A wide range of advanced oxidation technologies have been used for water treatment, especially those contaminated by organic pollutants. Electro-Fenton-based process have been used to remove these pollutants due to the production of hydroxyl radicals (•OH). A new electrochemical Fenton-type process between electrogenerated hypochlorous acid and Fe²⁺ have been reported to produce hydroxyl radicals [1]. Recent study has shown the capacity of this Fenton-like process to remove a textile dye [2]. In this context, this research deals with the characterization of the electrosynthesis of hypochlorous acid from the oxidation of Cl^- to be use in the future in a Fenton-like process. Microelectrolysis studies were performed to determine the anode potential range (1.6 < E < 1.9 V vs SHE) to avoid side reactions like oxygen evolution reaction, using 0.05 dm³ solution with 25 mM Na₂SO₄ + 35 mM NaCl at pH 3. The characterization of the electrosynthesis of active chlorine (mixture of hypochlorous acid, chlorine, and hypochlorite) was carried out in an undivided cell equipped with Ir-Sn-Sb oxide anode and stainless-steel cathode. The production of active chlorine by bulk electrolysis was formed at three anodic potentials (1.6, 1.7 and 1.9 V vs SHE) using 6 dm³ of electrolyte in recycle batch mode of operation at volumetric flow rate of 3.2 dm³ min^-1 obtaining a chlorine concentration of 0.32 mM HClO, as shown in Figure 1. The influence of current density and volumetric flow rate on the conversion of active chlorine was carried out at 5 ≤ j ≤ 20 mA cm^-2 and 0.8 ≤ Q ≤ 3.2 dm³ min^-1, respectively. The best electrolysis was obtained at 15 mA cm^-2 and 3.2 dm³ min^-1, giving values of 20 % of current efficiency with energy consumption of 4 KW h m^-3 for a production of 1.9 mM HClO. To elucidate if the active chlorine was reduced at the cathode, electrolysis trials were performed using the same electrolyser, which included a cationic membrane between electrodes.

References.

[1] K. Kishimoto, E. Sugimura, Water Sci. and Technol. 62 (210) 2321.

[2] Z.G. Aguilar, E. Brillas, M. Salazar, J.L. Nava, I. Sirés, Appl. Catal. B: Environ. 206 (2017) 44.