Magnetic core–shell CoFe2O4@ZnO nanoparticles have been successfully synthesized by using coprecipitation method to provide easy separated nanomaterials and high photocatalytic activity performance. Core–shell nanoparticles with various CoFe2O4-to-ZnO molar ratio (1:2, 1:3, 1:4, 1:5) have been investigated over x-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible spectroscopy, and vibrating sample magnetometer. XRD spectra confirm the cubic spinel ferrite phase structure of CoFe2O4 and the hexagonal wurtzite phase of ZnO. The crystallite size is found within the range of 14.9–20.6 nm. TEM measurement confirms the good crystallinity of the samples. The magnetic hysteresis shows that CoFe2O4@ZnO has high saturation magnetization of about 30 emu g−1 and coercivity of about 300 Oe. Photocatalytic investigation was carried out using methylene blue (MB) under UV irradiation. Our result yields the enhancement of MB degradation as ZnO content increases. The maximum photodegradation achieved by the core–shell nanoparticles is 57.2%, 60.5%, 65.5%, and 78.3% for molar ratio of 1:2, 1:3, 1:4, and 1:5, respectively. The enhancement of MB degradation can be attributed to the formation of internal structure between CoFe2O4 and ZnO in the form of heterojunction structure. The magnetic properties of core–shell lead to the easy separation between the magnetic core–shell nanoparticles and the final degraded solution by permanent magnet.

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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 Moct-O, Mtet-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 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.

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