Structural characterization of cerium-doped hydroxyapatite nanoparticles synthesized by an ultrasonic-assisted sol-gel technique

This present work focuses on the synthesis of cerium-doped hydroxyapatite (Ce/HAp-US) using an ultrasonic-assisted sol-gel technique under varying concentration of Ce from 0.5% to 2.0%. The preparative method utilized the stoichiometric molar ratio of Ca to P of 1.67 where the Ce/HAp samples were calcined at 600 degrees C for 2 h. The structural properties of Ce/HAp samples were characterized by various techniques including X-ray absorption near edge spectroscopy (XANES), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Results from the XANES spectra of xCe/HAp samples at the Ce L-3-edge reveal that the dominant species of cerium was Ce4+ along with some Ce3+, which have been incorporated into the HAp lattice. Results of the EDX analysis show that the Ca/P molar ratio of xCe/HAp decreased with an increase in Ce content. XRD analysis confirms that Ce3+ and Ce4+ were partially incorporated into the hexagonal framework of HAp and rhombohedral structure of beta-tricalcium phosphate (beta-TCP). FT-IR measurements identified the main functional groups of Ce/HAp to be hydroxyl (OH-), phosphate (PO43-) and carbonate (CO32-). The morphology obtained from TEM analysis illustrates that pure HAp-US is composed of very fine spherical particles. By incorporating Ce ions into the HAp lattice, the presence of dense dark spots, possibly the loaded Ce species, were observed.