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

Abstract 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.

[1]  W. J. Hickey,et al.  Degradation of Atrazine by Fenton's Reagent: Condition Optimization and Product Quantification. , 1995, Environmental science & technology.

[2]  Stefan H. Bossmann,et al.  New Evidence against Hydroxyl Radicals as Reactive Intermediates in the Thermal and Photochemically Enhanced Fenton Reactions , 1998 .

[3]  L. Lewis.  Chemical catalysis by colloids and clusters , 1993 .

[4]  D. Bahnemann,et al.  Photocatalytic Degradation of 4-Chlorophenol in Aerated Aqueous Titanium Dioxide Suspensions: A Kinetic and Mechanistic Study , 1996 .

[5]  D. Behar,et al.  Pulse radiolysis studies of aminobenzenesulfonates: formation of cation radicals , 1991 .

[6]  K. Tanaka,et al.  Photodegradation of phenoxyacetic acid and carbamate pesticides on TiO2 , 2002 .

[7]  D. Wolbert,et al.  Photocatalytic degradation of a phenylurea, chlortoluron, in water using an industrial titanium dioxide coated media , 2005 .

[8]  J. Newman,et al.  Triclosan: a review of effectiveness and safety in health care settings. , 2000, American journal of infection control.

[9]  Xinle Zhu,et al.  Photocatalytic degradation of pesticide pyridaben on TiO2 particles , 2005 .

[10]  André M. Braun,et al.  Photochemical processes for water treatment , 1993 .

[11]  G. Centi,et al.  Remediation of water contamination using catalytic technologies , 2003 .

[12]  J. Chovelon,et al.  Photocatalytic degradation of sulfonylurea herbicides in aqueous TiO2 , 2002 .

[13]  W. Arnold,et al.  Photochemical conversion of triclosan to 2,8-dichlorodibenzo-p-dioxin in aqueous solution , 2003 .

[14]  P. Kamat.  PHOTOCHEMISTRY ON NONREACTIVE AND REACTIVE (SEMICONDUCTOR) SURFACES , 1993 .

[15]  J. Tromp,et al.  Photogeneration of hydrogen peroxide in aqueous TiO2 dispersions , 1985 .

[16]  J. A. Santaballa,et al.  Reaction pathways and mechanisms of photodegradation of pesticides. , 2002, Journal of photochemistry and photobiology. B, Biology.

[17]  Steven L. Murov,et al.  Handbook of photochemistry , 1973 .

[18]  T. Albanis,et al.  Metolachlor photocatalytic degradation using TiO2 photocatalysts , 2004 .

[19]  P. Boule,et al.  Photocatalytic degradation of 2-phenylphenol on TiO2 and ZnO in aqueous suspensions , 2001 .

[20]  J. A. Santaballa,et al.  On the mechanism of TiO2-photocatalyzed degradation of aniline derivatives , 2005 .

[21]  A. Fernández-Alba,et al.  Pesticide chemical oxidation: state-of-the-art. , 2000 .

[22]  Alberto E. Cassano,et al.  Photocatalysis in water environments using artificial and solar light , 2000 .

[23]  Akira Fujishima,et al.  Titanium dioxide photocatalysis , 2000 .

[24]  A. Fernández-Alba,et al.  Liquid chromatography/time-of-flight mass spectrometric analyses for the elucidation of the photodegradation products of triclosan in wastewater samples. , 2004, Rapid communications in mass spectrometry : RCM.

[25]  E. Thurman,et al.  Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: a national reconnaissance. , 2002 .

[26]  B. K. Hodnett.  Photocatalytic purification and treatment of water and air : by D.F. Ollis and H. Al-Ekabi (Editors), Elsevier Science Publishers BV, Amsterdam, 1993, ISBN 0-444-89855-7, xiv + 820 pp., f450.00/$257.25 , 1994 .

[27]  H. Singer,et al.  Triclosan: occurrence and fate of a widely used biocide in the aquatic environment: field measurements in wastewater treatment plants, surface waters, and lake sediments. , 2002, Environmental science & technology.

[28]  P. A. Leonard,et al.  Triclosan: applications and safety. , 1996, American journal of infection control.

[29]  R. Talaat,et al.  Identification of Fenton's reagent‐generated atrazine degradation products by high‐performance liquid chromatography and megaflow electrospray ionization tandem mass spectrometry , 1995 .

[30]  A. Heller,et al.  The role of oxygen in photooxidation of organic molecules on semiconductor particles , 1991 .

[31]  J. Pignatello,et al.  Photochemical reactions involved in the total mineralization of 2,4-D by Fe3+/H2O2/UV , 1993 .

[32]  A. Fernández-Alba,et al.  Evidence of 2,7/2,8-dibenzodichloro-p-dioxin as a photodegradation product of triclosan in water and wastewater samples , 2004 .