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

Developing a rapid and reliable method for measuring the photoreactivity of TiO pigments is of great importance for industrial application. The photoactivity of industrial TiO pigments were evaluated via the photodegradation of a model azo dye, methyl orange (MO), in the present work. The TiO 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 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 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 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 pigments.