Facile Chemical Reduction Synthesis of Cu/Cu₂O Nanostructures: From Spherical Nanoparticles to Anisotropic Nanorods

Copper nanostructures are promising inexpensive substitutes for noble-metal nanomaterials. However, controlling their phase purity and morphology is challenging due to the facile oxidation of metallic copper during synthesis and storage. In this work, the effect of the amount of reducing agent on the phase composition and morphology of the copper nanostructures prepared by chemical reduction was investigated. Four samples (M1–M4) were obtained from CuCl2.2H2O in ethanol with sodium borohydride volumes of 0.2–0.8 mL, with polyvinylpyrrolidone added after the main reduction step as the stabilizer, and characterized by X-ray diffraction, scanning electron microscopy and ultraviolet–visible spectroscopy. The diffraction patterns reveal only the face-centered cubic Cu phase at low reducing agent content a dominant Cu2O phase at high reducing agent content. Electron micrographs reveal the evolution of the morphology from irregular aggregated particles, to the coexistence of spheres and nanorods up to about 1.3 µm long, to agglomerated spheres at the highest content. All the samples exhibit a localized surface plasmon resonance band that red-shifts from ~630–640 nm (M1, M2) to ~650–670 nm (M3, M4), indicating that metallic Cu is retained in all samples, plausibly as a Cu core covered by a Cu2O surface layer. Thus, the amount of reducing agent controls the phase composition and the growth mode, offering a simple route to tune copper nanostructures for catalytic, sensing and conductive-ink applications.