Photocatalytic Oxidation of Five Contaminants of Emerging Concern by UV/TiO 2 : Identification of Intermediates and Degradation Pathways

Abstract

Abstract

The simultaneous TiO₂/UV photocatalytic degradation of 1,4-dioxane, n-nitrosodimethylamine (NDMA), tris-2-chloroethyl phosphate (TCEP), gemfibrozil (GEM), and 17β-estradiol (E2) in water at pH 5.0 and 1.5 g/L TiO₂ using a 1-L slurry photoreactor was investigated. Intermediates originating from degradation of individual contaminants and interaction between them were evaluated and possible reaction pathways were suggested. Gas chromatography/mass spectroscopy analysis was used for identification of these intermediates. Results obtained showed that the compounds identified were mostly derived from 1,4 xylenol, a moiety from gemfibrozil. Isomerization and alkyl shift mechanisms were found to be responsible for formation of intermediates. Nitrogen compounds derived from NDMA degradation were reactive with other fragments and generated several other compounds such as pyridines, secondary amines, carbamate derivatives, and diazoles. Interaction between 1,4-dioxane and TCEP by-products was limited to formation of a few detected compounds. Some individual oxidation by-products of E2 were identified as estrogenic species such as testosterone and estrone. These findings are an important step to better understand the photocatalytic process applied to degradation of multiple organic contaminants in complex aqueous matrices.