A Simple Method for the Electrodeposition of WO3 in TiO2 Nanotubes: Influence of the Amount of Tungsten on Photoelectrocatalytic Activity

Although TiO 2 is used in a wide range of photocatalytic applications, its activity can be improved considerably by coupling with a metal oxide, such as WO 3 , in a bicomponent systems. However, the amount of WO 3 deposited onto TiO 2 is of crucial importance because it may influence the optical and electrochemical properties and, consequently, the photocatalytic activity. In the present study, a series of modified electrodes were prepared by electrochemical deposition of different amounts of WO 3 onto TiO 2 nanotubes (TiO 2 -NTs). Energy dispersive X-ray analysis revealed that increasing amounts of W were deposited with increased deposition times between 5 and 60 min, and that electrodes EW5, EW10, EW15, EW30, EW45, and EW60 contained 0.74, 1.27, 1.60, 4.85, 10.10, and 13.30 at.% W, respectively. X-ray diffraction patterns confirmed the presence of the WO 3 crystalline phase and the TiO 2 anatase. Diffuse reflectance spectra of electrodes EW5, EW10, and EW15 exhibited the most intense absorbances, and their energy band-gap values were in the region of 2.90 eV, which is comparable with the value for TiO 2 -WO 3 bicomponent. The photoactivities of electrodes EW5 and EW10 containing low amounts of W (~1 %) exhibited photocurrents that were, respectively, 13 and 25 % higher than that of the unmodified TiO 2 -NTs electrode. Electrodes containing larger amounts of W showed correspondingly reduced photocurrents. The application of electrodes E0 and EW10 on the photoelectrocatalytic oxidation of Bisphenol-A (BPA) revealed excellent removal rate which BPA was not detected after 30 min of reaction. The electrode EW10 achieved ~64 % of total organic carbon (TOC) in the end of degradation, more effective compared to the electrode E0 (58 %). These findings demonstrate that photoelectrocatalytic efficiency is strictly dependent on morphology and amount of WO 3 . Optimal deposition of WO 3 favors the formation of WO 3 -TiO 2 heterojunctions, thereby improving the performance of the semiconductor. Graphical abstract ᅟ