Synthesis and characterization of TiO2/ WO3, TiO2 nanotubes/WO3 and TiO2 nanotubes/titanate electrodes for application in the photoelectrocatalytic treatment of the endocrine desruptors bisphenol-A and propylparaben

Effective technologies for the water and wastewater treatment represent a challenges for our society; among the options, the photoelectrocatalysis can be considered a promising and interesting alternative. In this context, the objective of this study was to develop modified TiO2 electrodes for the photoelectrocatalytic treatment of endocrine disruptors. The synthesis of TiO2 nanotubes (TiO2-NT) on metallic Ti substrate was carried out via electrochemical anodization in NaH2PO4 /HF electrolyte. In order to minimize the limitations inherent of TiO2, the electrodeposition of WO3 was performed on the TiO2 nanotubes (Ti/TiO2-NT/WO3) and also in the metallic Ti substrate. The deposition on the Ti metallic produced a thin layer of TiO2 on the surface, subsequent to the heat treatment, generating a composite (Ti/TiO2/WO3). The X-ray diffraction analysis (XRD) confirmed the monoclinic phase of WO3 for both the syntheses and the anatase phase of TiO2 for the Ti/TiO2-NT/WO3 electrodes. For the two syntheses, the X-ray dispersive energy (EDX) analisys indicated an increasing amount of tungsten (W) in the composition of the electrodes with increasing of electrodeposition time. High W content (above 1.2%) showed a significant decrease in the photocurrent values. However, low content of W (between 0.4 and 1.2 %) indicated an increase of 20 % in the photocurrent values for the electrodes Ti/TiO2-NT/WO3 (20 mA cm-2) and Ti/TiO2/WO3 (17 mA cm-2) compared to the unmodified ones, at the potential of +2.0 V. Difuse reflectance analysis indicated low bandgap energy (≈ 2.90 eV, Ti/TiO2-NT/WO3 electrodes) and an increase in the UV-Vis irradiation absorption. The best electrodes modified with WO3 to the both syntheses were applied in the photoelectrocatalytic oxidation (PEC) of bisphenol-A (BPA) and propylparaben (PPB) compounds, under UV-Vis irradiation. The PEC method presented an excellent performance in acidic conditions, applying a bias potential of +1.50 V and +0.50 V for Ti/TiO2-NT/WO3 and Ti/TiO2/WO3 electrodes, respectively. The mineralization of BPA and PPB compounds was greater than 80% for both Ti/TiO2-NT/WO3 and Ti/TiO2/WO3. In relation to the removal rate, BPA and PPB were completely removed after 45 and 60 min, respectively, for Ti/TiO2/WO3 electrodes and after 30 minutes for Ti/TiO2-NT/WO3 electrodes. Additionally, the electrodes presented a low energy consumption and good chemical stability. Compared to the photocatalysis (PC), the PEC was 2 times higher to the mineralization efficiency for Ti/TiO2-NT/WO3 and almost 20% higher for Ti/TiO2/WO3. Thus, the modifications of the TiO2 electrodes with WO3 represent an important contribution to the performance of materials and, therefore, a positive step for the application in alternative treatments of decontamination of wastewater. It was also of interest in this work to propose a new method for the insertion of nanotubes (TiNT) and nanosheets (TiNS) of titanates inside of TiO2 nanotubes via electrophoretic deposition. In this study was developed a simple and efficient method for the modification of complex nanostructures. The movement of the counter electrode on the surface of the working electrode, adapted with a brush on the edges, reduced the thickness of the TiNS/TiNT layer. The potential applied (20 V) and the mechanical stimulation in the surface were important for the incorporation of TiNS/TiNT into the pores of TiO2-NTs. As a result, the electrodes increased the hydrophobicity and an improvement to the direct oxidation capacity compared to the unmodified electrode. (AU)