  Ferrite nanoparticles serve as potent heterogeneous Fenton-like catalysts,
producing reactive oxygen species (ROS) for decomposing organic pollutants. We
investigated the impact of temperature and copper content on the catalytic
activity of nanoparticles with different oxidation states of iron. Via
solvothermal synthesis, we fabricated copper-doped magnetite
(Cu$_x$Fe$_{3-x}$O$_4$) with a Fe$^{2+}$/Fe ratio ~0.33 for the undoped system.
Using a microwave-assisted method, we produced copper-doped oxidized ferrites,
yielding a Fe$^{2+}$/Fe ratio of ~0.11 for the undoped nanoparticles. The ROS
generated by the catalyst were identified and quantified by electron
paramagnetic resonance, while optical spectroscopy allowed us to evaluate its
effectiveness for the degradation of a model organic dye. At room temperature,
the magnetite nanoparticles exhibited the most $\cdot$OH radical production and
achieved almost 90% dye discoloration in 2 hours. This efficiency decreased
with increasing Cu concentration, concurrently with a decrease in $\cdot$OH
generation. Conversely, above room temperature, Cu-doped nanoparticles
significantly enhance the dye degradation, reaching 100% discoloration at
90$^\circ$C. This enhancement is accompanied by a systematic increase in the
kinetic constants, obtained from reaction equations, with Cu doping. This study
highlights the superior stability and high-temperature catalytic advantages of
copper ferrite holding promise for enhancing the performance of nanocatalysts
for decomposing organic contaminants.
