Photo- and electro-oxidation of tetracycline hydrochloride on self-doped titanium dioxide nanotubes modified by Pt sub-monolayers

Abstract

This work presents a methodology for obtaining self-doped titanium dioxide nanotubes(SD-TNT) and self-doped titanium dioxide nanotubes modified with Pt electrodeposition (SD-TNT/Pt) for electro-oxidation (EO) and photo-electro-oxidation (PEO) of Tetracycline Hydrochloride (TCH). The SD-TNT electrode was obtained by anodization of titanium foil and the Pt electrodeposition was performed by pulsed potentiometry. Uniform nanotubes distribution with diameters of ∼100 nm, wall thickness of ∼16 nm, and length of ∼11.2 µm in the anatase phase of TiO2 were obtained. Electron Paramagnetic Resonance (EPR) analysis suggest both electrodes, TNT and SD-TNT, presented a paramagnetic signal and SD-TNT showed a higher signal intensity which indicates reduction of Ti4+ species to Ti3+ during the self-doping treatment. Energy Dispersive X-ray Spectroscopy (EDS) confirmed the presence of 0.56% of Pt mass on SD-TNT/Pt. Cyclic voltammetry (CV) results also confirmed the presence of Pt. The SD-TNT showed a ∼5 order of magnitude higher value of the density of charge carriers (ND = 2.2 × 1020 cm–3) than the no doped one (2.9 × 1015 cm–3). In 180 min of EO and PEO, for both electrodes, there was 100% of TCH degradation and presented in all cases a first-order kinetic model. PEO using platinum-decorated (SD-TNT/Pt) electrodes showed poorer performance due to the light-blocking effect of Pt nanoparticles and the potential trapping of electrons. PEO of TCH with SD-TNT reached the best mineralization of pollutant, 94.2% of Total Organic Carbon (TOC) abatement, an Energetic Consumption per unit TOC removed (ECTOC) of 0.265 kWh (g TOCremoved)−1 and a Mineralization Current Efficiency (MCE%) of 15.2%. Thus, SD-TNT electrodes could be effectively used as an alternative to high-cost anodes such as BDD both in electro-oxidation and photo-electro-oxidation of organic contaminants.