Synthesis, structural characterization, DFT, kinetics and mechanism of oxidation of bromothymol blue: application to textile industrial wastewater treatment

Oxidation of bromothymol blue [BTB] by oxyanion potassium permanganate as a strong oxidizing agent in acid solutions using perchloric acid at a constant ionic strength has been obtained keto bromothymol blue [BTB] Keto and studied kinetically spectrophotometrically. Different characterization techniques for [BTB] and [BTB] Keto such as Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), and optical properties have been used. The order about the permanganate ion is first, while a fractional first order was released as regards [H + ] and [BTB] fractional first order. Dependence on the concentration of hydrogen ions in the concentrations indicates that the oxidation process is acid catalyzed. The absence of either transient Mn III and/or Mn IV as involving species in the oxidation process was verified by Mn II applied to the oxidation reaction. Formation of 1:1 intermediate complex formation kinetically was revealed during the rate-determination step. In the slowest step, two-electron transfer processes of the inner-sphere form have been proposed. A mechanism of the tentative reaction was proposed and explored concerning kinetic parameters. The density functional theory ( DFT ) by DMol 3 and CASTEP was used for the optimization of dye [BTB] and [BTB] Keto as an isolated molecule. From the UV–Vis spectrum of [BTB] and [BTB] Keto , the E Direct Opt values are 2.849 eV and 2.35 eV using Tauc`s equation, respectively, related to direct transitions of electrons. Using DMol 3 method with DFT simulation, the HOMO and LUMO values for [BTB] and [BTB] Keto as isolated molecule are 3.047 eV and 2.869 eV, respectively. The simulated FTIR, molecular electrostatic potential (MEP) and optical properties by Gaussian software and CATSTEP are in great agreement with the experimental study. Graphic Abstract