Abstract:Cu nanoparticles (CuNPs) have been synthesized through an easy route by chemical reduction at room temperature. The Cu²⁺ ions were reduced and stabilized with sodium borohydride and polyvinylpyrrolidone, respectively. The effect of the variation of the reducing agent/precursor-salt (RA/PS) ratio on the size and morphology of the CuNPs was evaluated. The synthesized material was studied by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The UV-Vis spectra showed a CuNPs plasmon peak at 569 nm and another peak belonging to Cu₂O at 485 nm. XRD analysis showed the fcc-Cu phase with a small amount of fcc-Cu₂O compound. SEM and TEM studies displayed that small semispherical CuNPs of approximately 7 nm were obtained at the RA/PS ratio of 2.6. The excess of polyvinylpyrrolidone stabilizer played an essential role in preventing CuNPs oxidation. On the other side, Cu₂O polyhedral particles with larger sizes up to 150 nm were identified in the RA/PS ratio range of 2.0-1.84. In addition, Cu₂O particles having star morphologies with quantum confinement at their tips were obtained at the RA/PS ratio of 1.66.

Key words: Cu nanoparticles; NaBH₄; chemical reduction; polyvinylpyrrolidone stabilization; Cu₂O