Engineered Zn_0.2Fe_2.8O₄@Cu(II)-Based Core@Shell Nanoparticles for Magnetic Hyperthermia-Enhanced Catalysis

Core@shell nanocatalysts that integrate magnetic and catalytic functionalities provide a versatile platform for remotely controlled reactions. Here, we report Zn_0.2Fe_2.8O₄ nanoparticles coated with a Cu-(II)-based shell, in which the zinc ferrite core generates heat under alternating magnetic fields, i.e., magnetic hyperthermia, while the copper shell exhibits heterogeneous Fenton-like activity. The ∼20 nm core shows high saturation magnetization (76 (4) emu/g) and superparamagnetic behavior at room temperature. Surface coating with an amorphous Cu-(II)-based phase is confirmed by XPS, EDS mapping, and ICP analysis. While bare Zn-ferrite nanoparticles show negligible Fenton-like activity, the copper-coated nanoparticles catalyze ·OH radical generation, as demonstrated by EPR experiments. The catalytic activity of the core@shell system remains low at room temperature but is strongly enhanced in magnetic hyperthermia conditions. Dye degradation assays using 100 ppm methylene blue and 1 mg/mL catalyst under alternating magnetic fields reveal that the core@shell system achieves 99% dye degradation in 1 h, exceeding the performance obtained under conventional thermal heating at equivalent bulk temperature. This enhanced performance could be attributed to a localized heating mechanism, in which the magnetic core acts as an internal heat source under alternating magnetic fields, promoting the heterogeneous redox reaction at the shell phase. These results demonstrate that the core@shell nanocatalysts with negligible activity at room conditions can be remotely enhanced by an alternating magnetic field, providing a promising strategy for applications where controlled catalytic activity is required.