Copper nanoparticles production by a novel non-dispersive membrane nanoprecipitation process

This study presents, for the first time, a novel route for producing elemental copper nanoparticles using a non-dispersive membrane nanoprecipitation process based on membrane contactors. Copper sulfate solutions ranging between 0.005 and 0.01 M Cu concentration were circulating through a hydrophobic polypropylene flat-sheet membrane, where hydrazine solutions with 1.84–3.64 M were fed by the other side of the membrane. The gradient of hydrazine concentration between both phases was the driving force that promoted the volatilization and transfer of hydrazine through the membrane pores, then reacting with cupric ions to precipitate elemental copper. The effects of copper concentration, hydrazine concentration, and temperature (20–40 °C) in the particle size distribution were assessed. Smaller nanoparticle sizes were obtained at the lowest copper concentration and the highest hydrazine concentration. Thus, the smallest copper nanoparticles were produced under the highest hydrazine/copper molar ratio, reaching values of around 200 nm. Besides, the precipitates showed a surface plasmon resonance, confirming the presence of elemental copper nanoparticles. Therefore, this study opens a new approach to producing metal nanoparticles with perspectives of application in industrial manufacturing, recovering valuable metals from mining effluent treatment, or even hydrometallurgical processes.