Kinetics of oxidation of transition-metal ions by halogen radical anions. Part I. The oxidation of iron(II) by dibromide and dichloride ions generated by flash photolysis

Thornton, Andrew T.; Laurence, Gerald S.

doi:10.1039/dt9730000804

Cited by 65 publications

(30 citation statements)

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“…The absorption band up to 2 ms follows the pattern observed for the transient absorption in the microsecond time domain (Figure 1). Due to the make up of the solution used in Figure 2 the long-lived transient signal is ascribed to photoinduced charge separation in agreement with observations by flash photolysis on FeCl3 carried out with longer period of light excitation (25). This photobleaching signal is due to the formation of Fe(II) species absorbing less than in the ground state at λ ) 380 nm.…”

Section: Resultssupporting

confidence: 85%

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Primary Photochemical Reactions in the Photo-Fenton System with Ferric Chloride. 1. A Case Study of Xylidine Oxidation as a Model Compound

Надточенко

Kiwi

1998

Environ. Sci. Technol.

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Environmental contamination in groundwater involving a variety of nonbiodegradable toxic xylidines from industrial or military effluents is a matter of growing concern. Besides the traditional nondestructive treating methods to remove these substances in water bodies, the application of advanced oxidation technologies such as Fenton photoassisted reactions seems a suitable way to remove and mineralize these contaminants and is the aim of the present study. Primary photochemical reactions in the water solutions of ferric chloride complexes in the absence and in the presence of H 2 O 2 were examined by laser photolysis (λ ) 347 nm) using xylidine (2,4-dimethylaniline, XYL) as probe molecule. The Cl 2 •radicals are formed as a result of the reaction of Cl • atoms and OH • radicals produced during the photodissociation of ferric chloride and ferric hydroxy complexes in the presence of Clanion. The oxidation of xylidine by Cl • or Cl 2 •lead to the formation of the XYL + radical-cation [C 8 H 9 NH 2 ] •+ , having an absorption maximum at λ ) 420 nm which was unambiguously identified by pulsed laser spectroscopy. The decay of XYL + radicals in solution takes place within 2 ms in a secondorder reaction with 2k ) 10 9 (M s) -1 . In solutions containing XYL/H 2 O 2 /FeCl 3 , increasing the oxidant concentration increased the amount of XYL + , indicating that the H 2 O 2 competes with the Cland XYL for the available Cl • in solution. This was not the case of the anion-radical Cl 2 •-. To decide if the radical Cl 2 •or ClOH •prevails after photoexcitation of ferric chloride solutions, a reaction scheme was considered for the formation of the radicals at acidic pH through simultaneous differential equations. The reaction sequence could be kinetically modeled on the basis of laser spectroscopic measurements. The rate constant of Cl 2 •with XYL was found (3.7 ( 0.3) × 10 7 (M s) -1 . Cl • atoms oxidize XYL in the reaction with a constant (4.0 ( 2.0) × 10 10 (M s) -1 . The Cl • atoms react with H 2 O 2 with (1.8 ( 0.7) × 10 10 (M s) -1 . The reaction of Cl • atoms with H 2 O 2 explains the decrease observed for XYL •+ and Cl 2 •radicals in solution with increasing H 2 O 2 concentration. The latter rate constant was observed to be about 5 orders of magnitude higher than the rate constant for the reaction k(Cl 2 •-+ H 2 O 2 f 2Cl -+ H + + HO 2 • ) ) (9.0 ( 0.4) × 10 4 (M s) -1 .

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Section: Resultssupporting

confidence: 85%

“…work (24)(25)(26)(27). To decide if radical Cl2 •or ClOH •prevails after photoexcitation in ferric chloride solutions, the complete scheme shown in Table 2 should be considered for the formation of radicals in solution.…”

Section: Resultsmentioning

confidence: 99%

Primary Photochemical Reactions in the Photo-Fenton System with Ferric Chloride. 1. A Case Study of Xylidine Oxidation as a Model Compound

Надточенко

Kiwi

1998

Environ. Sci. Technol.

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“…A simple calculation ( Millero et al ( 1987) d Moffett and Zika ( 1987b ), Millero and Sotolongo ( 1989) e Mopperand Zhou (1990) f Christensen and Sehested ( 1981) g Morel and Hering ( 1993) h Thornton and Laurence ( 1973) i See Rush and Bielski ( 1985) m Rate constants for photoreduction of dissolved and colloidal Fe( Ill) were calculated as follows: Dissolved Fe(///): From the pH-dependence of the reduction rate of Fe(///) in chloride solutions, King et al ( 1993) concluded that F eOH2+ is the dominant photoreactive inorganic Fe( III) complex in seawater. At pH 8, aFeOH2+ ~ 10-5 and therefore the first-order rate constant/or photoreduction of dissolved Fe( III) is approximately equal to: k = 10-5 x 0.15 min-1 = 2 x 10-6 min-1.…”

Section: Introductionmentioning

confidence: 99%

Iron Redox Cycling in Surface Waters: Effects of Humic Substances and Light

Voelker

Morel

Sulzberger

1997

Environ. Sci. Technol.

373

323

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The purpose of this study is to examine the mechanism of photo-oxidation of natural dissolved organic matter (DOM) in the presence of iron. This process is of interest in natural waters for several reasons: as a significant sink of DOM in sunlit surface waters; as a source and sink of reactive oxygen species (HO2/O2 •-, hydrogen peroxide, and HO•) and as a factor controlling iron speciation. Studies were conducted in laboratory model systems containing fulvic acid and lepidocrocite (γ-FeOOH) particles at pH 3 and pH 5, irradiated with simulated sunlight. Measured concentrations of dissolved Fe(II), total dissolved Fe, and hydrogen peroxide were interpreted as the net effects of competing reactions reducing and oxidizing Fe and producing and destroying hydrogen peroxide. A kinetic model constructed using information gained from separate experiments in simpler systems was used to assess the relative importance of individual reactions. Comparison of photoreductive dissolution rates in aerated and de-aerated systems at pH 3 and pH 5 indicated that the decrease in rate with increasing pH is mostly due to a decrease in the concentration of surface Fe(III)−fulvate complexes and that, in the presence of oxygen, some of the surface Fe(II) is re-oxidized (not necessarily by oxygen) before detachment can take place. Kinetic modeling indicated that fast redox cycling of Fe occurs at both pH values. The dark reduction of Fe(III) by fulvic acid and photochemical ligand-to-metal charge transfer reactions of dissolved Fe(III)−fulvate complexes play almost equally significant roles in the reduction of dissolved Fe(III). The main oxidants of dissolved Fe(II) are HO2/O2 •- (produced via reduction of O2 by photo-excited fulvic acid) and hydrogen peroxide [the product of Fe(II) reaction with HO2/O2 •-].

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“…[88][89][90] The reactions of Cl 2 À , Br 2 À , and I 2 À with Cr 2 þ are also similar. 91 The same radicals react with V 2 þ through an outer-sphere mechanism because of the relatively slow rate of ligand exchange.…”

Section: Electron Transfermentioning

confidence: 67%

Reactivity of Inorganic Radicals in Aqueous Solution

Stanbury

2010

Physical Inorganic Chemistry

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Kinetics of oxidation of transition-metal ions by halogen radical anions. Part I. The oxidation of iron(II) by dibromide and dichloride ions generated by flash photolysis

Cited by 65 publications

References 0 publications

Primary Photochemical Reactions in the Photo-Fenton System with Ferric Chloride. 1. A Case Study of Xylidine Oxidation as a Model Compound

Primary Photochemical Reactions in the Photo-Fenton System with Ferric Chloride. 1. A Case Study of Xylidine Oxidation as a Model Compound

Iron Redox Cycling in Surface Waters: Effects of Humic Substances and Light

Reactivity of Inorganic Radicals in Aqueous Solution

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