Evolution of the antibacterial activity and oxidation intermediates during the electrochemical degradation of norfloxacin in a flow cell with a PTFE-doped beta-PbO2 anode: Critical comparison to a BDD anode

Abstract

The electrochemical degradation of the antibiotic norfloxacin (NOR) was investigated using an electrode-posited polytetrafluoroethylene (PTFE)-doped beta-PbO2 anode; its attained performance was compared to that of a boron-doped diamond (BDD) anode to check out a literature claim of superior performance by the former anode. The PTFE content in the electrodeposition bath was optimized to lead to a significantly extended service life of the beta-PbO2 anode despite its titanium substrate. The NOR degradation electrolyses (100 mg L-1 NOR in 0.1 mol L-1 Na2SO4) were carried out in a filter-press flow cell (flow rate of 420 L h(-1)) using the following optimized conditions: no pH control, current density of 10 mA cm(-2), and 40 degrees C. The electrooxidation process performance under these conditions was assessed through the evolution of the attained removals of NOR, total organic carbon (TOC), and antibacterial activity against Escherichia coli; the evolution of oxidation intermediates (aromatic compounds and carboxylic acids) was also assessed. In spite of the complete oxidation of NOR, the TOC removal attained with the PTFE-doped beta-PbO2 anode was relatively low (70% after 12 h, compared to 90% after only 5 h for a Si/BDD anode). As a consequence of this inferior performance comparatively to that of a BDD anode, a higher number of aromatic intermediates was detected; these intermediates seemed to still present antibacterial activity against Escherichia coli, which lasted even after all NOR was oxidized, contrary to the case of the electrooxidation with a BDD anode. The performance of the PTFE-doped beta-PbO2 anode was not superior to that of a BDD anode, i.e. the doping of the b-PbO2 film with PTFE, making it hydrophobic, does not change the oxidation power of the anode despite increasing its service life. (C) 2018 Elsevier Ltd. All rights reserved.