Oxygen vacancy rich lanthanum doped nickel ferrite as a visible light driven peroxydisulfate activator for rapid degradation of tetracycline in water

Antibiotic residues in aquatic systems accelerate antimicrobial resistance and require efficient solar-driven advanced oxidation strategies. Herein, we engineer an oxygen-vacancy-rich La-doped NiFe₂O₄ spinel (NiLa₀․₂Fe₁․₈O₄) as a single-phase, magnetically recoverable visible-light peroxydisulfate (PDS) activator for tetracycline hydrochloride (TCH) degradation. La³⁺ incorporation into the spinel lattice induces structural distortion and increases surface oxygen-vacancy density, resulting in band-gap narrowing, suppressed electron-hole recombination, reduced charge-transfer resistance, and enhanced photocurrent response relative to pristine NiFe₂O₄. Under visible-light irradiation (λ > 420 nm), the optimized NiLa₀․₂Fe₁․₈O₄/PDS system achieved ∼90% TCH removal within 60 min, with a rate constant ~ 1.5 times that of undoped NiFe₂O₄. Mechanistic analysis indicates that oxygen vacancies facilitate electron transfer to PDS and promote Ni²⁺/Ni³⁺–Fe²⁺/Fe³⁺ redox cycling, generating SO₄•⁻ and •OH as dominant oxidizing species. The catalyst was magnetically recoverable and retained ~ 90% activity after four cycles. Compared with previously reported multi-component or noble-metal-modified ferrite systems, this work demonstrates that rare-earth defect engineering within a structurally simple spinel framework can simultaneously enhance visible-light utilization and sulfate radical generation. These findings highlight the potential of defect-engineered ferrites for scalable solar-assisted antibiotic remediation.