Photocatalytic oxidation of multicomponent mixtures of estrogens (estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2) and estriol (E3)) under UVA and UVC radiation: Photon absorption, quantum yields and rate constants independent of photon absorption

Abstract

The kinetics of photocatalytic degradation of multicomponent mixtures of four of the most powerful endocrine disrupting chemicals (estrogens) estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2) and estriol (E3) was studied in the presence and in the absence of TiO2 (Degussa P25) suspensions. Experiments were carried out with UVA and UVC radiation in a well characterized annular photoreactor. The results were analysed in terms of a simple first-order kinetic model, but including the explicit effect of photon absorption. This was accomplished by modelling the radiation field under heterogeneous (photocatalysis) conditions and by determining the spatial distribution of the local volumetric rate of photon absorption (LVRPA) in the reactor. The Six-Flux Absorption-Scattering Model (i.e., scattered photons follow the route of the six directions of the Cartesian coordinates) using optical parameters averaged across the spectrum of the incident radiation was used to determine the LVRPA. The intrinsic reaction kinetic constants, of E1, E2, EE2 and E3, independent of reactor geometry and level of radiation absorbed within the reactor were determined under each different oxidation conditions. The quantum yields (moles of estrogens degraded per Einstein of photons absorbed) were estimated. The quantum yields under UVC-TiO2 photocatalysis (2.1×10−3 to 3.9×10−3) are on average double the yields under UVA-TiO2 photocatalysis (1.2×10−3 to 1.8×10−3).The established model was found to be appropriate to predict the time-dependent degradation profiles of the estrogens in multicomponent systems. Using this simple approach, intrinsic kinetic data can be obtained.