Seed-Mediated Growth of Oxidation-Resistant Copper Nanoparticles

Copper nanoparticles (CuNPs) are of interest due to their localized surface plasmon resonance, conductive properties, and the low cost of copper; however, achieving CuNPs with controlled sizes that are resistant to surface oxidation from the environment is still an ongoing challenge. We synthesized CuNPs with tunable sizes ranging from 20 to 80 nm based on a seed-mediated growth process using polyvinylpyrrolidone (PVP) as a stabilizing agent. This synthetic strategy offered advantages of using lower reaction temperatures, controlled particle size through tuning the reaction medium, and protection from oxidation by the PVP stabilizing agent. The PVP polymer length influenced both the CuNP optical properties and overall shape, with longer PVP allowing for better control over particle shape and size and the shorter lengths producing polydisperse particles with broader spectra. The size was further controlled through addition of acetic acid, which resulted in larger particle sizes. Wide angle X-ray scattering measurements indicated that the particles were composed of copper with no oxide present and the crystallite sizes were comparable to the overall particle size. The ultraviolet–visible extinction peak positions of the particles showed limited dependence on the overall particle size. By examining the extinction and true absorbance measurements, we determined that all CuNPs had a true absorption peak due to interband transitions at around 590 nm and peaks observed at longer wavelengths were due to scattering effects from near field coupling of the particles. Finally, the particles were shown to be resistant to oxidation and remained stable over time, which suggests that this strategy is promising for formation of large copper particles that do not oxidize.