Here we report the photocatalytic efficiency of CuO and Cu 2 O nanowires studied by dye degradation in water. The CuO nanowires were synthesized on Cu foils by thermal oxidation. A subsequent thermal annealing induced a controllable phase transformation of the nanowires and the underlying film from CuO to Cu 2 O phase. A structural characterization was made by scanning and transmission electron microscopies, energy dispersive x-ray analysis and x-ray diffraction. The photocatalytic performances were …