Decolorization and degradation of Indigo Carmine dye from aqueous solution catalyzed by horseradish peroxidase

Abstract

We have studied the kinetics of decolorization of aqueous solutions of the dye Indigo Carmine and its biocatalytic degradation by the enzyme horseradish peroxidase (HRP). Experiments were carried out with a dye concentration of 2.5 × 10⁻⁵ mol L⁻¹ over a temperature range of 25–60°C and decolorization was monitored spectrophotometrically at 610 nm. Furthermore, the concentration of H₂O₂ (30%, 3%, 0.3%, 0.03% and 0.003%), essential for enzyme activation, the pH (4, 5, 6, 7, and 8) and the amount of enzyme (1, 2, and 3 mg) were varied. In the kinetic studies, it was observed that the decolorization curves followed first-order kinetics, which were used to determine the rate constants which ranged from 10⁻² to 10⁻³ min⁻¹, proving this to be a fast process, with color disappearance between 30 and 60 min. Acid conditions pH (4, 5, and 6), temperatures between 40°C and 60°C and hydrogen peroxide concentration between 0.3% and 0.003% with 2 mg of HRP enzyme, favored decolorization. The kinetic parameters [activation energy (E_a), activation enthalpy (ΔH^#), activation Gibbs energy (ΔG^#), and activation entropy (ΔS^#)] were determined using the Arrhenius and Eyring equations. The results obtained for the best experimental conditions were as follows: E_a = 15.6 kJ mol⁻¹, ΔH^# = 18.2 kJ mol⁻¹, ΔG^# = 7.3 kJ mol^{− 1}, and ΔS^# = 0.036 kJ mol⁻¹ K⁻¹, with an efficiency of 99% of decolorization. Studies showed that HRP combined with H₂O₂ is effective in the decolorization and degradation of the Indigo Carmine dye.

Keywords::

• Horseradish peroxidase
• Indigo Carmine
• decolorization
• degradation

Acknowledgments

The authors would like to thank INCT Catalysis and FAPESC (Santa Catarina, Brazil) for financial support and Toyobo do Brasil for the donation of the enzyme.

Declaration of interest: The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.