Synthesis of Ag@Cu2O core-shell metal-semiconductor nanoparticles and conversion to Ag@Cu core-shell bimetallic nanoparticles

Ag@Cu 2 O core-shell metal-semiconductor nanoparticles (NPs) were prepared by using solution phase strategy. It was found that Ag@Cu 2 O core-shell NPs were easily converted to Ag@Cu bimetallic core-shell NPs with the help of surfactant PVP and excessive reducer ascorbic acid in air at room temperature, which is a unique phenomenon. Varying volumes of Ag colloidal solutions were added into the reaction mixtures containing fixed initial concentrations of Cu 2+ and PVP, Ag@Cu 2 O and Ag@Cu core-shell NPs with fixed core size but varying outer shell thicknesses could be obtained. The composites, structures, morphologies and extinction properties of Ag@Cu 2 O and Ag@Cu core-shell NPs were systematically characterized by XRD, TEM and extinction spectra. Both of these NPs show wide tunable optical properties. The extinction peaks could be shifted from 421 nm to 700 nm. FTIR results reveal that Cu + ions on the surface of Cu 2 O nanocrystalline coordinate with N and O atoms in PVP and further are reduced to metallic Cu by excessive ascorbic acid and then form a nucleation site on the surface of Cu 2 O nanocrystalline. PVP binds onto a different site to proceed with the reduction until all the Cu sources in Cu 2 O NPs are completely assumed. And the shell of Cu 2 O is converted to Cu shell. The synthesis approach in this paper is simple and also a promising reference for synthesizing other core-shell NPs. Ag@Cu 2 O NPs can be easily converted to Ag@Cu NPs in air at room temperature, which is promising to be used in electronic devices.