UV-LED assisted catalytic wet peroxide oxidation with a Fe(II)-Fe(III)/activated carbon catalyst

This study assesses the effect of UV LED radiation on the activity and stability of an activated carbon supported iron catalyst in catalytic wet peroxide oxidation (CWPO). Experiments were carried out with a Fe(II)-Fe(III) on activated carbon catalyst, named Fe/ACM, (4 wt% Fe) in a counter-flow quartz concentric tubular reactor (useful volume: 100 mg/L) surrounded by a commercial LED strip (length: 5 m, 120 LEDs/m, wavelength: 400 nm, irradiance: 10 W/m2). Phenol was used as target compound at 100 mg/L and the H2O2 dose was varied within 100–500 mg/L, the latter corresponding to the theoretical stoichiometric amount. The rest of operating conditions were: Ccatalyst: 500 mg/L, pH0: 3 and T: 50 °C. UV-LED radiation promotes the reduction of Fe3+ to Fe2+ on the catalyst surface, increasing the oxidation rate as a result of the higher H2O2 decomposition into HOX (HO and HOO) radicals. Besides, UV-LED radiation easily mineralized oxalic acid, which dramatically reduces the leaching of the active phase (from 17% to less than 4%, without and with irradiation, respectively after 180 min) and increases the life cycle of the catalyst. Thus, a complete H2O2 decomposition and more than 98% TOC reduction were reached after 180 min with the stoichiometric amount of H2O2. Long-term continuous experiments also confirm the beneficial effects of combining both technologies. TOC reduction above 85% was maintained within the first 100 h on stream with an iron leaching close to 25% of the initial metal load. Longer times on stream led to a slow but continuously decrease of activity probably due to the blockage and/or loss of active sites.