Dependence of the Gold Nanorod Aspect Ratio on the Nature of the Directing Surfactant in Aqueous Solution

Abstract

A three-step seed-mediated growth method was used to make gold nanoparticles. Different surfactants, alkyltrimethylammonium bromides (CnTAB, n ) 10, 12, 14, 16, and 18) and cetylpyridinium chloride (C16PC), were chosen as stabilizers. In general, it was found that as the length of the surfactant chain increased, the resulting gold nanoparticles' aspect ratio increased: the aspect ratio was 1 (for C10TAB), 5 ( 2 (C12TAB), 17 ( 3 (C14TAB), and 23 ( 4 (C16TAB). The plasmon absorption maxima for the gold nanoparticles varied as a function of the shape, from 520 nm (spheres) to beyond 2000 nm (high aspect ratio nanorods). We propose that the surfactant binds as a bilayer to the growing nanoparticle and assists in nanoparticle elongation via a "zipping" mechanism.

Surfactant- and reducer-free synthesis of gold nanoparticles in aqueous solutions

“…However, surfactants and amphiphilic polymers would introduce complexities for understanding the mechanism on particle-size and -shape determination due to the incorporation of various factors such as adsorption of hydrophobic tail, hydrophilic head group and counter ions (in the case of ionic surfactants) on the surface of nuclei and/or small particles, and complexation of metal ions with surfactants and/or amphiphilic polymers. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] Then we considered the surfactant-and reducer-free metal nanoparticle synthesis from metal ions in aqueous solutions (in the absence of any stabilizing, capping and reducing agents) to evaluate the mechanism on size-, shape-and stability-control of metal nanoparticles formed in solutions. Simplified system (surfactant-and reducer-free conditions) should manifest the essential mechanism on size-, shape-and stability-control of metal nanoparticles synthesized in aqueous solutions.…”

Synthesis of Gold Nanorods from Metallic Gold by a Sonoelectrochemical Method

“…However, according to the authors [7,8], the C 16 TAB and TC 12 AB in solution form cylindrical-shape C 16 TAB-TC 12 AB micellar frameworks, which may assist nanorod formation as more and more gold ions are introduced into these micelle structures. At the appropriate temperature, the addition of acetone makes loosening the micellar framework, facilitating the introduction of the gold ions into the micellar frameworks, in this way the gold nanorods are easily developed.…”

A green chemical approach for synthesis of shape anisotropic gold nanoparticles

“…As both size and shape of Au NPs affect optical and electronic properties, a number of methods have been reported for the preparation of Au NPs with varying sizes and shapes [4][5][6]. The surface electrons of Au NPs exhibit a phenomenal behavior of collective oscillation and absorption of light, which is known as surface plasmon resonance (SPR).…”

“…The surface electrons of Au NPs exhibit a phenomenal behavior of collective oscillation and absorption of light, which is known as surface plasmon resonance (SPR). The remarkable shapedependent optical property of gold nanorods and spheres is a typical example, wherein gold nanorods exhibit two absorption peaks arising from the transverse and longitudinal surface plasmon resonances (SPRs), whereas the spherical particles display only a single SPR peak [4,5]. Au NPs can be synthesized by conventional chemical and physical methods [7][8][9].…”