Synthesis of Gold-Silver Bimetallic Nanoparticles and Catalytic Reduction of 4-Nitrophenol

Gold-silver bimetallic nanoparticles (Au-Ag NPs) were successfully synthesized by simultaneous reduction of HAuCl₄ and AgNO₃ using water-soluble chitosan (WSC) as the reducing agent and stabilizer. The effects of the volume ratio of gold and silver precursors(V(HAuCl₄)/V(AgNO₃)), reaction temperature and time, NaOH and WSC concentration were investigated. The Au-Ag NPs were characterized by ultraviolet-visible absorption spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The catalytic reduction performance of Au-Ag NPs towards 4-nitrophenol (4-NP) was investigated. The results showed that spherical or nearly spherical Au-Ag NPs with an average particle size of 4 nm were prepared using WSC as the reducing agent and stabilizer. The catalytic reduction activity of Au-Ag NPs towards 4-NP was better than that of AuNPs and AgNPs, and the highest catalytic activity was obtained for Au_0.5Ag_0.5(V(HAuCl₄)/V(AgNO₃)=1∶1). When Au_0.5Ag_0.5 was used as catalyst, the conversion of 4-NP could reach 99.1% when the catalytic reaction was carried out at 30 ℃for 30 min, the reaction rate constant was 0.190 3 min^-1, and the reaction activation energy E_a was 31.1 kJ·mol^-1.