Ponceau 6R dye decoloration and chromate reduction simultaneously in acid medium

Abstract

The degradation efficiency and kinetic degradation reaction of Ponceau 6R dye using potassium chromate have been investigated under various experimental conditions: different concentrations of H₂SO₄ and temperatures. The immediate change of the red coloration (λ_max = 518 nm) to colorless was observed after addition of inorganic oxidizing agent (K₂CrO₄) into the protonated form of Ponceau 6R dye after 48 h. This observation could be attributed to the highest oxidized form of this dye obtained (the quinoid one), which undergoes a hydrolysis reaction to produce p-hydroquinone (H₂Q) by a mechanism similar to Schiff-base hydrolysis. The cationic form of this matrix is a crucial feature for the hydrolysis process. A kinetic model for oxidation of Ponceau 6R by the combination of chromate was developed based on experimental results. The observed kinetic reaction coefficient was determined and correlated as a function of UV spectral intensity of Ponceau 6R at 518 nm. The degradation rate follows pseudo-first order kinetics with respect to dye concentration.