Enhanced photocatalytic activity in anodized WO3-loaded TiO2 nanotubes

• TiO2 and WO3-grafted TiO2 nanotubes were grown via single step anodizing of titanium foils.
• We were able to control morphology and growth mode of TiO2 nanotubes by changing the electrolyte composition.
• The grafting TiO2 nanotubes with WO3 enhances the photocatalytic activity.

In this work, TiO2 and WO3-grafted TiO2 nanotubes were grown via anodizing of titanium substrates in tungstate containing electrolytes. The samples were characterized in detail by XRD, XPS, SEM, EDX, and UV–Vis spectrophotometry techniques. Besides, photocatalytic characteristics were evaluated through measuring the degradation rate of 4-chlorophenol to establish a correlation between structure and photochemical properties. We were able to control morphology and growth mode of nanotubes from a tubular to a worm-like structure by changing the electrolyte composition. The samples possessed an anatase–rutile matrix where the anatase/rutile ratio was found to increase with the concentration of tungstate in the electrolyte. We attributed this observation to change in electrical conductivity of the electrolyte and the heat generated on the substrates. It was unambiguously revealed that a composite of WO3 and TiO2 forms and, in parallel, tungsten is doped into the crystalline lattice of TiO2. The maximum photocatalytic reaction rate constant for TiO2 and WO3–TiO2 samples was determined to be 0.0131 and 0.0174 min−1 respectively. The grafting TiO2 nanotubes with WO3 enhances the photocatalytic activity mainly due to the hindrance of charge carrier recombination and the formation of a more acidic surface. We established a correlation between structure, stoichiometry, and photocatalytic characteristics of nanotubes.