Several properties of thiourea and its derivatives are reported in biological, electrochemical, photochemical and radio-protective fields. This article proposed the use of thiourea derivative in the field of dye wastewater management where the color of the dye was reduced by the application of Diethylthiourea (DETU). For this purpose basic dye methylene green (MG) was selected at laboratory scale to monitor its color reduction by the addition of DETU. It was observed that DETU reacts with methylene green (MG) and reduced it into leuco dye where it oxidized into smaller fragments like urea, nitrate and sulphate. The reaction was favorable in acidic condition. A direct relation in between oxidation of DETU and MG to the concentration of H+ ions was observed through typical kinetics in two acids like HCl and H2SO4. The second order kinetics with respect to HCl and the first order with respect to H2SO4 indicated the protonation of the dye leading to reduction. In alkaline medium, the decline in the rate of reaction may be due to the suppressing effects of alkali on oxidation/degradation of DETU into smaller fragments or may be attributed with the de-protonation of DETU. Influence of addition of dye into reaction mixture retarded the bleaching process and follows zero order kinetics while rate of reaction enhanced by the addition of DETU in the reaction mixture and shows ¾th order with respect to DETU. Negative effect of added different electrolytes reflects that change of ionic strength of reaction mixture have some bearing on redox reaction of MG and DETU. Reaction was monitored at elevated temperature and activation parameters were computed. The mechanisms of oxidation of DETU with reduction of dye MG were discussed. Reduction of MG into leuco dye with the fragmentation of DETU was observed in acidic condition at elevated temperature.

Author(s) Details

Dr. Tehseen Ahmed
Department of Chemistry, University of Karachi, Karachi-75270, Pakistan.

Dr. Rafia Azmat
Department of Chemistry, University of Karachi, Karachi-75270, Pakistan.

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