Vacancy ordered γ-Fe ₂ O ₃ nanoparticles functionalized with nanohydroxyapatite: XRD, FTIR, TEM, XPS and Mössbauer studies

Vacancy ordered maghemite (γ-Fe ₂ O ₃ ) nanoparticles functionalized with nanohydroxyapatite (HAp – Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ) have been successfully synthesized using an inexpensive co-precipitation chemical route. Evidence for the presence of vacancy order in maghemite was shown by the superstructure lines observed in X-ray diffraction. The adsorption of carboxyl groups of citric acid (C ₆ H ₈ O ₇ ) onto γ-Fe ₂ O ₃ nanoparticles was investigated by FTIR, XPS and Mössbauer spectroscopy. From XPS surface analysis, two binding energies related to oxygen were attributed to bindings between C ₆ H ₈ O ₇ /γ- Fe ₂ O ₃ and C ₆ H ₈ O ₇ /HAp from an interfacial reaction promoted by strongly adsorbed H ₂ O molecules at the surface of these nanomaterials. Le Bail refinement of the XRD patterns showed the formation of well-crystallized pure tetragonal maghemite before and after functionalization with nanoHAp. The temperature dependence of hyperfine parameters of pure and functionalized γ-Fe ₂ O ₃ nanoparticles was investigated via Mössbauer spectroscopy. TEM revealed the formation of quasi-spherical γ- Fe ₂ O ₃ nanoparticles with an average diameter of ca. 12 nm and 16 nm before and after functionalization with nanoHAp in agreement with Le Bail refinement. Magnetometry measurements showed a saturation magnetization of 12 emu/g and a blocking temperature of 340 K for the functionalized γ- Fe ₂ O ₃ nanoparticles.