Extremely efficient catalytic ozonation of ammonia N to N₂ using Co/Mg(OH)₂ as catalysts

The development of highly efficient and selective ozonation catalysts is crucial for enhancing the treatment of nitrogen-containing wastewater. In this study, a Co/Mg(OH)₂ nano-hexagonal sheets ozonation catalyst was prepared by one-pot hydrothermal method, and the structural characteristics of this catalyst were comprehensively analyzed. The O_Sur/O ratio of this catalyst was 41.06 %. Under the optimal conditions (22 ℃, initial pH of 9.0, ozone dosage of 1.2 mg/L, catalyst dosage of 1.0 g/L, initial NH₃-N concentration of 10.00 mg/L), NH₃-N and total nitrogen (TN) removal efficiencies of 90.26 % and 63.44 % were respectively obtained, and the removal process exhibited pseudo-first-order kinetics. Moreover, at 4 ℃, the NH₃-N and TN removal efficiencies reached 95.49 ± 1.14 % and 65.61 ± 1.13 %. In a co-degradation process for the removal of both N and C, the ammonia and most organic compounds competed for active substances, but both pollutants were effectively removed. Hydroxyl radicals (•OH) were the main active substance involved in NH₃ removal. However, the massive loss of Mg²⁺ experienced after three cycles reduced the NH₃-N and TN removal efficiencies to 31.83 % and 6.55 %, respectively. Finally, the electron transfer generated by the variable-valence Co ion was determined to promote the selectivity of the reaction toward gaseous N products. These findings offer promising avenues for the development of more energy-efficient and effective nitrogen removal processes.