Nanotubos anódicos de TiO2 dopados com íons Fe3+ : síntese, caracterização e avaliação do potencial fotocatalítico

Abstract

Titanium dioxide (TiO2) is a compound with semiconductor characteristics that has been widely investigated due to its electronic, optical, magnetic, and catalytic properties. In the last two decades, TiO2 nanotubes have attracted special interest since they can be used as photocatalysts in the degradation of organic pollutants and the production of hydrogen from water electrolysis. However, there are limitations in the photocatalytic applications of TiO2, since this semiconductor has a relatively wide band gap (3.0-3.2 eV) and a high recombination rate of electron-hole pairs. Doping TiO2 nanotubes with Fe3+ is indicated as a strategy to overcome these limitations. The introduction of iron can be adopted to modify TiO2 nanostructures and reduce their band gap, extending their photoresponse to the visible region, which corresponds to 45% of the energy radiated by the sun. The present work aims to produce iron-doped nanotubes (Fe-TiO2) through electrochemical anodization within situ doping, characterize these nanostructures, and evaluate the effect of doping on the photoactivity of TiO2. The synthesis was carried out under a potential of 48 V for 2 hours. The nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy. The photoactivity was evaluated through chronoamperometry and linear voltammetry tests. EDS confirmed the presence of iron in the Fe-TiO2 sample. The SEM images showed that doping caused a reduction in the inner diameter of the nanotubes and the thickness of the anodic film. The average band gaps obtained were 2.962 (± 0.107) eV for Fe-TiO2 and 3.057 (± 0.049) eV for pure TiO2. In the photoelectrochemical tests, the doped samples presented a slightly higher photoresponse than the undoped ones, indicating that doping can cause changes in the photocatalytic properties of TiO2.