Towards understanding of heterogeneous Fenton reaction using carbon-Fe catalysts coupled to in-situ H2O2 electro-generation as clean technology for wastewater treatment

Abstract

Iron-supported catalyst on granular activated carbon was prepared for its use in heterogeneous Fenton reaction coupled to an in situ H₂O₂ electro-generation. For this process, an electrolysis cell was employed, using carbon felt as cathode and graphite as anode. A solution of H₂O₂ (electrogenerated at a rate of 30 mg L^-1 h^-1) was obtained using a current intensity of 12 mA. In order to promote the decomposition of H₂O₂ to OH, a Carbon-Fe catalyst was used. This catalyst was prepared by incipient wet impregnation using FeSO₄ as precursor salt to obtain samples with 9% wt of iron. Samples were characterized by EDX, FTIR and XPS spectroscopy before and after wastewater treatment using phenol as model molecule. Two iron oxidation states on the samples were found, Fe²⁺ and Fe³⁺. The ratio between Fe²⁺/Fe³⁺ was 1.29 which was later reduced to 0.92 after Fenton process; this might be associated with the metal oxidation (Fe²⁺ to Fe⁺³) occurring during Fenton-reaction, thus indicating that H₂O₂ decomposition was carried out by Fe²⁺ on carbon surface. Detection and quantification of hydroxyl radical were carried out by fluorescence spectroscopy, obtaining a radical concentration of 3.5 μM in solution. Iron in solution were determined, showing a concentration of 0.1 mg L^-1, making evident that the supported metal is stable and the reaction is carried out in a heterogeneous phase. Results showed an environmentally friendly process that can generate reagents in situ, with high efficiencies in the degradation of pollutants and minimizing the formation of toxic byproducts, which are common in conventional treatments.

Keywords: H(2)O(2) electrogeneration; Heterogeneous fenton; Hydroxyl radical (•)OH; Iron – activated carbon catalyst.