Tuning the degree of anatase crystal orientation in TiO 2 nanotube arrays has emerged as a new strategy to control their photoelectrochemical performance, since electron transport through the nanotubular film is favored. However, the existing literature fails to provide an accurate approach to evaluate the impact of anatase crystal orientation, since it is normally studied using TiO 2 nanotube films synthesized in different anodizing baths, which in turn affects the properties of the films. In this work, anatase crystal orientation was controlled by changing the heating rate during sample heat-treatment (450 • C for 30 min), which resulted in randomly oriented anatase crystals when the film was taken from room temperature to 450 • C, to highly crystalline films with preferential anatase crystal orientation when the heating rate was decreased to 5 • C min −1 and 1 • C min −1 . Even though the physicochemical properties of the films were almost unaltered, increasing anatase crystal orientation resulted in higher photocurrents and photoelectrocatalytic methyl orange discoloration, showing a maximum for the film treated at a heating rate of 5 • C min −1 .

Triethylamine (TEA) and NH 4 F-modified TiO 2 powders and thin films were prepared by combining solgel and hydrothermal processes. Modification with TEA results in increased specific surface area and induces energy states below the conduction band of TiO 2 . On the other hand, the use of NH 4 F decreases the band-gap, displacing the valence band. Employing radical-scavenging agents, it was found that formation of O 2 * is preferred in TEA-modified TiO 2 , whereas generation of both O 2 * and OH * results from simultaneous modification. Furthermore, the photocatalytic degradation rate was directly proportional to their specific surface area. However, this trend was reversed in a photoelectrocatalytic cell, due to the fact that the photogenerated electrons are rapidly transported to the rear contact, which restrains their transfer to the dissolved oxygen to generate O 2 * . Therefore, the presence of OH * radicals and direct charge transfer processes appears to play a key role in the photoelectrocatalytic process. Graphical Abstract

N-F codoped TiO 2 films were immobilized on stainless steel sheets through a combined approach involving a dip-coating technique and a hydrothermal treatment, followed by calcination at 400°C in the presence of air. Photocatalyst characterization was conducted using XRD, Raman and UV-VIS spectroscopy as well as SEM. The films were tested in a three-electrode cell for the photoelectrocatalytic degradation of CN-containing compounds. The results showed that the increase in the degradation rate of CN-containing compounds is both influenced by a synergistic effect of the doping agents and strongly dependent on the concentration of CN-containing compounds in the solution. Nitrogen contributed to the enhanced photoactivity under visible light due to the generation of localized states within the band gap of TiO 2 , whereas the presence of fluoride improved the superficial properties of the film, which resulted in higher amounts of CN-containing compounds that were degraded by direct charge transfer through the photogenerated holes.

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