattern indicating that the 3D-NPG has a face-centered-cubic polycrystalline structure. The ring patterns are indexed to be (111), (200), (220), (311), (222), (400), and (331) reflection planes from the center, in sequence. And it is noted that the 3D-NPG is composed of many nanopores (less than several tens of nanometers in diameter).Figure 3


Galvanic synthesis of three-dimensional and hollow metallic nanostructures.

Park SH, Son JG, Lee TG, Kim J, Han SY, Park HM, Song JY - Nanoscale Res Lett (2014)

TEM images of the 3D-NPG nanostructure. (a) BFTEM image and (b) SAED pattern.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493846&req=5

Fig3: TEM images of the 3D-NPG nanostructure. (a) BFTEM image and (b) SAED pattern.
Mentions: GRR in ultra-dilute electrolyte led to the formation of uniform and ultra-thin 3D-NPG nanostructures because the low concentration of the electrolyte decreased the concentration gradient between the cathodic surface and solution and formed a thick double layer (diffusive region) leading to a slow reaction-rate of galvanic replacement [26, 29, 30]. Therefore, for the ultra-dilute electrolyte (50 μM), the GRR occurred only on the surface of the silver islands and after 24 h resulted in the formation of the isolated 3D-NPG on the substrate (see yellow dotted lines in Additional file 1: Figure S2a). With further time up to 48 h, the GRR occurred over the entire bottom surface as well as the silver nanoislands, forming the interconnected 3D-NPG (see Additional file 1: Figure S2b). However, with the further GRR time up to 72 h, the nanopores of 3D-NPG gradually disappeared, and thick gold walls with smooth surfaces were produced by oxidizing silver in the core (Additional file 1: Figures S1d and S1h). In contrast, when the electrolyte concentration was increased to 200 μM HAuCl4 · nH2O, the initial hemispherical shape was not maintained and became rough because the GRR occurred faster and severely (Additional file 1: Figure S3). In addition, AgCl precipitates substantially formed on the nanostructure surface (see the yellow arrows marked in Additional file 1: Figure S3).Figure 3 shows the typical bright field TEM (BFTEM) image and selected area electron diffraction (SAED) pattern of 3D-NPG shown in Figure 2b. The SAED shows a ring-like pattern indicating that the 3D-NPG has a face-centered-cubic polycrystalline structure. The ring patterns are indexed to be (111), (200), (220), (311), (222), (400), and (331) reflection planes from the center, in sequence. And it is noted that the 3D-NPG is composed of many nanopores (less than several tens of nanometers in diameter).Figure 3

Bottom Line: Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG.During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V.The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

View Article: PubMed Central - PubMed

Affiliation: Korea Research Institute of Standard and Science, Daejeon, 305-340, Republic of Korea, psh@kriss.re.kr.

ABSTRACT
We report a low-cost, facile, and template-free electrochemical method of synthesizing three-dimensional (3D) hollow metallic nanostructures. The 3D nanoporous gold (3D-NPG) nanostructures were synthesized by a galvanic replacement reaction (GRR) using the different reduction potentials of silver and gold; hemispherical silver nanoislands were electrochemically deposited on cathodic substrates by a reverse-pulse potentiodynamic method without templates and then nanoporous gold layer replicated the shape of silver islands during the GRR process in an ultra-dilute electrolyte of gold(III) chloride trihydrate. Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG. During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V. And the GRR process of silver nanoislands was also applicable to fabrication of the 3D hollow nanostructures of platinum and palladium. The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

No MeSH data available.