Stability of tungsten oxide nanotubes film for improving photocatalytic oxidation reaction

Well-aligned anodic tungsten oxide (WO₃) nanotubes with lengths approaching 600 nm was successfully synthesised via electrochemical anodisation of tungsten (W) film at 40 V in a bath with electrolyte (pH 3) consisted of 1 M of sodium sulphate (Na₂SO₄) and 0.7 wt-% ammonium fluoride (NH₄F) for 15 min. It was found that the production of dense compact oxide layer on pure W film could be explained with high concentration of H⁺ ions accelerated the hydrolysis ability on the W surface to form thick WO₃ layer under acidic condition (pH: 3). The photocatalytic activity performance was increased by ≈15% for the dense WO₃ nanostructures film as compared to the thin and irregular WO₃ nanostructures film because of the high active surface area to absorb more photons from solar irradiation for triggering the charge carriers separation and then improvement of internal and external diffusion of the reactants.