Simultaneous removal of methylene blue and total dissolved copper in zero-valent iron/H₂O₂ Fenton system: Kinetics, mechanism and degradation pathway

This study aimed to investigate the simultaneous removal of methylene blue (MB) and total dissolved copper (TCu) by heterogeneous zero-valent iron (ZVI) Fenton-like system (ZVI/H₂O₂) and elucidate the mechanism of synergistic effect for co-contaminants removal. Hydroxyl radical (OH) formation was hypothesized to be the dominant pathway for the oxidation of MB, confirmed by the quenching experiments and ESR analysis. And the synergistic effect of TCu and ZVI greatly promoted the release of Fe²⁺, further accelerating the generation of hydroxyl radical (OH) via Fenton reaction. The generation process of OH was unveiled by quenching experiments and electron spin resonance (ESR) analysis, while the processes of ZVI corrosion and TCu reduction were revealed through several characterization approaches including SEM, XRD, FTIR and XPS. The degradation pathway of MB was also investigated by LC-MS analysis. The MB initial concentration, TCu initial concentration, H₂O₂ dosage, ZVI dosage and initial solution pH could play crucial roles in the removal of MB and TCu. The influence of water matrix including inorganic anions (Cl^-, NO₃^-, HCO₃^-) and actual water was finally conducted to elucidate the role of natural organic matter (NOM) in the environmental systems.