Facile Synthesis of Anisotropic Ag Nanostructures Using Molecular Double Agents

Facile solution-phase syntheses of anisotropic Ag nanocrystals with controlled growth, especially those of branched and dendritic nanostructures, continue to be both useful and challenging to achieve. Conventional techniques involve lengthy reaction times, expensive reagents, multistep syntheses, or some combination thereof. One-pot approaches to creating various crystal growth patterns from a single reaction have been underexplored. Herein, we report that the combination of acetonitrile and p -phenylenediamine allows one to synthesize a variety of Ag nanostructures under mild reaction conditions (100 °C, ambient pressure) in less than an hour of total reaction time. In particular, we demonstrate seven distinct morphologies that are developed from simple changes to the reaction temperature, reactant concentrations, reactant substitutions, or reaction pH. The novelty of this synthesis stems from the use of p -phenylenediamine as a one-electron reducing agent for Ag +, which can then polymerize into poly( p -phenylenediamine) and is shown to act as a capping agent for the growing Ag nanocrystal. XRD data reveal that poly( p -phenylenediamine) allows for preferential growth of {111}, allowing the development of flat plate-like structures. The Ag nanocrystals are capable of surface-enhanced Raman scattering due to their noble-metal composition and demonstrate weak fluorescence due to the poly( p -phenylenediamine) on their surface. Analogous structures to p -phenylenediamine are incapable of reproducing these dendritic Ag nanocrystals, indicating that the molecule is uniquely capable of controlling the crystal growth in these distinctive patterns. The general route of utilizing reductants that polymerize in situ to stabilize growing anisotropic nanostructures introduces an exploitable paradigm shift in the available syntheses of Ag nanocrystals.