Abstract
A series of novel four non-stoichiometric cobalt ferrite nanoparticles (NPs) with the chemical composition, Co-x(2+) Fe-8 2x/3 (3+) V-1 x/3 O-4 (x similar to 0.2, 0.4, 0.6, 1.0, V = vacancy) was synthesized by the polyol method. The produced NPs were systematically characterized and studied by several techniques including X-ray diffraction, energy dispersive X-ray, infrared spectroscopy, thermal analysis, transmission electron microscopy and SQUID magnetometry for their chemical composition, structure, microstructure, surface chemistry and magnetic properties. The nanosized particles (similar to 5-7 nm) are roughly spherical in shape and exhibiting superparamagnetic behavior with a reasonable saturation magnetization and a high Curie temperature. Additionally, the thermal stability of the NPs was studied, and a decomposition reaction scheme was proposed. The effects of various physicochemical parameters, such as the initial Cr(VI) concentration, the NPs dosage, the contact time and the commonly coexisting ions in wastewaters (Ba2+, Pb2+, Zn2+, Cl-, SO42-, PO43-, . . .), on the removal efficiency of Cr(VI) by low-temperature calcined NPs was studied at pH similar to 2.0. The best removal efficiency was found with the two nanoferrites with the composition x similar to 0.6 and similar to 1.0. Their respective adsorption capacity calculated from the Langmuir isothermal model for an adsorbent dosage of 4.0 g L-1, were similar to 17.0 and similar to 13.0 mg g(-1). Besides, for an industrial, economic and environmental purpose, the reusability efficiency of the NPs was tested for seven adsorption-desorption-regeneration cycles.