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Title of Thesis

Effects Of Solvents On The Reduction Of Methylene Green

Author(s)

Noshab Qamar

Institute/University/Department Details
Department Of Chemistry / Jinnah University For Women, Karachi
Session
2009
Subject
Chemistry
Number of Pages
247
Keywords (Extracted from title, table of contents and abstract of thesis)
Dielectric, Constant, Activation, Parameters, Binary Mixture, Single Sphere, Decoloration, Degradation, Solvents, Methylene, Effects, Green

Abstract
The photo reduction of methylene green (MG+) with ethylene diammine tetra acetic acid (EDTA) in aqueous alkaline and aqueous alkaline miscible organic solvent was carried out spectrophotometrically by visible light. Reaction was followed by change in opticaldensity of methylene green with time course. It was observed that change in solvent showed no significant change in wavelength but change in optical density showed the effect of solvent on dye reduction process. Therefore reaction was followed at λmax 658 nm. The influence of operational parameters, such as dye concentration, reductant concentration, change in pH, change in solvent composition, and change in ionic strength at different temperature revealed that these parameters strongly influence the decoloration of the dye. The apparent rate of decoloration was calculated from observed absorption data on the kinetics of bleaching of dye, showed that reaction follows pseudo first order kinetics. EDTA was found to be an effective reducing agent for the photo reduction of methylene green in aerobic condition. Consumption of EDTA in the reduction of methylene green leads to conclude that it is oxidized. This is an unexpected result since EDTA does not normally function as a reducing agent. The nitrogen containing chelating agents with secondary or tertiary nitrogen behaved, as electron donors in photochemical reduction of dye.
Results showed that dye reduction process depend upon the concentration of EDTA and alkali where as it was independent upon the dye concentration. The salting agent KNO3 has been found to decline overall rate of reduction of methylene green with EDTA in aqueous medium as well as in mixed solvent system. Detailed kinetics and thermodynamics aspects have been discussed in relevant section of discussion to realize the interaction between methylene green and EDTA. Regeneration of color was observed upon turning off source of light. Effect of increasing concentration (10-30%) of water miscible organic solvent (methanol and ethanol) on dye decoloration showed that rate of reaction increase as the dielectric constant of water decreases. Spectral intensities of dye in binary solvent mixture of different composition showed the dominating character of aqueous medium with no remarkable difference in values of λmax. This may be attributed to the similar reaction of H+ ion abstraction from reductant in mixed solvent system as in aqueous medium. During the course of study of the kinetics of reduction of methylene green, it was found that mixed solvent medium results in pronounced enhancement of rate in EDTA and at alkaline pH while in case of methylene green the following order was observed H2O > Methanol > Ethanol.
An attempt has been made to give an explanation of imperative role of dielectric constantof the medium taking into consideration of single sphere and double sphere complex in reaction mixture. Our study revealed that single sphere complex was found to be most suitable complex existed in the mixed organic solvent with dye and reductant. In presence of alkali and nitrate ion concentration the values of single sphere complex model were not coinciding with the values obtained theoretically in mixed solvent system. Therefore HPLC analysis was carried out to check the dye molecule degraded or not. HPLC analysis suggested that a significant amount of the dye degrade in presence of nitrate ion and alkali and additional peaks which may be off by product were produced. This leads to confirm the non identical values of single sphere and double sphere model in presence of nitrate and alkali. Rate of removal of color showed a linear relationship with respect to water content below 30% and temperature between 20- 40 oC where as increase in concentration of organic solvent showed the inhibition of dye decoloration at given optimum condition. Therefore study was restricted up to 30% of methanol/ ethanol binary mixtures.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 CONTENTS

 

 
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2

1

THEORETICAL ASPECTS

1.1 Methylene Green
1.2 Light, Color
1.3 Absorption Of Light
1.4 Dyes And Dye Stuffs
1.5 Auxochrome
1.6 Types Of Chromophore
1.7 Types Of Auxochromes
1.8 Water Soluble Dyes
1.9 Water Insoluble Dyes
1.10 Classification Of Dyes

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3 2 LITERATURE SURVEY

2.1 Photochemical Excited Species Of Methylene Green
2.2 Ionic Strength
2.3 Effect Of Ionic Strength On Rate Constant
2.4 Influence Of Temperature- Rate Constant On
2.5 Effect Of Ionic Strength On Energy Of Activation
2.6 Solvent Effect On Rate Constant Of Ionic Reaction
2.7 Single Sphere Activated Complex
2.8 Double Sphere Activated Complex
2.9 Reaction Of Photosensitized Dyes
2.10 Photodynamic And Photogalvanic Effect
2.11 Absorption Studies Of Thiazine Dyes
2.12 Photoreduction Reactions
2.13 Reaction Of Thiazine Dye With Edta
2.14 Reaction Of Thiazine Dyes With Inorganic Reductants
2.15 Reductions Of Thiazine Dyes With Organic Reductants
2.16 Photocatalytic Effect
2.17 Polymerization Of Methylene Blue
2.18 Photobleaching Of Thiazine Dyes
2.19 Aim Of The Present Work

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4 3 EXPERIMENTAL ASPECTS

3.1 Requirements Of Experiment
3.2 Reagents
3.3 Preparation Of Stock Solutions
3.4 Determination Of ?max And Molar Absorption Coefficient
3.5 Measurement Of Absorption Coefficent
3.6 Experiment Procedure

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5 4 RESULTS

4.1 Absorption Of Methylene Green
4.2 Maximum Absorbance Value
4.3 Effect Of Percentage Composition Of Solvent On Reduction Of Mg
4.4 Molar Absorptivity Coefficient Of Mg At Concentration 1 10-5 M In Various Solvent  Composition
4.5 Effect Of Alkaline Medium On Reduction Of Methylene Green With Edta In Aqueous And  In Mixed Solvent System
4.6 Effect Of Concentration Of Edta On The Reduction Of Methylene Green In Aqueous And  Mixed Solvent System
4.7 Effect Of Concentration Of Methylene Green On The Reduction In Aqueous And Mixed
Solvent System
4.8 Effect Of Ionic Strength On Rate Of Reduction Of Methylene Green In Aqueous And  Different Percentages Of
Solvent
4.9 Influence Of Temperature On Rate Constant Of Reduction Of Methylene Green With  Edta In Aqueous And Mixed
Solvent System 

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6 5 DISCUSSION


5.1 Photo Reduction Of Methylene Green
5.2 Absorption Spectra Of Methylene Green In Aqueous And Mixed Solvent System
5.3 Kinetics Of Reduction / Degradation / Decoloration Study Of Methylene Green
5.4 Variation Of Ph On Rate Constant Of Reduction Of Methylene Green With Reductant
5.5 Edta As A Reducing Agent In Alkaline Medium With Methylene Green
5.6 Relation Between Edta And Rate Constant “ K” In Aqueous Medium
5.7 Reduction Of Methylene Green By Edta In Aqueous Methanol
5.8 Reduction Of Methylene Green By Edta In Aqueous Ethanol
5.9 Effect Of Ionic Strength On Reduction Of Methylene Green In Aqueous And Mixed Solvent System
5.10 Influence Of Temperature And Ionic Strength On Reduction Of Methylene Green By Edta
5.11 Thermodynamics Activation Parameters Of Chemical Reduction Of Methylene Green With Edta.
5.12 Activation Parameters Of The Reaction
5.13 Effect Of Dielectric Constant On Activation Parameters
5.14 Effect Of Dielectric Constant Of Medium On Rate Of The Reaction
5.15 Radii Of Activated Complex
5.16 Theoretical Calculation Of Radii Of Activated Complex
5.17 Comparison Of The Values Of Radii Of Activated Complex
5.18 Mecanism Of Effect Of Visible Radiation On Solvent Molecule
5.19 Mecanism Of Dye Reduction In Solvent
5.20 Mecanism Of Reduction Of Methylene Green With Edta
5.21 Hplc Analysis Of Reaction Mixture For The Confirmation Of Values Of Ionic Radii In Mixed Solvent System
5.22 Comparison With Earlier Work
5.23 Comparisinof Effect Of “ K” Rate Constant
5.24 Comparision Of Effect Of Ph
5.25 A Comparision Of Effect Of Temperature
5.26 Conclusion
5.27 Research Application And Importance
5.28 Future Prospective
5.29 Research Project Patentability

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7 6 REFERENCES

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