Photo-Assisted Oxidation of Indigocarmine in an Acid Medium

Abstract

The kinetics of photo-oxidation of indigocarmine dye—5,5-indigosulfonate disodium (5,5-IDS)—in an acid medium has been studied to discover the effect of different parameters in the efficiency of the process. The experiments were conducted applying ultraviolet (UV)-polychromatic radiation to oxygen-saturated solutions. All kinetic experiments showed that the dye reaction order was zero, and its initial concentration did not influence the experimental rate constant. An increase in the rate was observed with an increasing UV radiation dose (D_uv) and/or the acidity. Temperatures—ranging from 290 K to 320 K—did not significantly affect the rate constant, indicating the photochemical activation of the oxidative process. 5-Isatinesulfonate sodium (5-IS) was identified as a photo-oxidation product. The effluent of the phototreatment had no color and contained no toxic products. Results showed that UV-induced oxidation of 5,5-IDS dye in an oxygensaturated aqueous medium, at room temperature, is an alternative treatment to conventional chemical oxidation for the decoloring of indigoid-dye wastewater from the textile industry.