Heterogeneous UV-Fenton Photodegradation Of Azocarmine B Over [FeEDTA]~- Intercalated ZnAl-LDH

In order to solve the problem of need for acidification in the commonly used heterogeneous photo-Fenton reaction system, a kind of novel heterogeneous photo-Fenton catalyst with iron complex was prepared and used to degrade Azocarmine B (ACB). In this study, response surface methodology (RSM) was employed to overcome the drawback of the traditional single factor experiment. In addition, the active species existed in the reaction systemwere detected and the reaction mechanisms of the studied system were discussed. Some new results were abtained:(1) [FeEDTA]- intercalated layered double hedroxide (EDTA-Fe-LDH) was prepared by ion exchange method. EDTA-Fe-LDH has high photocatalytic activity and stability under UV irradiation. The results of X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) indicate that [FeEDTA]- intercalate into the interlayer spaces of layered double hedroxide (LDH) successfully; The results of UV-vis diffused reflectance spectra shows that EDTA-Fe-LDH has a significant absorption in the UV region; The nitrogen adsorption-desorption isotherms and scanning electron microscope (SEM) show that EDTA-Fe-LDH has much lager specific surface area and pore volume compared to ZnAl-LDH.(2) Box-Behnken design (BBD) was employed to optimize the experimental conditions. The optimum conditions for ACB degradation were ACB concentration of 100 mg/L, pH of 6.54 and H2O2 concentration of 11.5 mM, respectively. Under these conditions, the maximum ACB decolorization efficiency and TOC removal could reach to 97.27% and 90.36%, respectively, which closely agreed with the predicted values.(3) Three kinds of active species, including hydroxyl free radical (·OH), superoxide radical (·O2-) and singlet oxygen (1C2), have been identified in the heterogeneous photo-Fenton reaction system. And the corresponding mechanism for the generation of these active species has been described in this study. In addition, the degradation mechanism of azocarmine B has been studied by UV-vis diffused reflectance spectra and GC-MS analysis. The results show that ACB dye is gives rise to benzenes such as 1-Nitroso-2,4-dimethylamino-benzene. With the continuous oxidation, the aromatic rings are opened which are responsible for the formation of butyric acid and other small molecular substances. Finally, these intermediate products convert to carbon dioxide and water.