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Observation of Coalescence Process of Silver Nanospheres During Shape Transformation to Nanoprisms

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ABSTRACT

In this report, we observed the growth mechanism and the shape transformation from spherical nanoparticles (diameter ~6 nm) to triangular nanoprisms (bisector length ~100 nm). We used a simple direct chemical reduction method and provided evidences for the growth of silver nanoprisms via a coalescence process. Unlike previous reports, our method does not rely upon light, heat, or strong oxidant for the shape transformation. This transformation could be launched by fine-tuning the pH value of the silver colloidal solution. Based on our extensive examination using transmission electron microscopy, we propose a non-point initiated growth mechanism, which is a combination of coalescence and dissolution–recrystallization process during the growth of silver nanoprisms.

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a Time resolved extinction of the formation of the silver nanoprism via coalescence processes. b Change in the absorbance at 403 nm (dipole band of the silver nanospheres) and 1,000 nm (in-plane dipole band of the silver nanoprisms) as a function of reaction time.
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Figure 4: a Time resolved extinction of the formation of the silver nanoprism via coalescence processes. b Change in the absorbance at 403 nm (dipole band of the silver nanospheres) and 1,000 nm (in-plane dipole band of the silver nanoprisms) as a function of reaction time.

Mentions: The synthesis was also carried out at different temperatures in the dark. We noticed that the transformation occurred even at the temperature down to 4°C in 2 weeks and the transformation occurred at room temperature in 24 h. Here, rising the reaction temperature would also increase the transformation rate from nanospheres into nanoprisms. However, as temperature increased to 37°C, smaller nanoprisms and irregular-shaped particles were formed within 24 h. In addition, there were only spherical silver nanoparticles obtained in the absence of citrate. Therefore, the citrate is not only capping molecules but also a reductant for the reaction over several hours in this synthesis. These results suggest that the strong oxidant, H2O2, addition, light, and heat are not required for the shape transformations. Figure 4a shows the time evolution of UV–Vis–NIR extinction spectra of the synthesized colloid (spherical nanoparticles) and nanoprisms. In the first hour, silver nanoclusters were formed (light yellow) then turned into nanoparticles immediately (yellow). The shape transformation of nanoprisms would occur automatically within 24 h (blue). These two transformation periods were marked in green and blue in Figure 4b, respectively. It is worth noticing that the peak position at the longer wavelength is fixed and only the intensity increased with time. Since the in-plane dipole resonance peak is very sensitive to the size and the aspect ratio, the result suggested that only the amount varies during the transformation while the size of the triangular structure remained constant.


Observation of Coalescence Process of Silver Nanospheres During Shape Transformation to Nanoprisms
a Time resolved extinction of the formation of the silver nanoprism via coalescence processes. b Change in the absorbance at 403 nm (dipole band of the silver nanospheres) and 1,000 nm (in-plane dipole band of the silver nanoprisms) as a function of reaction time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211880&req=5

Figure 4: a Time resolved extinction of the formation of the silver nanoprism via coalescence processes. b Change in the absorbance at 403 nm (dipole band of the silver nanospheres) and 1,000 nm (in-plane dipole band of the silver nanoprisms) as a function of reaction time.
Mentions: The synthesis was also carried out at different temperatures in the dark. We noticed that the transformation occurred even at the temperature down to 4°C in 2 weeks and the transformation occurred at room temperature in 24 h. Here, rising the reaction temperature would also increase the transformation rate from nanospheres into nanoprisms. However, as temperature increased to 37°C, smaller nanoprisms and irregular-shaped particles were formed within 24 h. In addition, there were only spherical silver nanoparticles obtained in the absence of citrate. Therefore, the citrate is not only capping molecules but also a reductant for the reaction over several hours in this synthesis. These results suggest that the strong oxidant, H2O2, addition, light, and heat are not required for the shape transformations. Figure 4a shows the time evolution of UV–Vis–NIR extinction spectra of the synthesized colloid (spherical nanoparticles) and nanoprisms. In the first hour, silver nanoclusters were formed (light yellow) then turned into nanoparticles immediately (yellow). The shape transformation of nanoprisms would occur automatically within 24 h (blue). These two transformation periods were marked in green and blue in Figure 4b, respectively. It is worth noticing that the peak position at the longer wavelength is fixed and only the intensity increased with time. Since the in-plane dipole resonance peak is very sensitive to the size and the aspect ratio, the result suggested that only the amount varies during the transformation while the size of the triangular structure remained constant.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

In this report, we observed the growth mechanism and the shape transformation from spherical nanoparticles (diameter ~6 nm) to triangular nanoprisms (bisector length ~100 nm). We used a simple direct chemical reduction method and provided evidences for the growth of silver nanoprisms via a coalescence process. Unlike previous reports, our method does not rely upon light, heat, or strong oxidant for the shape transformation. This transformation could be launched by fine-tuning the pH value of the silver colloidal solution. Based on our extensive examination using transmission electron microscopy, we propose a non-point initiated growth mechanism, which is a combination of coalescence and dissolution–recrystallization process during the growth of silver nanoprisms.

No MeSH data available.


Related in: MedlinePlus