Spin-polarization manipulation in Co-doped CuFe₂O₄ for boosted peroxymonosulfate activation toward pharmaceutical...

Transition metal photocatalysts face efficiency limitations in peroxymonosulfate (PMS) activation due to the rapid charge recombination and sluggish ion redox rate. To overcome this, a series of Co-doped CuFe_2-xCo_xO₄ (CFC_xO) photocatalysts were synthesized via a sol-gel approach to promote PMS activation through Cu²⁺/Cu⁺, Fe³⁺/Fe²⁺, and Co³⁺/Co²⁺ ion redox cycles, leading to efficient metronidazole (MTZ) degradation. Notably, the optimized CFC_0.6O exhibited a reaction rate constant k of 0.112 min^-1 without a magnetic field, approximately 14 times higher than that of CFO (0.008 min^-1). Remarkably, under a magnetic field, CFC_0.6O achieved a 165% performance enhancement, with the reaction rate constant k reaching 0.297 min^-1. The remarkable improvement confirms the crucial role of spin polarization induced by cobalt doping in promoting charge separation and accelerates ionic redox cycles, thereby enhancing PMS activation efficiency. X-ray photoelectron spectroscopy (XPS) spectra of the catalysts before and after the reaction confirmed that Co doping significantly accelerated the Cu²⁺/Cu⁺, Fe³⁺/Fe²⁺, and Co³⁺/Co²⁺ redox cycles during PMS activation. The CFC_0.6O catalyst exhibited excellent stability and broad pH adaptability (3-11). Scavenging tests suggested that SO₄^·-, ·OH, and ¹O₂ serve as the dominant active species for MTZ degradation. This work provides a valuable strategy for enhancing PMS activation efficiency through spin-polarization engineering and multi-ionic redox cycle optimization.