Magnetic field-enhanced activation of O2 by nano zero-valent iron for efficient treatment of copper-complexed wastewater

The pervasive threat of toxic and stable heavy metal-organic complexes to aquatic ecosystems necessitates efficient decomplexation strategies. In this study, we developed a magnetic field (MF)-enhanced nano zero-valent iron (nZVI) system that activated O-2 for the removal of Cu(II) and chemical oxygen demand (COD) from Cucomplexed wastewater (EDTA-Cu, citrate-Cu, tartrate-Cu). The introduction of MF significantly enhanced Cucomplex destruction and Cu2+ immobilization, while reducing toxicity and improving biodegradability. Mechanistic studies revealed that nZVI would displace Cu from complexes, reducing free Cu2+ to Cu0 on its surface. The resultant Cu-0, in synergy with Fe2+, activated O-2 to generate reactive oxygen species (ROS), which cleaved metal-organic bonds and oxidized organic ligands. MF amplified this process by enhancing paramagnetic O2 accumulation at nZVI/Cu-0 sites, accelerating ROS production via the O-2 -> O-2(center dot-)-> H2O2 ->center dot OH pathway, thereby boosting Cu-organic decomplexation and COD removal. Catalyst characterization further revealed that MF promoted Cu0 dispersion on nZVI, preventing cluster formation and optimizing electron utilization for O-2 activation. As demonstrated by our energy-cost efficiency analysis, the MF/nZVI/O2 process achieved 1.375-1.785 gCu/kWh for Cu-organic wastewater treatment, significantly outperforming many previously reported processes. This study introduces a novel MF-assisted nZVI system for efficient treatment of Cu-complexes, offering a promising cost-effective and sustainable solution for practical application.