Photocatalytic Reduction of Aqueous Mercury (II) Using Hybrid WO3-TiO2 Nanotubes Film

Background: Mercury pollution has become a serious and enduring threat to the environment. It has affected the organisms along the food chain, including humans. Thus, it is necessary to design an effective mercury removal system to overcome the huge threat of mercury pollution. Our study aim is to optimize the anodization duration of as-prepared WO3-loaded TiO2 nanotubes for improving their photocatalytic mercury (II) reduction performance. Method: Hybrid WO3-TiO2 nanotubes film were successfully formed via electrochemical anodization at applied potential of 40 V in ethylene glycol organic electrolyte containing 1 vol% of hydrogen peroxide (H2O2) and 0.3 wt% ammonium fluoride (NH4F) by varying the anodization time from 15 up to 120 minutes. A tungsten electrode was chosen as the cathode as an innovative and convenient approach to hybridize WO3 with TiO2 nanotubes film. Results: During electrochemical anodization, W6+ ions dissolve from the cathode into the electrolyte solution, migrate towards the titanium foil and are deposited evenly on the Ti foil. This study recorded a maximum photocatalytic mercury (II) reduction performance of 91% (with exposure to 96 W UV-B Germicidal light irradiation for 120 minutes) in the presence of WO3-TiO2 nanotubes film with the highest aspect ratio (53.04) and geometric surface area factor (345.68). Conclusion: The main reason might be attributed to the high specific surface area nanotubes architecture performed strong light scattering effects as well as better incident light absorption from any direction to trigger more charge carriers for photocatalytic reduction of mercury(II) into elemental mercury. WO3 acted as an effective mediator to trap the photo-induced electrons from the TiO2, by contributing intermediate energy band levels below the conduction band of TiO2. Keywords: WO3-loaded TiO2 nanotubes, anodization, aspect ratio, geometric surface area factor, photocatalytic reduction of mercury (II), electrochemical anodization.