[Characterization of Au-Ag nanoparticles biosynthesized by fungus Mariannaea sp. HJ]

Biosynthesis of gold-silver alloy nanoparticles (Au-AgNPs) is a simple operation and ecological friendly, but with limited reports on the availability of fungal resources. In this study, cell-free extracts of Mariannaea sp. HJ was used to synthesize Au-AgNPs, and the effects of the different ratios of Au and Ag ion concentrations on the synthesis of Au-AgNPs were also studied. The results clearly showed that the ratio of Au and Ag ion concentrations had an impact on the composition of Au-AgNPs. With the Ag ion increasing, the color of culture supernatant changed from light purple to brown and an obvious blue shift of characteristic absorption peak was observed in UV-vis spectra, indicating an increase of the percentage of Ag in the Au-AgNPs. Transmission electron microscope showed that the morphologies of the Au-AgNPs were mainly spherical and pseudo spherical, and the average particle sizes of the Au-AgNPs at three different ion concentrations, including 0.5:0.5, 0.5:1.5 and 0.5:3.0, were 19.24 nm, 15.99 nm and 19.33 nm, respectively. X-ray diffraction results showed that the Au-AgNPs had a surface-centered cubic structure. Fourier transform infrared spectroscopy was used to characterize and speculate the involvement of -OH, -NH₃ and -COOH functional groups in the reduction and stability process of Au-AgNPs. Furthermore, 4-nitrophenol (4-NP) was used to explore catalytic activity of Au-AgNPs. Catalytic experiments demonstrated that the Au-AgNPs had a good catalytic activity on 4-NP reduction with a catalytic reaction rate constant of 7.85×10⁻³ s⁻¹. In brief, the present study suggested that Mariannaea sp. HJ could synthesize Au-AgNPs with good dispersity, and had a potential application in the catalytic reduction of nitro aromatic hydrocarbons.