Oxygen Vacancy Rich La-Doped NiFe₂O₄ as a Visible-Light Peroxydisulfate Activator for Rapid Degradation of Tetracycline

Antibiotic residues in water are persistent and promote antimicrobial resistance, demanding efficient, solar-driven advanced oxidation. UV–Vis diffuse reflectance revealed a slight red shift and a narrowed band gap relative to NiFe₂O₄, while diminished PL intensity, smaller EIS semicircles, and higher transient photocurrent indicated suppressed recombination and improved charge transport. Under visible light (λ > 420 nm) with PDS (1 mM) and catalyst loadings of 0.2–0.3 g L⁻¹, NiLa₀․₂Fe₁․₈O₄ removed ∼90% TCH in 60 min and followed pseudo-first-order kinetics with an apparent rate constant ~ 1.5× that of pristine NiFe₂O₄. Optimal performance occurred at mildly acidic pH (~ 4); increasing initial TCH concentration slowed kinetics, and common anions, especially HCO₃⁻, partially inhibited degradation. Scavenger tests (EtOH, IPA, AO, BQ) identified SO₄•⁻ and •OH as the dominant oxidants, with contributions from h⁺ and O₂•⁻. The catalyst was magnetically recoverable and retained ~ 90% of its initial activity after four cycles; post-use XRD/XPS showed intact spinel and stable Ni/Fe/La valences with a modest decrease in surface-adsorbed oxygen. The synergy between oxygen-vacancy–rich surfaces and PDS activation under visible light underpins the high activity and durability. These findings position NiLa₀․₂Fe₁․₈O₄ as a practical, recyclable photocatalyst for antibiotic abatement and provide guidance for defect/dopant engineering of spinel ferrites for water remediation.