Effect of the rare-earth substitution on the structural, magnetic and adsorption properties in cobalt ferrite nanoparticles

Rare-earth (RE) substituted cobalt ferrite CoFe1.9RE0.1O4 (RE=Pr3+, Sm3+, Tb3+, Ho3+) nanoparticles are synthesized by a facile hydrothermal method without any template and surfactant. The effects of RE3+ substitution on structural, magnetic and adsorption properties of cobalt ferrite nanoparticles are investigated. Structure, morphology, particle size, chemical composition and magnetic properties of the ferrite nanoparticles are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high solution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS), Fourier transform spectroscopy (FTIR), Raman spectra and vibrating sample magnetometry (VSM). The results indicate that the as-synthesized samples have the pure spinel phase, uniform crystallite size and narrow particle size distribution. Meanwhile, the RE3+ substitution leads to the decrease in the particle size, magnetization and coercivity of the CoFe2O4 ferrite. Notably, it demonstrates that the RE3+ doping can apparently enhance the adsorption capacity for Congo red (CR) onto ferrite nanoparticles. Adsorption equilibrium studies show that adsorption of CR follows the Langmuir model. The monolayer adsorption capacities of CoFe1.9Sm0.1O4 and CoFe1.9Ho0.1O4 are 178.6 and 158.0 mg/g, respectively. The adsorption kinetics can be described by the pseudo-second-order model.