Cooling-trajectory-controlled cation redistribution in spinel CoFe2O4 for photooxidation and peroxide-assisted oxidation

Abstract

Solar-driven oxidation catalysis requires the coordinated optimization of light absorption, charge-carrier utilization, and surface redox activity. Spinel CoFe2O4 is a promising multifunctional catalyst because its visible-light response, magnetic recoverability, and multivalent Co/Fe redox chemistry enable both photoinduced oxidation and peroxide-assisted Fenton-like pathways. Here, we examine post-annealing cooling trajectory as a simple thermal-processing parameter for tuning apparent cation redistribution in CoFe2O4. After high-temperature annealing, nitrogen quenching, natural cooling, and slow oven cooling were used to regulate the extent of structural relaxation within the spinel lattice. Combined XRD refinement, XPS, and Raman analyses indicate cooling-dependent changes in local structure and surface chemistry, with semiquantitative apparent inversion degrees increasing from approximately 61% for the nitrogen-quenched sample to 68% and 76% for the naturally cooled and oven-cooled samples, respectively. The nitrogen-quenched sample exhibits slightly enhanced visiblelight absorption but stronger steady-state photoluminescence emission and more defect-associated surface oxygen species. By contrast, the oven-cooled sample shows weaker photoluminescence emission and the highest apparent activity in both malachite green photooxidation and peroxide-assisted dark oxidation. These results suggest that oxidation activity is governed by the balance among apparent cation distribution, surface defect states, carrier recombination behavior, and Co/Fe redox-site accessibility rather than by optical absorption alone. This work establishes a processing-structure-activity correlation and provides a practical cooling-trajectory strategy for tuning coupled photooxidation and Fenton-like oxidation functionality in spinel ferrite catalysts.