Abstract

In this study, the performance of the peroxymonosulfate/Mn3O4 (PMS/Mn3O4) and three-dimensional electrochemical (3D-EC) processes were investigated in removal of methylene blue (MB) and its respective chemical oxygen demand (COD) and total organic carbon (TOC). The Mn3O4 nanoparticles (NPs) were synthesized by a chemical precipitation method. The Pb/PbO2 electrode was prepared via electrodeposition in sulfuric acid solution. The structure of NPs and PbO2 were characterized using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) techniques. The effect of MB initial concentration as well as pH was studied for the both mentioned processes. The kinetics analyses displayed that the PMS/Mn3O4 and 3D-EC processes followed the first order and second order models, respectively. Under the optimum conditions of parameters studied (i.e. MB initial concentration 62 mg/L and pH 4), the maximum removal efficiencies of COD, TOC, and MB by the PMS/Mn3O4 process were found to be 48.43 , 29.20 , and 86.64 , respectively. At MB concentration 155 mg/L and pH 7 (as the optimum conditions for 3D-EC process) the respective values were specified to be 87.50, 83.04, and 98.34, respectively. The produced hydroxyl radicals on the Pb/PbO2 surface mineralized MB and converted it to CO2 and H2O. On the particle electrodes O2 could then reduce to H2O2. The later further oxidized to OH•. The radicals produced were capable to cleavage the loop in the structure of the intermediates via loop-opening reactions and finally produce 4,4-N·N-dimethylaminophenol compound. By continuing the electrolysis reaction, MB converted to CO2 and H2O. Therefore, the 3D-EC process can be considered as an effective method not only in removal efficiency, but also in mineralization performance. © 2021 Elsevier B.V.