The influence of solvents and surfactants on the preparation of copper nanoparticles by a chemical reduction method

Abstract A chemical reduction method for preparing colloidal copper nanoparticles in water and ethylene glycol (EG) is reported. The obtained copper nanoparticles were characterized by powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectrophotometry (UV-vis). Surface plasmon resonance peaks immediately after the synthesis appeared at 579 and 551 nm for the colloidal copper in water and EG, respectively. The stability of colloidal copper in EG was longer than that in water. The color of solution in water changed from light-red to black and the nanoparticles mostly precipitated after 22 days, which is attributed to the oxidation of copper nanoparticles in copper oxide (I), as was confirmed by optical absorption measurements. In EG, copper nanoparticles were red and stable even after 2 months. Ascorbic acid plays a role as antioxidant for colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Polyvinyl pyrrolidone works both as size controller and polymeric capping agent because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds.