Application of response surface methodology for optimization of reactive black 5 removal by three dimensional electro-Fenton process

The electrocatalytic degradation of reactive black 5 (RB5) from aqueous solutions was studied in a three dimensional electro-Fenton process (3DEF) using the Ti/TiO2-RuO2-IrO2 anode electrode in the presence of magnetic multi-walled carbon nanotube (MWCNTs/Fe3O4). The response surface methodology (RSM) was used to determine the effect of various parameters on the RB5 and COD removal efficiency, the production of H2O2, and the energy consumption. The results showed that the 3DEF system with MWCNTs/Fe3O4 worked at a wide range of pH from 4 to 6 without significant reduction in efficiency. Electrochemical production of H2O2 increased with increasing the concentrations of MWCNTs/Fe3O4 and decreasing the initial pH. The results also indicated an increase in the RB5 and COD removal efficiency in 3DEF system than various electrocatalytic processes. The efficiency enhancement is related to more production H2O2 and center dot OH on MWCNTs/Fe3O4 surface. The MWCNTs/Fe3O4 nanocomposites indicated a high degree of stability and reusability. The reactive oxygen species (ROSs) like center dot OH, HO2 center dot and O-2 center dot(-) were generated in the reaction and center dot OH was the main oxidizer for the removal of RB5. To achieve maximum removal of RB5 and COD, optimized condition was found at solution pH of 5.13, MWCNTs/Fe3O4 concentration of 55.27 mg/L, current density of 15.86 mA/cm(2), and electrolysis time of 57.91 min. A mechanism for production of ROSs and its catalytic decomposition using MWCNTs/Fe3O4 nanocomposites is proposed. The results of the GC-MS analysis showed that various types of acids such as oxalic and butyric acid can be produced in the 3DEF process.