Reaction pathways of dimethyl phthalate degradation in TiO 2–UV–O 2 and TiO 2–UV–Fe(VI) systems

Abstract

The photocatalytic degradation of dimethyl phthalate (DMP) in aqueous TiO 2 suspension under UV illumination has been investigated using oxygen (O 2) and ferrate (Fe(VI)) as electron acceptors. The experiments demonstrated that Fe(VI) was a more effective electron acceptor than O 2 for scavenging the conduction band electrons from the surface of the catalyst. Some major intermediate products from DMP degradation were identified by HPLC and GC/MS analyses. The analytical results identified dimethyl 3-hydroxyphthalate and dimethyl 2-hydroxyphthalate as the two main intermediate products from the DMP degradation in the TiO 2–UV–O 2 system, while in contrast phthalic acid was found to be the main intermediate product in the TiO 2–UV–Fe(VI) system. These findings indicate that DMP degradation in the TiO 2–UV–O 2 and TiO 2–UV–Fe(VI) systems followed different reaction pathways. An electron spin resonance analysis confirmed that hydroxyl radicals existed in the TiO 2–UV–O 2 reaction system and an unknown radical species (most likely an iron–oxo species) is suspected to exist in the TiO 2–UV–Fe(VI) reaction system. Two pathway schemes of DMP degradation in the TiO 2–UV–O 2 and TiO 2–UV–Fe(VI) reaction systems are proposed. It is believed that the radicals formed in the TiO 2–UV–O 2 reaction system preferably attack the aromatic ring of the DMP, while in contrast the radicals formed in the TiO 2–UV–Fe(VI) reaction systems attack the alkyl chain of DMP.