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Kinetics and Mechanism of Birnessite Reduction by Catechol

^a Dep. of Agronomy, Univ. of Kentucky, N-122 Ag. Sci. Ctr-North, Lexington, KY 40546-0091
^b Dep. of Plant and Soil Sciences, 147 Townsend Hall, Univ. of Delaware, Newark, DE 19717-1303
^c William R.Wiley Environmental Molecular Sciences Lab. (EMSL), Pacific Northwest National Lab., Richland, WA 99352

View larger version (24K): [in a new window]   Fig. 1. (A) Representative room temperature EPR spectra of 100 µM MnT as birnessite (0.45 m2 L-1) reacted with catechol (5 x 10-3 M) depicting the characteristic six-line spectra of the Mn(II) product. H0 and H1 indicate the peak and valley used to quantify Mn(II) concentrations. (B) Intercalibration standard curve relating EPR signal intensity at the 0.3435 T (H0) peak to flame AAS Mn(II) concentration

View larger version (11K): [in a new window]   Fig. 2. Typical stoichiometry of H+ consumed versus dissolved Mn(II) produced during birnessite reduction by catechol

View larger version (22K): [in a new window]   Fig. 3. Representative EPR-SF kinetics of reductive dissolution of birnessite by catechol at pH 4 as a function of [CAT] conducted at 23°C and 0.45 m2 L-1 [SA]

View larger version (14K): [in a new window]   Fig. 4. Initial rate of dissolved Mn(II) release measured by the EPR-SF technique as a function of: (A) [CAT] at pH 4 and 0.90 m2 L-1 [SA]; (B) [SA] at pH 4 and 5 (10-3 M [CAT]; and (C) [H+] at 0.90 m2 L-1 [SA]. The dotted lines represent the 95% confidence interval bands

View larger version (13K): [in a new window]   Fig. 5. Kinetics of catechol oxidation to o-quinone by birnessite and dissolved Mn(II) release at 23°C. Experimental conditions were: , , pH 4,

View larger version (14K): [in a new window]   Fig. 6. Activation parameters derived from (A) Arrhenius and (B) Eyring plots describing the reductive dissolution of birnessite by catechol