The mechanism and efficiency of MnO2 activated persulfate process coupled with electrolysis.

Pure three-dimensional manganese oxides (MnO2) were successfully synthesized by a simple one-step hydrothermal process. The obtained particles were characterized via XRD, BET, SEM, XPS and FTIR techniques. To enhance the efficiency of heterogeneous catalytic process, a facile and effective electrochemical method was introduced. The degradation of C. I. Acid Orange 7 (AO7) as the target pollutant in aqueous solution by an oxidation system involving MnO2 activated peroxydisulfate (PDS) coupled with electrochemical method is reported herein. Influences of some key reaction parameters such as initial pH (pH0), current density, initial AO7 concentration, dosage of MnO2 and anions (Cl-, NO3-, HCO3- and H2PO4-) were investigated. The cyclic voltammetry (CV) was performed to investigate the charge transfer process occurred at the surface of catalyst. LC-MS/MS analysis was applied to identify degradation intermediates and a plausible degradation mechanism is proposed accordingly. Activated sludge inhibition tests were carried out to evaluate the change of toxicity of the dye solution in the oxidation process. The inorganic by-products such as NO2-, NO3-, and NH4+ along with AO7 degradation were also identified. The stability of MnO2 catalyst was evaluated by recycling experiments and the electrical energy consumption was also investigated. Radical quenching tests with several scavengers (methanol, tert-butyl alcohol, 1,4-benzoquinone and phenol) were performed to clarify the dominating reactive species participating in this oxidation process and the underlying mechanisms involving the generation of radical from the proposed electro-assisted heterogeneous activated PDS system were identified.