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Dyes are naked-eye detectable even at low concentration levels and can cause environmental damage when released into aquatic effluents; therefore, methods for removing the residual color from the aquatic media are always a current issue. In this paper, degradation of three xanthene dyes, Rhodamine B, Eosin Y, and Sodium Fluorescein, using photoactivated persulfate was evaluated at pH 3.0 and 11.0. The dyes' degradation followed a pseudo-first-order reaction. Although the solution is completely decolorized in 40 min at pH 3.0, achieving 75% mineralization requires a longer reaction time of 180 min. Furthermore, GC-MS analyses indicate that degradation products are mainly low-molecular weight acids, CO 2 and H 2 O. Experiments carried out in dark and under UV irradiation showed substantial contribution of radical (SO 4 •- and HO • ) and non-radical pathways to dye degradation in both pH. Additionally, to get more insights into the degradation pathways, HOMO-LUMO energy gaps of the dyes were calculated by DFT using MPW1PW91/MidiXo level of theory and, in general, the lower the bandgap, the faster the degradation. Fukui functions revealed that the preferential sites to radical attack were the xanthene or the benzoate portion depending on the pH, wherein attack to the xanthene ring provided better kinetic and mineralization results., (© 2023. The Author(s), under exclusive licence to European Photochemistry Association, European Society for Photobiology.)

The use of the pulsed current can be an alternative to decrease the electrode polarization, as well as achieving lower energy consumption. This study investigated the electrocoagulation through pulsed current for the removal of natural organic matter from water. The experiments were carried out using Box-Behnken factorial design with the response surface methodology for the design of experiments, modeling and interpreting of the results. The electrocoagulation cell consisted of an acrylic reactor with 4 L capacity with four electrodes of aluminum, in parallel connection mode. The experimental independent variables studied were: current density (5.5 to 44.5 A m -2 ), electrodes spacing (2 to 7.6 mm), stirring rate (200 to 1,000 rpm), frequency (500 to 5,000 Hz), humic acid concentration (5 to 20 mg L -1 ) and NaCl (100 to 300 mg L -1 ) as supporting electrolyte, evaluating the residual apparent color (RAC) and electric energy consumption (EEC). The pH of the solution increased during the experiments, reaching basic values. The response surface regression procedure was employed to fit the second-order polynomial, and the model fitted well to the obtained values, reaching R 2 0.9995 (RAC) and R 2 0.9989 (EEC). The lowest RAC was 11.8 Hazen units (96.2% color removal), where the EEC was 0.393 kWh m -3 .