WO3 Deposited TiO2 Nanotube Arrays by Thermal Evaporation Method for Effective Photocatalytic Activity

Titania (TiO2) nanotube arrays were fabricated by anodising Ti foil in glycerol (HOCH2CH(OH)CH2OH) containing 0.7 g of ammonium fluoride (NH4F). The crystal structure was studied by X-Ray Diffraction (XRD) analysis and the morphology was observed via Field Emission Scanning Electron Microscopy (FESEM). The average inner diameter of the TiO2 nanotubes was 90 nm, and the length was approximately 2 μm. Tungsten (W) of various thicknesses was then thermally evaporated onto the TiO2 nanotubes and annealed at 400°C in an O2 atmosphere to form tungsten trioxide (WO3). The effect of various thicknesses of W on the degradation of methyl orange (MO) was investigated. The sample with a 2.5 nm thick layer of W showed the best performance. The deposited W layer of that thickness is believed to provide a shallow trap for photo-generated e^- and h^+, inhibiting the recombination and extending the lifetime of the charge carriers. Thus, this sample resulted in high degradation of methyl orange (MO) as compared with other samples.