Electrochemical oxidation of Naphthol Blue Black with different supporting electrolytes using a BDD /carbon felt cell

Abstract

The electrochemical oxidation of Naphthol Blue Black (NBB) solution by means of anodic oxidation with electro-generated H2O2 (AO-H2O2) and Electro-Fenton (EF) was studied, using boron doped diamond (BDD)/ carbon felt (CF) cell. The experiments were carried out in NaCl and Na2SO4 as supporting electrolytes with initial concentration of 0.1 mM of NBB. The studied parameters were pH, applied current, concentration of Fenton catalyst, concentration of supporting electrolytes, and Cl-/SO42- mixture. The degradation of NBB was almost total when NaCl was used compared to Na2SO4, thanks to the electro-generated active chlorine (HClO/ClO-). The higher degradation is found with EF compared to AO-H2O2 process, the kinetic of degradation of NBB always follows a pseudo first-order reaction. The optimum conditions for the mineralization of NBB (i.e., 0.1 mM NBB, 50 mM Na2SO4 at pH 3.0, 0.1 mM Fe2+, and a current of 300 mA) were determined. These conditions yielded a total color removal in less than 10 min and 98% of total organic carbon (TOC) removal at 120 min electrolysis time. The biochemical oxygen demand/ Chemical oxygen demand (BOD/COD) ratio was decreased from 0.5 to 0.3, during the same timescales. Whereas, the mineralization current efficiency (MCE%) dropped from 21.5% to 0.05% in the electrolysis time range from 15-120 min suggesting the concomitant parasitic reactions. The evolution of nitrite NO2-, nitrate NO3-, ammonium NH4+, and sulfate SO42- concentrations were also followed as the end-products during the electrolysis.