Selective Growth of Vertical-aligned ZnO Nanorod Arrays on Si Substrate by Catalyst-free Thermal Evaporation

By thermal evaporation of pure ZnO powders, high-density vertical-aligned ZnO nanorod arrays with diameter ranged in 80–250 nm were successfully synthesized on Si substrates covered with ZnO seed layers. It was revealed that the morphology, orientation, crystal, and optical quality of the ZnO nanorod arrays highly depend on the crystal quality of ZnO seed layers, which was confirmed by the characterizations of field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence measurements. For ZnO seed layer with wurtzite structure, the ZnO nanorods grew exactly normal to the substrate with perfect wurtzite structure, strong near-band-edge emission, and neglectable deep-level emission. The nanorods synthesized on the polycrystalline ZnO seed layer presented random orientation, wide diameter, and weak deep-level emission. This article provides a C-free and Au-free method for large-scale synthesis of vertical-aligned ZnO nanorod arrays by controlling the crystal quality of the seed layer

Preparation, characterization and photocatalytic performance of Mo-doped ZnO photocatalysts

A series of Mo-doped ZnO photocatalysts with different Mo-dopant concentrations have been prepared by a grinding- calcination method. The structure of these photocatalysts was characterized by a variety of methods, including N 2 physical adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, photoluminescence (PL) emission spectroscopy, and UV-vis diffuse reflectance spectroscopy (DRS). It was found that Mo 6+ could enter into the crystal lattice of ZnO due to the radius of Mo 6+ (0.065 nm) being smaller than that of Zn 2+ (0.083 nm). XRD results indicated that Mo 6+ suppressed the growth of ZnO crystals. The FT-IR spectroscopy results showed that the ZnO with 2 wt.% Mo-doping has a higher level of surface hydroxyl groups than pure ZnO. PL spectroscopy indicated that ZnO with 2 wt.% Mo-doping also exhibited the largest reduction in the intensity of the emission peak at 390 nm caused by the recombination of photogenerated hole-electron pairs. The activities of the Mo-doped ZnO photocatalysts were investigated in the photocatalytic degradation of acid orange II under UV light (? = 365 nm) irradiation. It was found that ZnO with 2 wt.% Mo-doping showed much higher photocatalytic activity and stability than pure ZnO. The high photocatalytic performance of the Mo-doped ZnO can be attributed to a great improvement in the surface properties of ZnO, higher crystallinity and lower recombination rate of photogenerated hole-electron (e -/h +) pairs. Moreover, the undoped Mo species may exist in the form of MoO 3 and form MoO 3/ZnO heterojunctions which further favors the separation of e -/h + pairs. © Science China Press and Springer-Verlag Berlin Heidelberg 2012