Electrochemical Degradation of Reactive Black 5 Using Three-Dimensional Electrochemical System Based on Multiwalled Carbon Nanotubes

The removal of Reactive Black 5 (RB5) dye and chemical oxygen demand (COD) was investigated using a three-dimensional (3D) electrochemical (3DE) reactor with multiwalled carbon nanotubes (MWCNTs). The experiments were performed according to a Taguchi design model, with the variables being the solution pH (2-9), current density (10-25mA/cm2), reaction time (15-60min), MWCNT concentration (25-200mg/L), and RB5 concentration (25-100mg/L). The best conditions for optimum removal of RB5 and COD were pH 3, MWCNT concentration 200mg/L, current density 15mA/cm2, RB5 concentration 100mg/L, and reaction time 60min. Among the main factors, the solution pH for removal of COD and RB5 and the current density for energy consumption had the highest impact. The 3D system generated more H2O2 and OH radicals compared with a two-dimensional (2D) system because the MWCNTs act as microelectrodes in the optimal conditions. In the 3D process, the production of high levels of reactive species led to an increase in the degradation of RB5 into aromatic compounds and various acids.