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Oxidation Kinetics of Organics Using Hydrogen Peroxide Catalyzed by "free" and Complexed Iron

出版	Vanderbilt University, 1998
URL	http://books.google.com.hk/books?id=JJrgNwAACAAJ&hl=&source=gbs_api

註釋The oxidation kinetics of refractory organics (substituted phenols, anilines, chlorobenzene were used as substrates) were investigated using hydrogen peroxide catalyzed by "free" and complexed iron over the pH range of 3 to 10. Fe(II) and Fe(III) in "free" form (aqueous solution of ferrous or ferric salts), or, complexed with NTA, EDTA, EGTA, DTPA, CDTA, or, TTHA, were used for catalytic activation of hydrogen peroxide. The kinetics of hydrogen peroxide decomposition catalyzed by "free" and complexed iron were initially investigated without the presence of substrate. A kinetic model for "free" iron catalyst was derived assuming the rate limiting formation of a reversible complex (Fe-HO2), followed by an irreversible decomposition. This resulted in a first order rate law at low H2O2 concentrations and a maximum or zero order rate at high H2O2 concentrations. The use of complexed-iron catalysts extended the region of activity from pH of 2 to 10 versus 2 to 4 when "free" iron was used. A rate expression for Fe(III) complexes was derived using a mechanism similar to that of "free" iron. A transient Ligand-Fe-HO2 complex was reversibly formed, which subsequently decayed irreversibly into products. The kinetics of substrate oxidation using hydrogen peroxide catalyzed by "free" and complexed iron were studied and kinetic model for substrate oxidation was developed assuming that the rate-determining step is the formation of a reversible intermediate complex between catalyst (in "free" or complexed form), substrate and hydrogen peroxide. The substrate is oxidized upon the irreversible decomposition of the complex. The experimental data for substrate oxidation were analyzed using the method of initial rates. The analysis of the data supported the proposed kinetic model and assumed reaction mechanism. With regards to pH, "free" iron was active catalyst only at low pH 3 to 4, and only when used in reduced form, i.e., as Fe(II). The Fe complexes, Fe-L, catalyzed the oxidation over the entire pH range from 2 to 10. The initial rates of substrate oxidation and hydrogen peroxide decomposition were higher at low pH (the maximum was at pH 3-4), and two to three orders of magnitudes lower in the neutral and alkaline ranges. The rate of substrate oxidation was functionally proportional to the rate of hydrogen peroxide decomposition for "free" and complexed forms of iron catalyst. After treatment with "free" and complexed iron and hydrogen peroxide the aqueous toxicity of dichlorophenols, nitrophenol, and phenol, were eliminated or significantly reduced. With regards to toxicity reduction the optimal ratios of reagents in terms of Substrate:Oxidant:Catalyst (S:O:C) were in the range of 1:10:1 to 1:30:3