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

The electrochemical degradation of the antibiotic norfloxacin (NOR) was investigated using an electrodeposited polytetrafluoroethylene (PTFE)-doped β-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 β-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 °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 β-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 β-PbO₂ anode was not superior to that of a BDD anode, i.e. the doping of the β-PbO₂ film with PTFE, making it hydrophobic, does not change the oxidation power of the anode despite increasing its service life.