Pre-oxidative catalytic treatment of toluidine blue with potassium permanganate in acidic solution

This article describes the potential of KMnO₄ for oxidation of the thiazine dye (Toluidine blue TB) in an acidic medium. The effect of different operational parameters like initial concentration of dye, potassium permanganate, pH, ionic strength, catalyst, acids and temperature were investigated spectrophotometrically at λ _max = 613 nm. The results showed a complete removal of the TB with mineralization of the dye solution. Smooth and complete decoloration was observed in the presence of monobasic acid (HCl) as compared to the H₂SO₄ where little color removal was observed. Pb was found to be an effective catalyst in oxidation for complete and fast decolorization with mineralization. No significant change at elevated temperatures showed that an intermediate complex degraded with slight change in the temperature. UV/visible spectrophotometry and GC mass analysis showed an intermediate activated complex demethylated sulophooxide of TB which later on degraded into smaller fragments.