Consideration of Photoactivity of TiO 2 Pigments via the Photodegration of Methyl Orange under UV Irradiation.

Developing a rapid and reliable method for measuring the photoreactivity of TiO ₂ pigments is of great importance for industrial application. The photoactivity of industrial TiO ₂ pigments were evaluated via the photodegradation of a model azo dye, methyl orange (MO), in the present work. The TiO ₂ pigments were characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The photoactivity test results showed that the anatase TiO ₂ pigment was responsible for accelerating MO degradation, while the rutile pigment acted as a stabilizer, and effective UV absorber retarded the photodegradation of MO. It was found that the photodegradation of MO was driven mainly by photoholes (h ⁺ ) and hydroxyl radicals (•OH), in the presence of TiO ₂ pigment with high photoactivity. With the help of the degradation intermediates during the photodegradation process and the calculated data, the preliminary degradation mechanism including azo bond cleaving, h ⁺ oxidation, and hydroxylated products' generation for MO was also elucidated. The photoactivity of TiO ₂ pigments can be rapidly evaluated in this work, which would be an efficient approach for assessing the product quality control and the end-use performance of TiO ₂ pigments.