The effect of crystal structure of MnO electrode on DMAC removal: degradation performance, mechanism, and application evaluation.

The crystal structure has a significant impact on the electrochemical properties of electrode material, and thus influences the electrocatalytic activity of the electrode. In this work, α-, β-, and γ-MnO electrodes were fabricated and applied for investigating the effect of crystal structure on electro-oxidation treatment of N,N-dimethylacetamide (DMAC) containing wastewater. The prepared MnO electrodes were characterized by scanning electron microscopy and X-ray diffraction, suggesting that different crystal structures of MnO electrodes with the same morphology of stacking-needle structure were successfully prepared. The electrochemical performances, including removal efficiencies of DMAC, chemical oxygen demand (COD) and total nitrogen (TN), and energy consumption, were compared between different MnO electrodes. Results indicated that β-MnO electrode presented the excellent electrochemical activity, and could remove 93% DMAC, 62% COD, and 78.9% TN, which was much higher than that of α- and γ-MnO; moreover, energy consumptions of 11.3, 9.7, and 10.5 kWh/m were calculated for α-, β-, and γ-MnO, respectively. Additionally, the oxidation mechanism of the MnO electrodes was presented, indicating that DMAC was mainly oxidized by hydroxyl radical through reactions of hydroxylation, demethylation, and deamination, and electrode characteristics of specific surface area, oxygen evolution potential, and hydroxyl radical production were the key factors for degrading DMAC on MnO electrodes. Finally, an actual DMAC containing wastewater was applied for testing the electrochemical performance of the three electrodes, and β-MnO electrode was verified as the suitable electrode for potential application which achieved removal efficiencies of 100%, 64.5%, and 73% for DMAC, COD, and TN, respectively, after system optimization.