Synthesis of TiO2 nanotubular arrays and their electrochemical and photoelectrochemical properties to determine their use in photodegradation processes

The synthesis of TiO2 nanotubular films is presented together with their physical, chemical, electrochemical and photoelectrochemical characterization in order to assess their use as photocatalyst. The synthesis was made through the anodic oxidation procedure using an inorganic fluoride based electrolyte. The nanotubes presented an inner diameter of 54 nm, a wall thickness of 18 nm and a length of 570 nm in amorphous condition. After annealing at 500 degrees C the alignment and definition of the nanotubes were improved observing more space between the nanotubes, contrary to that observed at 700 degrees C, in which a detrimental morphology was seen, presenting a disruption of a little portion of the superior edge of the nanotubes. The electrochemical characterization was made for four samples: the amorphous one and two crystallized samples at 500 (TNTC-5) and 700 degrees C (TNTC-7) and for Ti. The TNTC-5 (constituted by anatase-rutile) which improved its morphology and kept its mechanical strength after annealing, presented the best electrochemical stability after 5 days of exposure. In conclusion, TNTC-5 sample showed to be a good candidate for photocatalysis processes due to: (i) its better ordered 1D nanostructure geometry with longer nanotubes after annealing compared to that of the TNTC-7 sample, which conferred an increase of surface area, (ii) due to short length nanotubes, since better efficient light absorption and fast carrier transport is expected, and thus less unwanted recombination losses, (iii) its chemical structure composition of anatase-rutile in comparison to that at 700 degrees C that transformed completely in rutile, (iv) a clean top surface, (v) the preservation of stable morphology after exposing to corrosive electrolytes in long term showing a high corrosion stability and (vi) its major and stable photocurrent density.