Comparison of the heterogeneous GO-FePO4/electro-Fenton against the homogeneous Fe(II) ion and Fe(III)-oxalate complex/electro-Fenton for the degradation of metronidazole

Abstract

This study compared the effect of the homogeneous and the heterogeneous electro-Fenton (EF) processes on the degradation of Metronidazole (MTZ). Graphene oxide (GO)-FePO4 synthesized for use in the heterogeneous electro-Fenton process was characterized using FTIR, FE SEM-EDS and XRD analysis. The analyses showed that the amorphous composite structure formed as a result of FePO4 structures dispersed between the GO layers has an average particle size distribution of 141 nm. The activity of the GO-FePO4 catalyst was more effective at pH 3 than pH 5 which is the own pH value of metronidazole. In the heterogeneous EF process, the mineralization percentage was determined as 66% at pH 3, 0.5 g L−1 catalyst dosage after 5 h. No difference was observed in the structure of GO-FePO4, which can be used repeatedly with high performance, even after 4 cycles. In the homogeneous EF process, 0.2 mM Fe2+ ion and Fe(III)-oxalate complex containing the same amount of Fe ions were used for comparison under the same conditions. When Fe2+ ion and Fe(III)-oxalate complex were used at pH 3, 57% and 70% mineralization percentages were achieved respectively, in 5 h. However, the mineralization efficiencies of the Fe(III)-oxalate complex decreased to 47% at pH 5 and 41% at pH 7. The pseudo-first-order model to kinetically describe the removal mechanism of MTZ showed the best fit with the experimental kinetic data in all EF processes. Finally, active oxygen species were determined as hydroperoxyl radicals for the heterogeneous EF method and as hydroxyl radicals for the homogeneous EF method.