Syntheses of ZnO Nano-Arrays and Spike-Shaped CuO/ZnO Heterostructure

A low-temperature hydrothermal route was applied to fabricate ZnO nano-arrays on fluorinated tin oxide (FTO)-coated glass substrates. The effects of the molar ratios of the precursor concentrations on the ZnO nano-arrays were studied with respect to morphology, optical properties, and growth mechanism. The results show that the length reduced with the increased molar ratios of precursor concentrations, and the diameter first increased then decreased. In general, the change of optical band gap followed the same trend as that for the change in diameter. When the molar ratio of precursor concentrations is 5:5, the optical band gap is 3.2 eV, which is similar to the theoretical value at room temperature. We propose that the optimal molar ratio of zinc nitrate (Zn(NO3)(2)) to hexamethylenetetramine (HMT, C6H12N4) is 5:5 for the preparation of ZnO nano-arrays. Spike-shaped CuO/ZnO nano-arrays were also successfully synthesized using a two-step solution-system method. Field emission scanning electron microscope (FE-SEM) results show that there were a large number of copper oxide (CuO) nano-particles (NPs) deposited onto the ZnO nano-array surfaces to form spike-shaped structures. The covered CuO NPs exhibited improved photocatalytic properties over pure ZnO nano-arrays under UV irradiation, and the possible photocatalytic mechanism of the CuO/ZnO nano-heterojunction was discussed in detail.