Generation of Active Mn(III)_aq by a Novel Heterogeneous Electro-permanganate Process with Manganese(II) as Promoter and Stabilizer

Our study on the synergetic effect of electrolysis and permanganate (E-PM) revealed a novel alternative method for generating active Mn­(III)_aq heterogeneously by electrochemically activating PM with Mn²⁺ as promoter and stabilizer. We systematically explored the generation mechanism of Mn­(III)_aq. It indicated that all three components (electrolysis + PM + Mn²⁺) were necessary to facilitate the generation of active Mn­(III) in the E-PM-Mn²⁺ process. It was worth noting that Mn²⁺, as essential promoter and Mn­(III)_aq stabilizer, could considerably enhance the concentration of Mn­(III) in the E-PM-Mn²⁺ process. Further study revealed that the active Mn­(III) was mainly produced on cathode rather than in aqueous solution or on anode. In addition, the soluble Mn­(III)_aq generated in the E-PM-Mn²⁺ process was demonstrated to be very efficient for the degradation and mineralization of diclofenac (DCF) as well as methyl blue, carbamazepine, phenol, sulfamethoxazole, and nitrobenzene. Moreover, the effects of the main operating parameters (Mn²⁺ dosage, PM dosage, applied current density, pH of solution, and contaminant concentration) and different water matrices on the E-PM-Mn²⁺ process were investigated systematically. Possible degradation pathways of DCF in the E-PM-Mn²⁺ process were also proposed. The results demonstrated that the E-PM-Mn²⁺ system based on active Mn­(III)_aq could create a more efficient, sustainable, and less energy costing technology for water treatment.