Supercritical carbon dioxide-assisted synthesis of silver nano-particles in polyol process

Silver nano-particles have been synthesized by the polyol process with the assistance of supercritical carbon dioxide (SCCO2), with silver nitrate used as the base material, polyvinyl pyrrolidone (PVP) as the stabilizer for the silver clusters, and ethylene glycol as the reducing agent and solvent. Polyvinyl pyrrolidone not only protected nano-size silver particles from aggregation, but it also promoted nucleation. The silver nano-particles synthesized by SCCO2 were smaller and had a more uniform dispersion than those made under the same conditions by the conventional heating process. The superior fluidity and diffusivity of SCCO2 reduced the viscosity of the ethylene glycol and penetrated the entire solution to help increase the contact frequency of silver ions and electrons and in doing so, nucleation from silver ion to seed crystal was increased. The as-synthesized silver nano-particles were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM) and UV–vis spectrophotometer. The UV–vis spectrum of the silver nano-particles was sensitive to particle size. In particular, high dispersion stability synthesized silver nano-particles could be obtained by binding PVP on their surface in this work.