Roles of Reactive Oxygen Species and Holes in the Photodegradation of Cationic and Anionic Dyes by TiO2 under UV Irradiation

Abstract

AbstractThis study compared the roles of different reactive oxygen species (ROS) in the photodegradation of cationic dye methylene blue (MB) and anionic dye orange II (OII) by the TiO2/ultraviolet (UV) system using different radical quenchers to elucidate the oxidation mechanisms for cationic and anionic dyes. In this study, the holes and surficial HO• rather than HO• in the bulk solution were found to play the dominant role in the photodegradation of the two types of dyes, accounting for 60% of the total degradation (the remaining 40% degradation could be contributed by O2•−, O12, and the UV photolysis). Interestingly, potassium iodide (KI) as the scavenger for surficial radicals could inhibit the OII degradation but enhanced the MB degradation, probably due to the formation of oxidized products such as I2 or IO3− that could react with MB. O2•− played a more contributing role in the photodegradation of OII than MB, whereas O12 exhibited the same contribution to the photodegradation of OII and MB. The res...