Synergistic mineralization of ofloxacin in electro-Fenton process with BDD anode: Reactivity and mechanism

This study aimed at exploring the performance of the electro-Fenton (EF) process with a boron-doped diamond (BDD) anode and an electrochemically exfoliated graphene-based cathode (EEGr), for removal of antibiotic ofloxacin (OFLO) from contaminated water. Compared with anodic oxidation (AO) process with BDD anode, the EF process with BDD anode (EF-BDD) could improve the decay kinetics of OFLO by 1.4–2.6 times and reduce the disposal cost by 28 %–41 %. Removal efficiency of TOC in EF-BDD process under 4.2 mA cm −2 was better than in AO process under 8.3 mA cm −2 , pointing out that the cost effectiveness of the EF process for mineralization of OFLO under low current density conditions. This advantage is due to the simultaneous formation of homogeneous ( • OH) and heterogeneous (BDD( • OH)) hydroxyl radicals in the process. The synergistic factor of • OH and BDD( • OH) for mineralization of OFLO decreased with the current density rising from 4.2 (0.28) to 16.6 mA cm −2 (-0.08). Decay kinetics of OFLO in the EF-BDD and AO were more converging under higher current densities owing to the production of large amount of BDD( • OH). In the EF-BDD, a trade-off should be considered between accumulated BDD( • OH) on the surface of BDD anode and H 2 O 2 generation on the cathode. Absolute rate constant for oxidation of OFLO by • OH ( k OFLO ) was calculated to be 3.86 × 10 9 M −1 s −1 . Evolution of carboxylic acids and inorganic ions as well as toxicity assessment were followed during the treatment of OFLO solutions. Results obtained proved that the EF-BDD process is outstanding for oxidative degradation of OFLO thanks to the synergistic effect of •OH and BDD( • OH). These very strong oxidants being non-selective, this result can be extended to the treatment of antibiotic organic pollutants.