Iron-doped cathodes for electro-Fenton implementation: Application for pymetrozine degradation

The degradation of a pesticide, pymetrozine, by heterogeneous electro-Fenton was performed. Thus, several cathodes were prepared based on carbon felt (CF) by immersion in dispersed solution of carbon black, PTFE and carbon nanofibers (CFN) or biochar (CFB). After evaluating H2O2 electro-generation of the different cathodes, it was detected that by including nanofibers the hydrophilic property of the cathode was improved and H2O2 production was also enhanced, achieving a stable concentration around 140 mg dm−3 after 4 h. Iron fixation in the different cathodes permitted the operation of heterogeneous electro-Fenton process at pH 3 and 7. The best results were obtained with CFN doped with Fe2+/Fe3+ solution (CFNFe). In addition, operating with CFNFe cathodes increased H2O2 production rate with current intensity that was directly related with the pymetrozine degradation. Thus, degradation rate at 200 mA is near the double than the one at 100 mA. Based on these results, the procedure was validated using a pre-treated wastewater spiked with pymetrozine at two initial concentrations (5 and 100 mg dm−3). Although pymetrozine removal rate was lower, wastewater constituents had slight effect on mineralization, thus TOC removal with values around 90% was similar to the one obtained using ultrapure water after 5 h of treatment. Finally, pymetrozine intermediate compounds were determined by chromatography technology.