Synthesis and Characterization of High Purity Hydroxyapatite Nanorods by Hydrothermal Technique

High purity hydroxyapatite (HAp) nanorods were synthesized by hydrothermal technique using Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ as starting materials in a hydrothermal reactor at 150–200 °C for 12–24 h with pH6 and pH9.5, respectively. The prepared HAp nanorods were characterized by XRD, FTIR, and TEM techniques. The XRD results confirmed the formation of pure phase of HAp at pH9.5. With increasing temperature and time, the crystallinity of the HAp was increased, showing the hexagonal structure of HAp with the lattice parameter a in a range of 1.144–1.148 nm and c of 0.723–0.724 nm. The crystalline sizes of the powders were found to be 44–85 nm as evaluated by the XRD line broadening technique. The chemical compositions of the HAp nanorods were characterized by FTIR spectroscopies. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the samples. The morphology of the HAp was nanorods of diameter less than 100 nm, as revealed by TEM. Increasing the temperature and time resulted in the transition from polycrystalline to single crystalline phase of the HAp, as clearly confirmed by the analysis of TEM diffraction patterns.