Low temperature preparation of CuO nanospheres and urchin-shaped structures via hydrothermal route

•We demonstrated a facile hydrothermal synthesis of cupric oxide (CuO) nanoparticles.•Two types of nanostructures were synthesized by switching between NaOH or NaBH4.•NaOH resulted in nanospheres, whereas NaBH4 gave rise to urchin-like structures.•CuO nanosphere exhibited the bandgap of 1.54eV due to quantum size effect.