Intertwining Roles of Silver Ions, Surfactants, and Reducing Agents in Gold Nanorod Overgrowth: Pathway Switch between Silver Underpotential Deposition and Gold-Silver Codeposition

The past two decades have witnessed great success achieved in the geometry-controlled synthesis of metallic nanoparticles using the seed-mediated nanocrystal growth method. Detailed mechanistic understanding of the synergy among multiple key structure-directing agents in the nanocrystal growth solutions, however, has long been lagging behind the development and optimization of the synthetic protocols. Here we investigate the foreign ion- and surfactant-coguided overgrowth of single-crystalline Au nanorods as a model system to elucidate the intertwining roles of Ag+ foreign ions, surface-capping surfactants, and reducing agents that underpin the intriguing structural evolution of Au nanocrystals. The geometry-controlled nanorod overgrowth involves two distinct underlying pathways, Ag underpotential deposition and Au-Ag electroless codeposition, which are interswitchable upon maneuvering the interplay of the Ag+ ions, surfactants, and reducing agents. The pathway switch governs the geometric and compositional evolution of nanorods during their overgrowth, allowing the cylindrical Au nanorods to selectively transform into a series of anisotropic nanostructures with interesting geometric, compositional, and plasmonic characteristics. The insights gained from this work shed light on the mechanistic complexity of geometry-controlled nanocrystal growth and may guide the development of new synthetic approaches to metallic nanostructures with increasing architectural complexity, further enhancing our capabilities of fine-tuning the optical, electronic, and catalytic properties of the nanoparticles.