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

Abstract

Although TiO2 is used in a wide range of photocatalytic applications, its activity can be improved considerably by coupling with a metal oxide, such as WO3, in a bicomponent systems. However, the amount of WO3 deposited onto TiO2 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 WO3 onto TiO2 nanotubes (TiO2-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 WO3 crystalline phase and the TiO2 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 TiO2-WO3 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 TiO2-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 WO3. Optimal deposition of WO3 favors the formation of WO3-TiO2 heterojunctions, thereby improving the performance of the semiconductor.