Ultrastructure characterization of hydroxyapatite nanoparticles synthesized by EDTA-assisted hydrothermal method

Hydroxyapatite (HA) nanoparticles with the length of 50-150 nm were synthesized by hydrothermal method with EDTA surfactant. The orientation and ultrastructure of the as-synthesized nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). 50 mL of a mixed solution of Ca(NO3)2. 4H2O and EDTA was first prepared and then added dropwise into 50 mL of Na2HPO4 under intense stirring. After mixing with Na2HPO4, the pH of the new mixed solution was adjusted to 9 by adding NaOH solution, and then, the mixed solution was magnetically stirred on a hotplate for 2 h. After that, the mixed solution was kept in Teflon flasks and sealed tightly for hydrothermal reactions. After hydrothermal processing, white HA precipitates were filtered, washed thoroughly with deionized water, and oven-dried at 50°C for 24 h. The result shows that calcium phosphate precipitates were produced by hydrothermal method in the presence of EDTA.