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.

Gold nanoparticles/graphene oxide/chitosan (GO/CHS) hydrogels (AuNPs/GO/CHS) were prepared by in situ reduction of chloroauric acid using graphene oxide/chitosan (GO/CHS) hydrogels as the carrier. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and specific surface and porosity analyses were used to characterize AuNPs/GO/CHS. The effect of AuNPs/GO/CHS prepared from chitosan with different degrees of deacetylation and molecular weights on the catalytic reduction of 4-nitrophenol (4-NP) was investigated using NaBH₄ as a hydrogen donor.The results showed that GO improved the catalytic activity of AuNPs, and the catalytic reduction of 4-NP by AuNPs/CS and AuNPs/GO/CS satisfies the pseudo-primary reaction kinetics with rate constants of 0.027 0 and 0.157 0 min^-1, respectively, and conversions of 55.7% and 93.7% at 30 min of reaction. The low-deacetylation degree and low molecular weight chitosan-prepared catalysts with low deacetylation degree and low molecular weight chitosan had higher 4-NP catalytic activity. When AuNPs/GO/N2 prepared from chitosan with a deacetylation degree of 64% was used as the catalyst, the conversion of 4-NP could reach 97.7% with a rate constant k of 0.230 9 min^-1 and an activation energy E_a of 37.2 kJ·mol^-1 for 30 min at 30 ℃. The catalysts with a low deacetylation degree and low molecular weight had higher 4-NP catalytic activity.

In this work, reduced graphene oxide/carboxymethyl chitosan/nanogold (rGO/CMC/AuNPs) composites were synthesized using carboxymethyl chitosan (CMC) as the reducing and stabilising agent. The structures of the rGO/CMC/AuNPs composites were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM-EDS), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FT-IR). The catalytic reduction of 4-nitrophenol (4-NP) by the complexes was investigated when NaBH₄ was used as the hydrogen donor. The results showed that rGO with a C/O ratio of 3.97 was obtained by using CMC with a substitution degree of 0.665 as the reducing agent. rGO/CMC/AuNPs composites showed that spherical or quasi-spherical AuNPs were uniformly distributed on the surface of rGO. rGO/CMC/AuNPs composites showed high catalytic activity for the catalytic reduction reaction of 4-NP. The average particle size of AuNPs in rGO/CMC/AuNPs composites, which prepared by CMC with a substitution degree of 0.456, was (54.7±13.3) nm. And when it was used as catalyst, the conversion of 4-NP could reach 98.1% at 30 ℃ for 30 min, the reaction rate constant could be up to 0.152 0 min^-1, and the activation energy of the reaction E_a was 31.2 kJ·mol^-1.