Elementary Steps in Steady State Kinetic Model Approximation for the Homo-Heterogeneous Photocatalysis of Carbamazepine

Abstract

Elucidating physicochemical processes in the degradation of pollutants may optimize their removal from water sources. Although the photodegradation of carbamazepine (CBZ) in Advanced Oxidation Processes (AOPs) has been widely studied, there is no detailed report on the elementary steps of the kinetics. This study proposes a set of elementary steps for the AOP of CBZ, combining short-wave ultraviolet radiation (UVC), a homogeneous reagent (H2O2), and a heterogeneous catalyst (TiO2), which includes the excitation of both reagents/catalysts by UVC photons, the adsorption of CBZ by the excited TiO2, or its oxidation by hydroxyl radicals. Assuming the steady-state approximation on the intermediate products (excited TiO2, CBZ-excited TiO2 complex, and hydroxyl radicals) leads to rate laws for the degradation of CBZ, in which UVC radiation, TiO2, and H2O2 are pseudo-first-order at all concentrations or intensities and have no direct influence on CBZ pseudo-order, whereas CBZ shifts from pseudo-first-order at low concentrations to pseudo-zero-order at high concentrations. Several experiments to test the mechanism were conducted by varying CBZ, H2O2, and TiO2 concentrations and UVC radiation intensities. The measured results indeed fit the suggested mechanism for the first three, but the irradiation intensity appears to shift the CBZ influence from pseudo-second- to pseudo-first-order with increased intensities. Part of the elementary steps were changed to fit the results.