Investigation of structural, photocatalytic and magnetic properties of dy doped cofe2o4 nanoparticles prepared by hydrothermal method

Abstract

Magnetic nanoparticles of undoped CoFe2O4 and 10% Dy doped CoFe2O4 (nominal composition of CoFe1.8Dy0.2O4) were successfully prepared by using hydrothermal synthesis technique at 200oC reaction temperature. Further, heat treatment at 400oC in Ar atmosphere was applied for Dy doped CoFe2O4 nanoparticles to get improved property of the material as well as to compare their structural, morphological, elemental, magnetic, optical and photocatlytic properties with undoped and Dy doped CoFe2O4. Different characterization techniques were applied to investigate their required properties. X-ray diffraction technique was performed for the structural analysis and phase identification of the material. Rietveld refinement process is applied to obtain information about crystallographic phases. Rietveld refined XRD patterns of the synthesized materials confirmed the formation of cubic spinel crystal structure (Fd-3m space group) but also confirmed the presence of few secondary phases of cubic Dy2O3 (space group la-3). The crystallite size was estimated from Scherrer equation using strong reflection peak of XRD patterns. The crystallite size increased with substitution of Dy3+ ion in place of Fe3+ ion while it decreased after heat treatment in Ar atmosphere. Lattice parameter was found to increase due to the replacement of smaller ionic radii (0.645 Å) of Fe3+ in CoFe2O4 by the larger ionic radii of Dy3+ (0.938 Å) as well as heat treatment The FESEM images were obtained to observe the surface morphology, shape, size and distribution of particles above the surface. The FESEM observation revealed the formation of cubic shape particles of CoFe2O4 and also nanowire Dy2O3 for the Dy doped CoFe2O4 samples (with and without heat treatment). The particles size of CoFe2O4 nanoparticles was found to increase with Dy doping and further heat treatment, the size of Dy doped CoFe2O4 nanoparticles was slightly decreased. However, morphology of the nanoparticles was good for the heat treated Dy doped CoFe2O4 samples. All the desired elements of the proposed material were presented in the prepared samples which was ensured by analyzing the Energy Dispersive X-ray spectra. From magnetization versus magnetic field hysteresis loops, the ferromagnetic nature of the synthesized samples was confirmed. The heat treated Dy doped CoFe2O4 samples provided significantly higher magnetization than those of undoped and Dy doped CoFe2O4 samples. Furthermore, analyzing the light absorption spectra, it was revealed that all the prepared samples have the ability to absorb light in visible region. Again, the band gap energies of prepared samples were estimated using diffuse reflectance data in Kubleka-Munk function. The estimated band gap energy was decreased in the range of 1.55-1.43 eV due to doping and heat treatment. The photocatalytic RhB dye degradation experiment was examined under visible light irradiation from 500W Xenon lamp and dye absorbance data were recorded using UV-Visible spectrometer. The photodegradation of CoFe2O4 samples was enhanced for both Dy doping and heat treatment in Ar atmosphere. This is probably due to the fact that Dy substitution reduced the band gap energy and inhibited the recombination of electron-hole pairs. The maximum photodegradation efficiency was obtained for heat treatment in Ar atmosphere of Dy doped CoFe2O4 sample. The outcome of this investigation suggest that the substitution of Dy in CoFe2O4 along with heat treatment at 400oC temperature in Ar atmosphere using inert furnace provides a strong catalyst which influences the optical properties of the materials and consequently enhances their photocatalytic properties. The synthesized nanoparticles may be used for energy related applications, e.g. to solar produce hydrogen through water splitting.