Electrocatalytic generation of radical intermediates over lead dioxide electrode doped with fluoride

Electrochemical processes have provided promising contributions for environmental protection. A novel lead dioxide electrode doped with fluoride was investigated for wastewater treatment. The modified beta-PbO2, electrode showed high chemical stability and catalytic activity for contaminants abatement and organic mineralization. Evidence for active free radicals generation in electrochemical degradation was shown by electron spin resonance spectroscopy (ESR). 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was used as spin trapping agent. The characteristic of hydroxyl radicals, 5,5-dimethyl-2-hydroxypyrrilidine-N-oxyI (DMPO-OH) spin adduct, was observed and the additions of hydroxyl radical scavengers reduce the signal of DMPO-OH. This indicated that hydroxyl radicals were indeed formed and played a critical role in water treatment. 4-Chlorophenol was chosen as model pollutant and the prepared electrode exhibited the perfect catalytic activity. The origin of the electrode and the structure of the anodic layer were examined to understand the mechanism of hydroxyl radical formation. The electrochemical reactions occurred at beta-PbO2 electrode was rather complex and involved the crystal-hydrated layer. It is the most environmentally friendly treatment method to use electrogenerated hydroxyl radicals as oxidants.