Kinetics and mechanism of the non-catalyzed and copper (II) catalyzed oxidation of thionine and methyl violet dyes with hydrogen peroxide. A model for waste water treatment from textile industry.

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Time resolved spectra for the oxidation of 3.34 x 10-5 M of thionine with M hydrogen peroxide in presence of 3.34 x10-5 of Cu +2 at 40oC and pH =

Effect of initial hydrogen peroxide conc. on initial reaction rate for the reaction of H 2 O 2 with 3.34 x M thionine dye (left figure) and methyl violet (right figure) at pH = 7.0, 40 o C, in absence (b) and in presence of 3.34 x 10-5 M Cu +2 (a). 3

Dependence of the initial rate on the initial concentration of thionine for its reaction with M hydrogen peroxide at 25 o C and pH =

Dependence of the initial reaction rate on the initial concentration of Cu +2 for the reaction of H 2 O 2 with 3.34 x M thionine (left figure) and methyl violet (right figure) at pH = 7.0 and at different temperatures. 5

Variation of the initial reaction rate with pH 6

√μ / (1+√μ) Variation of the rate constant with the ionic strength for the oxidation of Thionine (left) and Methyl Violet (right) dyes. 7

Decomposition of hydrogen peroxide with copper (II) in absence and in presence of 4% t-butanol at 25oC. Variation of the initial reaction rate with different concentrations of SDS 8

Reaction mechanism and rate equation for the non-catalyzed reaction H 2 O 2 + H + DH + + DH (HO 2 ) Peroxo-dye intermediate DH(HO 2 ) oxidation products (slow) Rate = The rate attains a first-order dependence on the substrate, a first-order dependence on hydrogen peroxide only at lower concentrations, and is inversely proportional to [H + ]. However, the order of reaction in H 2 O 2 decreases with increasing concentration and becomes zero at very high concentrations. 9

Reciprocal initial rate versus reciprocal initial hydrogen peroxide concentration for the oxidation of 3.34 x M methyl violet at pH = 7.0 and 25 o C. k 2 and k 3 values for methyl violet system were calculated from the corresponding figure and found to be equal to 3.16 X 10 2 mol -1 L s -1 and 5.65 X s - 1 respectively, 10

Reaction mechanism and rate equation for copper catalyzed reactions Cu 2+ + H 2 O 2 Cu 2+ (OOH) + 2 H + 11

Reciprocal initial rate versus reciprocal initial hydrogen peroxide concentration for the oxidation of 3.34 X M Dye at pH = 7.0 in the presence of 2.0 X M of Cu 2+ k 7 values are equal to 5.34 X 1010 M -1 s -1 and 6.89 X 1010 M -1 s -1 for thionine and methyl violet at 40 o C and 25 o C respectively. k 4, gave values of 2.50 X and 7.94 X mol -1 Ls -1 for thionine and methyl violet at 40 o C and 25 o C 12

Methyl VioletThionine % element Product C 8 H 10 NOCl Pure Product C 12 H 11 N 3 OS Pure foundcalculatedfoundcalculatedfoundcalculatedfoundcalculated C % H % N % S % Elemental analysis and IR spectra for the dye and its degradation products 13

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