Uniform Silver Nanowires Synthesis by Reducing AgNO₃ with Ethylene Glycol in the Presence of Seeds and Poly(Vinyl Pyrrolidone)

Abstract

A solution-phase approach has been demonstrated for the large-scale synthesis of silver nanowires with diameters in the range of 30−40 nm, and lengths up to ∼50 μm. The first step of this process involved the formation of Pt (or Ag) nanoparticles by reducing PtCl2 (or AgNO3) with ethylene glycol (EG) heated to ∼160 °C. These Pt (or Ag) nanoparticles could serve as seeds for the heterogeneous nucleation and growth of silver (formed by reducing AgNO3 with EG) because of their close match in crystal structure and lattice constants. In the presence of poly(vinyl pyrrolidone) (PVP), the growth of silver could be directed into a highly anisotropic mode to form uniform nanowires with aspect ratios as high as ∼1000. UV−visible spectroscopy, SEM, TEM, XRD, and electron diffraction were used to characterize these silver nanowires, indicating the formation of a highly pure phase, as well as a uniform diameter and bicrystalline structure. Both morphology and aspect ratios of these silver nanostructures could be varied from nanoparticles and nanorods to long nanowires by adjusting the reaction conditions, including the ratio of PVP to silver nitrate, reaction temperature, and seeding conditions. Measurements of the transport properties at room temperature indicated that these silver nanowires were electrically continuous with a conductivity (∼0.8 × 105 S/cm) approaching that of bulk silver.