Chemical actinometry and paraben decomposition in aqueous solution utilizing ultraviolet radiation combined with hydrogen peroxide

In this paper, ultraviolet radiation combined with hydrogen peroxide is presented to investigate the degradation of methyl, ethyl, and propyl parabens. The proposed kinetic model incorporates photochemical, chemical reactions, and reaction-rate constants to formulate the overall kinetic rate expressions, which are integrated into MATLAB. Thus, the chemical actinometry has been investigated to identify the incident ultraviolet-light intensity (1.59 × 10−6 Einstein.cm−1 s−1) and the optical path-length (5.83 cm) of the new reactor. Based on the optimal parameters of the previous study, an experimental campaign was performed at fixed hydrogen peroxide concentration to compare the half-life of the decomposition of these parabens and to determine the evolution of the pH and the pseudo-first-order rate constant. Accordingly, the study provides a comparison between numerical results and experimental data. The use of hydrogen peroxide at 25 µM resulted in 80% removal of propyl paraben (10 mg/L) within 90 min reaction time, while 50% of methyl and ethyl was oxidized. The performed model had a satisfactory predictive performance of paraben removal during the reaction, and the numerical pseudo-first-order rate constant was in agreement with the experimental value. Although the proposed model slightly overestimates the decrease of experimental pH, it provides insight into the evolution of hydroxide, superoxide, and hydroperoxyl ions. Finally, this paper proposes a discussion on the limitations of the study and suggests future work concerning the effects of water matrix, carbonate species, paraben mixture, and cytotoxicity of degradation by-products.