Study on the mechanism of high effective mineralization of Rhodamine B in three dimensional electrochemical system with γ-Fe2O3@CNTs particle electrodes

Three-dimensional electrochemical reactor (3DER) is an efficient technology for the treatment of printing and dyeing wastewater. The particle electrode between anode and cathode is the core unit of 3DER, which determines the treatment efficiency of wastewater. However, the deactivation of the particle electrode caused by the coverage of the catalytic sites seriously hindered the continuous operation of 3DER. In this work, γ-Fe2O3@CNTs particle electrode was prepared by immersion calcination, and its performance was evaluated by degradation of Rhodamine B (RhB) wastewater in 3DER. The study showed that in γ-Fe2O3@CNTs/Mn@FNE-3DER, the removal rate of RhB reached the best of 99.16% within 7 min under the conditions of γ-Fe2O3@CNTs dosage of 1.00 g·L-1, initial RhB concentration of 100 mg·L-1, pH 7.0, and current density of 20 mA·cm−2. The superior catalytic activity of the system is mainly due to the charge transfer channel in γ-Fe2O3@CNTs structure, which improves the mass transfer efficiency of electrons. According to LC-MS analysis, the degradation process of RhB can be divided into five stages: deethylation, chromophore cracking, debenzylation and deamination, ring opening and mineralization. Hydroxyl radicals play an important role in this process. After the reaction, most RhB is converted into CO2 and H2O. In addition, the study also showed that the Fe3+/Fe2+ circulating system formed between the anode and cathode was the important reason for the high degradation efficiency of RhB. After five cycles of experiments, the degradation efficiency of 92.55% was still maintained, indicating that the particle electrode has significant stability and reusability in the catalytic process. To sum up, the excellent performance of γ-Fe2O3@CNTs particle electrode in three-dimensional electrochemical system provides a promising idea for the actual treatment of printing and dyeing wastewater.