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/TiO 2 -RuO 2 -IrO 2 anode electrode in the presence of magnetic multi-walled carbon nanotube (MWCNTs/Fe 3 O 4 ). The response surface methodology (RSM) was used to determine the effect of various parameters on the RB5 and COD removal efficiency, the production of H 2 O 2 , and the energy consumption. The results showed that the 3DEF system with MWCNTs/Fe 3 O 4 worked at a wide range of pH from 4 to 6 without significant reduction in efficiency. Electrochemical production of H 2 O 2 increased with increasing the concentrations of MWCNTs/Fe 3 O 4 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 H 2 O 2 and OH on MWCNTs/Fe 3 O 4 surface. The MWCNTs/Fe 3 O 4 nanocomposites indicated a high degree of stability and reusability. The reactive oxygen species (ROSs) like OH, HO 2 and O 2 − were generated in the reaction and 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/Fe 3 O 4 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/Fe 3 O 4 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. [ABSTRACT FROM AUTHOR]