Effect of post-synthesis acid activation of TiO₂ nanofilms on the photocatalytic efficiency under visible light

Nanosized TiO₂ films were deposited by spray pyrolysis and thermally treated at 400^oC. Then the films were dipped in 1M aqueous solution of HCl. The activated samples were divided into two parts - one part was dried (A) and another was annealed (AT) in air. The photocatalytic degradation of Reactive Black (RB5) textile dye under visible light was tested. The following instrumental methods: X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied for the phase and surface characterization of obtained samples. According to Raman and XRD analyses all films are anatase. The XRD showed that activated films are better crystallized than non activated TiO₂ film. The presence of chlorine at 200.3 eV was registered for acid activated samples by X-Ray photoelectron spectroscopy. The acidic activated films exhibited higher rate of dye photodegradation than that of the reference TiO₂ sample. The photocatalytic efficiency decreases in the order A > AT> non activated TiO₂ films. The degradation rate constant for acid activated films is two times higher than those of the reference film. The hydroxyl content in TiO₂ acidic activated films is greater than that of the non- activated films, which results in significant increase in the photocatalytic activity. In addition, the presence of chlorine may also lead to enhancement in efficiency