Mechanism of reductive decomposition of pentachlorophenol by Ti-doped beta-Bi(2)O(3) under visible light irradiation.

The reductive decomposition of pentachlorophenol (PCP) by photocatalysis with Ti-doped beta-Bi(2)O(3) was investigated under visible light (lambda > 420 nm) irradiation. The results indicated that hydroxyl radical (*OH) and singlet oxygen ((1)O(2)) could not be detected with electron spin resonance (ESR) on the photocatalyst under light irradiation. An electron scavenger weakened the photocatalytic activity of the photocatalyst for the decomposition of PCP; however, scavengers of reactive oxygen species (ROS) enhanced the activity. The decomposition intermediates of PCP detected by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) suggested the existence of phenol, cyclohexanone, cyclohexanol, glycol, and propylene. All the evidence suggested that reductive dechlorination was the major route in the decomposition of PCP, during which the photogenerated electron under visible light irradiation acted as reductant. The reliability of the proposed reductive mechanism was further verified by comparing the reduction potential (E(re)) of PCP with the conduction band potential (E(cb)) of the photocatalyst. The decomposition pathway of PCP with electron reduction under visible light irradiation was also investigated.