Novel fabrication and catalytic application of poly(ethylenimine)-stabilized gold–silver alloy nanoparticles

Novel synthesis of amine-stabilized Au–Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au–Ag alloy nanoparticles was readily controlled by varying the initial relative amount of HAuCl4 and AgNO3. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation problem of Ag+ in the presence of Cl− from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl4 and AgNO3 salts were used for the fabrication of Au–Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include the co-reducing agents for HAuCl4 and AgNO3, the stabilizing agents for Au–Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use in catalysis, the Au–Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction of 4-nitrophenol in the presence of NaBH4. As the Au content was increased in the Au–Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased from pure Ag to pure Au.