Green electrochemical synthesis of ultra-small and highly stable silver nanoparticles in an electrolyte solution of polyethylene glycol-1000

A green electrochemical method was developed to synthesize silver nanoparticles using silver plate electrodes and polyethylene glycol 1000 (PEG-1000) as the sole electrolyte. Optimum conditions were established at 2 % (w/v) PEG-1000, an applied voltage of 24 V for 15 min and a temperature of 60 °C. The deprotonated terminal hydroxyl groups of PEG-1000 played multiple roles, including facilitating Ag + extraction from the anode, promoting Ag + migration to the cathode for reduction to Ag, and directly reducing Ag + to Ag in the electrolyte solution, while they undergoing oxidation to carboxylates. Diffusion serves as an electron transfer model that drives redox reactions in the electrolyte solution, with each PEG-1000 molecule facilitating a single electron transfer. The remaining terminal hydroxyl groups of PEG-1000 molecules formed hydrogen bonds with each other, creating a rigid structure that provided a confined space for silver nanoparticle growth. Meanwhile, the negatively charged carboxylates at the opposite end of the PEG-1000 molecules extended outward, creating an electrostatic barrier that prevented nanoparticle agglomeration. As a result, highly stable, ultra-small silver nanoparticles with well-defined plasmon peaks, a nearly spherical morphology, and a uniform average size of 3.96 ± 0.04 nm were successfully synthesized.