Microwave-assisted polyol synthesis of Cu nanoparticles

Microwave heating was applied to synthesize copper colloidal nanoparticles by a polyol method that exploits the chelating and reducing power of a polidentate alcohol (diethyleglycole). The synthesis was carried out in the presence of eco-friendly additives such as ascorbic acid (reducing agent) and polyvinylpirrolidone (chelating polymer) to improve the reduction kinetics and sols stability. Prepared suspensions, obtained with very high reaction yield, were stable for months in spite of the high metal concentration. In order to optimize the suspensions, synthesis parameters were modified and the effects on particle size, optical properties, and reaction yield were investigated. XRD analysis, STEM and DLS measurements confirmed that prepared sols consist of crystalline metallic copper with a diameter ranging from 65 to 130 nm. Surface plasmon resonance of Cu nanoparticles was monitored by UV-VIS spectroscopy showing both a red shift and a band weakening for nanoparticles diameter increase. Microwave use provides rapid and uniform heating of reagents and solvent, accelerating the reduction of metal precursor and the nucleation of metal cluster, resulting in monodispersed nanostructures. The proposed microwave assisted synthesis, usable also in large scale continuous production, enables process intensification, making this method of preparation an environment-friendly route for metallic nanoparticles synthesis