Abstract
The seed-mediated method in presence of high concentrations of CTAB is frequently implemented in the preparation of high aspect ratio gold nanorods (i.e., nanorods with aspect ratios of 5 or more); however, the reproducibility has still been limited. We rendered the synthesis procedure simpler, decreased the susceptibility to impurities, and improved the reproducibility of the product distribution. As a result of the high aspect ratios, longitudinal plasmon absorptions were shifted up to very high absorption maxima of 1955 nm in UV-vis-NIR spectra (since this band is completely covered in aqueous solution by the strong absorption of water, the gold species were embedded in poly(vinyl alcohol) films for UV-vis-NIR measurements). Finally, the directed particle growth in (110) direction leads to the conclusion that the adsorption of CTAB molecules at specific crystal faces accounts for nanorod growth and not cylindrical CTAB micelles, in agreement with other observations.
Highlights
The preparation of gold nanorods has found wide attention during the last decade since many characteristics of nanoscale materials are size- and shape-dependent including their optical, electronic, and catalytic properties
Essential particularities of the seed-mediated method created here are rapid addition of a small volume of seed solution in the final step of the synthesis procedure and modification of the pH value by a defined quantity of sodium hydroxide. Parameters such as growth time, age of the seed and growth solution, and growth temperature were varied which resulted in the propitious conditions described in the Experimental section
At a CTAB concentration of 0.5 M, only a few very big spherical particles and triangles emerged (Figure 11). These findings are different from those of other seed-mediated methods where the yield of high aspect ratio nanorods increased with decreasing CTAB concentration [13], while, in contrast, other authors report that the aspect ratio increases with higher CTAB concentrations [26]
Summary
The preparation of gold nanorods has found wide attention during the last decade since many characteristics of nanoscale materials are size- and shape-dependent including their optical, electronic, and catalytic properties. Journal of Nanomaterials nm Figure 1: TEM image of an area with representative product distribution in samples containing low aspect ratio gold nanorods, prepared according to the seed-mediated method (in presence of small quantities of silver ions [3, 4, 7,8,9]). This image strongly resembles those reported elsewhere and shows that the synthesis of low aspect ratio gold nanorods is well reproducible (in contrast to high aspect ratio nanorods described so far). The evaluation of electron diffraction patterns and other aspects provided information on the principal growth mechanism of the high aspect ratio nanorods
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