Photodegradation of organic dyes in the presence of [Fe(III)-salen]Cl complex and H2O2 under visible light irradiation

Photodegradation of persistent organic dyes (Rhodamine B (RhB), Malachite Green Oxalate (MG) and Crystal Violet 10B (CV)) is studied with Fe(III)-salen complex (λmax 494 nm), and hydrogen peroxide under visible light irradiation (λ ≥ 400 nm). The complete decolourization of the dyes (60 mg/L each) was achieved in the aqueous medium. The pseudo-first-order degradation rate constants of RhB, MG, CV were found to be 2.83 x 10-3 s-1, 1.57 x 10-3 s-1 and 1.34 x 10-3 s-1, respectively. The effect of various parameters like concentration of H2O2, pH of the medium, and influence of electrolytes are investigated on the degradation of RhB. A modified benzoic acid hydroxylation method has been used to detect the active oxygen species (OH radicals) in this study. The hydroxyl radical production is increased with the increase in irradiation time. Interestingly, even an excess amount of scavenger could not arrest the degradation of the dyes. This may be due to the formation of some secondary oxidants. Here, active ferryl ion was identified as the secondary oxidant. Degradation products of the dye (RhB) were determined by GC-MS, and phthalic acid was identified as the major one. From the results, a possible photodegradation mechanism has been proposed.