Photocatalysis and Photoelectrochemical Properties of Tungsten Trioxide Nanostructured Films

Tungsten trioxide (WO(3)) possesses a small band gap energy of 2.4–2.8 eV and is responsive to both ultraviolet and visible light irradiation including strong absorption of the solar spectrum and stable physicochemical properties. Thus, controlled growth of one-dimensional (1D) WO(3) nanotubular structures with desired length, diameter, and wall thickness has gained significant interest. In the present study, 1D WO(3) nanotubes were successfully synthesized via electrochemical anodization of tungsten (W) foil in an electrolyte composed of 1 M of sodium sulphate (Na(2)SO(4)) and ammonium fluoride (NH(4)F). The influence of NH(4)F content on the formation mechanism of anodic WO(3) nanotubular structure was investigated in detail. An optimization of fluoride ions played a critical role in controlling the chemical dissolution reaction in the interface of W/WO(3). Based on the results obtained, a minimum of 0.7 wt% of NH(4)F content was required for completing transformation from W foil to WO(3) nanotubular structure with an average diameter of 85 nm and length of 250 nm within 15 min of anodization time. In this case, high aspect ratio of WO(3) nanotubular structure is preferred because larger active surface area will be provided for better photocatalytic and photoelectrochemical (PEC) reactions.