Enhanced visible light photocatalytic activity of C e‐doped Ni–Cu spinel ferrites for methyl orange degradation

Water pollution from synthetic dyes requires efficient and durable remediation technologies. In this work, cerium‐doped nickel‐copper spinel ferrite nanoparticles (Ni₀.₆Cu₀.₄CeₓFe₂ − ₓO₄, x = 0.0–1.0) were synthesized by coprecipitation and evaluated as visible‐light photocatalysts for methyl orange degradation. XRD confirmed a dominant cubic spinel phase (~91% purity), with the remaining ~9% attributed primarily to minor α‐Fe₂O₃ (detected from x ≥ 0.50) and trace CeO₂ (at x = 1.0) secondary phases, alongside systematic lattice expansion consistent with Vegard's law, while UV–Vis DRS showed progressive band‐gap narrowing from 3.70 to 2.50 eV with increasing Ce content. Composition screening identified x = 0.25 as the optimum catalyst, giving 83.2% methyl orange degradation in 120 min under visible light and a 3.47‐fold increase in the surface‐area‐normalized rate constant relative to the undoped host. The apparent pseudo‐first‐order rate constant at this composition was 0.0148 min −1 . Scavenger tests identified •OH as the dominant reactive species, and the improved performance at low Ce loading is consistent with enhanced charge separation and favorable surface chemistry. The catalyst retained 83.4% of its initial activity after five cycles, and thermal regeneration at 300°C restored 97% of the lost activity. These results demonstrate that Ce‐doped Ni–Cu ferrites are promising magnetically recoverable photocatalysts for solar‐driven wastewater treatment.