Hydroxyl radical generation in electro-Fenton process with a gas-diffusion electrode: Linkages with electro-chemical generation of hydrogen peroxide and iron redox cycle

ABSTRACT

The hydroxyl radical generation in an electro-Fenton process with a gas-diffusion electrode which is strongly linked with electro-chemical generation of hydrogen peroxide and iron redox cycle was studied. The OH radical generation subsequent to electro-chemical generations of H₂O₂ was examined under the constant potential in the range of Fe²⁺ dosage from 0 to 1.0 mM. The amount of generated OH radical initially increased and gradually decreased after the maximum was reached. The initial rate of OH radical generation increased for the Fe²⁺ dosage <0.25 mM and at higher Fe²⁺ dosages remained constant. At higher Fe²⁺ dosages the precipitation of Fe might inhibit the enhancement of OH radical generation. The experiments for decolorization and total organic carbon (TOC) removal of azo-dye Orange II by the electro-Fenton process were conducted and the quick decolorization and slow TOC removal of Orange II were found. To quantify the linkages of OH radical generation with dynamic behaviors of electro-chemically generated H₂O₂ and iron redox cycle and to investigate effects of OH radical generation on the decolorization and TOC removal of Orange II, novel reaction kinetic models were developed. The proposed models could satisfactory clarify the linkages of OH radical generation with electro-chemically generated H₂O₂ and iron redox cycle and simulate the decolorization and TOC removal of Orange II by the electro-Fenton process.

KEYWORDS:

• Azo-dye Orange II degradation
• electro-Fenton process
• gas-diffusion electrode
• hydroxyl radical
• iron redox cycle