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Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1-5 nm) has been done by reducing Ag over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV-Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles. [ABSTRACT FROM AUTHOR]

Abstract: Spherical, hexagonal, triangular and bar shaped silver nanostructures have been synthesized at large scale in aqueous media using methyl cellulose (MC) as soft template. Synthesis is based on the reduction of Ag+ by hydrogen at different temperatures. Morphology of particles is mostly spherical at 60°C with an average diameter 4–8nm, whereas hexagonal, triangular and truncated hexagon silver nanostructures are obtained at 80°C. On the other hand bar shaped silver nanoparticles are formed as the reaction is carried out at 90°C. Silver nanoparticles are characterized using UV–Vis and TEM study. Formation of silver nanostructures of variable morphologies has been explained in terms of different shaped template formed by MC at different temperature due to its thermogelation properties. [Copyright &y& Elsevier]

Abstract: Solution-phase synthesis of nanometer-sized silver particles is reported by sodium borohydride reduction of AgNO3. Two isomeric dicarboxylates (sodium maleate and sodium fumarate) have been used as stabilizing agents. The dicarboxylate-stabilized silver nanoparticles are characterized by UV–vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and fourier transform infrared (FT-IR) spectroscopy. A qualitative comparison is made between the UV–vis spectral characteristic of the SPR band and the simulated curve obtained from modified Mie''s theory. Silver nanoparticles prepared using these two isomeric dicarboxylates show intense fluorescence in the visible region. DFT with hybrid functional (B3LYP)-based frequency (IR) calculation of both the dicarboxylates and the respective nanoparticles are in good agreement with the experimental IR frequency. On the basis of this calculation a model has been proposed for the stabilization of silver nanoparticles by these two isomeric dicarboxylate anions. [Copyright &y& Elsevier]