Green synthesis and electrochemistry of Ag, Au, and Ag–Au bimetallic nanoparticles using golden rod (Solidago canadensis) leaf extract

Silver (Ag) nanoparticles (NPs), gold (Au) NPs, and silver–gold (Ag–Au) bimetallic nanoparticles (BNPs) were synthesized by use of golden rod leaf extracts. Aqueous solutions of the precursor compounds HAuCl₄·xH₂O and AgNO₃ were mixed individually and jointly with aqueous extract of golden rod leaf and heated with stirring at 80 °C for 1 h. There were observed periodic changes in color which indicate the formation of nanoparticles, and were confirmed by use of UV–Vis spectroscopy. Sizes of NPs were determined by X-ray diffraction and transmission electron microscopy while bioreductants were examined using Fourier transform infrared spectroscopy. In BNPs, both Au and Ag were detected in an unequal ratio. This observation shows that the gold ions were more prone to reduction by the plant biomolecules than the silver ions which may be a unique character due to Solidago canadensis leaf extract and different reduction potentials of the metals. Formation of Ag, Au, and Ag–Au BNPs were suggested by appearance of bands at 420, 560, and 530 nm, respectively. Sizes and shapes of Ag–Au BNPs resemble pure Au NPs more than they do Ag NPs. Electrochemical characterization of NPs by use of cyclic voltammetry showed that Ag–Au BNPs were more electroactive compared to other electrodes. This work therefore accentuates the effect of substrate and precursor concentrations towards nanoparticle formation which could enhance material application depending on the reaction techniques.