Photo-Fenton degradation of a dye under visible light irradiation

Abstract

The photodegradation of Malachite Green (MG) under visible light irradiation ( λ>470 nm) in the presence of Fe 3+/H 2O 2 or Fe 2+/H 2O 2 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 Fe 3+/H 2O 2 under visible irradiation is discussed, which involves an electron transfer from the excited dye by visible light into Fe 3+ in the initial photo-Fenton degradation. Conversion of Fe 3+ to Fe 2+ 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 Fe 3+/C 2O 4 2−/H 2O 2 system irradiated by UV or visible light and reacted in the dark provided another proof of the proposed mechanism.