Phototransformation of triclosan in the presence of TiO2 in aqueous suspension:: Mechanistic approach

The photocatalytic degradation of the antimicrobial triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) was studied using different types of TiO2 suspension photocatalysts (Degussa P25, PC50 and PC 500) and excitation wavelength of 365 nm. In all cases, the degradation process mainly involved the formation of hydroxyl radicals. Under our experimental conditions and in aerated solutions, the irradiation in the presence of TiO2 P25 permitted the evaluation of the half-lifetime to about 10 min. The intermediate byproducts were identified by means of HPLC/MS/MS using electrospray (ES) interfacing technique. They were obtained as a result of three main primary processes: (i) homolytic scission of C-O bond leading to the formation of 2,4-dichlorophenol and chlorocatechol, (ii) hydroxylation of the phenolic group and (iii) dechlorination process leading to the formation of 5-chloro-2-(4-chlorophenoxyl)phenol. Under prolonged irradiation efficient mineralisation of triclosan solution was observed as evidenced by means of total organic carbon (TOC) evolution as well as chloride anions formation as a function of irradiation time. (c) 2006 Elsevier B.V. All rights reserved.