Electric‐Field‐Directed Growth of Gold Nanorods in Aqueous Surfactant Solutions

Abstract

The factors affecting the nucleation and growth of gold nanorods, (Jana et al., Adv. Mater. 2001, 13, 1389) have been investigated. It is shown that the size and aspect ratio can be controlled through the use of different sized seed particles. The length of the rods can be tuned from 25–170 nm, while the width remains almost constant at 22–25 nm. The formation of rods requires the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Lower temperature favors rod formation, although this reduces CTAB solubility. The addition of chloride ions or the use of dodecyltrimethylammonium bromide (DTAB) leads to shorter‐aspect rods. AuIII and AuI are shown to be quantitatively bound to the CTAB micelles. We propose an electrochemical mechanism for rod formation, whereby the flux of AuI bound to cationic micelles to the seed surface is maximized at points of highest curvature, where the electrical double layer gradient is highest. Initial numerical solutions to the electric potential and field around an ellipsoid in a 1:1 electrolyte are provided, which indicate that the field at the particle tip scales linearly with the aspect ratio. Mean free passage times for ions are found to be shortest at the tips. The results provide a general explanation for the formation of non‐equilibrium crystal habits and a mechanism for controlling crystal growth.

Shape‐Dependent Electrocatalysis: Oxygen Reduction on Carbon‐Supported Gold Nanoparticles

“…[27,80] Quasi-spherical AuNPs ( % 30 nm) were synthesised using the standard citrate reduction method. [81] In brief, aqueous HAuCl 4 (0.25 mm) was heated to boiling.…”

Highly Sensitive Visual Detection of Copper Ions Based on the Shape-Dependent LSPR Spectroscopy of Gold Nanorods

“…In this work, using cetyltrimethylammonium bromide (CTAB)-stabilized gold nanorods (GNRs), the color of which is dependent on the aspect ratio, 19,20 we have proposed a simple and sensitive visual sensor for Cu 2+ based on the catalytic etching of GNRs. In this system, CTAB acts not only as a stabilizer but also as an ion-association reagent.…”

Two-step synthesis of high aspect ratio gold nanorods

“…All spectra are quite complex although a transversal and longitudinal plasmon band typical for rodlike particles is clearly seen. Two possible mechanisms for rod formation have been proposed in literature: a direct surfactant templating mechanism with or without an electric-field directed growth of gold nanorods [12,15] and a mechanism suggesting the lowering of the interfacial tension of a specific crystal facet [16]. Since the formation of rods is observed well below the cmc of CTAB, a templating mechanism seems unlikely.…”