Reaction pathways of dimethyl phthalate degradation in TiO2-UV-O2 and TiO2-UV-Fe(VI) systems

• Published in: Chemosphere (Oxford) Vol. 72; no. 2; pp. 197 - 204
• Main Authors: YUAN, Bao-Ling, LI, Xiang-Zhong, GRAHAM, Nigel
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier 01.05.2008
• Subjects: Applied sciences; Catalysis - radiation effects; Chromatography, High Pressure Liquid; Drinking water and swimming-pool water. Desalination; Exact sciences and technology; Gas Chromatography-Mass Spectrometry; General purification processes; Iron - chemistry; Oxygen - chemistry; Phthalic Acids - chemistry; Pollution; Titanium - chemistry; Ultraviolet Rays; Wastewaters; Water treatment and pollution; Reaction intermediate; Oxygen; Photocatalysis; DMP; Synergism; Dimethyl phthalate; Phthalates; Heterogeneous catalysis; Ester; Ultraviolet radiation; Decontamination; Iron VI; Reaction mechanism; Fe(VI); Aromatic compound; Physicochemical purification; Water pollution; Ferrate; Waste water purification; Titanium oxide; Electron acceptor; Organic compounds; Photochemical degradation
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2008.01.055

The photocatalytic degradation of dimethyl phthalate (DMP) in aqueous TiO2 suspension under UV illumination has been investigated using oxygen (O2) and ferrate (Fe(VI)) as electron acceptors. The experiments demonstrated that Fe(VI) was a more effective electron acceptor than O2 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 TiO2-UV-O2 system, while in contrast phthalic acid was found to be the main intermediate product in the TiO2-UV-Fe(VI) system. These findings indicate that DMP degradation in the TiO2-UV-O2 and TiO2-UV-Fe(VI) systems followed different reaction pathways. An electron spin resonance analysis confirmed that hydroxyl radicals existed in the TiO2-UV-O2 reaction system and an unknown radical species (most likely an iron-oxo species) is suspected to exist in the TiO2-UV-Fe(VI) reaction system. Two pathway schemes of DMP degradation in the TiO2-UV-O2 and TiO2-UV-Fe(VI) reaction systems are proposed. It is believed that the radicals formed in the TiO2-UV-O2 reaction system preferably attack the aromatic ring of the DMP, while in contrast the radicals formed in the TiO2-UV-Fe(VI) reaction systems attack the alkyl chain of DMP.