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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.

No MeSH data available.


UV–Vis–NIR spectra of the silver nanoparticles prepared with different pH value: a pH 9.17, b pH 9.32, c pH 9.43, and d pH 9.89. The inset shows photographs from left to right corresponding to pH high to low.
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Figure 3: UV–Vis–NIR spectra of the silver nanoparticles prepared with different pH value: a pH 9.17, b pH 9.32, c pH 9.43, and d pH 9.89. The inset shows photographs from left to right corresponding to pH high to low.

Mentions: When the amount of NaBH4 is increased above 1,100 μL, the tips of nanoprism would become more rounded and turn into a disk-like nanoplate, which is marked with circles in Figure 1e, f. As nanoprism transform into disk-like nanoplate, blue-shift in the in-plane dipole mode was observed [23]. To determine the effect of reducing agent concentration in shape transformation, the pH value of each as-synthesis nanoparticles was measured. The pH ranged from 9.28 to 9.48 and the pH increases as the concentration of reducing agent increases. The pH value corresponding to the amount of NaBH4 is listed in Figure 2a. To evaluate the effect of pH on shape transformation from spheres to nanoprisms, NaOH and HNO3 were added to the system to probe the particle dependence on pH. The pH values ranged from 9.17, upon the addition of HNO3, to 9.89, with the addition of NaOH. Even though the change in pH was relatively small, very large differences in NIR–Vis–UV absorption spectrum were observed as shown in Figure 3. At a relatively acidic condition (pH 9.17), the transformation does not proceed and there is no evidence of prism formation. At the other end of the pH, the in-plane dipole resonance peak at long wavelength was obtained. It is noticed that the blue-shift was observed at higher pH, which is consistent with NaBH4 variation data.


Observation of Coalescence Process of Silver Nanospheres During Shape Transformation to Nanoprisms
UV–Vis–NIR spectra of the silver nanoparticles prepared with different pH value: a pH 9.17, b pH 9.32, c pH 9.43, and d pH 9.89. The inset shows photographs from left to right corresponding to pH high to low.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: UV–Vis–NIR spectra of the silver nanoparticles prepared with different pH value: a pH 9.17, b pH 9.32, c pH 9.43, and d pH 9.89. The inset shows photographs from left to right corresponding to pH high to low.
Mentions: When the amount of NaBH4 is increased above 1,100 μL, the tips of nanoprism would become more rounded and turn into a disk-like nanoplate, which is marked with circles in Figure 1e, f. As nanoprism transform into disk-like nanoplate, blue-shift in the in-plane dipole mode was observed [23]. To determine the effect of reducing agent concentration in shape transformation, the pH value of each as-synthesis nanoparticles was measured. The pH ranged from 9.28 to 9.48 and the pH increases as the concentration of reducing agent increases. The pH value corresponding to the amount of NaBH4 is listed in Figure 2a. To evaluate the effect of pH on shape transformation from spheres to nanoprisms, NaOH and HNO3 were added to the system to probe the particle dependence on pH. The pH values ranged from 9.17, upon the addition of HNO3, to 9.89, with the addition of NaOH. Even though the change in pH was relatively small, very large differences in NIR–Vis–UV absorption spectrum were observed as shown in Figure 3. At a relatively acidic condition (pH 9.17), the transformation does not proceed and there is no evidence of prism formation. At the other end of the pH, the in-plane dipole resonance peak at long wavelength was obtained. It is noticed that the blue-shift was observed at higher pH, which is consistent with NaBH4 variation data.

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.