Formation of Gold Nanorods by Seeded Growth: Mechanisms and Modeling

Abstract

Seeded growth is one of the most successful and well-studied methods of making nanorods of face-centered cubic (FCC) metals such as Ag, Au, Pt, etc. In this method separately prepared tiny metal seeds (typically smaller than 10 nm) are added to a growth solution containing metal precursor, a weak reducing agent such as ascorbic acid, and a capping agent. The mechanisms that lead to specific shape selection and growth of nanoparticles, in this method, are poorly understood. We propose a mechanism of nanorod growth based on the physical phenomenon of twinning and develop a population balance based model. Briefly, on mixing with growth solution, the seeds start growing isotropically, during which some of the seeds undergo twinning and transform their growth habit to form nanorod nuclei. The nanorod nuclei grow along one dimension to form nanorods, and a mixture of nanorods and nanospheres is obtained after a short aging time (typically < 3 h). The simulations capture the salient features of one-dimensional growth of nanorods, along with the kinetics. The trends in experimental data are reproduced well by this model, and we are able to predict the yield of nanorods. Simulations also reveal that the growth of nanospheres competes with the nucleation and growth of nanorods; their relative magnitudes decide the yield of specific shapes in the system. The model is quite general and will apply to the seeded growth of nanorods of any material that has an FCC crystal structure.

Photochemical Formation of Tunable Gold Nanostructures Using Versatile Water‐Soluble Thiolate Au(I) Precursor

“…At the same time, increasing AA concentration above 2.5 × 10 −3 m (e.g., 5 × 10 −3 m ; 4:1 AA‐to‐Au molar ratio) results in blueshift with the decrease in LSPR intensity. Thus, AA is also found to function as a shape selective agent by favoring star‐like structures through the kinetics of the growth . Optimal AA concentrations for the studied conditions of the photochemical synthesis of AuNSs using Au(I)‐thiolate precursor are found to be in the range of 1.25–2.5 × 10 −3 m (AA‐to‐Au molar ratios from 1:1 to 2:1).…”

Nonspherical Metal‐Based Nanoarchitectures: Synthesis and Impact of Size, Shape, and Composition on Their Biological Activity

“…The surfactant molecules adsorb on the high‐energy side facets {100} or {110} to stabilize the enlarging nanocrystals, resulting in octagonal nanorods. [ 60,32,61,62 ]…”

Noble Metal Nanostructured Materials for Chemical and Biosensing Systems

“…The basic process is adding a certain concentration of seed crystals to the growth liquid, and under the action of the surfactant, orienting the seed particles to grow into NRs. The yield and radial ratio of NRs can be controlled by adjusting the ionic strength (pH) of the solution [49,50]. Zhang and his co-workers synthesized a tunable-aspect ratio AuNRs using a modified seed-mediated synthesis method for near-infrared photoacoustic imaging [51].…”