Decolorization of Rhodamine B by Fenton Processes Enhanced by Cysteine and Hydroxylamine Reducers

Fe3+-reducing agents have been used to enhance Fenton process efficiency in degrading dyes commonly found in textile wastewater. The present work consisted of evaluating the effect of two compounds that reduce Fe3+, cysteine (Cys) and hydroxylamine (HA), on the oxidative decolorization of Rhodamine B dye by homogeneous Fenton processes, Fe2+/H2O2 and Fe3+/H2O2. The kinetics of the reactions were analyzed to better interpret the decolorization data. Due to the addition of the two reducing agents and the increase in temperature, there were increases in decolorization and the values of the reaction rate constants. The first-order reaction kinetic model was the one that best fit the experimental data. Comparing the two reducers, Cys was more effective. As an example, for reactions initially containing Fe2+ in just 20 min and at a temperature of 30 °C, the HA and Cys reducers increased the decolorization from 33% to 48% and 64%, respectively. It was possible to verify a decrease in the activation energy (Ea) due to the presence of the two reducing agents, but more significantly for reactions containing Fe3+. The values of Ea to Fe3+/H2O2, Fe3+/H2O2/Cys, and Fe3+/H2O2/HA were 85.7, 52.2, and 50.9 kJ∙mol−1, respectively. This way, it can be inferred that the two reducers decreased the energy barrier to enhance the Fenton-based oxidation of Rhodamine B.