Investigation of the roles of active oxygen species in photodegradation of azo dye AO7 in TiO2 photocatalysis illuminated by microwave electrodeless lamp

A novel microwave electrodeless lamp (MWL) was used as the light source for microwave assisted TiO2 photocatalysis to degrade azo dye Acid Orange 7 (AO7). This technique aims to provide a new way to study the synergetic effect of both UV–vis light and microwave irradiations on aqueous solution of catalysts. The roles of active oxygen species in the photodegradation of AO7, such as hydroxyl radical (HO), positive holes (h+) and hydrogen peroxide (H2O2), were investigated to understand the photodegradation mechanism. The presence and roles of these oxidative species were examined using appropriate quenchers. It was found that the degradation of AO7 proceeded via three pathways, namely, UV-induced photocatalytic degradation, visible light-induced dye self-photosensitized degradation and direct photolytic degradation. The percentages of dye degradation by the three pathways were about 31.1%, 39.0% and 19.5%, respectively.