Effect of annealing temperature on phase transitions and photo-Fenton catalytic activity of CoFe2O4 nanopowder

In this work, the hydrothermal technique was used to synthesize cobalt ferrite (CFO) magnetic nanoparticles. Then, the as-prepared CFO sample was annealed at four different temperatures (600, 700, 800, and 900 °C) to study the effect of the annealing temperature on the crystallite growth, magnetic properties, phase transitions, and photo-Fenton catalytic activity of CFO powder samples. The properties of CoFe2O4 were characterized by X-ray powder diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, Brunauer–Emmet–Teller analysis, vibrating sample magnetometry, and catalytic tests. The results showed that the annealing temperature significantly affected the phase structure, crystallite size, morphology, specific surface area, magnetic properties, and catalytic activity of CFO powder samples. The calcined CFO sample had higher catalytic activity than the as-prepared CFO. At the annealing temperature of 600 °C (CFO-600), the catalytic efficiency and rate constant of this material for the degradation of methylene blue under ultraviolet A irradiation for 60 min reached 95% and 3.16 h−1, respectively, in the presence of oxalic acid as a potential oxidizing agent. We also found that a higher number of Fe3+ ions occupying octahedral sites on the CFO surface resulted in a higher activity of the CFO photo-Fenton catalyst. In particular, the CFO-600 powder with excellent magnetic properties exhibited a good recycling catalytic performance. The present material holds promise as a potential practical candidate for treating pollution caused by organic dyes and limiting secondary contaminants released during the photocatalyst process. [Display omitted] •Reusable CFO powders were successfully prepared by a simple, economical, and eco-friendly hydrothermal method.•The change in the ratios between Fe3+ ions in octahedral (Oh) and tetrahedral sites (Th) [Fe3+(Oh):Fe3+(Th)] was estimated from the XPS spectra.•A higher number of Fe3+ ions occupying octahedral sites on the CFO surface resulted in a higher activity of the CFO photo-Fenton catalyst.•The CFO-600 catalyst exhibited the best performance and a significantly unchanged catalytic efficiency after five cycling tests.