Cadmium-tetracycline complexation enhances interfacial reactivity on Fe0@γ-Fe2O3/carbon for coupled contaminant removal.

The coexistence of heavy metals and antibiotics in water poses unique remediation challenges, because their interactions can alter adsorption and redox reactivity. Here, resorcinol-formaldehyde carbon sphere-supported Fe0@γ-Fe2O3 nanoclusters (RFCS-Fe0@γ-Fe2O3) were employed to elucidate the interactions between cadmium (Cd) and tetracycline (TC). Binary-system experiments further revealed that concentration, pH, and addition sequence regulated the competitive and synergistic interactions. Quantum chemical calculations revealed that Cd-TC complexation narrowed the frontier orbital gap of TC and strengthened its interaction with Fe0@γ-Fe2O3. The adsorption energy of Cd-TC complex was -3.92 eV, compared with -2.79 eV for Cd(II) and -2.92 eV for TC, indicating a stronger affinity of the complex for the reactive interface. Multimodal characterization indicated the synergy of surface hydroxyls and oxygen vacancies (OV) in Fe0@γ-Fe2O3 clusters: hydroxyl-rich iron sites favored Cd(II) coordination, whereas OV facilitated electron transfer and reactive oxygen species (ROS) generation for TC oxidation. Moreover, effective treatment performance was maintained over a broad pH rang, in the presence of competing ions, natural organic matter, in real water samples, and over repeated reuse cycles. These findings suggest that the Cd-TC complexation enhances interfacial reactivity and provides a mechanistic basis for designing defect-rich iron-carbon interfaces for co-contaminant remediation.