Application of Fe(III)–EDDS complexes and soybean peroxidase in photo-Fenton processes for organic pollutant removal: insights into possible synergistic effects

Photo-Fenton processes activated by biodegradable Fe(III)-EDDS complexes have attracted huge attention from the scientific community, but the operative mechanism of the photo-activation of H₂O₂ in the presence of Fe(III)-EDDS has not been fully clarified yet. The application of the Fe(III)-EDDS complex in Fenton and photo-Fenton (mainly under UV-B light) processes, using 4-chlorophenol (4-CP) as a model pollutant was explored to give insights into the operative mechanism. Furthermore, the potential synergistic contribution of soybean peroxidase (SBP) was investigated, since it has been reported that upon irradiation of Fe(III)-EDDS the production of H₂O₂ can occur. SBP did not boost the 4-CP degradation, suggesting that the possibly produced H₂O₂ reacts immediately with the Fe(II) ion with a quick kinetics that does not allow the diffusion of H₂O₂ into the bulk of the solution (i.e., outside the solvent cage of the complex). So, a concerted mechanism in which the photochemically produced H₂O₂ and Fe(II) react inside the hydration sphere of the Fe(III)-EDDS complex is proposed.