A novel photochemical system of ferrous sulfite complex: kinetics and mechanisms of rapid decolorization of Acid Orange 7 in aqueous solutions.
We previously reported the decolorization of the azo dye Acid Orange 7 (AO7) by sulfate radical (SO4(-)) in the presence of iron(II) sulfite complex and oxygen under UV-vis irradiation (photo-iron(II) sulfite system). This system, however, achieves very limited mineralization of AO7 (in terms of total organic carbon (TOC) removal), which is not in accordance with literature reports on the oxidation of organic contaminants by SO4(-). In the present work, kinetics and products under irradiation of xenon lamp (350 W) were analyzed to reveal the reaction pathway of decolorization of AO7. Steady-state approximation (SSA) of SO4(-) radicals and apparent kinetics of AO7 were examined. The reaction between AO7 and SO4(-) was found to proceed in two steps, namely, electron transfer and SO4(-) addition. The second-order rate constant for the reaction between AO7 and SO4(-) was found to be 8.07 ± 1.07 × 10(9) M(-1) s(-1) by SSA and 6.80 ± 0.68 × 10(9) M(-1) s(-1) by competition kinetics method. The apparent kinetics of the decolorization of AO7 under irradiation closely fits the mechanism of radical chain reactions of various reactive sulfur species. By liquid chromatography coupled with mass spectrometry, we identified the sulfate adduct AO7-SO4 and confirmed the two-step reaction between AO7 and SO4(-). This stable sulfate adduct provides a good explanation of the poor TOC removal during decolorization of AO7 by the photo-iron(II) sulfite system.
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China. Electronic address: zdncug@163.com.
Danna
D
Zhou
Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, 430079, PR China.
Long
L
Chen
Agro-environmental Protection Institute, Ministry of Agriculture, Tianjin 300191, PR China.
Changbo
C
Zhang
Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, 430079, PR China.
Yingtan
Y
Yu
Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, 430079, PR China.
Li
L
Zhang
Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, 430079, PR China.
Feng
F
Wu
D001391:Azo Compounds / Q000737:chemistry* / Q000528:radiation effects*; D001557:Benzenesulfonates / Q000737:chemistry* / Q000528:radiation effects*; D002853:Chromatography, Liquid; D004396:Coloring Agents / Q000737:chemistry / Q000528:radiation effects; D005296:Ferrous Compounds / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D055668:Photochemical Processes; D013447:Sulfites / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000528:radiation effects*
D001391:Azo Compounds; D001557:Benzenesulfonates; D004396:Coloring Agents; D005296:Ferrous Compounds; D013447:Sulfites; D014874:Water Pollutants, Chemical; C014722:2-naphthol orange
Competition kinetics method; Ferrous sulfite complex; Photochemical reaction; Steady-state approximation; Sulfate adduct; Sulfate radical