Magnetically separable CeO₂/CoFe₂O₄ heterojunction photocatalysts for dye degradation: characterization and mechanism

This study developed magnetically separable CeO2/CoFe2O4 heterojunction photocatalysts for dye degradation to reduce water pollution. The CeO2/CoFe2O4 nanocomposites with different CeO2 ratios (10, 20, and 30 wt%) were prepared by a precipitation method. The nanocrystalline 20%CeO2/CoFe2O4 photocatalyst with a surface area of 117 m(2).g(-1), E-g 2.37 eV, and uniform distribution of quasi-spherical CeO2 minor phase (cubic fluorite structure with particle size 3 +/- 1 nm) throughout the distorted spherical CoFe2O4 major phase (cubic spinel structure with particle size 9 +/- 3 nm) showed the best photocatalytic performance for methylene blue (MB) degradation under UV light irradiation at the efficiency of 88.7% and the apparent rate constant (k) of 0.0138 min(-1). The 20%CeO2/CoFe2O4 photocatalyst had a good magnetic response and could be easily separated from the dye solution by applying an external magnetic field. The reusability test showed lower photodegradation efficiency due to the adsorption of residual MB dye on the photocatalyst surface. The formation of heterojunction at the interfaces of CeO2/CoFe2O4 facilitated the photogenerated charge separation and increased availability of active species of holes (h(+)) and hydroxy radicals ((OH)-O-center dot), which were the key factors in improving the photocatalytic activity.