Decolorization of reactive orange 16 azo dye in wastewater using CAT/ IrCl3/HClO4 redox system: Delineation of kinetic modeling and mechanistic approaches

- Optimum conditions for CAT/IrCl3/HClO4 redox system have been established.
- Mechanistic schemes and kinetic modelings have been worked out.
- Toxicity analysis, cost analysis and COD were determined for RO16 dye.
- IrCl3 catalyzed reactions is six-fold faster than uncatalyzed reactions.
- This method can be adopted for treating RO16 dye present in industrial wastewater.

Reactive orange 16 (RO16) is a reactive azo dye, which is chiefly used in textile industry. In the present research, a simple and expeditious decolorization technique has been developed for the removal of this dye present in the wastewater. Kinetics and oxidative decolorization of RO16 dye with chloramine-T (CAT) in HClO4 medium catalyzed by iridium (III) chloride (IrCl3) have been investigated spectrophotometrically (λmax = 496 nm) at 303 K. The reaction exhibited a first-order dependence of rate on [CAT]o and [RO16]o respectively. The rate of the reaction was retarded with increase in [H+] and shows an order less than unity. The order with respect to [IrCl3] was fractional. Oxidation products were identified as 6-acetamido-3,4-dioxo-3,4-dihydro naphthalene-2-sulfonic acid and 2-(phenyl sulfonyl)-ethyl hydrogen sulphate by mass spectral analysis. IrCl3 catalyzed decolorization reaction is about six times faster than the uncatalyzed reaction. Activation parameters have been computed. The kinetic modelings and mechanistic pathway have been worked out. The oxidative decolorization process has significantly reduced the COD. Phytotoxicity studies demonstrated that the treated dye was less toxic than untreated dye sample. Economic analysis was performed. Notably, the developed oxidative decolorization technique is expected to be helpful for treating RO16 dye present in industrial wastewater with suitable modifications.

Graghical abstractThe stoichiometry of the reaction is in the mole ratio of 1:1(RO16:CAT) in HClO4 medium catalyzed by IrCl3 as shown here:118