Removal of bromothymol blue dye by the oxidation method using KMnO4: Accelerating the oxidation reaction by Ru (III) catalyst

Abstract

Oxidation is the preferred method that used for the removal of colored toxic dyes from wastewater. Various oxidizing agents such as permanganate ion, chromate ion, ferricyanide ion have been studied kinetically to remove these colored dyes from water. In compared to the other oxidizing agents, potassium permanganate is inexpensive, water-soluble, eco-friendly oxidant, and it can be used in acid, alkaline, and neutral conditions. In addition, it has been widely used for treatment of pollutants in drinking water and waste-water applications for over 50 years. In this work, the kinetics of bromothymol blue (BTB) oxidation by KMnO4 were investigated using a conventional spectrophotometer in neutral solutions. The oxidation reaction rates were accelerated to notable rates by using of Ru (III) as a homogeneous catalyst. The pseudo-1st - order model showed a 1st order in terms of both reactant's concentration, and 2nd overall reaction. The kinetic data indicated the founding of a 1:1 intermediate species with the intervention of free radicals into the reaction mechanism. At the reaction conditions of [BTB]=1 × 10–5, [MnO4–] = 4 × 10–4 mol dm–3, and 25 °C, the pseudo-first order rate constant values were calculated to be 1.13×10–4 s–1 without Ru (III) and 1.66×10–4 using Ru(III) as a catalyst (4 × 10–4 mol dm–3). Considering the kinetic results, a putative the mechanism of the reaction in the stated redox reaction is postulated and examined. Activation parameters without and with using of Ru (III) were calculated.