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

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 CuFe2-xCoxO4 (CFCxO) 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 CFC0.6O 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, CFC0.6O 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 CFC0.6O 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.