Facile synthesis of magnetic hydroxyapatite-supported nickel oxide nanocomposite and its dye adsorption characteristics

A novel magnetic hydroxyapatite-supported nickel oxide nanocomposite (NiO–HAP@γ-Fe₂O₃) was successfully prepared using a combination of co-precipitation and wet impregnation methods and was applied to the adsorption of methylene blue from aqueous solution. The presence of HAP, γ-Fe₂O₃, NiO and all elements in NiO–HAP@γ-Fe₂O₃ was confirmed by XRD, SEM–EDX and ICP-AES. The structure of the resulting nanocomposite was shown by TEM and SEM–EDX to be rod-shaped, measuring 55.8 ± 16.5 nm in length and 27.1 ± 6.2 nm in width, and on the surface of which was uniformly interspersed with NiO nanoparticles (about 21.4 nm average crystallite size) and γ-Fe₂O₃ nanoparticles (6.7 ± 2.6 nm in diameter). The novel NiO–HAP@γ-Fe₂O₃ exhibited a high adsorption rate during the first 20 min and reached an equilibrium within 3 h. The adsorption capacity of NiO–HAP@γ-Fe₂O₃ was significantly higher than that of its precursors (7.20 mg g⁻¹ vs 0.79–1.31 mg g⁻¹). The superior adsorption performance of the novel nanocomposite, which occurred despite its relatively low surface area, is likely attributable to the synergistic mechanisms facilitated by the presence of mixed metal oxides (NiO and γ-Fe₂O₃) on the adsorbent as well as by the Lewis acidity and basicity of the components of the adsorbent and the adsorbate. The adsorption kinetics and isotherms were well-fitted by the pseudo-second-order kinetic model and the Langmuir isotherm model, respectively.