Preparation of THPC-generated silver, platinum, and palladium nanoparticles and their use in the synthesis of Ag, Pt, Pd, and Pt/Ag nanoshells

Seed nanoparticles of silver, platinum, and palladium (typically ≤4 nm in diameter) were prepared using tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the reducing agent and utilized to generate pure silver, platinum, and palladium nanoshells, along with hybrid platinum/silver nanoshells, on silica cores. The sizes, size distributions, morphologies, chemical compositions, and optical properties of the THPC-metal nanoparticles (THPC-mNPs) were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED) analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared (FT-IR) spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy. Characterization of the resulting nanoshells was performed using scanning electron microscopy (SEM), TEM, and UV-vis spectroscopy. While the use of THPC-gold nanoparticles to seed metal nanoshells is well known, the process is time consuming and requires highly concentrated seeding solutions. Our THPC-mNPs were used to seed the growth of a variety of metal nanoshells in rapid fashion, including the successful generation of highly uniform platinum and palladium nanoshells grown from their own seeds. Efforts to optimize our nanoshell syntheses produced expedited procedures for generating metallic shells with continuous, smooth surfaces.