Degradation of phenols by heterogeneous electro-Fenton with a Fe3O4-chitosan composite and a boron-doped diamond anode

Four phenolic compounds, either as single molecules or in mixtures, were treated by heterogeneous electro-Fenton using an undivided cell with a Ti mesh cathode, put in contact with a composite made of Fe3O4 nanoparticles (NPs) on chitosan (CS) made by chemical reduction, and a boron-doped diamond (BDD) anode. The removals attained upon the application of 2.3 V for 4 h to model solutions with 0.5 mol dm−3 H2SO4 as electrolyte were: 93% for phenol, 30% for m-chlorophenol, 24% for o-chlorophenol and 22% for p-chlorophenol. COD removal efficiencies reached 95% for phenol and m-chlorophenol, 88% for p-chlorophenol and 57% for o-chlorophenol. The degradation was feasible thanks to the production of hydroxyl radicals, both on the BDD surface (i.e., BDD(OH)) from water oxidation and in the bulk from Fenton’s reaction. The composite cathode allowed the continuous H2O2 electrogeneration and Fe(III) reduction to Fe(II). The reaction between H2O2 and Fe(II) in solid or liquid phase yielded OH. The disappearance of phenols was much slower in the absence of the composite catalyst.