Degradation of indigo carmine dye with peroxydisulphate ion in aqueous sulphuric acid phase: Kinetic study

The quest for cleaner environments is a global concern. Hence, the investigation of degradation of the indigo carmine dye (IC) with peroxydisulphate ion in an aqueous sulphuric acid system with a view to understanding its kinetic degradation and mechanism. The degradation depicts first-order kinetics in [S₂O₈²⁻] and [IC], and the degradation mole ratio of IC: S₂O₈²⁻ is 1:1. The degradation rate is dependent on the change in ionic strength and medium permittivity of the system. Also, added ions (NH₄⁺ and NO₃⁻) influence the degradation rate of the dye which further supported the outcome of the change in ionic strength. Free radical participation is ruled out. The experimental rate law is given as (Kk₃[H⁺])[IC][S₂O₈²⁻]. Owing to the absence of detectable intermediates in the degradation process, an outer-sphere mechanism is proposed. The study is significant in textile industries and medical settings for making environments less toxic with a well-understood degradation rate pathway.