Oxidative degradation of dye pollutants over a broad pH range using hydrogen peroxide catalyzed by FePz(dtnCl2)4

The oxidative degradation of rhodamine B (RhB) with hydrogen peroxide activated by iron(II) tetra-(5,6-dichloro-1,4-dithiin)-porphyrazine (abbreviated as FePz(dtnCl2)4) was studied by means of UV–Vis spectra, GC–MS and TOC analysis, in which the effects of pH, light, concentration of hydrogen peroxide and the degraded products of the RhB were investigated. The results indicate that FePz(dtnCl2)4 was found to exhibit high catalytic activity to activate hydrogen peroxide for the oxidative degradation of RhB and good stability over a broad pH range under visible light irradiation (λ > 420 nm). The conversions of RhB in 80 min were 99%, 85%, 52% and the TOC removals in 240 min were 91%, 64%, 18% when the initial solutions pHs were 2, 7, 11, respectively. HO radicals were testified to generate in the biomimetic catalytic system both at pH 2 and 7 by means of spin-trapping electron spin resonance. However, control experiment with scavenging of HO radicals displayed the quite different results at pH 2 and 7. Based on experiment results together with theoretic deduction, a mechanism for RhB oxidation involving two kinds of reactive oxidizing species was proposed, the homolytic cleavage generating the HO radicals and the heterolytic cleavage generating the Pz+FeIVO radicals.