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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.


Variation of open circuit voltage (OCV) and current density. (a) Variation of OCV during GRR process in a 50 μM HAuCl4 · nH2O electrolyte and (b) variations of current densities with the bias voltage (V) of (i) OCV, (ii) 0.2, (iii) -0.3, and (iv) -0.64 during the GRR process, respectively.
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Fig4: Variation of open circuit voltage (OCV) and current density. (a) Variation of OCV during GRR process in a 50 μM HAuCl4 · nH2O electrolyte and (b) variations of current densities with the bias voltage (V) of (i) OCV, (ii) 0.2, (iii) -0.3, and (iv) -0.64 during the GRR process, respectively.

Mentions: As shown in the open circuit voltage variation with the GRR time up to 48 h (see Figure 4a), the voltage slowly decreased from 0.32 to 0.24 V. This suggests that the GRR might be controlled by applying an external bias voltage to the cathodic substrate. When the bias voltage was 0.2 V, the porosity of the final nanostructure was almost identical to that of 3D-NPG nanostructure, and the formation of AgCl was reduced (Figures 4b-ii and S4). Accordingly, the porosity of the 3D-NPG was controlled by applying the bias voltage in the range of 0.2 to -0.62 V. With the increase of bias voltage, the current density increased, as shown in Figure 4b. The increase of current density implied more supply of electrons which are needed for the reduction of AuCl4- ions. Figure 5 shows that the increase of bias voltage decreased porosity and resulted in the formation of nanoshell gold structures. It is presumed that the bias voltage plays a role of supplying electrons and reducing the expense of silver atoms during the GRR process because AuCl4- ions are reduced to one gold atom at the expense of three electrons supplied by silver, according to Equation 1. Thus, the consumption of silver atoms decreases, and then the porosity decreases when electrons are externally provided. This process is not only affected by the chemical reaction for galvanic replacement, but also the underpotential deposition of a metallic adlayer onto a different metallic substrate [30].Figure 4


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)

Variation of open circuit voltage (OCV) and current density. (a) Variation of OCV during GRR process in a 50 μM HAuCl4 · nH2O electrolyte and (b) variations of current densities with the bias voltage (V) of (i) OCV, (ii) 0.2, (iii) -0.3, and (iv) -0.64 during the GRR process, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig4: Variation of open circuit voltage (OCV) and current density. (a) Variation of OCV during GRR process in a 50 μM HAuCl4 · nH2O electrolyte and (b) variations of current densities with the bias voltage (V) of (i) OCV, (ii) 0.2, (iii) -0.3, and (iv) -0.64 during the GRR process, respectively.
Mentions: As shown in the open circuit voltage variation with the GRR time up to 48 h (see Figure 4a), the voltage slowly decreased from 0.32 to 0.24 V. This suggests that the GRR might be controlled by applying an external bias voltage to the cathodic substrate. When the bias voltage was 0.2 V, the porosity of the final nanostructure was almost identical to that of 3D-NPG nanostructure, and the formation of AgCl was reduced (Figures 4b-ii and S4). Accordingly, the porosity of the 3D-NPG was controlled by applying the bias voltage in the range of 0.2 to -0.62 V. With the increase of bias voltage, the current density increased, as shown in Figure 4b. The increase of current density implied more supply of electrons which are needed for the reduction of AuCl4- ions. Figure 5 shows that the increase of bias voltage decreased porosity and resulted in the formation of nanoshell gold structures. It is presumed that the bias voltage plays a role of supplying electrons and reducing the expense of silver atoms during the GRR process because AuCl4- ions are reduced to one gold atom at the expense of three electrons supplied by silver, according to Equation 1. Thus, the consumption of silver atoms decreases, and then the porosity decreases when electrons are externally provided. This process is not only affected by the chemical reaction for galvanic replacement, but also the underpotential deposition of a metallic adlayer onto a different metallic substrate [30].Figure 4

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.