No abstract

It is now well-known that the size, shape, and composition of nanomaterials can dramatically affect their physical and chemical properties, and that technologies based on nanoscale materials have the potential to revolutionize fields ranging from catalysis to medicine. Among these materials, anisotropic particles are particularly interesting because the decreased symmetry of such particles often leads to new and unusual chemical and physical behavior. Within this class of particles, triangular Au and Ag nanoprisms stand out due to their structure- and environment-dependent optical features, their anisotropic surface energetics, and the emergence of reliable synthetic methods for producing them in bulk quantities with control over their edge lengths and thickness. This Review will describe a variety of solution-based methods for synthesizing Au and Ag triangular prismatic structures, and will address and discuss proposed mechanisms for their formation.

Silver nanoprisms with a unimodal size distribution are synthesized through a novel thermal route that permits some control over nanoprism‐edge length (see Figure). The influences of citrate, poly(vinylpyrrolidone), H2O2, and NaBH4 on the nanostructures are described. This protocol allows control over nanoprism thickness, an architectural parameter not accessible via known preparative methods for such structures.

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.

A straightforward method is investigated for controlling and reinitiating the growth of single‐crystalline Au nanoprisms. This work is based on seeding methodology, and depends on the slow reduction of metal ions onto the surface of a growing nanoprism. In this manner, we can tailor the edge length of Au nanoprisms between 100 and 300 nm without changing their thickness or crystallinity. Each nanoprism size has been characterized by UV‐vis‐NIR (NIR: near‐IR) spectroscopy, transmission electron microscopy (TEM) techniques, and statistical analysis. Based on this work and existing silver halide crystal‐growth theories, a preliminary mechanism is proposed which comments on the interplay between crystal growth and surface chemistry that ultimately dictates the morphology of the resulting nanostructure.