γ-Radiation induced synthesis of silver nanoparticles in aqueous poly (N-vinylpyrrolidone) solution

Abstract

The formation of silver nanoparticles (Ag NPs) in an aqueous solution using gamma-radiolysis in the presence of poly (N-vinylpyrrolidone) (PVP) is followed at various doses. At lower dose spherical Ag NPs are formed, however, with increase in dose an increasing fraction of nano decahedron and truncated triangles are developed. With dose spherical, decahedron and/or truncated triangles grew independently indicating separate nucleation pathways. To gain quantitative information of plasmonic properties we have compared optical spectra of Ag NPs obtained under different conditions. The effects of the concentrations of silver ions and stabilizer, counter anion, ionic strength, solvent and pH of the reaction medium on the dipolar plasmon frequency are investigated. Synthesized Ag nanoplates and NPs are characterized using various techniques; X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy (UV–vis). A high yield of nanoplates is obtained under optimized conditions, 3.0 × 10−2 M Ag+ ions and 0.01% (w/v) PVP. Change in the concentrations of Ag+ ions and PVP resulted in samples with fewer nanoplates compared to nanospheres indicating inhibition of growth of nanoplates. Use of alcohols instead of water resulted in samples with only nanospheres. Neither the effect of counter anion nor the change in pH (5–9) has any influence on the yield of nanoplates. Ag nanoplates are found to be highly stable under deaerated condition. However, presence of oxygen plays a role in transforming nanoplates to nanospheres. A plausible mechanism for the effect of O2, aging and solvent is discussed.