Active-chlorine-mediated oxidation of 5-fluorouracil on a hierarchically ordered macroporous RuO2 electrode

The effect of crystal structure of MnO2 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-MnO2 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 MnO2 electrodes were characterized by scanning electron microscopy and X-ray diffraction, suggesting that different crystal structures of MnO2 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 MnO2 electrodes. Results indicated that β-MnO2 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-MnO2; moreover, energy consumptions of 11.3, 9.7, and 10.5 kWh/m3 were calculated for α-, β-, and γ-MnO2, respectively. Additionally, the oxidation mechanism of the MnO2 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 MnO2 electrodes. Finally, an actual DMAC containing wastewater was applied for testing the electrochemical performance of the three electrodes, and β-MnO2 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.

From black water to flushing water: potential applications of chlorine-mediated indirect electrooxidation for ammonia removal

Removing ammonia from black water is one of the most urgent issues before it can be recycled as flushing water. In this study, an electrochemical oxidation (EO) process with commercial Ti/IrO₂-RuO₂ anodes to treat black water could remove 100% of different concentrations of ammonia by adjusting the dosage of chloride. Through the relationship between ammonia, chloride, and corresponding the pseudo-first-order degradation rate constant (K_obs), we could determine the chloride dosage and predict the kinetics of ammonia oxidation based on initial ammonia concentration in black water. The optimal N/Cl molar ratio was 1:1.8. The difference between black water and the model solution in terms of ammonia removal efficiency and oxidation products was explored. A higher chloride dosage was beneficial for removing ammonia and shortening the treatment cycle, but it also led to the generation of toxic by-products. Especially HClO and ClO₃^- generated in black water were 1.2 and 1.5 times more than the synthesized model solution under 40 mA cm^-2. Through SEM characterization of electrodes and repeated experiments, the electrodes always maintained a high treatment efficiency. These results demonstrated the potential of the electrochemical process as a treatment method for black water.