Transition metal oxide loaded ZnO nanorods: Preparation, characterization and their UV-vis photocatalytic activities

A series of transition metal oxides (MOx/ZnO nanorods, where MOx = WO3, CuO and NiO) loaded ZnO catalyst was successfully prepared by a hydrothermal-deposition method. The catalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. The results showed that the crystallized MOx/ZnO had a hexagonal wurtzite phase with the respective transition metal oxides being attached on ZnO nanorods. The MOx/ZnO photocatalysts with the transition metal oxides, namely WO3 and CuO were responsive to visible light. Photocatalytic activities over pure ZnO and MOx/ZnO catalysts were compared and the observed rate constant (k) values were calculated from the kinetic studies of phenol degradation under UV-vis light irradiation. The extent of degradation of phenol and their mineralization were verified further by HPLC and TOC analyses. 2 at% WO3/ZnO displayed the best photocatalytic performance with the highest degradation efficiency (100%) and highest k (0.0135 min−1) after 5 h irradiation. Moreover, the photoactivity of 2 at% WO3/ZnO was found to be higher than those of pure ZnO and commercial TiO2 photocatalyst. Remarkably high UV-vis light photocatalytic activity of WO3/ZnO heterojunction could be explained by inter-semiconductor electron and hole transfer mechanism between the WO3 and that of ZnO nanorods. The evidence for the electron and hole transports between WO3 and ZnO nanorods was obtained by monitoring the PL and PL-Terephthalic acid (TA) measurements.