title: Identification of the reactive oxygen species responsible for carbon tetrachloride degradation in modified Fenton's systems.
abstract: The reactive oxygen species responsible for the transformation of carbon tetrachloride (tetrachloromethane, CT) by modified Fenton's reagent using hydrogen peroxide (H2O2) concentrations >0.1 M was investigated. Addition of the hydroxyl radical scavenger 2-propanol to modified Fenton's reactions did not significantly lower CT transformation rates. Scavenging by 2-propanol not only confirmed that hydroxyl radicals are not responsible for CT destruction, but also suggested that a major product of an iron (III)-driven initiation reaction, superoxide radical anion (O2-), is the species responsible for CT transformation. To investigate this hypothesis, CT degradation was studied in aqueous KO2 reactions. Minimal CT degradation was found in CT-KO2 reactions; however, when H2O2 was added to the KO2 reactions at concentrations similar to those in the modified Fenton's reactions (0.1, 0.5, and 1 M), CT degradation increased significantly. Similar results were obtained when 1 M concentrations of other solvents were added to aqueous KO2 reactions, and the observed first-order rate constant for CT degradation correlated strongly (R2 = 0.986) with the empirical solvent polarity (E(T)N) of the added solvents. The results indicate that even dilute concentrations of solvents, including H202, can increase the reactivity of O2- in water, probably by changing its solvation sphere. The higher reactivity of O2- generated in modified Fenton's reagent, which has a less polar nature due to the presence of H2O2, may result in a wider range of contaminant degradation than previously thought possible.
authors.affiliation: Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington 99164-2910, USA.
authors.forename: Brant A
authors.initials: BA
authors.lastname: Smith
authors.forename: Amy L
authors.initials: AL
authors.lastname: Teel
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Watts
mesh_terms: D002251:Carbon Tetrachloride / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D017382:Reactive Oxygen Species / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013481:Superoxides / Q000737:chemistry*; D014835:Volatilization; D018505:Waste Management / Q000379:methods
chemical_list: C045076:Fenton's reagent; D017382:Reactive Oxygen Species; D012997:Solvents; D013481:Superoxides; C039316:potassium superoxide; D006861:Hydrogen Peroxide; D002251:Carbon Tetrachloride; D007501:Iron