Photo-Fenton degradation of a dye under visible light irradiation

The photodegradation of Malachite Green (MG) under visible light irradiation (lambda > 470 nm) in the presence of Fe3+/H2O2 or Fe2+/H2O2 was studied in comparison with the dark reaction. It was found that visible Light irradiation can accelerate significantly the rate of MG degradation, comparing to that in the dark. This provides possibly another approach to the treatment of dye-polluted waters using visible light or sunlight. Evidence for enhancement of OH radical generation by visible light irradiation was obtained using DMPO spin-trapping EPR spectroscopy. A probable degradation mechanism of MG by Fe3+/H2O2 under visible irradiation is discussed, which involves an electron transfer from the excited dye by visible light into Fe3+ in the initial photo-Fenton degradation. Conversion of Fe3+ to Fe2+ was detected in the degradation process of MG. The results of the total organic carbon (TOC) reduction in the photodegradation of MG under visible light irradiation supported the proposed mechanism by comparing to those in the degradation of sodium dodecylbenzenesulfonate (DBS). The photodegradation of MG in a Fe3+/C2O42-/H2O2 system irradiated by UV or visible light and reacted in the dark provided another proof of the proposed mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.