Reusability of Photocatalytic CoFe₂O₄@ZnO Core–Shell Nanoparticles for Dye Degradation

The reusability of CoFe₂O₄@ZnO core–shell nanoparticles (NPs) for the photocatalytic degradation of methylene blue (MB) under UV radiation was successfully investigated. CoFe₂O₄@ZnO NPs with various CoFe₂O₄–to–ZnO concentration ratios were synthesized as magnetic photocatalysts. The X-ray diffraction spectra showed that the NPs had a cubic spinel ferrite phase structure and a hexagonal wurtzite phase of ZnO. Fourier-transform infrared spectra showed the presence of M_oct-O, M_tet-O, and Zn–O at 593, 347–389, and 410–429 cm⁻¹, respectively. The CoFe₂O₄@ZnO NPs had a saturation magnetization of approximately 30 emu g⁻¹ and a coercivity of approximately 280 Oe. The absorbance spectra showed that the absorbance peak of the CoFe₂O₄@ZnO NPs broadened and shifted to the right (higher wavelength) with increasing ZnO concentration. The CoFe₂O₄@ZnO NPs with higher ZnO concentrations exhibited higher photocatalytic activities and degradation rates. The enhancement of MB degradation can be attributed to the formation of an internal structure between CoFe₂O₄ and ZnO. The degradation rate of CoFe₂O₄@ZnO decreased slightly after each successive recycle. The results indicated that the recycled CoFe₂O₄@ZnO NPs could be reused three times for photocatalytic degradation. As there is no significant decrease in the photocatalytic degradation after four successive recycles, the CoFe₂O₄@ZnO NPs are suitable for application in dye degradation.