Sustainable removal of nitrite waste to value-added ammonia on Cu@CuO core-shell nanostructures by pulsed laser technique.

The biochemical reduction of nitrite (NO) ions to ammonia (NH) requires six electrons and is catalyzed by the cytochrome c NO reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO) and NO in wastewater, to produce the more valuable NH product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO reduction reaction (NORR), but the NORR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO to NH using Cu@CuO core-shell NPs to simultaneously treat wastewater by removing NO and producing valuable NH. The Cu@CuO core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO and the ammonium (NH)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@CuO core-shell NPs exhibited outstanding NORR activity, demonstrating a maximum NO removal efficiency of approximately 94% and a high NH-N yield rate of approximately 0.03 mmol h.cm at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NORR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO to NH via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO to NH.