Solar photocatalytic decolorization of dyes in solution with TiO2 film

Application of TiO2 film to solar photocatalysis of organic dyes, including Methylene Blue (MB) (λmax, 660 nm), RR195 (λmax, 540 nm) and RY145 (λmax, 420 nm), was investigated. It was found that after 6-h solar irradiation, the extent of color degradation of dyes using solar photocatalytic system without TiO2 film was quite limited. The color removal percentage for MB, RR195, and RY145 was found to be 23.3, −9.3, and −20.7%, respectively, resulting from competitions between the photosensitizing reaction and formation of colored intermediates during solar irradiation. However, as TiO2 film was applied, the color degradation capability of solar photocatalytic system was significantly improved, in spite of the fact that only approximately 7% of solar irradiation belongs to the UV region. The color removal percentage for MB, RR195, and RY145 was up to 93.6%, 85.3%, and 71.1%, respectively, after 6-h irradiation. We believed that in such a solar photocatalytic system immobilized with TiO2 film, both the maximum absorbance wavelength of the dye and the adsorbability of the dye on TiO2 film played significant roles on the rate and efficiency of color removal of the dye solutions. Moreover, the possible reaction mechanism was proposed. The solar photocatalytic process with immobilized TiO2 film was found to follow the pseudo-first order reaction kinetics. Color removal rate of MB was almost twice of that of RY145. Accordingly, the photocatalytic degradation process using solar light as an irradiation source, and immobilized TiO2 as a photocatalyst, showed potential application for the decolorization of wastewater.