Comparing The Performance Of The Peroxymonosulfate/Mn3o4 And Three-Dimensional Electrochemical Processes For Methylene Blue Removal From Aqueous Solutions: Kinetic Studies

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 O-2 could then reduce to H2O2. The later further oxidized to OH center dot. 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 center dot 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.