Tunable synthesis solid or hollow Au-Ag nanostructure, assembled with GO and comparative study of their catalytic properties

In this work, we demonstrated a simple and efficacious two-step method for the synthesis of Ag@Au core–shell nanoparticles (Ag@AuNPs) and the Ag/Au hollow nanocages (Ag/AuNCs) with Ag nanoparticles (AgNPs) as seeds by adjusting pH, and the preparation of hybrid Ag@AuNPs- or Ag/AuNCs-graphene oxide nanocomposites (Ag@AuNPs-GO or Ag/AuNCs-GO) based on the self-assembly. It was noticed from the electrostatic assembly experiment that the loading amount of Ag/AuNCs on GO nanosheet was more than that of Ag@AuNPs. The as-synthesized hybrid materials were characterized by transmission electron microscopy, atomic force microscopy, ζ-potential, high-angle annular dark-field scanning transmission electron microscopy, thermogravimetric analyzer and X-ray diffraction. Catalytic activities of Ag@AuNPs, Ag/AuNCs and Ag/AuNCs-GO nanostructures were investigated in the reduction of 4-, 3- or 2-nitrophenol to 4-, 3- or 2-aminophenol, and on the basis of comparative kinetic studies the following trend was obtained for the related catalytic activity: Ag/AuNCs-GO > Ag/AuNCs > Ag@AuNPs. These observations were attributed to the simultaneous effects of surface area available for catalytic reaction and composition of the hybrid nanostructures.