Determination of Activation Energy from Decolorization Reactions of Synthetic Dyes by Fenton Processes Using the Behnajady–Modirshahla–Ghanbary Kinetic Model

Abstract

The present work used the Behnajady–Modirshahla–Ghanbary (BMG) kinetic model to determine the initial reaction rates (1/m), which were used to calculate the activation energy (Ea) from the decolorization of synthetic dyes by Fenton processes (Fe2+/H2O2, Fe2+/H2O2/reducer and Fe3+/H2O2/reducer). When increasing the temperature and adding Fe3+-reducing compounds (3-Hydroxyanthranilic Acid, Hydroquinone, Gallic Acid, Cysteine or Ascorbic Acid), increases in the 1/m values were observed. When studying the classical Fenton reaction (Fe2+/H2O2), almost all added reducers had decreased Ea. For example, 3-Hydroxyanthranilic Acid decreased the Ea related to the decolorization of the Phenol Red dye by 39%, while Ascorbic Acid decreased the Ea of Safranin T decolorization by 23%. These results demonstrate that the reducers increased the initial reaction rate and decreased the energy barrier to improve Fenton-based decolorization of dyes. When comparing the reaction systems in presence of reducers (Fen+/H2O2/reducer), the reactions initially containing Fe2+ presented lower Ea than reactions catalyzed by Fe3+. That way, the activation energy obtained through the 1/m values of the BMG model highlighted the pro-oxidant effect of reducers in Fenton processes to degrade dyes.