Oxidative removal of 4-chloro-hydroxybenzene using catalyzed S2O82− with Fe2+ under UV-LED irradiation

Abstract Among the halogenated aromatic compounds, as toxic and carcinogenic materials, 4-chloro-hydroxybenzene (4CHB) has been known as a priority pollutant that is present in industrial effluents at high concentrations. Unlike previous studies that have used nanoscale zero valent iron (nZVI) for activation of S2O82− in various catalytic processes, in the present study, Fe2+ was used in UV-LEDs/S2O82−/Fe2+ process to remove 4CHB from aqueous solutions. Moreover, the effects of various parameters, including contact time, solution pH, 4CHB concentration, Fe2+ concentration, and S2O82− concentration were evaluated on the process efficiency. Results showed that under optimal conditions (including contact time 90 min, 4CHB concentration 30 mg/L, S2O82− 1.27 mM, and Fe (II) concentration 0.3 mM), the removal efficiency of 4CHB and chemical oxygen demand (COD) using the UV-LEDs/S2O82−/Fe2+ process were 98% and 58%, respectively. The calculated synergistic effect (SE) for the UV-LEDs/S2O82−/Fe2+ process was obtained to be 1.88, which is higher than 1, indicating the SE of iron ions and UV-LED radiation in the activation of S2O82− and production of persulfate and hydroxyl radicals for 4CHB removal. Voltammetric experiments demonstrated that 4CHB was completely degraded, and there was no electroactive intermediate in the solution after 120 min of reaction. While longer contact time was required to mineralize 4CHB and other intermediates. In this regard, increasing the retention time to 120 min improved the COD removal efficiency up to 69%. Based on the results of this study, it can be concluded that the use of Fe+2 under UV-LED irradiation can be used as an efficient, cost-effective, and practical process for 4CHB removal. Therefore, this process does not require much time and cost to produce nZVI or other iron species.