LAUSR

The green and controllable synthesis of Au–Ag alloy nanoparticles (NPs) in one-pot has been a challenge in nanotechnology. Here, the soluble starch was employed as a reducing and capping agent to synthesize stable Au–Ag alloy NPs without using any toxic agent. The surface plasmon resonance wavelength and the composition of Au–Ag alloy NPs could be continuously adjusted only by the synthesis time in one-pot. Au–Ag alloy NPs were characterized by means of various techniques. It could be found as-prepared NPs were quasi-spherical with a small average size and a face-centered cubic polycrystalline structure. The above green synthesis method, facile, efficient and eco-friendly, can be extended to the controllable synthesis of other bimetallic NPs. Obtained Au–Ag alloy NPs exhibited a superior photocatalytic activity and stability for the 4-nitrophenol (4-NP) degradation due to abundance hydroxyl groups of the soluble starch and the synergistic effect between Au and Ag elements. The rate constant of 4-NP degradation could be linearly tuned by the composition of Au–Ag alloy NPs and their synthesis time besides their addition amount. The above methods to control the rate constant provide promising routes for other photocatalytic reactions using bimetallic NPs as photocatalysts.Graphical Abstract